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Changing characteristics of deformation, sedimentation, and magmatism as a result of island arc -continent collision

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Changing characteristics of deformation, sedimentation, and magmatism as a result of island arc -continent collision

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Content CHANGING CHARACTERISTICS OF DEFORMATION, SEDIMENTATION, AND MAGMATISM AS A RESULT OF ISLAND ARC-CONTINENT COLLISION Copyright 2005 by Helge Alsleben A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (EARTH SCIENCES) August 2005 Helge Alsleben Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 3219867 INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. ® UMI UMI Microform 3219867 Copyright 2006 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS The research reported in this dissertation was funded through two Graduate Research Grants from the Geological Society of America (#6838-01; #7076-02), a grant from Sigma Xi - The Scientific Research Society (Grants-in-Aid of Research, 2001), and the Department of Earth Sciences at the University of Southern California. Research facilities, time, and a number of geochronological and geochemical data were donated by George Gehrels, Mihai Ducea, and Paul Wetmore at the University of Arizona and their help and support is gratefully acknowledged. First of all, I would like to thank my advisor Scott Paterson. He provided constant support, encouragement, expertise, and taught a number of classes that provided deep insight into many aspects of structural geology and the evolution of magmatic arcs. His openness to discussion and balanced presentation of facts that he clearly separated from interpretations have left a lasting impression. Outside the classroom, he pushed me to excel and always believed in my abilities as a geologist and a writer and his role during the completion of this project is greatly appreciated. I would like to extend my gratitude to Greg Davis, who served on my qualifying and dissertation committees and taught several interesting, enjoyable, and demanding classes with outstanding field trip. It was great to experience his relentless enthusiasm for geology, his vast knowledge about Cordilleran geology and tectonics, and his constant desire to teach and educate. Over the years I have learned more from him than I thought possible and he has become a great mentor and friend. I am glad our paths crossed at USC. ii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I would like to extend thank to my other committee members. Ed McCann served on my qualifying and dissertation committees and Steve Lund and Jean Morrison served on my qualifying committee. I have to admit that trying to schedule five professors for meetings was one of the most humbling experiences during the course of my graduate studies at USC. Thank you for finding time to schedule meetings and exams and for making it all possible. There are also a number of other faculty members from the Department of Earth Sciences that I need to mention and who contributed to my education and research at USC. Besides serving on my committee, Steve Lund gave me the opportunity to work as a Research Assistant in his paleomagnetism lab and was always willing to discuss paleomagnetic data or lab procedures and certainly kindled my curiosity to learn more about Earth’s magnetism. Thanks to Lawford Anderson for great field trips (Geol. 108 is a blast!) and sharing his enthusiasm for undergraduate teaching and igneous petrology. Thanks to Bob Douglas and Donn Gorsline for some great trips to Baja and great SGP meetings (See you next time). Thanks to Ann Blythe for helping me with mineral separations. Special thanks are also extended to the office staff (Vardui, Cindy, Barbara, Dana, Stan, and John) and John McRaney, who make many things possible and solve problems as soon as they arise. My work in Baja would not have been possible without the knowledge and expertise of Keegan Schmidt and Paul Wetmore. They both taught me that there is more to working in Baja then just getting in your car and take a drive. Thank you for iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. giving me the opportunity to join you in the field, for your friendship, and for the discussions about your work and the geology of Baja California. Paul has become a great friend and has done too many countless things to list and I’m looking forward to continue our collaborations in Baja. I need to mention a number of faculty and students from other universities. Thanks to David Kimbrough, John Fletcher, Jorge Ledesma, Richard Sedlock, Erwin Melis, Scott Johnson, and Kurt Burmeister for their hospitality and insightful discussion on the Mesozoic geology of western Mexico, geology in general, and things other than geology. I would also like to acknowledge my former Master’s advisor Bob Miller at San Jose State, who led me onto the path as a geologist and who over the years has become a great friend. A very special thank you needs to go to Oscar Gonzalez, his wife Jennifer and their kids (Oscar Jr. & Erica). Thank you for your friendship, taking me into your house when I needed shelter, and cooking some of the best meals I had in Baja. My experiences in Ensenada and Baja wouldn’t have been the same without you. Muchas gracias! Thanks to all the current and past members of the ‘Strain group’ at USC. My graduate school days wouldn’t have been the same without you. I would like to particularly thank Geoff Pignotta for sitting next to me almost every day for the past three years and at the same time teaching me more about stoping and magma chamber processes than I ever wanted to know, while also patiently listening to my Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. theories on the geologic evolution of Baja. My days would have been very boring without you there. Just remember that I’ll call whenever I have a computer problem. Thanks to Keegan Schmidt, Michael Potter, Paul Wetmore (again!), Markus Albertz, David Farris, Melissa Boysun, Luke Jensen, Rita Economos (my only field assistant), and Vali Memeti. Other people around the ‘Strain group’ were Brian Darby, who was a hoot to have around, and more recently Claire Coyne and Frances Cooper (Good luck). Thanks also to all the other graduate and undergraduate students in the Department of Earth Sciences who made my time there so much more fun. Special thanks are due to Coco Corral, who lives on a pluton in the Sierra Calamajue that now bears his name. Regardless of who you are, Coco provides shelter from the summer heat, drinking water or a cold beer, a shower, and a bed under the stars if you need one. Coco’s Comer will always be a special place for me and every time I’m coming back, I hope he’s still around in that desolate little place. This work would not have been possible without the constant support and love of my family throughout the many, many, many years of my education. I miss all of you every day and hope we’ll see each other soon. The final and greatest thank you is reserved for my wonderful and beautiful wife and best friend Alejandra. This degree is as much your achievement as it is mine. Without you and your encouragement, patience, and support, I would have quit years ago. Thank you for everything and so much more. I love you! Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS ACKNOWLEDGEMENTS....................................................................................ii LIST OF TABLES.................................................................................................. xi LIST OF FIGURES.................................................................................................xii LIST OF PLATES.................................................................................................. xvi ABSTRACT .......................... xvii CHAPTER 1: INTRODUCTION............................................................................ 1 Purpose of study,..................................................................................................1 Outline of dissertation.........................................................................................6 Geology of the Peninsular Ranges batholith (PRB)............................................8 Litho-stratigraphic basement assemblages..........................................................14 Alisitos arc (western zone)............................................................................14 Santiago Peak arc (western zone).................................................................16 Mesozoic basin assemblages (central zone)................................................. 17 Paleozoic continental margin units (eastern zone).......................................18 CHAPTER 2: THE SIERRA CALAMAJUE - GEOLOGIC HISTORY OF AN ARC-CONTINENT COLLISION ZONE.............................. 20 Introduction........................................................................................................ 20 Previous work.................................................................................................... 25 Lithology............................................................................................................26 Canon Calamajue unit.................................................................................. 30 Alisitos Formation........................................................................................30 Canon de los Frailes unit............................................................................. 31 La Mision unit..............................................................................................32 La Josefina unit............................................................................................33 Summary...................................................................................................... 34 Deformation....................................................................................................... 35 Phase 1 ........................................................................................................... 35 Phase 2...........................................................................................................37 Phase 3...........................................................................................................53 Phase 4 .......................................................................................................... 58 Summary of deformation............................................................................. 58 Metamorphism................................................................................................... 59 Discussion..........................................................................................................61 Original tectonic setting of lithologic units,................................................. 61 Cause and timing of Phase 1 (Pre-Cretaceous) deformation.........................65 Cause and timing of Phase 2 deformation,.....................................................66 Cause and timing of Phase 3 deformation,.................................................... 68 Cause and timing of Phase 4 deformation.................................................... 70 vi Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Effects of pre-existing geology on Cretaceous deformation.........................71 Conclusions..........................................................................................................72 CHAPTER 3: RECONNAISSANCE PLUTON GEOCHEMISTRY AND GEOCHRONOLOGY...............................................................................................75 Introduction.........................................................................................................75 Plutonic units,.......................................................................................................77 Deformed plutons (Orthogneiss)...................................................................77 Piedra Blanca pluton,................................................................................77 Chapala Ring Complex............................................................................80 Undeformed plutons...................................................................................... 81 Geochronology and geochemistry....................................................................... 82 Geochronology,.............................................................................................. 82 Geochemistry................................................................................................. 84 Discussion............................................................................................................88 Geochronologic constraints,...........................................................................88 Significance of the ~144 Ma Calamajue pluton......................................,88 Significance of the ~95 Ma Las Palmas pluton.......................................,97 Constraints on basement stratigraphy from single crystal zircon analyses..............................................................................98 Geochemical considerations,........................................................................,100 Importance of trace element geochemistry............................................ 100 Constraints on crustal thickening,...........................................................100 Conclusions........................................................................................................105 CHAPTER 4: COMPLEX DEFORMATION AS A RESULT OF ARC-CONTINENT COLLISION - QUANTIFYING FINITE STRAIN IN THE ALISITOS ARC...................................................................... 109 Introduction........................................................................................................109 Geology of the Peninsular Ranges batholith (PRB).......................................... 114 Study areas.........................................................................................................116 San Vicente area..........................................................................................,116 Santiago Peak arc....................................................................................117 Alisitos arc............................................................................................. 119 Summary................................................................................................ 121 Northern Sierra San Pedro Martir................................................................121 Southern Sierra San Pedro Martir...............................................................,126 Sierra Calamajue......................................................................................... 129 Summary of qualitative structural observations................................................ 134 Strain analyses...................................................................................................136 Introduction................................................................................................. 136 Summary of strain data,............................................................................... ,141 vii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Calculation of finite strain removal............................................................. ,148 Discussion.......................................................................................................... 151 Causes of strain heterogeneity..................................................................... 151 Variations in lithology............................................................................ 151 Temperature, pressure, and strain rate.................................................... 153 Primary fabrics........................................................................................154 Volume change.......................................................................................157 Regional tectonic strain and local strain effects..........................................,162 Deformation gradient.................................................................................. ,166 Bulk shortening and crustal thickening estimates.......................................,167 Factors controlling along-strike character of the fold-thrust belt................,171 Conclusions........................................................................................................ 174 CHAPTER 5: ALISITOS ARC PROVENANCE....................................................176 Introduction........................................................................................................ 176 Detrital zircon provenance.................................................................................178 Introduction.................................................................................................,178 Regional setting............................................................................................182 Sierra Calamajue and adjacent ranges..........................................................182 Provenance of Canal de Las Ballenas Group......................................... 182 Provenance of Canon Calamajue unit................................................... ,187 Provenance of La Mision unit.................................................................187 Provenance of Canon de los Frailes unit............................................... 190 Southern Sierra San Pedro Martir...............................................................,194 San Vicente area..........................................................................................,196 Discussion....................................................................................................,201 Paleozoic passive margin units.............................................................. 201 Triassic-Jurassic accretionary prism units,.............................................203 Cretaceous marine deposits................................................................... 205 Summary and implications....................................................................,207 Paleomagnetism.................................................................................................209 Introduction..................................................................................................,209 Santiago Peak arc........................................................................................,217 Alisitos arc,.................................................................................................. ,219 Methodology............. ............................................................................ 219 Preliminary Results................................................................................ 223 Discussion....................................................................................................226 Results from reconnaissance paleomagnetic work................................ 226 Value of future paleomagnetic investigations........................................226 Linking paleomagnetic results and detrital zircon geochronology............... ,231 Hypothesis 1:..........................................................................................231 Hypothesis 2:..........................................................................................232 Hypothesis 3:..........................................................................................233 viii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Hypothesis 4:..........................................................................................233 Hypothesis 5:,.........................................................................................,234 Hypothesis 6:,......................................................................................... 234 Hypothesis 7:..........................................................................................,235 CHAPTER 6: REGIONAL SYNTHESIS AND CONCLUSIONS.........................236 Introduction........................................................................................................236 Geology, geochemistry, and geochronology of the arc-continent collision zone in the Sierra Calamajue.............................................................. 237 Structural geology,....................................................................................... 237 Geochemistry and geochronology...............................................................,239 Complex displacement fields in the island arc-continent collision zone.......... 240 Evolution of the sedimentary system: Lessons learned from detrital zircon provenance..............................................................................................243 Paleomagnetic data from the PRB: another look at an old controversy,........... 244 A speculative tectonic model for the Paleozoic and Mesozoic evolution of the PRB..........................................................................................................246 Ordovician through Permian.......................................................................,246 Triassic through middle Jurassic (>164 Ma)............................................... ,248 Middle Jurassic to Early Cretaceous........................................................... ,249 Early to mid-Cretaceous.............................................................................. 251 Mid- to Late Cretaceous.............................................................................. 253 Future research directions................................................................................. 255 Paleomagnetism...........................................................................................,255 Strain studies and characterization of overall displacement field,...............,257 Detrital zircon studies................................................................................. 258 Regional studies...........................................................................................258 REFERENCES CITED............................................................................................261 APPENDIX A: U-PB GEOCHRONOLOGIC ANALYTICAL PROCEDURE OF ZIRCONS..................................................................................290 U-Pb geochronologic analyses of zircon.......................................................... 290 APPENDIX B: STRAIN ANALYSES METHODOLOGY AND RELATIONSHIP BETWEEN FOLIATION AND THE XY- PLANE OF THE STRAIN ELLIPSOID.................................................................326 Introduction....................................................................................................... 326 Methodology..................................................................................................... 326 Relationship between foliation and XY-plane of strain ellipsoid.....................327 APPENDIX C: GEOLOGY OF CANYON LAS PALMAS AREA.......................333 ix Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Introduction.......................................................................................................333 Las Palmas Canyon section.............................................................................333 Lower plate,..................................................................................................,335 Middle plate.................................................................................................339 Upper plate.................................................................................................. ,341 APPENDIX D: RAW DATA FOR PALEOMAGNETIC ANALYSES.................344 Introduction 344 x Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES Table 3.1. Major, trace, and rare earth element chemistry,........................................ 85 Table 3.2. Normative compositions of plutons.......................................................... 87 Table 3.3. Major element geochemistry from Punta Final and La Guera plutons... 101 Table 4.1. Strain data from Alisitos arc,................................................................... 137 Table 4.2. Recalculation of finite strain data............................................................149 Table 4.3. Summary table of studies related to volume change...............................158 Table 5.1. Summary table of previous studies in the PRB.......................................212 Table A.I. LA-IC-PMS analyses of igneous zircon from the Sierra Calamajue area............................................................................................301 Table A.2. Laser-Ablation IC-PMS detrital zircon analyses results........................303 Table B.l. Orientation data for geographically reoriented strain ellipsoid and field data..........................................................................................330 Table D.l. Bulk natural remanent magnetization (NRM) measurements................352 Table D.2. Bulk magnetic susceptibility measurements..........................................355 Table D.3. In situ and bedding corrected declination and inclination data.............. 358 xi Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES Figure 1.1. Regional overview of the PRB................................................................ 3 Figure 1.2. Simplified map of the fault-bounded Alisitos arc....................................12 Figure 2.1. Simplified map of the Sierra Calamajue study area............................... 21 Figure 2.2. Highly simplified tectono-stratigraphic section through the Sierra Calamajue study area................................................................. 28 Figure 2.3. Picture showing compositional layering..................................................36 Figure 2.4. Stereoplot of plunges of fold axes in Paleozoic strata related to Phase 1 deformation................................................................................................38 Figure 2.5. Picture showing open/tight folds in compositional layering...................39 Figure 2.6. Picture showing zone of brecciation associated with El Toro fault........ 42 Figure 2.7. Picture showing evidence for early ductile deformation.........................43 Figure 2.8. Picture showing isoclinal folds in Paleozoic units being tightly refolded....................................................................................................... 45 Figure 2.9. Picture showing open to tight outcrop-scale fold in Mesozoic units 46 Figure 2.10. Stereoplots of stmctural measurements of Phase 2 deformation folds.................................................................................................... 47 Figure 2.11. Picture showing locally abundant pinch-and-swell structures.............. 48 Figure 2.12. Picture showing discrete crenulation cleavage..................................... 49 Figure 2.13. Stereoplots showing structural data from Alisitos Formation...............51 Figure 2.14. Stereoplots showing structural data from Sierra La Josefina................52 Figure 2.15. Picture showing outcrop-scale kink folding..........................................54 Figure 2.16. Stereoplots showing poles to foliation in three domains in the Sierra Calamajue...........................................................................................55 Figure 2.17. Stereoplots showing plunges of lineation in three domains in the Sierra Calamajue............................................................................ 56 xii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 2.18. Stereoplot showing poles to kink fold axial planar cleavage................57 Figure 2.19. Picture showing graded bedding in the weakly metamorphosed Alisitos Formation...................................................................................................60 Figure 3.1. Simplified map of the Sierra Calamajue study area emphasizing the different plutons...........................................................................76 Figure 3.2. Picture of strong subsolidus deformation in Piedra Blanca fault............ 79 Figure 3.3. Plots of 2 0 6 Pb/2 3 8 U single crystal zircon ages,..........................................83 Figure 3.4. IUGS classification of phaneritic feldspathic rocks................................ 89 Figure 3.5. SiC >2 versus FeO*/MgO plot....................................................................90 Figure 3.6. K2O versus SiC >2 plot.............................................................................. 91 Figure 3.7. A/NK versus A/CNK plot.......................................................................92 Figure 3.8. Alkali-lime index of samples collected in the Sierra Calamajue............ 93 Figure 3.9. Plot of Rare Earth Element concentrations normalized to chondrite 94 Figure 3.10. Comparison between Rare Earth Element patterns..............................103 Figure 3.11. Plot of Sr/Y ratio versus La/Yb-ratio...................................................106 Figure 3.12. Comparison between the La/Yb evolutionary pattern of the Andean arc and Alisitos arc........................................................................ 107 Figure 4.1. General overview of the PRB................................................................ 110 Figure 4.2. Simplified map of the fault-bounded Alisitos arc emphasizing the approximate location of fold-thrust belt and suture........................................ I ll Figure 4.3. Geologic map of the San Vicente area..................................................118 Figure 4.4. Geologic map of the northern Sierra San Pedro Martir.........................123 Figure 4.5. Geologic map of the western part of the fan structure in the southern Sierra San Pedro Martir..........................................................................127 Figure 4.6. Geologic map of Sierra Calamajue area................................................130 Figure 4.7. Modified Flinn plot showing apparent volume loss lines and all strain data from the PRB.................................................................................................142 xiii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 4.8. Plots of strain intensity versus distance to the northern and eastern edges of the Alisitos arc,............................................................................143 Figure 4.9. Diagram explaining recalculation of finite strain shortening and extension values............................................................................................. 150 Figure 4.10. Example of ‘unstraining’ a volume of rock........................................ 152 Figure 4.11. Modified Flinn diagrams showing data subdivided according to local strain setting.............................................................................155 Figure 4.12. Summary diagram for studies calculating volume changes.................160 Figure 5.1. Map of PRB showing detrital zircon localities..................................... 180 Figure 5.2. Detrital zircon analyses probability plot from sample of the Canal de Las Ballenas Group.................................................................................184 Figure 5.3. Comparison between detrital zircon probability plots from samples in the Sierra Calamajue and Devonian Cordilleran strata.......................185 Figure 5.4. Comparison between detrital zircon probability plots from samples in the Sierra Calamajue and Ordovician Cordilleran strata.................... 186 Figure 5.5. Map of the Sierra Calamajue study area showing detrital zircon sample locations......................................................................................... 188 Figure 5.6. Detrital zircon analyses probability plot for sample from the Canon Calamajue unit......................................................................................189 Figure 5.7. Detrital zircon analyses probability plot for sample from the La Mision unit................................................................................................. 191 Figure 5.8. Detrital zircon analyses probability plot for sample from Canon de los Frailes unit...................................................................................... 193 Figure 5.9. Detrital zircon analyses probability plot for sample from the southern Sierra San Pedro Martir.................................................................... 195 Figure 5.10. Stratigraphic column for Alisitos Formation in the San Vicente area,.......................................................................................................... 197 Figure 5.11. Detrital zircon analyses probability plot for sample PHW-6-6-00-F from the San Vicente area........................................................... 198 Figure 5.12. Detrital zircon analyses probability plot for sample PHW-5-19-00-A from the San Vicente area......................................................... 200 xiv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 5.13. Comparison between detrital zircon populations of all samples......... 208 Figure 5.14. Generalized geologic map of the PRB showing locations of previous paleomagnetic studies........................................................................211 Figure 5.15. Generalized map of the PRB showing average values for suggested latitudinal translation......................................................................215 Figure 5.16. Generalized map of the PRB showing average values for suggested rotations...........................................................................................218 Figure 5.17. Generalized geologic map of the Erindera area.................................. 220 Figure 5.18. Geologic map of the Arroyo San Jose section.................................... 221 Figure 5.19. Diagram showing paleomagnetic data in west to east transect........... 228 Figure A.I. Tera-Wasserburg concordia diagrams for single zircon grain analyses................................................................................................................. 292 Figure B.l. Stereoplots showing field and strain ellipsoid orientation data............ 329 Figure C.l. Generalized geologic map of the Canyon Las Palmas area..................334 Figure C.2. Stereoplot showing poles to foliation in the lower plate of the Canyon Las Palmas area.............................................................................336 Figure C.3. Stereoplot showing plunges of stretching lineations in the lower plate of the Canyon Las Palmas area....................................................336 Figure C.4. Picture of the Las Palmas fault zone.....................................................337 Figure C.5. Close-up picture of the Las Palmas fault zone...................................... 338 Figure C.6. Stereoplot showing poles to bedding in the middle plate of the Canyon Las Palmas area............................................................................ 340 Figure C.l. Stereoplot showing poles to foliation in the middle plate of the Canyon Las Palmas area............................................................................ 340 Figure C.8. Stereoplot showing plunges of stretching lineations in the middle plate of the Canyon Las Palmas area..................................................340 Figure C.9. Regional view of the La Equis thrust in steep cliff face.......................342 Figure C.10. Stereoplot showing poles to bedding in the upper plate of the Canyon Las Palmas area............................................................................ 343 xv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure C. 11. Stereoplot showing poles to foliation in the upper plate of the Canyon Las Palmas area.............................................................................343 Figure C.l2. Stereoplot showing plunges of stretching lineations in the upper plate of the Canyon Las Palmas area....................................................343 Figure D.l. Normalized NRM versus temperature plots.........................................345 Figure D.2. Bulk susceptibility versus temperature plots........................................ 348 PLATES Plate 1. Geologic map of the Valle Calamajue, Baja California (in back pocket) xvi Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT Studies of the collision zone between the Cretaceous Alisitos island arc, which accreted to North America between 115 and 100 Ma, and the continental margin in the Peninsular Ranges batholith (PRB), Baja California provide a means of evaluating the temporal evolution of (1) paleo-displacement fields and gradients within the arc and continental margin; (2) geochemical changes in the magmatic system; and (3) sedimentary basins in the collision zone and source changes for sediments in these basins. The paleo-displacement field in the Sierra Calamajue is characterized by a SW-vergent fold-thrust belt that records collision-related contraction, but also preserves evidence for Paleozoic deformation along the southern margin of North America. Comparison between the Sierra Calamajue and the collision zone in the Sierra San Pedro Martir (SSPM) and near San Vicente shows that paleo- displacements inferred from structural characteristics change along strike due to (1) changes in tectonic setting from sinistral transpression in the north to normal convergence along the eastern margin of the arc; (2) the pre-existing geometry of the continental margin, including a promontory of miogeoclinal strata east of the SSPM; and (3) rheologic changes caused by the transition from Paleozoic shallow to deep- water deposits at 30.5°N latitude and southward decrease of Cretaceous sedimentary deposits. Bulk shortening (including finite strain) estimates in the collision zone support arc-perpendicular shortening of >60% and crustal thickening (up to 10 km) xvii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. that is greatest along the east side of the arc. Geochemical analyses, which suggest magma generation at depth >40 km after 110 Ma (a significant increase in depth from 30 to 35 km or less prior to collision), further support crustal thickening. Provenance links between Paleozoic and early Mesozoic units in the PRB and North America are established using detrital zircons. The data are also used to distinguish marine basins. Basin deposits north and east of the Alisitos arc are dominated by arc detritus between 117 and 110 Ma, whereas deposits farther east received input from arc and cratonal sources. By ~110 Ma syn-collisional sediments in the Alisitos arc show links to cratonally-derived sources suggesting close proximity between the arc and North America. xviii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 1: INTRODUCTION Purpose of Study Understanding the evolution of active tectonic environments in their entirety has been identified as a prime target for physical (including earth) science investigations. Several multi-disciplinary initiatives (e.g., MARGINS, Earthscope) are currently underway to achieve this goal along continental margins. These initiatives focus on how these complex continental margin systems form and evolve in various tectonic settings. They set out to investigate and determine rates of active processes (e.g., lithospheric deformation and earthquakes, magmatism and mass fluxes, sedimentation) that fundamentally govern the evolution of continental margins. However, science plans developed for these programs mostly downplay the effects of island arc collision, which is actively occurring in Taiwan (Kao et al., 1998), northern Australia (Genrich et al. 1996), the Aleutian-Kamchatka Peninsula (Geist et al., 1994), and along the South American - Caribbean plate boundary (AveLallement, 1997), on continental margin processes. Although the advancement of technology has led to a revolution in geologic investigations with millimeter precision measurements (geodesy), making active geologic environments the targets of choice, ancient systems provide critical information about middle and deep crustal processes and long-term rates of processes (paleo-geodesy). Thus, this study was designed to start to test long-term effects of island arc collision on continental margin systems. 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The locality for this project was chosen after recent studies in the Peninsular Ranges batholith (PRB) of Baja California, which includes the Jura-Cretaceous batholithic rocks and host strata, identified the Alisitos arc as a collided island arc that accreted to North America in the mid-Cretaceous (Fig. 1.1) (e.g., Gastil et al., 1981; Todd et al., 1988; Busby et al., 1998; Johnson et al., 1999a, Wetmore et al., 2002). While the details of the Mesozoic tectonic evolution of the entire PRB, which extends from the Transverse Ranges in southern California to the tip of Baja California (e.g., Kimbrough et al., 2002; Langenheim and Jachens, 2003), remain debated most workers would now agree that the Alisitos arc represents an accreted tectonic element. The existence of a collided island arc in the PRB makes it an ideal field laboratory to evaluate how different parts of the whole island arc and continental margin system (e.g., magmatic and sedimentary systems, displacement field) change in a subduction-collision setting. Important aspects that can be addressed include, for example, deformation associated with collision (Chapters 2 and 4), geochemical changes in the magmatic system (Chapter 3), source changes for sedimentary detritus and displacements (i.e. translation and/or rotation) of tectonic domains within the arcs and continental margin (Chapter 5). Furthermore, we can start to evaluate how local and/or regional along strike heterogeneities (e.g., rigid indenters) and rheologic variations along the continental margin influence deformation and control arc processes. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Los Angeles Vicente v Quintin Explanation: \ SAF ABF MSM? Pm-Tr Santiago Peak arc Alisitos arc Bedford Canyon Complex Mesozoic clastic sediments Undifferentiated Paleozoic passive margin strata Proterozoic basement Study areas (see Figure caption) Depositional contact Fault zontact (thrust, strike-slip) Gulf of California (incipient spreading centers and transform faults) San Andreas fault Agua Blanca fault Mojave-Sonora Megashear? Permo-Triassic U.S./Mexican highways Figure 1.1. Overview of the PRB including outlines of study areas discussed throughout the text. ASJ=Arroyo San Jose (Chapter 5); BLA=Bahia de Los Angeles area (Morgan et al., 2005); EM=E1 Marmol area (Buch and Delattre, 1993); ERJ=Erindera area (see Chapter 5); PP=Punta Prieta area (Chapter 4); l=San Vicente area (Wetmore, 2003); 2=northem Sierra San Pedro Martir (Johnson et al., 1999a; b; 2003); 3=southem Sierra San Pedro Martir (Schmidt, 2000); 4=Sierra Calamajue (this study; Griffith and Hoobs, 1993). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Evidence that support collision and accretion of the Alisitos arc include a non-terminal suture (Dewey, 1977) juxtaposing the arc with strata of North American origin. Suturing was associated with formation of a fold-thrust belt that now rims the arc along its northern and eastern margin. While this fold-thrust belt has been studied in significant detail along the northern margin of the arc (Wetmore, 2003; Wetmore et al., 2002; 2003a) and in the Sierra San Pedro Martir along the east side of the arc (e.g., Johnson et al., 1999a; b; Schmidt, 2000), it has received limited attention towards its southern extremes in the Sierra Calamajue (Fig. 1.1). Until now, our understanding of this part of the arc suture zone and adjacent continental margin units was based on reconnaissance-style mapping by Master’s students from San Diego State University (Hoobs, 1985; Griffith, 1987; see also Griffith and Hoobs, 1993). However, with recent advances in the understanding of the regional geology, extension of reconnaissance mapping in this area was warranted and more detailed mapping was completed as part of this Ph.D. project. Mapping in the Sierra Calamajue confirmed the existence of a fold-thrust in which the Alisitos arc is in fault contact with continental margin units of likely North American affinity. The fold-thrust belt is characterized by brittle and ductile deformation that differs significantly from deformation in the Sierra San Pedro Martir and San Vicente areas farther to the north (Fig. 1.1; Johnson et al., 1999a; b, Schmidt, 2000; Wetmore, 2003). The recognition of these along-strike variations led to a broader question: How is deformation and finite ductile strain in particular, accommodated in the arc, suture zone, and continental margin strata and what factors 4 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. control how deformation is accommodated? Furthermore, important questions regarding the response and changes of geologic systems (e.g., depositional systems, magmatic system) due to collision can be asked. The presence of abundant strain markers, such as lithic fragments and clasts, allows the quantification of the finite strain component of deformation associated with arc collision and the overall contribution of ductile strain to shortening in the fold-thrust belt. Thus, I collected samples for strain analysis throughout the Sierra Calamajue and collaborated with previous workers, who collected (but had not necessarily analyzed) similar samples in the San Vicente area (Wetmore, 2003) and the northern and southern Sierra San Pedro Martir (Johnson, 1999a; Schmidt, 2000). Thus, the data is a collection of new and previously analyzed samples, which constrain the amount of finite strain associated with collision of the arc, as well as provide information about vertical extension and possible crustal thickening. To address questions regarding changes in the magmatic and depositional systems, reconnaissance geochemistry and geochronology from the Sierra Calamajue was combined with observations by earlier workers elsewhere in the arc (e.g., Tate et al., 1999; Tate and Johnson, 2000; Wetmore, 2003). Furthermore, several sedimentary samples were collected for detrital zircon analyses to constrain depositional ages of various units and make inferences about changing sediment sources for units deposited prior to and during collision of the Alisitos arc. Finally, the question of how far from the North American continent the Alisitos arc formed remained to be addressed. Two competing end-member models 5 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. for the Mesozoic tectonic evolution of the PRB have been proposed (e.g., Busby et al., 1998; Johnson et al., 1999a). While Busby and coworkers favor formation of the Alisitos arc as a fringing island arc following a Jurassic rifting event, Johnson and colleagues suggest that the arc may be exotic, potentially formed a large distance from the North American margin, and accreted to the North American continent after closure of an ocean basin and complete subduction of a separate oceanic plate. To address these issues, I started reconnaissance paleomagnetic analyses on Alisitos arc volcanic units. This study builds on earlier work that has been conducted on numerous sedimentary and igneous rocks (e.g., Teissere and Beck, 1973; Hagstrum et al., 1985; Beck, 1991; Lund andBottjer, 1991; Hagstrum and Sedlock, 1998), but not the arc strata itself. Furthermore, the samples collected for detrital zircon analyses (see above) shed light on the provenance of detritus deposited prior to and during collision of the arc. Outline of dissertation Each chapter in the dissertation deals with one aspect outlined above and includes background information on the subject and a general description and discussion of the significance of the data presented in the chapter. It should be noted that some of the chapters are being prepared for publication, which in places leads to redundancies in the text. In addition to information about the purpose of study and the general dissertation outline, I summarize the regional geology of the PRB and provide a 6 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. general description of the various basement assemblages that are important for this study in Chapter 1. In Chapter 2 ,1 present the geology of the Sierra Calamajue study area. Data include general rock descriptions and structural data from the collision zone between the Alisitos arc and the continental margin. One outcome of this work is a regional map at a 1:50,000 scale (back pocket). Chapter 3 contains reconnaissance geochemical and geochronological analyses of plutons in the Sierra Calamajue area. These data include U-Pb zircon crystallization ages of two plutons and whole rock and trace element geochemistry of three intrusions. Preliminary data are placed in a regional context and compared to similar data from the San Vicente area (Wetmore, 2003) and the northern Sierra San Pedro Martir (Tate et al., 1999; Tate and Johnson, 2000). Chapter 4 focuses on the along-strike character of the arc-bounding fold- thrust belt as well as finite strain analyses. Within the fold-thrust belt finite strain is variable, but generally increases towards the suture zone. Heterogeneous finite strain magnitudes and ellipsoid shapes are caused by the superposition of primary fabrics, tectonic strain, and contributions from local effects, such as matrix-lithic ratios, proximity to intrusive bodies, or shear zones. Furthermore, I estimated bulk shortening and crustal thickening in the fold-thrust belt associated with arc collision and estimates are given in the text. Detrital zircon data are presented in Chapter 5, where I also address questions regarding the origin of the Alisitos arc and provenance of the sediments within and 7 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. adjacent to the arc. Also included in this chapter is a review of paleomagnetic analyses in the PRB, as those data pertain to provenance and origin of the Alisitos arc, and some preliminary paleomagnetic results on Alisitos arc volcanics. That chapter concludes with several hypotheses regarding the evolution of the PRB and the sedimentary system that can be tested with additional and more detailed detrital zircon and paleomagnetic data. In Chapter 6 ,1 summarize the data presented in the preceding Chapters and provide a regional synthesis of results from previous studies in the PRB. The chapter ends with future directions, which I think are valuable avenues for future research in the PRB. An extensive Appendix contains various datasets that contain supplemental data, which represent the raw data and build the foundation for discussions in the chapters (Appendix A, B, and D). In addition to the data presented in Chapter 2 ,1 mapped in considerably more detail (1:25,000 scale) in the Canyon Las Palmas area to the east-southeast of the main study area because the intricate structure of the fold- thrust belt is preserved. Results from that work are provided in Appendix C. Geology of the Peninsular Ranges batholith (PRB) The Peninsular Ranges batholith (PRB), which includes the Jura-Cretaceous batholithic rocks and the host strata, extends from the Transverse Ranges in southern California to at least the 28th parallel. The PRb is bounded by the San Andreas-Gulf of California transform-rift system to the east and Neogene transcurrent faults of the 8 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Continental Borderlands to the west (e.g., Legg et al., 1991; Sedlock et al., 1993). Extension of the PRb southward past the 28th parallel to the tip of the peninsula is based on correlating the intrusives of the Late Cretaceous Los Cabos block in southern-most Baja California Sur with those of the PRb to the north (Kimbrough et al., 2002) and the presence of a strong magnetic high below the mostly Neogene cover of Baja California Sur (Langenheim and Jachens, 2003). The nature, number, and continuity of tectono-stratigraphic basement units that comprise the PRB have long been controversial. Significant geologic, petrologic, geochemical, and isotopic across-strike (E-W) variations (e.g., Gastil et al., 1975, Taylor and Silver, 1978; DePaolo, 1981; Gromet and Silver, 1987; Silver and Chappell, 1988; Gastil et al., 1990) led early workers to suggest three main NW- trending litho-stratigraphic basement assemblages. From west to east these include: (1) Jura-Cretaceous volcanic arc assemblages (western zone); (2) Triassic(?)-mid Cretaceous volcanic and clastic assemblages (central zone); (3) Paleozoic passive margin sequences with North American affinities (eastern zone) that can further be subdivided into Ordovician-Permian slope-basin clastic assemblages and Upper Proterozoic-Permian miogeoclinal carbonate-siliciclastic assemblage (e.g., Gastil et al. 1991; Gastil and Miller, 1993; Gehrels et al., 2002; Alsleben and Paterson, 2002). The primitive geochemical and isotopic character of the intrusions into the western part of the PRB led to the interpretation that the western zone is underlain by oceanic basement that accreted to the continental margin. In contrast, the geochemically and isotopically more evolved intrusions in the eastern PRB support 9 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. underlying lithosphere that is older and of continental composition (e.g., Gastil et al., 1975, Taylor and Silver, 1978; DePaolo, 1981; Gromet and Silver, 1987; Silver and Chappell, 1988; Gastil et al., 1990). Besides these apparent across-strike transitions, Gastil et al. (1975; 1981) also noted several north to south transitions to the geology/geophysics of the volcanics-dominated western Peninsular Ranges. These differences appeared to be most pronounced across the trace of the Agua Blanca fault (ABF) (Fig. 1.1) and include (1) a change in the environment of deposition of the volcanics and reworked volcaniclastics, (2) an apparent age break, and (3) dramatic steps in the gravity and aeromagnetic signatures across the fault. Specifically, the Santiago Peak arc to the north of the ABF is characterized by subaerially deposited Jurassic to Early Cretaceous volcanics (although later constrained to just Early Cretaceous; Wetmore et al., 2003a) and both low gravity and magnetic signatures. In contrast, the subaqueously deposited Early Cretaceous (Aptian-Albian) volcanics/volcaniclastics of the Alisitos arc to the south of the fault exhibits both a gravity and magnetic high. In the accompanying tectonic model, Gastil et al. (1981) proposed that the western zone north and south of the ABF were once a continuous fringing arc that had rifted from the continental margin and was subsequently re-accreted diachronously with the Santiago Peak arc segment re-accreting first in the Aptian-Aptian followed by the Alisitos arc segment late in the Albian. These N-S variations observed by Gastil et al. (1975; 1981) were largely ignored until Wetmore et al. (2002; 2003a) revisited the concept of a potential 10 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Mesozoic history to the ABF approximately 20 year later. The latter authors identified several additional variations in the geology of the two western arc segments, all seemingly centered on the newly identified ancestral ABF (aABF), a mid-Cretaceous, oblique slip (sinistral and southwest-vergent) ductile shear zone located approximately 2-3 km south of the active ABF (Fig. 1.2). These additional variations include the presence or absence of Late Triassic- Jurassic continentally- derived turbidite strata, the structural relationships between Cretaceous volcanics and continentally-derived strata, the presence or absence of xenocrystic Precambrian zircons in Cretaceous volcanics/plutonics, and the amount and location of deformation exhibited by the Cretaceous strata (Wetmore et al., 2002; 2003a). Based on these new and previously identified variations in geology across the aABF, Wetmore et al. (2002; 2003a) proposed a different tectonic model than Gastil et al. (1981). Wetmore et al. (2003a) argue that the Late Triassic-Jurassic turbidite sequences (named the Bedford Canyon Complex) present to the north of the aABF exhibit a geometry and style of deformation (Sutherland et al., 2002) consistent with that commonly observed within upper levels of an accretionary prism (e.g., Sample and Moore, 1987). The presence of Precambrian detrital zircons (Gastil and Girty, 1993) and olistostromes with detrital zircon signatures equivalent to parts of the North American Paleozoic passive margin sequences (Gehrels et al., 2002) further suggests that this accretionary prism formed in situ along the southwestern margin of North America. The Early Cretaceous Santiago Peak Volcanics are likewise interpreted to have been emplaced in their present position atop the Bedford Canyon 11 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. zTx F lat to gently ^ inclined stra ta « U i F olds (upright, T T O o v ertu rn ed ) Inferred c o n ta c t H ighw ays <^> f5rv'*, s jr e (in kbar) D irection of strain in c re a s e __________ p e G satic)’ Figure 1.2. Simplified map of the fault-boimded Alisitos arc with approximate location of fold-thrust belt and suture between the arc and adjacent units. Note location of the aABF. Plutons are removed for added simplicity. ABF=active Agua Blanca fault; aABF=ancestral Agua Blanca fault; MMT=Main Martir thrust; ETF=E1 Topo fault. Baromtery is from Rothstein (1997), Kopf and Whitney (1999), Kopf et al. (2000), Schmidt (2000), and Schmidt and Paterson (2002). 12 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Complex. This follows from the lack of observed shear across exposures of the contact between the strata (Herzig, 1991; Sutherland et al., 2002), the presence of Precambrian xenocrystic zircons in both plutonics and volcanics of the Santiago Peak arc (ages consistent with those observed in the underlying Bedford Canyon Complex; Anderson, 1991; Herzig, 1991; Carrasco et al., 1995; Premo et al., 1998), and dikes that cut the underlying Bedford Canyon Complex, the contact, and can be shown to have fed flows in the overlying Santiago Peak Volcanics (Herzig, 1991). Hence, Wetmore et al. (2002; 2003a) argue that the Santiago Peak arc was a continental margin arc built on and through the earlier formed North American accretionary prism. In contrast to the Santiago Peak arc segment, the Alisitos arc segment to the south of the aABF (Fig. 1.1) is interpreted to have been an island arc that developed on and through oceanic lithosphere not associated with the North American margin prior to its accretion in the late Early Cretaceous (Johnson et al., 1999a). This follows from the observations that the volcanics and plutonics of the arc segment have not yielded Precambrian zircons (Carrasco et al., 1995; Johnson et al., 1999a, b, 2003; Tate et al., 1999), as well as the fault-bounded nature of the Alisitos arc and the presence of a broad (15->30 km) fold-thrust belt that is best-developed within the Cretaceous volcaniclastic strata (Alisitos Formation) along the boundaries of the arc segment with continental margin sequences including the Santiago Peak Volcanics to the north (Wetmore et al., 2002) and basinal assemblages of unknown tectonic 13 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. setting (possibly intra arc basin or remnant ocean basin) to the east (e.g., Johnson et al., 1999a; Schmidt, 2000). Litho-stratigraphic basement assemblages A general understanding of four of the litho-stratigraphic basement assemblages as identified by Wetmore et al. (2003a) will valuable for subsequent Chapters in this dissertation. As such, I provide an overview of the lithologies, metamorphic grade, depositonal environment, and age of the Alisitos arc, Santiago Peak arc, Mesozoic basin assemblages, and Paleozoic deep-water sequences in the following sections. Alisitos arc (western zone) The Alisitos Formation of Allison (1955; 1974) constitutes all of the arc strata. In many places, depositional and volcanic features are superbly preserved and rocks are essentially unaltered. The formation is composed of volcanic flows and breccias, pyroclastic deposits, volcaniclastics, volcanogenic argillites and sandstones, calc-silicates, and a regionally-extensive prominent limestone member. Metamorphism is mostly sub-greenschist facies and alteration is mostly minimal. Towards the northern and eastern margins of the arc, metamorphism increases to greenschist facies and reaches upper greenschist facies conditions near the suture in the northern Sierra San Pedro Martir (Johnson et al., 1999a). Other exceptions to the general low metamorphic grade are places of hydrothermal 14 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. alteration and in pluton aureoles, where the metamorphic grade can be higher (amphibolite facies). Based on abundantly preserved marine fossils and presence of basaltic lava flows exhibiting pillow structures, subaqueous deposition dominated during the emplacement of the Alisitos Formation (Leedom, 1967; Reed, 1967; Allison, 1974; Beggs, 1983; 1984; Suarez-Vidal, 1987; 1993; Fackler-Adams, 1997), although subaerial deposition occurred locally near inferred volcanic edifices (Fackler-Adams and Busby, 1998). Furthermore, although sedimentary and volcanic strata are often intimately interleaved, distinct packages dominated by either sediments or volcanic debris have been described and sedimentary basins seem to be prevalent along the northern and eastern flanks of the arc (Fig. 1.2) (e.g., Suarez-Vidal et al., 1987; 1993; Johnson et al., 1999b; Schmidt, 2000; Wetmore, 2003). The age of the arc is confined by Early Cretaceous (Albian) fossils (e.g., Allison, 1955, 1974; Silver et al., 1963) that are found in the prominent limestone unit and a limited geochronologic dataset. Carrasco et al. (1995) and Johnson et al. (2003) obtained U/Pb ages of 116±2 Ma, 115±1.1 Ma, and 114.8±1.5 Ma on volcanic flows. Based on these few constraints, the arc is mid-Cretaceous in age. However, this has to be regarded as a minimum age as the deeper parts of the arc are not exposed. 15 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Santiago Peak arc (western zone) The Santiago Peak arc is comprised of the Santiago Peak Volcanics, which are composed of dominantly subaerially deposited volcanic flows, welded tuffs, hypabyssal intrusions, and rare epiclastic deposits (Larsen, 1948; Schroeder, 1967; Adams, 1979; Gorzolla, 1988; Herzig, 1991; Reed, 1992; Carrasco et al., 1993; Meeth, 1993). The volcanics, which show limited metamorphism comparable to that of the Alisitos arc, are inferred to be dominantly subaerially deposited based on the abundance of accretionary lapilli, preserved paleosols, and the absence of pillow lavas, thick and laterally extensive epiclastic deposits, and other marine deposits (e.g., Herzig, 1991). Recent U/Pb geochronology studies of the Santiago Peak Volcanics yield mildly discordant ages that range from 128 to 116 Ma (Anderson, 1991; Meeth, 1993; Carrasco et al., 1995). The basal unit of the Santiago Peak Volcanics in southern California yielded a U/Pb zircon age of 127±2 Ma (Anderson, 1991; Herzig, 1991). The 116 Ma age, derived from a sample 200 m below the mapped top of the Santiago Peak Volcanics section, is assumed to be a minimum age for the end of Santiago Peak arc magmatism (Meeth, 1993). Overlying the Santiago Peak Volcanics are coarse clastic forearc strata of Late Cretaceous age and the true termination of Santiago Peak volcanism is between 116 Ma and the Late Cretaceous. 16 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Mesozoic basin assemblages (central zone) The Alisitos arc strata are overthrust along its eastern edge by schistose and gneissic metavolcanic and metasedimentary strata. These units have in the past been referred to as ‘flysch’ assemblage, central zone sediments, or transitional zone (e.g., Gastil et al., 1975; Gastil, 1993; Schmidt, 2000; Schmidt and Paterson, 2002). The protoliths to these units include basalts, silicic lithic crystal tuffs, tuff breccias, and tuffaceous sandstones, shales, as well as uncommon, relatively pure limestone and quartzite layers (Johnson et al., 1999b; Schmidt, 2000). In the Sierra San Pedro Martir (SSPM), these units record the highest metamorphic pressure (between 5 and 6 kbar) anywhere in the PRB (e.g., Rothstein, 1997; Kopf et al., 2000; Schmidt, 2000; Rothstein and Manning, 2003). However, units of similar composition exposed to the south in the Sierra Calamajue that have tentatively been correlated with units in the SSPM preserve a significantly lower temperature-pressure regime (greenschist to lower amphibolite facies). The original tectonic setting for these basin deposits remains speculative and has not been adequately addressed. Several authors have labeled these deposits according to their proposed tectonic model as either inter-arc, intra-arc, remnant ocean, or back arc basin deposits (e.g., Busby et al., 1998; Johnson et al., 1999a). New results comparing detrital zircon populations from several locations along strike of the PRB extending from southern California to about the 28th parallel, show that zircon population are comparable (Morgan et al., 2005). Thus, these deposits may 17 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. have formed in an accretionary wedge setting as suggested by Wetmore et al. (2003a) for the strata east of the Santiago Peak arc. Similarly to the tectonic setting, the depositional age of these basinal assemblages is uncertain. A maximum depositional age comes from detrital zircon samples, which contain Triassic (and older) grains suggesting an early Mesozoic age (Morgan et al., 2005). A significantly younger age is precluded since these basinal assemblages are intruded by Jurassic (164.4±1.4 U-Pb SHRIMP zircon age) biotite muscovite orthogneisses (Schmidt, 2000; Schmidt and Paterson, 2002). The existence of 128 to 133 Ma old intrusions in the northern and southern Sierra San Pedro Martir suggests that these deposits may represent the remnants of a continental margin arc that was active along the North American margin to the east of the oceanic Alisitos island arc (Johnson et al., 1999a). Paleozoic continental margin units (eastern zone) Along the length of the PRB, Paleozoic to possibly earliest Mesozoic strata are exposed along the east side of the peninsula (e.g., Gastil et al., 1975; Gastil and Miller, 1993 and references therein). While several studies have been completed on these strata (e.g., Gastil and Miller, 1993), the exposure appears spotty and structural analyses are largely missing, making the relationships between these units and similar units in the southwestern Cordillera still poorly understood. In general, these strata are subdivided into Ordovician-Permian, deep marine, continentally derived clastic strata are juxtaposed with Upper Proterozoic(?)-Permian 18 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. miogeoclinal carbonate-siliciclastic assemblages (Fig. 1.1). These subdivisions, age assignments, and association with North American miogeoclinal and deep-water strata are largely based on fossils that have been found at various locations (e.g., Gastil and Miller, 1984; Campbell and Crocker, 1993; Leier-Engelhardt, 1993; Griffith and Hoobs, 1993). Recent analyses of detrital zircon populations in two locations have substantiated Paleozoic ages for these strata and possibly North American affinities (Gehrels et al., 2002). Relationships between deep-water and miogeoclinal sequences have not been described in Baja California. One possibility is that Late-Permian to Middle Triassic, north-directed thrusting of slope-basin rocks over miogeoclinal strata in the Caborca block in central Sonora, Mexico (Stewart, 1988; Stewart et al., 1990; Poole et al., 1995) could be extended to the eastern Baja California. 19 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 2: THE SIERRA CALAMAJUE - GEOLOGIC HISTORY OF AN ARC-CONTINENT COLLISION ZONE Introduction Recent studies in the Peninsular Ranges batholith (PRB) have dominantly focused on the relationships between western Jura(?)-Cretaceous volcanic assemblages and Triassic(?) through mid-Cretaceous continental margin clastic sedimentary sequences and affiliated Jura-Cretaceous igneous rocks, which comprise the central zone (Fig. 2.1.; e.g., Gastil et al., 1975; 1981; Todd et al., 1988; Busby et al., 1998; Johnson et al., 1999a; Schmidt, 2000; Schmidt and Paterson, 2002; Wetmore et al., 2002; 2003a). A clearer picture of the Jura-Cretaceous tectonic evolution of the southwestern North American Cordillera emerged from these studies, which led to the recognition of an in situ continental margin arc (Santiago Peak arc) and a collided oceanic island arc (Alisitos arc). Accretion of the latter was associated with formation of a suture zone and fold-thrust belt that now rims this collided entity and caused widespread mid-Cretaceous (-115 to -103 Ma) deformation in the arc and continental margin (e.g., Johnson et al., 1999a; Schmidt and Paterson, 2002; Wetmore et al., 2003a). Detailed studies of the collision zone between the Alisitos arc and continental margin units have been completed in the San Vicente area (Wetmore, 2003; Wetmore et al., 2002; 2003a) and the northern (Johnson et al., 1999a; 2003) and southern (Schmidt, 2000; Schmidt and Paterson, 2002; Schmidt et al., 2002) Sierra 20 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SarTFrancjsqultolH]! Explanation: Quaternary/ Tertiary ^ N orthern^ Cretaceous Plutons Alisitos Formation ‘ -I;----- Canon de las Frailes unit Molino fault La Mision unit Canon Calamajue Unit La Josefina unit ..Eastpra Depositional contact n a ssic Cretaceous thrust faults 125 Ma t Folds (upright, ♦ u overturned) C alam aju e C an w m m m New U-Pb age Detrital zircon age Fossil locality (G&H 1993) U-Pb age (G&H 1993) Paaaaaaarf ’ 1 -i A l -'.< : i A ■ & ' V V ; ' ' K < ' i ' , - j V P rd o v ic ia n C . - w . .... M ississippian fossils [Las P alm as L_c Canyon m \ C ^ ' > ‘ s > y > ' » \ > \ - k - >1 m m s m m m i ' w IlL as Palmas :pluton': ■ s r Mid- S Cretaceoush^^ 5 k m ^ 14°10’N I 2 9 15’N Figure 2.1. Simplified map of the Sierra Calamajue study area. Main mountain ranges are labeled and domains discussed in the text are outlined. G&H 1993= Griffith and Hoobs (1993). Detailed 1:50,000 scale map of the same area is in back pocket. 21 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. San Pedro Martir (SSPM). These study areas, however, are located at or near the northern end of the Alisitos arc and detailed studies have not been completed farther towards the southern end of the arc, which is at latitude ~28°N (Figs. 1.1. and 1.2.). Exposures of the collision zone south of the study areas mentioned above have been described in San Diego State University Master’s theses and include the El Marmol (Buch, 1983; Buch and Delattre, 1993) and Calamajue Canyon areas (Fig. 1.1.) (Hoobs, 1985; Griffith, 1987; Griffith and Hoobs, 1993). Other, more cryptic and little explored exposures of the collision zone have been described form the Bahia de Los Angeles (Morgan et al., 2005) and El Arco areas (Bathelmy, 1979). Although lithologic descriptions and reconnaissance structural analyses have been presented from these areas, detailed structural analyses in light of the better understood Mesozoic tectonic evolution had not been completed. A better understanding of the southward extension of the collision zone was desirable after high ductile strains, exhumation of mid-crustal strata across the suture between the Alisitos arc and continental margin, and the development of a doubly- vergent fan structure were recognized in the SSPM (Fig. 1.1.) (Johnson, 1999a; Schmidt; 2000; Schmidt and Paterson, 2002). Questions regarding the southward extent of ductile deformation and fan structure had not been answered, and the structural style and general characteristics of deformation to the south was open to speculation. Furthermore, relationships between central zone basement assemblages and Paleozoic units in the eastern PRB received little attention during previous studies 22 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and the deformational history of Paleozoic rocks in Baja California remained to be clarified. In fact, Paleozoic rocks in the eastern PRB form the least understood of the main basement assemblages (Fig. 1.1.). A limited number of studies on the Paleozoic rocks provide a basic geologic framework that includes 1) lithologic description, 2) subdivision into shallow and deep-water assemblages, 3) identification of Paleozoic fossils with apparent North American affinities, and 4) recognition of an unexplained, but more complex structural history (e.g., Gastil, 1993; Gastil and Miller, 1993). Thus, even basic geologic questions regarding these units, which delineate the southern extent of Paleozoic North America (Stewart, 1988; Stewart et al., 1990), including the nature, magnitude, exact age, and extent of pre-Cretaceous deformation needed to be addressed. The following chapter addresses some of the issues raised above. Below, I summarize mapping that I completed in the Sierra Calamajue study area (see map in back pocket). This area includes the Calamajue Canyon section initially mapped by Hoobs (1985) and Griffith (1987; Griffith and Hoobs, 1993), but also extends into adjacent mountain ranges (Fig. 2.1.). The study area covers the transition from the Alisitos arc to the North American continent and can be described as a brittle to ductile fold-thrust belt. The intricate structure of the fold-thrust belt is preserved in the Canyon Las Palmas area (described separately in Appendix C) in the Sierra La Asamblea east-southeast of Calamajue Canyon (Fig. 2.1.). Furthermore, all three basement assemblages are exposed in a locally rather narrow (<10 km) zone and 23 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. therefore allows to evaluate the structural relationships between all major basement assemblages of the PRB. As part of the mapping project, I focused on the various lithologies, using Griffith and Hoobs (1993) work as a basic guide, and completed detailed structural mapping of the fold-thrust belt focusing on structural relationships between Paleozoic strata, Mesozoic sedimentary assemblages, and the Cretaceous arc strata. The structural data is clearly divided into Paleozoic deformation related to tectonism along the southern margin of the North American continent and Cretaceous deformation related to collision of the Alisitos island arc. The lithologic correlations and structural descriptions below are supplemented with geochemical and geochronologic, including U-Pb pluton crystallization and detrital zircon ages, data, which is presented in subsequent chapters (Chapters 3 and 5). The data below shows that the exposed basement rocks can be correlated with basement strata described farther north, but along-strike differences in the structural style exists between the study area and the San Vicente and SSPM areas. These differences are related to 1) slight differences in the tectonic setting and 2) differences in the pre-existing geology (i.e. lithology and structural history). The effects of the latter strongly influenced where Cretaceous deformation associated with accretion of the oceanic Alisitos island arc was concentrated. In the study area, much of the deformation was focused in a broad area east of the colliding arc, whereas deformation was concentrated in a wedge between arc and continental 24 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. margin units in the SSPM, which led to the exhumation of mid-crustal strata that are not exposed in the Sierra Calamajue. Previous work The Sierra Calamajue study area is located east of Mexican Highway 1, approximately 400 km south of Ensenada, Mexico (Fig. 1.1.). Initial mapping was conducted by Hoobs (1985) and Griffith (1987; see also Griffith and Hoobs, 1993) in a -200 km2 area. These authors suggested that this area represents the suture between North America and an oceanic island arc (Alisitos arc) and noted that deformation is concentrated in a <10-km-wide zone with maximum deformation in Calamajue Canyon. The cause for the narrowness of the deformation zone was not addressed by the authors, but they noted that it widens to >10 km to the northwest and southeast of the canyon (Fig. 2.1.). Griffith and Hoobs (1993) described the structural stratigraphy through Calamajue Canyon and estimated structural thicknesses’ of various units that total -7500 m of section. They also conducted initial geochronologic and structural analyses of the weakly metamorphosed volcanic, volcaniclastic, and sedimentary strata. Based on those analyses, the basement strata in the Sierra Calamajue ranges in age from Mississippian through Cretaceous. Mississippian (Chesterian age) conodonts of North American affinity were retrieved from the structurally lowest section. A Jurassic age (-156 Ma) was assigned to the overlying unit. This age was questioned following a second analysis of the same sample, which was interpreted as 25 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Early Cretaceous (~125 Ma; D.L. Kimbrough, pers. comm., 2001). Early Cretaceous ages were also obtained from a siliceous welded tuff (-125 Ma) structurally higher in Calamajue Canyon section and poorly-preserved Albian-Aptian fossils found in a reef-forming limestone unit -10 km to the NW of the volcanic strata (Griffith and Hoobs, 1993). Basement assemblages in Calamajue Canyon are intruded by plutons, whose crystallization ages are constrained by a single age of -100 Ma (Griffith and Hoobs, 1993). Farther northeast, Goldfarb (1996) obtained a highly discordant age of 81±121 and 516±560 Ma thought to be largely the result of inheritance. Based on petrologic similarities and a lack of magmatic or subsolidus deformation, most intrusions were initially interpreted as post-kinematic (see Chapter 3 for new U-Pb ages and interpretations). Structural analyses included recognition of three deformational events of regional significance (Griffith and Hoobs, 1993). The first event was associated with regional folding and faulting and formation of spaced to continuous cleavage. Small- scale conjugate kink folding was assigned to a second deformation event (Windh et al., 1989) followed by formation of a map-scale sinistral flexure during a third phase of deformation. Using mostly regional constraints from Goetz (1989), timing of these events was bracketed between -107 and -97 Ma. Lithology Following Griffith and Hoobs’ (1993) composite section through the Sierra Calamajue, I used their lithologic descriptions and my mapping to construct a 26 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. tectono-stratigraphic column that identifies the main units, keeping previously assigned unit names for simplicity, and clarifies the structural relationships between them (Fig. 2.2.). However, I did not measure thickness’ of individual units or beds as they tend to be laterally discontinuous and highly variable in thickness with an apparent minimum in the narrow Calamajue Canyon, while widening to the northwest and southeast (Fig. 2.1.). Furthermore, structural repetition as a result of faulting and/or folding is possible (see Appendix C). Below, I describe the main structural units from structurally lowest in the southwest of the study area to structurally highest in the northeast (Fig. 2.2.). The base of the section is partly intruded by Cretaceous plutonic material and partly covered by Quaternary deposits. The structurally highest units are not exposed in Calamajue Canyon, but relationships between the units near the top of the canyon and overlying units are observed to the northwest and east (Fig. 2.1.). Primary, depositional and volcanic features are often well-preserved in southwestern most volcanic strata and also remain observable in the central part of the study area, although high ductile strains and increasing metamorphism complicate these observations. Identifying original protoliths becomes more complicated to the northeast, where deformation and metamorphic overprint are more severe. 27 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (Meta-)Sedimentary units Olistostromal breccia Pebble conglomerate S andstone/arenite Shale Macrocrystalline quartzite (metachert) Limestone/marble Volcaniclastic/epiclastic (Meta-)Volcanic units m Amphibolite (metabasalt) Figure 2.2. On next page. Highly simplified tectono-stratigraphic section through the Sierra Calamajue study area modified from Griffith and Hoobs (1993). Unit thickness varies significantly along strike and estimates in text are taken from Griffith and Hoobs (1993). Section was not properly measured and figure is meant to help visualizing the structural/stratigraphic complexity in the area. 28 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. i El Molino fault ^ Early Triassic (Detrital zircon) Volcanito fault O U-Pb-125 Ma £ Mid-Cretaceous (Detrital zircon) El Toro fault Cerro Colorado fault Albian/Aptian (Cretaceous) fossils U-Pb 156 or 125 Ma Contact poorly exposed Chesterian (Mississippian) fossils Ordovician (Detrital zircon) La Josefina unit: thickness undetermined, regionally extensive, in fault contact with underlying, younger units. Protoliths o f shale, siltstone, fine sandstone, and m icro crystalline quartzite (chert?) interlayered with locally abundant amphibolite (metabasalt?). Amphibolite grade metamorphism. Age based on fossils and detrital zircon analyses o f the Canal de Las Ballenas Group. La M ision unit: structural section >1000 m, in fault contact w ith other units, mostly metasedimentary turbidite sequences, protolith: shale, immature sandstone, arenite, and rare limestone & pebble conglomerate. Triassic age is maximum age based detrital zircon analyses. Canon de los Frailes unit: thickness o f -1400 m in Calamajue Canyon (but probably thickens significantly to SE), in fault-contact with adjacent units and internally abundantly faulted, metavolcanics intimately interleaved w ith volcaniclastic/epiclastic and metasedimentary units. Protoliths include welded and crystal-rich lithic tuffs (typically plagioclase-pheric, lithic-rich ash fall or flow tuffs) o f an intermediate to siliceous composition. Age determined by U-Pb age o f siliceous w elded tuff (Griffith and Hoobs, 1993) and detrital zircon analyses o f equivalent units in the Sierra La Asamblea. Alisitos formation (volcanic-rich): thickness - 4000 m. lower contact poorly exposed, upper contact m ajor fault structure separating arc volcanics from overlying continental margin units, metavolcanics dominated by basalt and andesite grading to dacite and locally rhyolite (Griffith and Hoobs, 1993), mainly ash flows and airfall tuffs, locally preserved mafic pillow breccias indicate submarine deposition, lesser amount o f volcaniclastics and m inor amounts o f metasedimentary units such as limestone, arenite, and sandstone, age is constrained by Albian/Aptian fossils and a U-Pb age (Griffith and Hoobs. 1993). Canon Calamajue units: Structurally lowermost section in excess o f 1000m. Base is covered by Quaternary alluvium and intruded out by Cretaceous pluton (Calamajue pluton). w eakly metamorphosed bedded chert interleaved with shale and fine grained sandstone, top o f section is composed o f pebble conglomerate and limestone units, upperm ost part is olistostromal unit with large (boxcar- size) clasts in fine-grained matrix. Ages are constrained by Chersterian conodont fossils and detrital zircon analysis. Figure 2.2. continued. 29 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Canon Calamajue unit The Canon Calamajue unit is exposed along the southwestern part of the study area and comprises the lower -1000 m in the structural column. The sequence of metasedimentary units consists of layered chert and shale (phyllite) interbedded with subordinate limestone and arenite. The section is topped by a -50 m thick olistostromal unit that contains blocks of chert and limestone that are locally very large (boxcar size) in a volcaniclastic matrix (Griffith and Hoobs, 1993). Mississippian conodont fossils have been identified in the section and were initially used to assign an age to this unit (Griffith and Hoobs, 1993). The presence of large allochthonous limestone blocks in a limestone cobble conglomerate with a volcaniclastic matrix made the age at least suspect. To further substantiate the age of the Canon Calamajue unit, I processed a detrital zircon sample, whose age spectra is comparable to Ordovician units in the southwestern North American Cordillera, and the unit is assigned a Paleozoic age (see Chapter 5 for further discussion of provenance). Alisitos Formation Metasedimentary units of the Canon Calamajue unit are overlain by -4000 m of the Alisitos formation. The contact between metavolcanic units of the Alisitos Formation and underlying metasedimentary section is not well-exposed and relationships could not be conclusively established. The top of the Alisitos 30 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Formation is marked by the El Toro fault, which separates the arc section from overlying units (Fig. 2.1.). Compositionally, metavolcanic strata are dominated by basalt and andesite grading to dacite and locally rhyolite. Volcanic deposits formed mainly from ash flows and airfall tuffs and contain mafic pillow breccias. Interlayered with the metavolcanic units are metavolcaniclastic/epiclastic units and minor amounts of metasedimentary strata such as limestone, arenite, and sandstone comprise the remainder of the stratigraphic sequence. Originally, Griffith and Hoobs (1993) suggested a Jurassic through Cretaceous age for this unit based on a -156 Ma U-Pb age and Albian-Aptian marine fossils, which are similar to those elsewhere in the Alisitos Formation (Allison, 1955; 1974; Silver et al., 1963). Reanalysis of the same volcanic flow sample by Kimbrough (pers. comm., 2001) suggests a late Early Cretaceous (-125 Ma) age, which is more consistent with the age of the fossils and the expected age of the Alisitos formation, as Jurassic units have not been described anywhere else in units assigned to the formation. Cafion de los Frailes unit The Alisitos Formation is overlain by intimately alternating primary volcanic, volcaniclastic, and sedimentary strata that reach a structural thickness of-1400 m in Calamajue Canyon, but thicken significantly in the Sierra La Asamblea to the southeast (Fig. 2.1.). This section is structurally complex and faulting may have 31 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. resulted in repetition of units and/or incorporation of units that belong to the underlying Alisitos Formation or overlying units (see below). The structural top of the sequence is the Volcanito fault, which marks the transition to the overlying early Mesozoic units. Metavolcanic material consisting of welded and crystal-rich lithic tuffs (typically plagioclase-pheric, lithic-rich ash fall or flow tuffs) of an intermediate to siliceous composition is widespread and interbedded with volcaniclastic and epiclastic units. Metasedimentary units such as shale, immature sandstone, and arenite are rare in Calamajue Canyon, but comprise a significantly larger proportion in the Sierra La Asamblea to the southeast (Fig. 2.1.). The age of the unit is based on a U-Pb age of -125 of a siliceous welded tuff (Griffith and Hoobs, 1993) and is comparable to the -115 Ma depositional age inferred from a detrital zircon sample in the Sierra La Asamblea (see Chapter 5). These ages overlap or are slightly younger than ages from the underlying Alisitos Formation. Thus, a correlation with the Alisitos Formation is possible. Alternatively, these units are related to Early Cretaceous deep water strata described in the Sierra San Pedro Martir (Johnson et al., 1999a; Schmidt, 2000). La Mision unit The fault-bounded La Mision unit reaches a thickness o f-1000 m. The top of the section is another major fault (El Molino fault) that separates Mesozoic from overlying Paleozoic basement assemblages. 32 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The unit consists of thick sections of metamorphosed, alternating fine-grained shale and sandstone in turbidite sequences. Immature sandstone and arenite, carbonate, calc-silicate, and pebble conglomerate units are less abundant and metavolcanics are conspicuously absent. An Early Triassic depositional age is inferred from a detrital zircon analyses (Chapter 5). Further substantiating this age, is a similar detrital zircon age spectra from a unit -15 km to the northwest (Morgan et al., 2005). This suggests that these units are similar in age to other early to middle Mesozoic basement units (i.e. Bedford Canyon Formation, Julian Schist, etc.) that are found along the axis of the PRB from southern California to at least the Bahia de Los Angeles area (Gastil and Miller, 1993; Morgan et al., 2005). La Josefina unit A variety of different metasedimentary units that are intercalated with locally abundant amphibolite layers comprise the structural top of the section and are assigned to Paleozoic units that comprise the eastern PRB. Protoliths include mostly sand/shale turbidite(?) sequences that are metamorphosed to fine-grained phyllitic and argillaceous units grading locally, near intrusions, to pelitic schist and paragneiss (e.g., Goldfarb, 1996). Microcrystalline quartzite (metachert?) is very abundant and fine-grained metasandstone and marble are minor constituents. Amphibolite layers occur throughout the study area and may represent metabasalts, although primary volcanic features have not been recognized. 33 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. No direct age constraints exist for these units since fossils have not been recovered and a processed detrital zircon sample did not yield zircons. The observed rock types are interpreted as Paleozoic passive margin slope-basin deposits as units strongly resemble Ordovician to Devonian strata described in the Canal de Las Ballenas Group near Punta Calamajue, ~15 km to the north of the study area (Campbell and Crocker, 1993) and similar strata are described in other parts of the eastern PRB (e.g., Gastil, 1993; Leier-Engelhardt, 1993). Summary Five major lithologic units have been identified in the Sierra Calamajue study area (Fig. 2.2.). These include, from structurally lowest to highest, 1) Paleozoic (Ordovician through Mississippian?) sedimentary assemblages, 2) Cretaceous volcanic-dominated strata, 3) Cretaceous volcanic and sedimentary units, 4) early Mesozoic (Triassic) turbidite sequences, and 5) Paleozoic deep-water units. These lithologies strongly resemble basement assemblages described elsewhere in the PRB (Fig. 1.1.) (e.g., Gastil, 1993; Johnson et al., 1999a; Schmidt, 2000; Wetmore, 2003) suggesting continuous belts of 1) volcanic arc strata along the west side of the PRB, 2) Triassic through Cretaceous volcanic and sedimentary assemblages along the axis, and 3) Paleozoic strata along the east side (see discussion below). The main exception to this subdivision is the Canon Calamajue unit at the base of the structural section with a clear Paleozoic signature. Identifying 34 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. relationships to overlying units is complicated by the poor exposure of the contact between units and several possible interpretations are discussed in Chapter 5. Deformation The following description of structural fabrics in the Sierra Calamajue and adjacent ranges is subdivided into four (4) phases of deformation. Paleozoic units record deformation that is not seen in Mesozoic units and the oldest fabrics observed in outcrop are described as Phase 1. Deformation Phase 2 and 3 affect all units and therefore superpose older fabrics in Paleozoic units, but only original bedding in Mesozoic units. Thus, the common convention of assigning numbers is considered confusing as Di, Si, etc. in Mesozoic units would correspond to D2, S2, etc. in Paleozoic units. Therefore, I decided not to follow this convention and try to clearly describe and separate the different structures that formed during the different deformational events. Phase 4 deformation is related to intrusion of post-kinematic plutons, which cross-cut existing structures and caused only very localized deformation in thin structural aureoles. Phase 1 Original bedding is best preserved in quartz-rich units such as microcrystalline quartzite (metachert?; Fig. 2.3.). In places, bedding can be followed for several meters, but overall it is laterally discontinuous and in many places strongly transposed resulting in locally preserved floating fold hinges. 35 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Figure 2.3. Picture showing compositional layering in fine grained quartzite (metachert?) and phyillite units. Lower limb of recumbent, isoclinal fold in quartzite pinches out. Note that compositional layering above and below fold hinge is parallel to axial planar fabrics. Fold is outlined (white) to clarify picture. Lens cap is ~5 cm in diameter. O n Bedding is tightly to mostly isoclinally folded with hinge lines and fold axes showing variable plunge directions (Fig. 2.4.). Transposition of bedding is in places accompanied by formation of an incipient axial planar cleavage (Fig. 2.5.). The axial planar cleavage is best developed in units with a shale protolith and outcrops are now dominated by compositional layering, which is parallel to axial planar cleavage, of slate, argillite, and locally schist (Fig. 2.3.). Phase 2 Following deposition of Triassic(?) through Cretaceous volcanic and sedimentary units, a second phase of regional deformation is recognized in all Paleozoic and Mesozoic units including the easternmost part of the Alisitos Formation. This phase of deformation resulted in formation of a regional fold-thrust belt that has been recognized along the northern and eastern edge of the Alisitos arc (Johnson et al., 1999a; Schmidt, 2000; Wetmore et al., 2003a). Development of the fold-thrust belt in the Sierra Calamajue study area resulted in juxtaposition of all units across reverse faults (Figs. 2.1. and 2.2.). Deformation associated with fold- thrust belt development is not uniform, but rather a steep southwest to northeast deformation gradient exists. Volcanic and sedimentary strata in the Alisitos Formation and Canon Calamajue unit along the southwest side of the study area show only limited open folding, spaced cleavage, and few brittle faults. This changes rapidly northeastward over ~ 2 to 3 km where folds tighten, cleavage becomes 37 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Lower Hem . ■ ■ ■ ■ Total D ata : 108 Equal A rea Figure 2.4. Stereoplot of plunges of fold axes in Paleozoic related to Phase 1 deformation (n=108). Significant scatter is the result of widespread refolding of Paleozoic units during collision-related Phase 2 deformation and kink folding during phase 3 deformation. See text for discussion. 38 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Figure 2.5. Picture showing open/tight folds in compositional layering defined by quartzite and phyillite units. Axial planar cleavage is well-developed, particularly in the phyllitic units. Mexican one (1) peso coin is ~2 cm in diameter. V O continuous, and faults are increasingly more abundant with greatest deformation being recorded in Calamajue Canyon, which is quantitatively constrained by finite strain measurement (Chapter 4). Faulting is most widely recognized in the Canon de los Frailes and La Mision units and is significantly less widespread in underlying Alisitos formation and overlying units of the Paleozoic La Josefina unit (Figs. 2.1. and 2.2.). Four major faults, three of which bound major lithostratigraphic units, and numerous smaller faults have been identified. The El Toro fault separates the Alisitos Formation from overlying Cretaceous volcano-sedimentary units. This fault is either the shallower equivalent to the Main Martir thrust (Fig. 1.2.) or, alternatively, the equivalent to the Rosarito fault, which separate litho-stratigraphic packages in the SSPM (Johnson et al., 1999a; Schmidt, 2000). While the former separates the Alisitos arc from the continental margin and the latter the volcanic-rich from sediment-rich Alisitos arc units, the El Toro fault in the study area separates volcanic-rich arc strata from mixed volcanic-sedimentary assemblages of comparable age. The Volcanito fault separates the Cretaceous Canon de los Frailes units from the overlying La Mision unit. The latter unit is capped by the El Molino fault, which places Paleozoic deep-water strata over early Mesozoic units. The other distinct fault in the study area is the Cerro Colorado fault (Fig. 2.1.), which parallels the El Toro fault and is located ~200 to 300 m to the southwest of it. The Cerro Colorado fault is interpreted as a secondary splay of the El Toro fault and probably merges with the latter to the northwest of the mapped surface trace and at depth. 40 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. All major faults in the area have a brittle character and include zones of brecciation, locally several meters thick (Fig. 2.6.), and fault gouge. Brittle deformation overprints ductile deformation (Fig. 2.7.). Both brittle and ductile kinematic indicators, such as tension cracks locally filled with quartz, fractured clasts, deflection of foliation, s-c fabrics, and sigma clasts, suggest reverse (top-to- west and southwest) motion parallel to the mineral and stretching lineation (see below). Displacement magnitudes on these structures are unconstrained. Parallelism between faults and outcrop structures, lack of marker horizons, and change from ductile to brittle deformation makes determination of offset on individual faults impossible. Faults locally truncate units, which are often laterally discontinuous and in places may have been repeated. The presence of both brittle and ductile fabrics allows prolonged displacement along these structures in which case displacement can be significant. However, the metamorphic grade does not change significantly across these structures, which supports that episodic activity and reactivation of reverse faults under different temperature-pressure conditions is a more likely interpretation. Folding on a regional and outcrop-scale accompanied faulting in the study area. Regional, kilometer-scale folds are recognized only near the top of the structural section in the La Mision and La Josefina units, where they are tight and upright and tight and overturned to the southwest, respectively. These folds have shallowly plunging hinge lines that are subparallel to trends of steep reverse faults (Fig. 2.1. and map in back pocket). 41 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Figure 2.6. Picture showing zone of brecciation associated with El Toro fault (possible equivalent to Main Martir thrust). Note that brittle deformation overprints earlier ductile deformation (not shown). 4^ K > Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Figure 2.7. Picture showing evidence for early ductile deformation in the central zone in the Sierra Calamajue. Note that early ductile fabrics are often overprinted by more brittle deformation. U ) Open to tight (to locally isoclinal) outcrop-scale folds are more widely recognized than regional folds. As a result of Phase 2 deformation, earlier, isoclinal (Phase 1) folds in Paleozoic units are tightly refolded (Fig. 2.8.), whereas folds in Mesozoic units affect original bedding (Fig. 2.9.). Orientations of fold axes of younger, open to tight folds show significant scatter (Fig. 2.10.). A weak, NW- plunging maximum can be seen in the orientation of fold axes measured in Paleozoic units, whereas greater scatter exists for fold axes measured in Mesozoic units (Fig. 2.10.a.). The increased scatter in orientations in the latter units is interpreted as a result of greater non-coaxial shear in the central part of the fold-thrust belt, which led to rotation of fold axes towards the shear direction similar to observations in the northern SSPM (Johnson et al., 1999a). Axial planes trend roughly NW-SE (Fig. 2.10.b.) parallel to the general trend of the transposition foliation (see below). Locally, strain was large enough to dismember isoclinal folds leading to boudinage of isoclinally folded layers (Fig. 2.11.). During fold-thrust belt formation, a regionally dominant foliation with a moderately to steeply plunging mineral and stretching lineation developed throughout the study area. In Mesozoic units, this foliation is axial planar to outcrop- scale, open to tight folds and locally expressed as a pressure solution cleavage leading to apparent volume loss in fold hinges (Fig. 2.9.), but eventually becomes a continuous cleavage. In Paleozoic units the foliation is mostly a zonal to discrete crenulation cleavage (Fig. 2.12.) transposing structures formed during Phase 1 deformation. The foliation trends NW-SE parallel to axial planes of younger open to 44 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 2.8. Picture showing isoclinal folds (Phase 1 deformation) in Paleozoic units being tightly refolded during Phase 2 deformation. Ruler for scale. Figure 2.9. Picture showing open to tight outcrop-scale fold in Mesozoic units transposing original bedding. Note development of pressure solution axial planar cleavage with apparent volume loss. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. a. Lower Hem. C 0 Total Data : 52 Equal Area b Lower Hem. ♦ Total Data : 38 Equal Area Figure 2.10. Structural measurements of Phase 2 deformation folds, a. Stereoplot of plunges of fold axes in Paleozoic (O) (n=24) and Mesozoic (•) (n=28) units. Note that greater scatter is probably related to greater ductile shear in Mesozoic units. See text for discussion, b. Steroplot of poles to axial planar cleavage (n=38). Average orientation is 330°/49°, which is subparallel to trend of transposition foliation. 47 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 2.11. Picture showing locally abundant pinch-and-swell structures in the Mesozoic volcano-sedimentary strata in Calamajue Canyon. 48 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 2.12. Picture showing discrete crenulation cleavage that formed during Phase 2 deformation and in this view transposes Phase 1 folds in Paleozoic units. Coin for scale is ~2 cm in diameter [Mexican one (1) peso coin]. 49 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. tight folds described in the previous paragraph and dips moderately to steeply to the NE. Although this general pattern is complicated during Phase 3 deformation, particularly in the Calamajue Canyon area and to the northwest and east of the canyon (see below), the NW-SE trend can clearly be recognized in the Alisitos Formation (Alisitos domain) and the La Josefina unit in the Sierra La Josefma domain (Fig. 2.1.). In the Alisitos Formation (Alisitos domain), bedding dips moderately to steeply, homoclinally to the northeast [avg. 315°/75° (n=9); Fig. 2.13.a.)]. Northeastward, towards the structural top of the Alisitos formation, units contain a northwest-southeast striking moderately to steeply northeast-dipping, bedding parallel foliation [avg. 318°/70° (n=49), Fig. 2.13.b.] that changes gradually over a 2- 3 km distance (i.e. steep deformation gradient) from a spaced to continuous cleavage. A moderately northeast plunging mineral and/or stretching lineation [mean 70°/037° (n=25), Figs. 2.13.C.) is found within the cleavage plane. Approximately 5 km to the northeast of Calamajue Canyon, in the Sierra La Josefina domain (Fig. 2.1.), the transposition foliation related to Phase 2 deformation has again a rather uniform NW-SE-trend with moderate northeast dips [average 305°/61° (n=145), Fig. 2.14.a.) and lineations plunge dominantly moderately to the northeast [mean 64°/056° (n=69), Fig. 2.14.b]. Limited scatter in the orientations of foliation is related to outcrop-scale kink folding related to Phase 3 deformation (see below). 50 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. a. Lower Hem. ■ ■ Equal Area (n-9) b Lower Hem . Equal A rea Total Data: 49 C. Low er H em . Equal A rea Total D ata: 25 Figure 2.13. a. Stereoplot showing poles to bedding in Alisitos arc strata in the Sierra Calamajue. Average orientation = 315°/75° (n=9). b. Stereoplot showing poles to foliation in Alisitos arc strata in the Sierra Calamajue. Average orientation = 318°/70° (n=49). c. Stereoplot showing plunges of stretching lineations in Alisitos arc strata in the Sierra Calamajue. Mean orientation = 70°/037° (n=25). 51 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. a. Lower Hem. • • Equal Area Total Data: 145 b Lower Hem. Total Data: 69 Equal Area Figure 2.14. a. Stereoplot showing poles to foliation in the Paleozoic units in the Sierra La Josefina. Average orientation = 305°/61° (n=145). b. Stereoplot showing plunges of stretching lineations in the Sierra La Josefina. Mean = 64°/056° (n=69). 52 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The Piedra Blanca pluton, which is located in the Sierra La Josefina domain, (Fig. 2.1.) is the only pluton in the study area that displays strong, pervasive subsolidus fabric parallel to the regional fabrics in the domain (map in back pocket). Thus, this pluton predates regional Phase 2 deformation. Unfortunately, a sample collected for U-Pb analyses to constrain timing of deformation did not yield enough zircons for analyses (see Chapter 3). Phase 3 Subsequent to phase 2 deformation, widespread kink folding affected the Canon de los Frailes, La Mision, and structurally lowest part of the La Josefina units. The scale of kink fold formation ranges from centimeter to regional scale (Fig. 2.15.). The Calamajue Canyon area is a regional-scale ‘megakink’ or sinistral flexure (Griffith and Hoobs, 1993) that can be divided into three domains (Fig. 2.1.). The northern domain shows mostly N-S-trending structural fabrics (including faults, folds, and foliation) (Fig. 2.16.a. and 2.17.a.). Orientations change to more NW-SE- trends in the middle (Fig. 2.16.b. and 2.17.b.) and approach E-W-trends in the eastern domain (Fig. 2.16.C. and 2.17.C.). Scatter in the data results from outcrop- scale kink folding (Fig. 2.15). The hinge region between the northern and middle domains contains a rarely developed foliation that trends NNE (Fig. 2.18.), which is subparallel to the inferred strike of the axial plane of the regional kink fold. 53 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 2.15. Picture showing widespread kink folding that formed during Phase 3 deformation, which affected most units in the study area. Arrow points at lens cap, which is ~5 cm in diameter. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. a. (•A A A. E q u a l A r e a T o t a l D a t a : 2 6 E q u a l .A r e a c ▲ A \ A • E q u x i l A r e a Figure 2.16. Stereoplot showing poles to foliation in the three domains defined in text in the Sierra Calamajue. a. Northern domain . A=Mesozoic strata; average orientation = 359°/79° (n=67). •=Paleozoic strata; average orientation = 176°/75° (n=28). b. Middle domain. A average orientation = 318°/76° (n=26). c. Eastern domain. A average orientation = 263°/74° (n=26); • average orientation= 263°/85c (n=28). Note that scatter mostly produced by locally abundant kink folding. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. a. ▼ ▼ w w T o t a l D a ta : 7 0 | — Equal A r e a C ▼ o E q u a l A r e n Figure 2.17. Stereoplot showing plunges of stretching lineations in the three domains in the Sierra Calamajue defined in text. a. Northern domain. ▼ = Mesozoic units; mean orientation = 70°/141° (n=46); 0 = Paleozoic units; mean orientation = 82°/232° (n=24). b. Middle domain. ▼ mean orientation = 73°/086° (n=24). c. Eastern domain. T mean orientation = 567078° (n=18); 0 mean orientation = 627080° (n=21). 56 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Lower Hem. Figure 2.18. Stereoplot showing poles to axial planar cleavage associated with kink folding in the Sierra Calamajue. Average orientation = 020°/85° (n=ll). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Phase 4 Phase 4 deformation is very localized and only recognized along the edges of plutons and very thin structural aureoles. The Las Palmas, Corral, and other plutons along the northern edge of the study area cross-cut existing structural elements in the study area, have sharp and steep host rocks contacts, and contain a very weak magmatic to high-temperature subsolidus, margin-parallel fabric along their outermost edges (200 to 300 m). Fabrics were not observed in the central portions of these plutons, and aureoles are mostly homfelsed and lack distinct fabrics. An exception is the aureole of the ~95 Ma Las Palmas pluton (Fig. 2.1.), where Phase 2 foliation is locally deflected or weakly folded with a new pluton margin-parallel axial planar cleavage within <300 m of pluton contact. Summary of deformation Four phases of deformation are recognized in the Sierra Calamajue study area. Phase 1 deformation is only recognized in the oldest (Paleozoic) units in the study area. During this deformation, bedding was isoclinally folded and transposed, which resulted in formation of compositional layering and incipient development of axial planar foliation, which is best developed in fine-grained shale units. After deposition of early Mesozoic through mid-Cretaceous sedimentary units and offshore evolution of the Alisitos arc, Phase 2 deformation resulted in the development of a fold-thrust belt and juxtaposition of all units in the study area across reverse faults. Widespread brittle to ductile, southwest-vergent faulting and 58 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. dominantly open to tight folding caused widespread deformation in Mesozoic units and led to transposition of older fabrics and development of a crenulation cleavage in Paleozoic units. Centimeter- to kilometer-scale kink folds (Phase 3) overprint earlier deformation and are common in and around Calamajue Canyon, while their presence decreases to the northeast and southwest of the canyon. Limited deformation is associated with deformation Phase 4, which affects the outermost edges of intrusions and narrow (<300 m) host rock structural aureoles. Magmatic and subsolidus structures are weakly developed and margin-parallel. Metamorphism A northeastward increasing metamorphic gradient is present in the study area. The Alisitos Formation records minimal (subgreenschist to lower greenschist facies) metamorphic conditions resulting in preservation of primary depositional features such as bedding and sedimentary structures (e.g., cross-bedding, graded bedding) (Fig. 2.19.). A gradual northeastward increase of metamorphic temperatures and pressures in Triassic(?) through mid-Cretaceous volcanic and sedimentary units to greenschist facies conditions is shown by increasing presence of chlorite and eventually biotite. Metamorphism reaches lower amphibolite facies conditions across the El Molino fault, which separates Mesozoic from Paleozoic units. Here andalusite, biotite, and garnet are locally abundant and sillimanite can be found in pluton aureoles consistent with higher temperatures in these environments. Amphibolite 59 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 2.19. Picture showing graded bedding in the weakly metamorphosed Alisitos Formation along the southwestern edge of the study area. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. facies conditions have been confirmed by a thermobarometry analysis in the Sierra San Francisquito (Fig. 2.1.), which yielded pressure-temperature conditions of 3.2±0.5 kbar and 476±18°C (Rothstein, 1997; Rothstein and Manning, 2003). Qualitative observations suggest that these conditions prevail throughout much of the Paleozoic units in the study area and remain constant northeastward towards the Gulf of California. Metamorphic conditions have not been adequately evaluated on the opposite (Sonoran) side of the gulf (Gastil et al., 1991). Discussion Original tectonic setting of lithologic units Five distinct litho-stratigraphic assemblages that are composed of variable lithologies have been distinguished (Fig. 2.2.). Based on comparisons between lithologies, basement assemblages in the study can be correlated with other basement assemblages in the PRB and a tectonic setting can be assigned. Correlating units based on lithology is ambiguous and correlations below represent educated guesses. I also took into consideration constraints from new detrital zircon data, which provide more quantitative controls on origin and provenance of these units and are presented in detail in Chapter 5. The volcanic-dominated sequences along the southwestern edge of the study area (Figs. 2.1. and 2.2.) are comparable in character with respect to lithology, depositional environment, and age to the Alisitos Formation in the type section near Punta China along the Pacific Coast (Allison, 1955; 1974). Similar units have been 61 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. described along the western edge of the PRB from the type section to at least 29°N latitude (e.g., Beggs, 1984; Wack, 1988; Johnson et al., 1999a; Schmidt, 2000; Wetmore, 2003) and units in Calamajue Canyon have already been correlated with the Alisitos Formation (Griffith and Hoobs, 1993). Based on these correlations, giving the same formational name as for exposures elsewhere is appropriate. The Canon de los Frailes units contains similar lithologies as the Alisitos Formation and also overlaps in age. Therefore, these units could be correlative. However, a greater proportion of metasedimentary units, particularly in the Sierra La Asamblea to the southeast, including abundant turbidite sequences interpreted as deep marine deposits suggest that there are significant differences between these units. My preferred interpretation is that the Canon de los Frailes unit is correlative with similar deep water facies units described from the Sierra San Pedro Martir (Johnson et al., 1999a; Schmidt and Paterson, 2002) and therefore represent the remnants of a Cretaceous deep marine basin that received detritus from both the Cretaceous arc units and from continental sources (see Chapter 5). The La Mision unit is dominated by metasedimentary units (sand/shale, carbonates) typical of moderate to deep water environments. Based on a detrital zircon age (Chapter 5), the La Mision units is older than the structurally underlying Canon de los Frailes unit and these units are not the same. The approximate early Triassic depositional age is comparable to ages from similar units that have been described along the axis of the PRB (e.g., Criscione, 1978; Germinario, 1993; Reed, 1993; Morgan et al., 2005). These units have been described as accretionary prism 62 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. units (Wetmore et al., 2003a) and a similar setting is envisioned for the La Mision unit. A Triassic arc is well-documented in southern California (e.g., Barth et al., 1997), and, although no Triassic magmatism has been reported this far south, I think that convergence and subduction had initiated, an accretionary prism started to form, and Triassic magmatism has not be documented because of the sparse geochronologic data and significant Cenozoic overprint associated with formation of the Sierra Madre Occidental (e.g., Ferrari et al., 2000; Rossotti et al., 2002). The La Josefina unit along the northeast side of the study area (Figs. 2.1. and 2.2.) and Paleozoic deep-water units along the east side of the PRB share many lithologic characteristics (e.g., Leier-Engelhardt, 1993; Campbell and Crocker, 1993). The predominance of fine-grained shale and sandstone intimately interlayered with microcrystalline quartzite (metachert?) is indicative of Paleozoic deep water strata in the PRB. Although fossils have not been recovered and a sample collected for detrital zircon analyses did not yield any zircons, the strong similarity and apparent continuity (i.e. lack of shear zones) between the La Josefina unit and Devonian to Ordovician Canal de Las Ballenas group ~ 20 km to the north supports deposition of the La Josefina unit in a slope-basin environment as part of the Paleozoic passive margin of North America (e.g., Alsleben and Paterson, 2002; Alsleben et al., 2002). The Canon Calamajue unit can also be correlated with Paleozoic passive margin sequences based on lithologies, but more importantly Mississippian conodonts with North American affinities (Griffith and Hoobs, 1993) and a detrital 63 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. zircon population that is typical for Ordovician strata (Chapter 5). What is problematic is not the correlation, but the location of this ~5 km2 area that forms the structurally lowest unit in the study area overlain by younger units that formed in an offshore depositional environment (Figs. 2.1. and 2.2.). Griffith and Hoobs (1993) interpreted these units as the basement to the overlying Alisitos Formation. However, the Canon Calamajue unit is not cut by dikes and the Calamajue pluton, which intrudes the units, lacks a component of inheritance (see Chapter 3) that is typical for plutons in the eastern PRB (Walawender et al., 1990; 1991; Goldfarb, 1996). Combining these observations with the uncertain structural relationships to the overlying strata, allows alternative interpretations. I propose two alternative hypotheses for the presence of these units at the base of the structural section through Calamajue Canyon. First, these units may represent a thrust slice or klippe that was originally thrust over the Alisitos arc early during collision and was subsequently incorporated near the base of the section during final suturing of the arc to the continent. As a result, the unit now structurally underlies the Alisitos Formation. The nearest exposure of Paleozoic units is ~7 km away, which represents the minimum displacement for the Canon Calamajue unit. Alternatively, the Canon Calamajue unit represents a major olistostromal block that slid from the continental margin during subduction prior to arrival of the approaching Alisitos arc. Mass wasting can be significant in active tectonic environments (e.g., Bierly et al., 2003; Lundberg, 2003) and large allochthonous blocks that are interpreted as olistostromes have been described from elsewhere in 64 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the PRB (Lothringer, 1993). Furthermore, Paleozoic rocks lying west of Cretaceous strata have been reported from the El Marmol area (Fig. 1.1.) suggesting that large olistostromal blocks are common in the PRB and other collision zones (Buch and Delattre, 1993; Phillips, 1993; Morgan et al., 2005). At present I favor the latter hypothesis since similar blocks have been described, whereas low-angle thrust faults as those required by the first hypothesis are not generally observed in the PRB. These hypotheses are easily testable by more detailed mapping of the contact between the Canon Calamajue unit and Alisitos Formation and additional geochemical (including isotopic) and geochronologic analyses of intrusive material that intrudes both units. Cause and timing of Phase 1 (Pre-Cretaceous 1 deformation In the Sierra Calamajue study area, the Paleozoic (Ordovician to Devonian?) La Josefina and (Ordovician to Mississippian) Canon Calamajue units contain tight to isoclinal folds (Griffith and Hoobs, 1993). In the former these folds are refolded, which has not been conclusively described from the latter. However, the similarities in fold-style suggest that both units record Phase 1 deformation, which is not seen in Mesozoic including the early Triassic units. To place the closest constraint on timing of Phase 1 deformation, the main assumption is that the Triassic depositional age of the La Mision unit inferred from detrital zircon analyses is valid (Chapter 5). The Triassic age is indirectly supported by the absence a younger (Jurassic or Cretaceous) population of zircons, which are 65 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. expected since a Jura-Cretaceous magmatic arc is well-known to the east of the units (Anderson, 1991; Miller and Busby, 1995) and, although the absence of Jurassic grains is not a definitive prove, Jurassic or younger units in the same belt of rocks (e.g., Bedford Canyon Formation, Julian Schist) contain abundant Jurassic detrital zircon grains (Morgan et al., 2005). Furthermore, Jurassic orthogneisses have been dated and mapped in the southern Sierra San Pedro Martir, where they intrude lithologically similar strata as the inferred Triassic units in the Sierra Calamajue (Schmidt and Paterson, 2002). Based on the above constraints, Phase 1 deformation is Paleozoic and occurred between the Chesterian (Mississippian) and Permian. Late Paleozoic deformation is consistent with Permo-Triassic deformation along the southern margin of North America (e.g., Stewart, 1988; Stewart et al., 1990). Thus, Paleozoic rocks in the study area record deformation that is related to thrusting of deep-water units over miogeoclinal strata during formation of Pangea and structures of similar ages can be found throughout Paleozoic units in Baja California (e.g., Anderson, 1993; Schmidt, 2000) and Sonora, Mexico (Stewart, 1988; Stewart et al., 1990). Cause and timing of Phase 2 deformation During much of the Mesozoic, the western North American Cordillera was dominated by a convergent margin with mostly east-directed subduction and an Andean-type continental margin arc (e.g., Burchfiel et al., 1992). Intermittently, accretion of tectonic elements occurred, which is well-documented along much of 66 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the western North American Cordillera (e.g., Coney et al., 1980) including parts of the PRB (e.g., Gastil et al., 1981; Sedlock et al., 1993; Wetmore et al., 2002; 2003a). In the PRB, the Alisitos arc, which extends from the approximate latitude of the Agua Blanca fault (Fig. 1.1.) southward to about 28° N, collided with and accreted to North America between -115 Ma and 103 Ma (e.g., Johnson et al., 1999a; Wetmore et al., 2003a). Although the specifics of the origin (fringing or exotic arc) and exact tectonic setting (back-arc basin collapse or two subduction zones) of the Alisitos arc are still debated, most workers agree that an arc collided with the North American continent in the mid-Cretaceous (e.g., Gastil et al., 1981; Todd et al., 1988; Busby et al., 1998; Johnson et al., 1999; Wetmore et al., 2003a). Accretion of the Alisitos arc was accompanied by formation of a suture zone and development of a fold-thrust belt that changes its character along-strike (e.g., Johnson et al., 1999a; Schmidt and Paterson, 2002; Alsleben et al., 2003; 2005; Alsleben et al., in preparation; see also Chapter 4). In the Sierra Calamajue study area, the minimum age of Phase 2 deformation is constrained by 1) Albian-Aptian fossils (Griffith and Hoobs, 1993), 2) a volcanic flow unit (U-Pb age o f-125 Ma) in Calamajue Canyon (Griffith and Hoobs, 1993), and 3) a detrital zircon analyses that suggest a Cretaceous (-115 Ma) depositional age for a turbidite sequence (Alsleben et al., in preparation; see Chapter 5). All these units are strongly deformed during Phase 2 deformation, which suggests a minimum age for initiation of deformation of -115 Ma. 67 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cessation of deformation is constrained by pluton ages. A ~95 Ma U-Pb crystallization age from the Las Palmas pluton (Chapter 3) and the small, unnamed stock that intrudes the La Mision unit at -100 Ma (Griffith and Hoobs, 1993) do not record magmatic or subsolidus deformation, which suggests that intrusion postdates widespread regional deformation. Bracketing deformation between -115 Ma and 100 Ma can easily be placed in a regional context, where deformation is constrained between 115 and 103 Ma in the San Vicente and Sierra San Pedro Martir (e.g., Johnson et al., 1999a; 2003; Schmidt, 2000; Schmidt and Paterson, 2002; Wetmore, 2003). These constraints on deformation are complicated by the fact that the Calamajue pluton at the southwest edge of the study area has a U-Pb crystallization age of -144 Ma (Chapter 3). The pluton, which, as many other plutonic bodies in the area, shows no evidence for significant magmatic or subsolidus deformation, intrudes rocks that record Cretaceous (115 to 100 Ma) deformation. The complications and possible solutions are addressed in Chapter 3, where the U-Pb data is discussed in detail. Cause and timing of Phase 3 deformation The timing of widespread kink fold formation is better constrained than the cause. Kink folds at various scales deform all prior structural fabrics in the study area. This suggests that formation of kink folds occurred after -115 Ma, which is the youngest known, albeit inferred, depositional age of deformed strata in the area. 68 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Allowing for accretion-related deformation in the ~115 Ma strata, kink fold formation must be (significantly?) younger than 115 Ma. The lower age limit for kink folding is provided by 100 to 95 Ma plutons, which lack evidence for deformation or kink folding. Based on these age constraints, kink folding occurred between « 1 15 Ma and 100 Ma and followed regional Phase 2 deformation. Furthermore, I suggest that outcrop-scale kink folding and formation of the regional megakink are contemporaneous. Previous workers (Windh et al., 1989; Griffith and Hoobs, 1993) suggested that the regional megakink postdates small- scale kink folds without providing supporting evidence. I think that the overall appearance and orientation of kink folds at any scale are similar and therefore that they formed at the same time. The cause of kink folding is uncertain. Kink fold formation may record the late increment of tectonic strain just prior to cessation of regional tectonism in the area. Alternatively, kink folds formed in response to widespread plutonism at ~ 100 Ma. In this case, kink fold formation is one of several local mass transfer processes that accommodated the addition of magmatic material into the crust and are temporally close to regional plutonism. The former appears a more viable explanation for formation of kink folds because 1) kink folding is widespread on a regional scale and 2) there is no apparent increase in kink folding in or near pluton structural aureoles. A tectonic cause for kink band formation in Calamajue Canyon was also proposed by Windh et al (1989), who suggested elastic relaxation and roughly NW- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SE contraction following a prior, most likely Cretaceous deformational event. Furthermore, similarly oriented kink folds are preserved in Cretaceous intrusions such as the Tuolumne batholith in the Sierra Nevada, where these folds are also interpreted to represent a Cretaceous increment of tectonic strain due to elastic relaxation (Economos et al., 2005), similar to structures elsewhere in the central Sierra Nevada (Paterson, 1989). Cause and timing of Phase 4 deformation The restricted nature of Phase 4 deformation, which occurs only along the outermost edges of plutons, within the very narrow structural aureole of the ~95 Ma Las Palmas pluton, and the margin-parallel orientation of this fabric suggests that deformation was emplacement-related and associated with intrusion of the individual plutons. The best evidence for local deflection of host rock structure and development of a margin-parallel axial planar cleavage comes from aureole of the -95 Ma Las Palmas pluton. This suggests that deformation associated with intrusion is close in time and the timing is close to the crystallization age. For the study area, this suggests that deformation in the aureoles occurred at -144 Ma (Calamajue pluton) and between -100 and -95 Ma, based on ages from the unnamed stock, the Las Palmas pluton, and the La Guera pluton (Goldfarb, 1996). 70 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Effects of pre-existing geology on Cretaceous deformation The distribution of Paleozoic shallow- and deep-water assemblages that comprise the eastern PRB is very distinct (Fig. 2.1.). The contact between miogeoclinal and deep-water strata is oriented almost E-W at the latitude (-30.5° N) of the southern Sierra San Pedro Martir (SSPM) and, after removing -300 km of Neogene tectonism in the Gulf of California (e.g., Gastil et al., 1991, Oskin and Stock, 2003) is roughly continuous with similar strata exposed in Sonora, Mexico. North of the southern SSPM, the contact between Paleozoic units is generally inferred to be oriented -NNE-SSW, but is poorly defined largely because it is intruded-out and/or covered by younger strata. To the south, shallow water strata are absent. These lithologic variations strongly influenced the crustal rheology during Cretaceous tectonism. Where shallow-water strata dominate, folds and cleavage are oriented nearly E-W (e.g., Schmidt, 2000; Gastil and Miller, 1993; Schmidt, unpublished mapping), similar to structures developed in miogeoclinal rocks in Sonora (e.g., Stewart, 1988; Stewart et al., 1990). Accretion of the Alisitos island arc during the Cretaceous did not significantly transpose or obliterate these structures and, in fact, deformation was largely concentrated west of these assemblages and only locally affected Paleozoic strata in very narrow zones (Schmidt, 2000). In contrast, south of 30.5° N, deep water strata are strongly affected by Cretaceous deformation and, although evidence for Paleozoic deformation exists, distinct (E-W) older structural trends cannot be recognized. This suggests that Cretaceous 71 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. deformation was transmitted over a much broader region away from the colliding arc where deep-water units dominate, while crust composed of miogeoclinal assemblages behaved more rigidly and did not deform significantly during Cretaceous tectonism (e.g., Gastil et al., 1991b; Schmidt, 2000; Schmidt and Paterson, 2002). In addition, the absence of deep-water strata in the southern SSPM and the existence of an apparent protrusion (Fig. 2.1.) strongly controlled the local strain field (Alsleben et al., in preparation; Chapter 4). In the southern SSPM, the protrusion acted as a crustal indenter. With a rigid arc approaching, deformation and strain was concentrated between the arc and miogeoclinal units and the doubly- vergent fan structure evolved in sediment (shale)-rich units, which were strongly deformed and forced up towards the surface (Schmidt, 2000; Schmidt and Paterson, 2002). This deformation pattern differs strongly from observations farther south, where slope basin rocks accommodated a significant proportion of the total finite strain during Cretaceous contraction. Furthermore, this variation in strain explains why the deepest known levels of the PRB are exposed in the SSPM. Greater shortening in this zone is expected to correspond with greater crustal thickening and thus more buoyant crust that was subject to greater denudation. Conclusions The Sierra Calamajue study area spans the collision zone between the Alisitos arc and the Cretaceous North American continental margin and basement 72 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. assemblages that have been described throughout the PRB are present in the study area. These basement assemblages include 1) western volcanics associated with the Alisitos arc, 2) early Mesozoic turbidite sequences that are located in the central (or transitional) zone and are part of the ‘flysch belt’ of Gastil et al. (1975; 1981), and 3) eastern metasedimentary units that can be correlated with the Paleozoic passive margin of North America. Furthermore, Cretaceous deep-water sediments and associated volcanic units correspond to similar units along the western North American margin described from the Sierra San Pedro Martir (Johnson et al., 1999a; Schmidt and Paterson, 2002) and present the remnants of a deep marine basin. Four different phase of deformation are recognized in the study area. Paleozoic units record a phase of Mississippian to Permian deformation that is now well-documented along the Paleozoic southern margin of North America in Baja California and Sonora, Mexico (Anderson, 1993; Schmidt, 2000; Stewart, 1988; Stewart et al., 1990). Subsequent Phase 2 deformation occurred between >115 and 100 Ma, affected all units in the area, and was caused by accretion of the Alisitos arc to the North American continental margin. Kink folding occurred during Phase 3 deformation and resulted from elastic relaxation following accretion of the arc (Windh et al., 1989). The last structures observed are related to pluton intrusion and are areally restricted to the outer margins of plutons and narrow (<300 m) structural host rock aureoles. The presence of Paleozoic deep-water units between -30.5° N and 28°N latitude along the North American continental margin during collision of the Alisitos 73 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. arc and miogeoclinal strata farther to the north, strongly controlled the locus of Cretaceous deformation. North of latitude 30.5°N, miogeoclinal strata formed a rigid buttress that led to focusing of deformation in mostly sedimentary units between the arc and miogeoclinal units. This resulted in greater exhumation of units than to the south and is also responsible for the development of a doubly-vergent fan structure in the southern Sierra San Pedro Martir (Schmidt and Paterson, 2002). South of latitude 30.5°N, deep-water units were more easily deformed during accretion and a much broader region was affected by deformation, resulting in overall less exhumation. 74 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 3: RECONNAISSANCE PLUTON GEOCHEMISTRY AND GEOCHRONOLOGY Introduction Reconnaissance geochemistry and geochronology was completed as part of this study with several goals in mind. U-Pb zircon geochronology was conducted to 1) constrain the timing of magmatism in the Sierra Calamajue study area, 2) bracket the timing of deformation, and 3) determine whether xenocrysts from basement units were incorporated into the magmas, and if so, whether they are continental (Precambrian or Paleozoic in age) in origin. Five (5) plutons were sampled (Fig. 3.1.), but only two yielded enough zircons to warrant analyses using the LA-IC-PMS at the University of Arizona. Geochemical analyses were completed in order to add to the growing database being compiled under the lead of Dr. Paul Wetmore (University of Arizona/University of South Florida). Basic questions about the geochemical evolution of the PRB and the Alisitos arc in particular have not yet been addressed. The available data suggests that crustal thickening occurred along the eastern margin of the Alisitos arc between 116 and 110 Ma and magma generation depths increased from ~28 to ~43 km (Tate and Johnson, 2002). This crustal thickening event, which Tate and Johnson (2000) relate to deformation associated with island-arc accretion, has not been observed along the northern margin of the arc (Wetmore et al., 2003b; 2005). Thus, the following data from three (3) plutons were gathered in order to evaluate whether evidence for crustal thickening exists in the Sierra Calamajue, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ~ 5 km to North A Punta Final pluton I Explanation: Quaternary/ Tertiary Cretaceous Plutons Basement Assemblages 29 30 N \ \ Depositional contact I pluton ypi'c.anitp Cretaceous thrust faults Piedra Blanca pluton t ^ Folds (upright overturned) U-Pb age (G&H 1993) New U-Pb age Geochemical sample site ,'Pi, — . & ft & f t^ '- -* to Chapala pluton '' 1 X £ 1 -- V'vV< VC 1 T VC1 T V ><1o X< Las Palmas pluton < A \ %\N> 14"10'N / 29°15;N?I S 5 Figure 3.1. Simplified map of the Sierra Calamajue study area emphasizing the different plutons sampled and analysed for zircon geochronology and geochemistry. G&H 1993=Griffith and Hoobs (1993). Note that basement assemblages have been simplified. Detailed 1:50,000 scale map of the same area is in back pocket. 76 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. which spans the transition from the Alisitos arc to the continental margin along the eastern margin of the Alisitos arc (see Chapter 2). Plutonic units Deformed plutons ('Orthogneiss') I recognized two deformed plutons during my mapping in the PRB. The Piedra Blanca pluton is located in the Sierra Calamajue study area (Fig. 3.1.), whereas the Chapala Ring Complex is located outside the main study. Both intrusives have been sampled, but neither was successful. A sample collected from the Piedra Blanca pluton was not processed due to its small size and therefore limited success rate to yield enough zircons to determine U-Pb crystallization ages and was considered too altered for geochemical analyses. The sample from the Chapala Ring Complex was also too altered for geochemical analyses, but was processed for U-Pb zircon analyses. However, standard mineral separation techniques did not yield any zircons and crystallization ages could not be determined. Below, I describe the general lithologies and structural characteristics of these intrusive complexes and tiy to place them into a regional framework, but subsequent interpretations do not consider these plutons as constraints are too scarce. Piedra Blanca pluton The Piedra Blanca pluton intruded Paleozoic units along the northeast side of the study area (Fig. 3.1.) and is the only orthogneiss (deformed pluton) recognized in the study area. The orthogneiss was recognized during reconnaissance work 77 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. northwest of Calamajue Canyon and was only mapped during a single transect through the area. Thus, detailed mapping has not been completed on this body. The orthogneiss body is composed of layers of various thickness (centimeter to about hundred meters) defined by 1) compositional variations ranging from tonalite to 2-mica granite with the latter being dominant and 2) apparent mica- content. Tonalitic to granodioritic layers are dominated by quartz, plagioclase ± orthoclase, and biotite, whereas 2-mica granites contain a greater proportion of orthoclase, both, biotite and muscovite, and rare garnet. Minerals are sub- to anhedral and medium- to coarse grained (up to 10 mm large phenocrysts) and rock textures are equigranular to porphyritic and hypideomorphic. All phase show pervasive subsolidus deformation (Fig. 3.2.) with fabrics parallel to regional NW-SE-trending host rock fabrics (map in back pocket). Although deformation varies, foliation and lineation are consistently recognized and biotite wraps feldspar phenocrysts to define the subsolidus foliation. Lineation is defined by stretched quartz crystals and aligned feldspar and biotite. Subparallelism between host rock and pluton fabrics suggests that the fabric formed contemporaneously. Although a crystallization age or geochemical analyses were not completed, the sample is lithologically (i.e. 2-mica granite and locally garnet-bearing) very similar to Jurassic orthogneiss described from the Sierra San Pedro Martir (Schmidt, 2000; Schmidt and Paterson, 2002) and similar units in southern California (Todd et al., 1988; Thomson and Girty, 1994; Shaw et al., 2003). Thus, this pluton is 78 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 3.2. Picture of strong subsolidus deformation in Piedra Blanca fault. Note that foliation is parallel to regional continuous cleavage. 79 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. interpreted as another example for the enigmatic Jurassic magmatism that is recognized in the central and eastern PRB at ~ 164 Ma. Chapala Ring Complex The Chapala complex is located outside the study area, ~20 km west of Calamajue Canyon (Fig. 3.1.). The complex is composed of several different magmatic pulses ranging in composition from gabbroic to granitic to, locally, ultramafic (homblendite) material. Several of the more leucocratic (tonalite to granodiorite) pulses are ~5 to 10 m thick, separated by host rock screens, contain abundant mafic enclaves, and form apparent ring structures around a magmatic center. Homfelsed host rocks are composed of very fine grained siliceous to quartzitic material. Locally marble is present and plagioclase-phenocrysts in a fine grained matrix have been recognized and are probably metavolcanic units. Strong recrystallization and limited exposure complicate exact protolith identification. The intrusive ring structures surrounding the center range from undeformed to strongly deformed and host rocks generally show a strong fabric. Fabrics are parallel to the trend of the ring structures and local kinematic indicators (s-c fabric) suggest center up motion. The central magmatic portion, which is composed of various pulses of different sizes, is undeformed. The complex is located far from the zone of widespread regional deformation recognized in the Sierra Calamajue area. This suggests that deformation of the outer plutonic sheets and in the aureole is related to formation of the ring complex rather 80 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. than regional tectonism. Ring complexes have been widely recognized in the Alisitos arc and ring complex structures (Burro Complex, Zarza Intrusive Complex) have been described in some detail in Baja California (e.g., Johnson et al., 1999a; Tate et al., 1999). Undeformed plutons Besides the above, all other plutons in the study area are undeformed and petrological field observations are similar for all of them, including the Calamajue, Las Palmas, and Corral plutons, which have been analyzed for U-Pb geochronology and/or geochemistry. All plutons are homogeneous, show limited compositional variations, and lack distinct zonation. However, these observations are based on limited mapping and detailed traverses through the plutons have not been completed. The mineralogy of the intrusions is dominated by quartz, feldspar (plagioclase±orthoclase), and biotite and rock types are classified in the field as diorite, tonalite, and granodiorite. In outcrop, most rocks are medium-grained (up to 5 mm large phenocrysts) and equigranular. Magmatic textures are hypideomorphic and few mafic enclaves, stoped blocks, or host rock rafts have been recognized. Throughout the study area, contacts between plutons and host rocks are sharp, steep, and cut across structural elements in the host rock. A limited deflection of host rock foliation and locally folding of that foliation and development of a margin-parallel axial planar cleavage is best developed around the Las Palmas pluton. Plutons do not show pervasive magmatic or subsolidus deformation and only the outermost margins of most plutons contain a weak magmatic to high temperature 81 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. subsolidus, margin-parallel fabric. These observations are confirmed by thin section analyses, which show magmatic textures and no discemable fabric. Geochronology and geochemistry Five (5) plutons were sampled for geochronologic (U-Pb on zircon) and geochemical analyses. However, only two samples yielded enough zircons to determine crystallization ages and three samples were processed for whole rock, major, and trace element analysis. U-Pb and geochemical analyses were completed on the Las Palmas pluton (Sample HA-068-04) and the Calamajue pluton (Sample HA-070-04). Furthermore, geochemical analyses were completed on the Corral pluton (Sample HA-071-04). In addition to the Corral pluton, the Chapala and Piedra Blanca plutons did not yield yielded enough zircons for analyses and samples from the latter two plutons were considered too altered for geochemical analyses. Geochronologic analyses were completed by Dr. Paul Wetmore under the direction of Dr. George Gehrels using an LA-MC-ICPMS at the University of Arizona (see Appendix A for details on the analytical procedures and Appendix B for the raw data for individual spot analyses). Geochronology Eighteen (18) analyses of zircon crystals were completed in sample HA-070- 04 from the Calamajue pluton (Fig. 3.3.a.). These zircons yield a range in 2 0 6 Pb/2 3 8 U ages from ~138 to 150 Ma with a mean weighted standard deviation (MWSD, Ludwig, 2001) age of 143.9±2.1 Ma, which is interpreted to represent the age of 82 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 154 150 < U CO 142 Age = 143.9±2.1 Mean = 143.7±1.9 138 MSWD = 3.0 134 106 Age = 95.3±1.9 Ma Mean = 95.3±1.7 Ma MSWD - 3.0 102 Figure 3.3. Plots of 2 0 6 Pb/2 3 8 U single crystal zircon ages (with 1-sigma error bars) from the Sierra Calamajue study area. a. Calamajue pluton (Sample HA-070-04), b. Las Palmas pluton (Sample HA-068-04). The weighted mean of the individual analyses is calculated according to Ludwig (2001). See Appendix A for details of analytical procedure and text for discussion. 83 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. crystallization for this pluton. All analyses are concordant to slightly discordant and the determine age is considered sound. Interpretation of the analytical results of sample HA-068-04 from the Las Palmas pluton left only ten (10) analyses of zircon crystals that are considered reproducible (Fig. 3.3.b.). The discarded grains were highly complex with dramatic changes in Pb/ U ratios throughout the runs, resulting in big errors. The complexity is probably the result of inheritance of older (Early Cretaceous or Jurassic) grains (Paul Wetmore, pers. comm., 2005). Zircon analyses considered satisfactory, yield a range in 2 0 6 Pb/2 3 8 U ages from -92 to 99 Ma with an MWSD age of 95.3±1.9 Ma. Geochemistry Three samples, one each from the Las Palmas (HA-068-04), Calamajue (HA- 070-04), and Corral (HA-071-04) plutons, were analyzed for whole rock, major, and trace element analysis. The results of these analyses are given in Table 3.1. In general, the chemical compositions of plutons in the study area do not exhibit significant variations or gradients. Silica contents range from 62 to 69 wt% and all three samples have similar Magnesium numbers (MgO wt%/MgO + Fe2C >3 wt%) and Fe* (FeOto t/(FeOto t + MgO) at ~ 0.35 and -0.65, respectively (Table 3.1.). Using the data from Tables 3.1., normative compositions were calculated using GDCkit freeware from Janousek et al. (2003; 2004 in review) and results are shown in Table 3.2. Using the norm calculations, all three samples classify as granodiorites on an IUGS classification diagram (Streckeisen, 1974; 1976a; b) (Fig. 84 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.1. Major, trace, and rare earth element chemistry from the Las Palmas, Calamajue, and Corral plutons. Las Palmas Calamajue Corral Pluton pluton pluton pluton Samples HA-068-04 HA-070-04 HA-071-04 Si02 68.90 62.36 66.99 Ti02 0.52 0.76 0.55 A 12 0 3 16.29 16.57 16.14 Fe20 3* 2.65 6.30 3.55 MnO 0.04 0.11 0.06 MgO 1.46 3.19 2.06 CaO 3.48 5.76 3.97 Na2 0 4.75 3.03 4.54 k2 o 2.60 2.42 2.17 p2 o 5 0.13 0.15 0.13 LOI 0.25 1.12 0.40 Total 101.07 101.77 100.56 Trace Elements (ppm) Ba 856.09 815.38 697.24 Rb 61.05 87.13 74.72 Sr 625.98 293.06 459.30 Y 10.52 25.43 12.16 Zr 168.99 175.26 151.20 Nb 6.40 5.70 6.05 Th 5.85 9.57 6.47 Pb 10.23 8.02 12.07 V 40.87 141.98 68.69 Hf 4.72 5.33 4.34 Cs 0.88 7.34 3.64 Sc 18.24 24.86 18.79 Ta 0.39 0.49 0.56 U 1.17 1.18 1.28 Sn 1.33 2.12 1.90 Be 9.45 nd 3.08 Zn 139.58 111.32 107.74 Ge 0.66 1.40 1.08 Tm 0.14 0.42 0.18 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.1. continued. Trace Elements (ppm) W nd 0.56 0.32 T 1 0.36 0.53 0.53 Yb 0.84 2.70 1.16 Li 21.46 25.18 31.86 Bi 0.07 0.09 0.05 P 544.45 681.42 651.41 Ti 3238.03 4646.13 3685.02 Cr 36.17 66.09 76.43 Co 5.99 18.02 11.83 Ni 8.91 16.81 20.05 Cu 2.17 18.11 4.03 As nd 1.59 2.00 Mo 0.29 0.51 0.18 Ag nd 0.07 0.08 Cd nd nd nd Sb nd 0.64 0.39 Rare Earth Elements (ppm) La 21.69 19.50 13.85 Ce 46.31 43.39 30.50 Pr 5.56 5.57 3.81 Nd 21.11 22.34 15.18 Sm 3.88 4.94 3.22 Eu 1.15 1.17 0.96 Gd 3.26 5.13 2.91 Tb 0.37 0.75 0.39 Dy 1.98 4.73 2.30 Ho 0.36 0.94 0.42 Er 0.97 2.86 1.22 Lu 0.11 0.39 0.17 nd=not detected Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.2. Normative compositions of the Las Palmas, Calamajue, and Corral plutons calculated using GDCkit freeware from Janousek et al. (2003; 2004 in review). Las Palmas pluton Calamajue pluton Corral pluton Sample HA-068-04 HA-070-04 HA-071-04 Q 22.26 19.47 21.41 c 0.00 0.00 0.00 Or 15.37 14.30 12.82 Ab 40.19 25.64 38.42 An 15.45 24.46 17.25 Di 0.00 0.71 0.00 Hy 3.64 7.61 5.13 01 0.00 0.00 0.00 1 1 0.09 0.24 0.13 Tn 0.68 1.56 1.12 Ru 0.20 0.00 0.02 Ap 0.31 0.36 0.31 Pr 0.00 0.00 0.00 Sum 98.18 94.36 96.62 QAP 93.27 83.88 89.90 Q 23.87 23.22 23.82 A 16.47 17.05 14.26 P 59.66 59.73 61.92 100.00 100.00 100.00 Q=quartz, C=Corundum, Or=Orthoclase, Ab=Albite, An=Anorthite, Di=Diopside, Hy=Hyperstene, 01=01ivine, Il=Ilmenite, Tn=Titanite, Ru=Rutile, Ap=Apatite, Pr=Perovskite, A=Alkali feldpar, P=Plagioclase Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.4.). Furthermore, using the basic chemical results, these samples are calc-alkaline (Fig. 3.5.), medium- to high-K series (Fig. 3.6.), metaluminous (Fig. 3.7.) plutons, with a Peacock (or alkali-lime) index of ~63 (Fig. 3.8.). These whole rock and major element discrimination diagrams show that the -144 Ma Calamajue pluton is slightly different from the -95 Ma Las Palmas and undated Corral plutons, which tend to cluster more closely (Figs. 3.5. to 3.7.). While whole rock and major element comparisons between the different plutons suggest similarities, evaluating the REE pattern of the plutons analyzed in this study (Fig. 3.9.) reveals their differences. Samples HA-068-04 and HA-071-04 exhibit minor light rare earth element (REE) enrichment with respect to heavy REE (Fig. 3.9.), which is commonly attributed to a garnet-bearing source for magma generation. In contrasts, sample HA-070-04 shows less light REE enrichment and a slight Europium anomaly, which indicates a plagioclase-bearing magma source. Strontium concentration ranges from 293 to 625 ppm and Sr/Y ratios are between 12 and 60. Discussion Geochronologic constraints Significance of the ~144 Ma Calamajue pluton The new ages from the study area provide new constraints and intriguing new problems to the understanding of the evolution of the PRB. The 143.9±2.1 Ma Calamajue pluton represents the oldest dated pluton that intrudes strata that have been correlated with the Alisitos arc (see Chapter 2). To date, older (Jurassic) plutons 88 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 0 0 100 100 Figure 3.4. IUGS classification of phaneritic feldspathic rocks (after Streckeisen, 1976). After norm calculation, all three samples collected in the Sierra Calamajue classify as granodiorites. ©=HA-068-04; ©=HA-070-04; ©=HA-071-04. Note that samples collected from the Sierra San Francisquito are also plotted (Goldfarb, 1996). 89 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Calc-alkaline - Tholeiitic (after Miyashiro, 1975) 75 Calc-alkaline 70 HA068-04 O HA071-04 © 65 HA070-04 © 60 55 50 Tholeiitic 45 40 4 5 2 .3 0 1 FeO*/MgO Figure 3.5. Si02 versus FeO*/MgO plot (after Miyashiro, 1975). All three samples collected in the Sierra Calamajue classify as calc-alkaline plutons. Note that samples collected from the Sierra San Francisquito are also plotted (Goldfarb, 1996). 90 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. S i0 2 -K2 0 Plot (after Peccerillo and Taylor, 1976) .oshonite Scries O H A 070-04 H A 068-04 H A 071-04 M edium -K Serie C N Low-K Series o 45 50 55 60 65 70 75 Si02 Figure 3.6. K2 0 versus Si02 plot (after Peccerillo and Taylor, 1976). Samples collected in the Sierra Calamajue are medium- to high-K series plutons. Note that samples collected from the Sierra San Francisquito are also plotted (Goldfarb, 1996). 91 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A/NK vs. A/CNK plot (after Shand, 1943) Metahimin! reraiu m m em s H AO 70-04 HA071-04 f HA068-04 f t o 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 A/CNK Figure 3.7. A/NK versus A/CNK plot (after Shand, 1943). Samples collected in the Sierra Calamajue are metaluminous. Note that samples collected from the Sierra San Francisquito are also plotted (Goldfarb, 1996). 92 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Peacock / Alkali-lime index (after Peacock, 1931) Alkalic Alkali-calcic Calc-alkali Calcic a > E 5 16 14 12 10 8 6 4 2 0 46 51 56 61 66 wt% Si02 Figure 3.8. Alkali-lime index of samples collected in the Sierra Calamajue (after Peacock, 1931). Alkali-lime index is -63. VO u > Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 100-1 H A 070-04 H A -0 7 1-04 G O H A 068-04 Dy La Ce Pr Nd Pm Sm Gd Tb Eu Yb Ho Er Tm Lu Normalized by REE chondrite (Boynton, 1984) Figure 3.9. Plot of Rare Earth Element concentrations normalized to chondrite (after Boynton, 1984). ■£ >. and similar Early Cretaceous age (~133 to 128 Ma) plutons in the PRB have only been reported from the central (transitional) zone of the Sierra San Pedro Martir (Johnson et al., 1999a; 2003; Schmidt and Paterson, 2002) and southern California (Silver et al., 1979), where they are interpreted to represent the remnants of a Jura- Cretaceous continental margin arc. The presence of Early Cretaceous magmatism in the Alisitos arc has tectonic implications for this part of the North American Cordillera that need to be explored. Furthermore, explanations for the presence of an undeformed, -144 Ma pluton, which intrudes Alisitos arc units that are deformed during arc accretion between -115 to -100 Ma (Chapter 2), have to be found and several of the implications are discussed below. Accepting a single crystallization age from sample HA-070-04 as the age of the whole Calamajue pluton, the Alisitos arc in the area must be older than the -125 Ma suggested by D. Kimbrough (pers. comm., 2001) and the original age o f-156 Ma reported by Griffith and Hoobs (1993) is a more appropriate minimum age for the Alisitos in the Sierra Calamajue. Thus, magmatism in the Alisitos arc and the continental margin arc (Santiago Peak arc) are temporally close. The simplest explanation to account for roughly coeval magmatism is the presence of two simultaneously active, east-directed subduction zones along the margin, with one subduction zone along the continental margin and one along the offshore, Alisitos island arc (e.g., Gastil et al., 1981; Johnson et al., 1999a; Wetmore et al., 2003a). Another important question is why the -144 Calamajue pluton is undeformed while intruding strata that have been deformed in a fold-thrust belt between -115 and 95 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. -100 Ma (Chapter 2)? One possible explanation is that the pluton acted as a rigid entity during accretion and, in fact, contributed to the narrowness of deformation in Calamajue Canyon, which until now has not been adequately explained (Chapter 2; cf. Griffith and Hoobs, 1993). Predating regional deformation by -30 m.y., the Calamajue pluton was probably completely solidified prior to accretion of the arc as it intruded into unmetamorphosed to low-grade metamorphic host rocks at shallow crustal levels. During collision, which led to juxtaposition of the main basement assemblages across reverse faults (Chapter 2), the pluton and its thin, homfelsed aureole were Theologically stronger than the layered country rocks dominated by fine-grained metasediments, volcaniclastic deposits, and volcanic units. A steep deformation gradient formed as a result and is now preserved in the Calamajue Canyon section with greatest deformation concentrated in the canyon -3 km northeast of the pluton. The existence of other undeformed plutons (e.g., -116 Ma Zarza Intrusive Complex and -114 Ma Burro complex) that predate widespread regional deformation and are in close proximity (-3 km) to the edge of the fold- thrust belt (Johnson et al., 1999b) are consistent with the above observation, although I do not want to imply that the latter acted as rigid entities as well. The above constraints have to be carefully evaluated in future studies. There are two main reasons to be cautious. First, the new constraints are based on a single U-Pb sample and more analyses from the same pluton to constrain the absolute age are desirable as it is increasingly clear that the temporal evolution of magmatic systems is very complex (e.g., Matzel, 2004). Second, detailed mapping of the Calamajue pluton has not been conducted. It is possible that better field constraints 96 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. reveal that the Calamajue pluton intruded the Paleozoic Canon Calamajue unit (Chapter 2) and that the sampled pluton simply represents a raft or stoped block in a Cretaceous pluton, which postdates the main phase of regional deformation. Alternatively, the sampled zone represents an old phase that is intruded out by a younger pluton. The first scenario does not require that the Alisitos arc is Jurassic or Early Cretaceous in age, whereas the second alternative still mandates the older age. To support intrusion into continental margin units, one expects plutons to show continental inheritance, which is not seen in the Calamajue pluton sample (see below). However, additional geochronologic analyses would help to elucidate this problem. Significance of the -95 Ma Las Palmas pluton Although the Calamajue pluton does not aide in constraining the timing of Cretaceous deformation, the Las Palmas plutons provides a lower age constraint. At 95.3±1.9 Ma the Las Palmas pluton coincides in age with so-called La Posta-type intrusions that are post-kinematic and intruded in a voluminous magmatic pulse along the axis of the PRB between 99 and 92 Ma (e.g., Walawender et al., 1990; 1991; Kimbrough et al., 2001). Similarly, the Las Palmas pluton truncates regional structures, such as folds and faults (Fig. 3.1.) along its northwest end. Locally, the dominant continuous cleavage in the host rock is deflected or folded in a narrow structural aureole. These observations indicate that the pluton postdates regional deformation, which had ceased by 95 Ma. This observation is consistent with Griffith and Hoobs’ (1993) observation that the small, ~100 Ma stock, which 97 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. intrudes and cross-cuts structures in the La Mision unit near the northern end of Calamajue Canyon, lacks any magmatic or subsolidus deformation and therefore intrusion must have followed regional deformation (Fig. 3.1.). It should be noted, that it is possible that localized deformation along discrete faults other than the ones cut by the intrusions occurred after their emplacement. Constraints on basement stratigraphy from single crystal zircon analyses Beside providing crystallization ages and helping constraining the timing of deformation, U-Pb analyses of plutonic zircon populations may also provide information about the host rock stratigraphy present beneath the arc (e.g., Wetmore, 2003). Specifically, the absence of xenocrystic, continentally-derived zircon in any of the U-Pb analyses conducted on Alisitos arc volcanics and plutonics, has been used to argue for evolution of the Alisitos arc on oceanic lithosphere, away from continental sources (Johnson et al., 1999a; 2003; Wetmore et al., 2003b; 2005). Data from the Calamajue pluton add to the mounting evidence that there is no significant crustal component associated with formation of the Alisitos arc, as xenocrystic grains have not been identified in the zircon population of the pluton. Although other explanations, such as 1) magma ascent without host rock assimilation or 2) a limited sample size (18 analyses) may account for the absence of these xenocrystic grains, the fact that numerous studies (e.g., Carrasco et al., 1995; Johnson et al., 1999a, 2003; Wetmore, 2003), including this one, have not detected any continental component in the zircon population suggests that continentally derived sediments do not comprise a significant component of the Alisitos arc basement. 98 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Older (Paleozoic or Precambrian) zircons have not been identified in the -95 Ma Las Palmas pluton either. However, the zircon population in this sample is significantly more complex than that of the Calamajue pluton. This added complexity is the result of zoning of the grains and probably the inheritance of Early Cretaceous or Jurassic zircon cores in the population (Paul Wetmore, pers. comm., 2005). These grains are derived from either Jura-Cretaceous plutons or accretionary wedge-like sediments that are common in the basement of the PRB. The fact that younger plutons, such as this one, entrain grains from either the underlying metasedimentary host rock strata or older plutons suggests that the same should be expected for older intrusions, which is not seen in the Calamajue pluton and other intmsions in the Alisitos arc (Carrasco et al., 1995; Johnson et al., 1999a, 2003; Wetmore, 2003). Furthermore, where plutons clearly intrude through continental margin units of the eastern PRB, a significant component of inheritance is common. This inheritance is found in La Posta-type intrusions (Kimbrough et al., 2001) as well as in the La Guera pluton at the northern end of the Sierra Calamajue study area (Fig. 3.1.). Here, an analysis presented by Goldfarb (1996) shows highly discordant zircon fractions with lower and upper intercepts of 81±121 Ma and 519±560 Ma, respectively. The most obvious problem for determining the crystallization age of this pluton is inheritance (Goldfarb, 1996). 99 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Geochemical considerations Importance o f trace element geochemistry Comparison between the whole rock and major element chemistry from this study and the data presented by Goldfarb (1996) from the La Guera and Punta Final plutons (Table 3.3.) located <5 km to the north of the Sierra Calamajue study area (Fig. 3.1.) shows significant similarities between the datasets (Fig. 3.5. to 3.7.). With the exception of the alumina content, which suggests that pluton to the north are slightly more aluminous, and minor differences between individual analyses, all samples are medium- to high-K, tholeiitic to calc-alkaline plutons, which is typical for continental margin arc intrusions. If REE element analyses or geochronology had not been completed, these similarities would have suggested that all plutons in the study area are genetically related and of the same age. Having completed REE and U-Pb geochronologic analyses, which reveal significant differences between the intrusions, shows how valuable these tools are. Thus, it is critical that future investigations place significant emphasis on these types of analyses. Constraints on crustal thickening The most detailed geochemical study of intrusive bodies was completed by Tate et al. (1999) and Tate and Johnson (2000) in the northern SSPM. Plutons in that area fall into two age groups of 114-115 Ma (Pre-110 Ma) and 108 to 103 Ma (Post- 110 Ma). Both groups exhibit similar major and trace element compositions, but show substantial differences with respect to REE abundances. Older plutons show flat REE patterns with a distinct Europium anomaly, while younger plutons are Light 100 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table 3.3. Major element chemistry by Goldfarb (1996) from the Punta Final and La Guera plutons Pluton Punta Final Punta Final La Guera pluton pluton pluton La Guera pluton La Guera pluton La Guera pluton La Guera pluton La Guera pluton La Guera pluton Hornblende diorite biotite biotite biotite biotite biotite biotite muscovite Samples BG146 BG276 BG284 BG360 BG361 BG362 BG363 BG366 BG364 BG365 Si02 68.36 65.52 69.47 68.28 67.91 68.67 68.40 68.89 75.43 59.89 Ti02 0.47 0.61 0.28 0.26 0.34 0.27 0.25 0.22 0.03 0.95 A1203 16.54 16.59 16.49 17.04 16.81 16.91 16.87 16.89 14.27 16.12 Fe2 0 3* 2.86 3.77 2.56 2.45 3.28 2.64 2.35 2.21 0.42 5.60 MnO 0.07 0.07 0.06 0.06 0.07 0.07 0.06 0.06 0.03 0.09 MgO 1.27 1.64 0.66 0.54 0.81 0.61 0.56 0.55 0.10 4.89 CaO 3.74 4.36 3.34 3.44 3.47 3.08 2.96 3.16 0.85 5.87 Na2 0 3.72 3.15 4.09 4.34 4.01 4.04 4.17 4.21 4.28 3.33 K2 0 2.84 2.12 2.64 2.68 2.57 3.51 2.98 2.84 4.44 1.58 P2 0 5 0.12 0.15 0.11 0.10 0.13 0.10 0.11 0.10 0.04 0.21 LOI nd nd nd nd nd nd nd nd nd nd Total 99.99 97.98 99.70 99.19 99.40 99.90 98.71 99.13 99.89 98.53 o REE enriched and heavy REE depleted (Fig. 3.10.a. and b.). Tate and Johnson (2000) explained these changes by a dramatic increase in crustal thickness from -28 km during the generation of the pre-110 Ma plutons (Tate et al., 1999) to greater than -43 km during the generation of post-110 Ma plutonic suites. This crustal thickening drives the source region for these melts to depths where garnet and amphibole become stable phases in the residuum at the expense of plagioclase during melting of amphibolite. Wetmore et al. (2003b; 2005) compared the REE patterns between the northern SSPM and the San Vicente area and concluded that the model proposed by Tate and Johnson (2000) does not to apply to the San Vicente area. Plutons in the San Vicente area overlap with patterns of the older plutons in the SSPM, but not the younger ones (Fig. 3.10.C.). Since the plutons in the San Vicente area are younger than 110 Ma and postdate most contractional deformation in the region, Wetmore et al. (2003b; 2005) concluded that the area experienced a smaller degree of crustal thickening relative to that of the SSPM. The REE patterns from plutons in the Sierra Calamajue study area are in accord with observations from the northern SSPM (Fig. 3.10.d). The pre-110 Ma Calamajue pluton has a flat REE pattern with a weak Europium anomaly, whereas the post-110 Ma Las Palmas and, by inference, Corral plutons are light REE enriched and heavy REE depleted. These observations support Tate and Johnson’s (2000) model that significant crustal thickening occurred along the east side of the Alisitos arc. 102 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 3.10. On next page. Comparison between Rare Earth Element patterns from different areas in the Alisitos arc. a. Pre-110 Ma intrusions from northern Sierra San Pedro Martir (after Tate et al., 1999; Tate and Johnson, 2000). b. Post-110 Ma intrusions from northern Sierra San Pedro Martir (after Tate et al., 1999; Tate and Johnson, 2000). c. Post-110 Ma intrusions from the San Vicente area (after Wetmore et al., 2005). d. Intrusion from the Sierra Calamajue. See text for discussion. 103 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. REE Plots pre-110 Ma plutons (N SSPM) 1000 • a 1 0 - La* Ce* Pr* N d* Sm* Eu* G d* Tb* Dy* H o* Er* Yb* REE Plots post-110 Ma plutons (San Vicente) 1000 I '" 1 1 I I I I .............................................................................................................. La* Ce* Pr* N d* Sm* Eu* G d* Tb* Dy* H o* Er* Yb* b REE Plots post-110 Ma plutons (N SSPM) 10001 a lo o La* Ce* Pr* N d* Sm* Eu* Gd* Tb* D y* H o* Er* Y b* Lu* d. REE Plots of plutons (Sierra Calamajue) 10001 a lo o HA-070-04 (-143 M ai HA-068-04 & H A -071-04 (-95 Ma) La* Ce* Pr* N d* Sm* Eu* Gd* Tb* Dy* H o* Er* Y b* Lu* The similarities and differences between these pluton groups can also be recognized on a Sr/Y- versus La/Yb-ratio plot (Fig. 3.11.). Two distinct groups form with pre-110 Ma plutons from the SSPM, the pre-110 Ma Calamajue pluton, and post-110 Ma plutons from the San Vicente area having low ratios and Post-110 Ma plutons in the SSPM have high ratios. The Las Palmas and Corral plutons plot between these two groups (Fig. 3.11.). Using the same La/Yb ratios and plot them versus crystallization age provides an estimate of crustal thickening with time (Fig. 3.12.a. after Haschke and Gunther, 2003). Haschke and Gunther (2003) observed an increase of the La/Yb ratio with in the Andean continental margin arc, which they interpreted as an indicator of crustal thickening. A similar pattern can be seen for the Alisitos arc (Fig. 3.12.b.). This pattern suggests that early (pre-110 Ma) magmas were generated at depth of 30 to 35 km or less, while younger magmas along the east side were generated at depth of >40 km. Thus, significant crustal thickening as a result of collision of the Alisitos arc with the North American continental margin occurred. However, this thickening is not observed along the northern margin of the arc, where less contraction and more transcurrent deformation is observed (Wetmore, 2003; Wetmore et al., 2003b; 2005). Conclusions The whole rock and major element analyses and resulting discrimination diagrams do not yield detectable differences between intrusions that have crystallization ages that differ by ~50 Ma. Displaying similar structural 105 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Trace Element Signatures 160 N SSPM (posl-110 Mu intrusions) 140 120 H 100 * 80 60 40 , N SSPM (pre-110 Ma intrusions) 20 - \ San Vicente )ost-l 10 Ma intrusions) 0 0 5 10 15 20 25 30 La/Yb Figure 3.11. Plot of Sr/Y ratio versus La/Yb-ratio. Fields for San Vicente area and northern Sierra San Pedro Martir (after Wetmore et al., 2005; Tate et al., 1999; Tate and Johnson, 2000). Numbered samples are from Sierra Calamajue. O = HA068-04, ©=HA070-01, © = HA071-04. Note transitional character between the Sierra Calamajue and other areas. 106 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Evolutionary pattern of Andean La/Yb ratios Crustal thickness Magmatic gap Magmatic gap Magmatic gap correlations after Hildreth&Moorbath (1988) 60 125-90 Ma arc | 78-37 Ma arc 26-0 Ma arc 195-130 Maarc 50-55 km 40 £ > 20 30-35 km 0^= 200 150 100 50 0 Age (Ma) b. Evolutionary pattern o f Alisitos arc La/Yb ratios Age vs La/Yb 25- 2 0 - 4 0 km 95 M a 143 Ma 10- 30-35 km 110 108 1 0 2 118 116 114 112 106 104 100 Age (Ma) Figure 3.12. Comparison between the La/Yb evolutionary pattern of the Andean arc and Alisitos arc. a. Plot of La/Yb ratio vs. age for Andean arc (modified from Haschke and Gunther, 2003). b. Plot of La/Yb ratio vs. age for Alisitos arc (data from Tate et al., 1999; Tate and Johnson, 2000; Wetmore et al., 2005; this study). Note increased La/Yb ratio in younger intrusions suggesting deeper crustal magma sources. Age for plutons in the Sierra Calamajue are inferred from 100 Ma stock dated by Griffith and Hoobs (1993). 0=HA-068-04; ©=HA-070-04; ©=HA-071-04. 107 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. characteristics, a genetic link between these intrusions would be a reasonable interpretation without available geochronology and/or geochemical analyses. Differences become obvious when looking at REE patterns. Thus, detailed trace element geochemistry is desirable in order to continue to unravel the geochemical evolution of the PRB. Additional work on the exact age of the Calamajue pluton now dated at -144 Ma, and a better understanding of field relationships between the pluton and host rocks are important in the future, as a Jurassic or Early Cretaceous age for the Alisitos arc would add important information on the Mesozoic tectonic evolution of the southwestern North American Cordillera. The geochemical and geochronologic data from the Sierra Calamajue study area supports a crustal thickening event between 144 and 95 Ma. These conclusions are supported by 1) a flat REE pattern and Europium anomaly in the -144 Ma Calamajue pluton with, based on the La/Yb-ratio, a possible magma generation depth of -30 km and 2) light REE enrichment and heavy REE element depletion in the -95 Ma Las Palmas pluton, with a possible magma generation depth of >40 km. The limited data results in temporal constraints that are less well-defined than in the northern SSPM, where the event can be bracketed between -116 and 110 Ma (Tate and Johnson, 2000). 108 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 4: COMPLEX DEFORMATION AS A RESULT OF ARC- CONTINENT COLLISION: QUANTIFYING FINITE STRAIN IN THE ALISITOS ARC Introduction The mid-Cretaceous accretion of the Alisitos island arc of Baja California (Fig. 4.1.) with North America (e.g., Todd et al., 1988; Johnson et al., 1999a; Wetmore et al., 2002; 2003a) left a superb geologic record of how continental and arc crust respond to collision. Preservation of this record is aided by restricted pre- and post-accretion deformation, magmatism, and metamorphism. Suturing of the arc to the continental margin units was accompanied by formation of a fold-thrust belt that rims the arc along the northern and eastern margin. However, the structural character of this suture zone and finite strain in the fold-thrust belt change significantly along-strike. The mechanical behavior of the colliding arc and these along-strike variations are the focus of this chapter. Along-strike variations in the structural character of the fold-thrust belt partly reflect changes in the tectonic setting, but also document the importance of changes in continental margin geometry and geology (Figs. 4.1. and 4.2.). Sinistral transpression has been documented along the northern end of the arc (Wetmore, 2003), whereas mostly orthogonal convergence occurred along the east side (Johnson et al., 1999a; Schmidt, 2000). Nevertheless, even where orthogonal convergence dominated, deformation is recorded variably. The presence of rheologically-strong, 109 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Los AngelesV San Vicente San v Quintin Explanation: Santiago Peak arc □ \ Alisitos arc Bedford Canyon Complex Mesozoic clastic sediments Undifferentiated Paleozoic passive margin strata Proterozoic basement Study areas (see Figure caption) Depositional contact Fault zontact (thrust, strike-slip) Gulf of California (incipient spreading centers and transform faults) SAF San Andreas fault ABF MSM? Pm-Tr Agua Blanca fault Mojave-Sonora Megashear? Permo-Triassic U.S./Mexican highways Figure 4.1. Overview of the PRB including outlines of areas discussed throughout the text. l=San Vicente area (Wetmore, 2003); 2=northem Sierra San Pedro Martir (Johnson et al., 1999a); 3=southem Sierra San Pedro Martir (Schmidt, 2000); 4=Sierra Calamajue (this study); ASJ-Arroyo San Jose; PP=Punta Prieta. 110 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cairalu / / S ' * C a p ftip liy A Figure 4.2. Simplified map of the fault-bounded Alisitos arc emphasizing the approximate location of fold-thrust belt and suture between the arc and adjacent units. Note location of the aABF. Plutons are removed for added simplicity. Boxes outline areas of detailed study by Wetmore (2003), Johnson et al. (1999a; 2003), Schmidt (2000), and this study discussed in text.ABF=active Agua Blanca fault; aABF=ancestral Agua Blanca fault; MMT=Main Martir thrust; ETF=E1 Topo fault. 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Paleozoic miogeoclinal units in the Sierra San Pedro Martir (SSPM) east of the Alisitos arc (Fig. 4.1.) resulted in significant ductile deformation in sediment- dominated basinal assemblages between the arc and continental margin units (e.g., Johnson et al., 1999a), whereas a promontory of miogeoclinal units in the southern part of the range led to formation of a doubly-vergent fan structure (Schmidt, 2000; Schmidt and Paterson, 2002). In contrast, farther south in the Sierra Calamajue, where weaker Paleozoic deep-water assemblages dominate, a fan structure did not develop, and deformation is expressed as a brittle-ductile fold-thrust belt that extends eastward into Paleozoic units (Chapter 2). The width of the collided Alisitos arc strata affected by ductile deformation also varies from north to south. Along the northern end of the arc, high ductile strains are recorded by Alisitos arc strata at a distance of -12 km southwest of the suture. Along the eastern margin of the arc, Alisitos arc strata show high ductile strain in a 10- and 5-km-wide-zone in the northern and southern SSPM, respectively. This zone narrows to <3 km in the Sierra Calamajue. Consequently, continental margin units east of the arc in the SSPM and the Sierra Calamajue experienced greater finite ductile strains during collision. The development of the fold-thrust belt rimming the arc suggests that translation, rigid rotation, and ductile strain played significant roles during accretion of the arc. The presence of abundant strain markers allowed quantification of the finite strain component of deformation, which in its strict sense encompasses 1) translation, 2) rotation, 3) strain, and 4) volume change (e.g., Davis, 1996). Finite 112 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. strain determinations can be used to estimate the overall contribution of ductile strain to shortening and crustal thickening in the fold-thrust belt. The data show that flat- lying to gently folded strata on the west side of the arc have no measurable ductile strain. Faulting and folding increase towards the suture zone and although maximum finite strain also increases towards the bounding suture, in detail it becomes increasingly variable. Throughout the arc-bounding fold-thrust belt, finite strain reaches maximum values of 60 to 70% shortening in Z (where X>Y>Z) and maximum finite strain is concentrated near the interface between the colliding entities. Based on these strain values, I re-emphasize the importance of considering ductile strain when creating balanced cross sections (e.g., Woodward et al., 1985; Mukul and Mitra, 1998) and that without incorporating ductile finite strain, shortening estimates in fold-thrust belts are minimum estimates. Although finite strain maxima are comparable along-strike, strain heterogeneity is expected (e.g., Cobbold; 1977; Ramsay, 1982; Treagus, 1983) due to several factors: 1) variations in the matrix-lithic ratios between sampled units, 2) changes in composition and original shape of fragments, 3) different size distributions of lithic constituents (e.g., Hossack, 1968), and 4) variable, deformation mechanisms, which are a function of pressure-temperature conditions and strain rate. Furthermore, variably developed primary fabrics and contributions from localized deformation processes such as folding, faulting, and/or pluton emplacement have added to the observed overall strain heterogeneity. 113 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Below I briefly introduce the geology of the regional geology of the Peninsular Ranges batholith (PRB) and described the Sierra Calamajue (see Chapter 2 for greater detail), San Vicente area (Wetmore, 2003) and the northern (Johnson et al., 1999b) and southern (Schmidt, 2000) Sierra San Pedro Martir, because the available and new strain data comes from these areas. Following the description of the general structural characteristics, I discuss the nature of strain and its distribution in the fold-thrust belt and the Alisitos arc in general. I will conclude with a discussion of the likely controls on the along strike variability of structures and strain in the collision zone and the behavior of the arc and continental margin during collision. Geology of the Peninsular Ranges batholith (PRB) The PRB is defined by at least five different basement assemblages (Fig. 4.1.), which include from west to east: (1) Cretaceous volcanic arc assemblages that can be subdivided into a northern in-situ continental margin arc (Santiago Peak arc) and a southern accreted oceanic island arc (Alisitos arc); (2) Triassic(?)-mid Cretaceous volcanic and clastic assemblages; and (3) Paleozoic passive margin sequences with North American affinities comprised of Ordovician-Permian slope- basin clastic assemblages and Upper Proterozoic-Permian miogeoclinal carbonate- siliciclastic assemblages (e.g., Gastil et al. 1991; Gastil and Miller, 1993; Schmidt, 2000; Alsleben et al., 2002; Gehrels et al., 2002; Wetmore et al., 2002; 2003; Morgan et al., 2005). 114 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. These basement assemblages are intruded by Jura-Cretaceous plutons, which show significant geologic, petrologic, geochronologic, geochemical, and isotopic across-strike (E-W) variations (e.g., Gastil et al., 1975, Taylor and Silver, 1978; DePaolo, 1981; Gromet and Silver, 1987; Silver and Chappell, 1988; Gastil et al., 1990; Thomson and Girty, 1994; Tate and Johnson, 2000; Schmidt and Paterson, 2002; Shaw et al., 2003) The Alisitos arc, which is the main focus of this study, is a Cretaceous, dominantly submarine ocean island arc (Allison, 1955, 1974; Silver et al., 1963; Carrasco et al.; 1995; Fackler-Adams, 1997; Johnson et al.; 2003) that accreted to North America between 115 and 103 Ma (Johnson et al., 1999a; Schmidt, 2000; Wetmore et al., 2002; Wetmore, 2003). The arc is rimmed by a fold-thrust belt that formed in response to collision of the arc. The suture between the arc and the continent is called the ancestral Agua Blanca fault (aABF) and Main Martir thrust along the northern and eastern edge of the Alisitos arc, respectively (Johnson et al., 1999a; Schmidt, 2000; Wetmore et al., 2002). To the north of the Alisitos arc, lie the volcanics of the Early Cretaceous Santiago Peak arc (e.g., Wetmore et al., 2002; 2003), whereas Triassic through Cretaceous schistose and gneissic metavolcanic and metasedimentary strata lie to the east (Johnson et al., 1999a; Schmidt, 2000; Alsleben et al., 2003; Morgan et al., 2005). The existence of Jurassic (164.4±1.4 Ma; Schmidt, 2000; Schmidt and Paterson, 2002) and Early Cretaceous (128 to 133 Ma; Johnson et al., 1999a; 2003) intrusions in the northern and southern Sierra San Pedro Martir suggests that these 115 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. deposits represent the remnants of a continental margin arc that was active along the North American margin to the east of the oceanic Alisitos island arc (Johnson et al., 1999a). Study areas Detailed studies of the fold-thrust belt geometry and finite strain were completed in four localities (Fig. 4.2.). I first summarize the structural observations from previous studies in the San Vicente area (Wetmore, 2003; Wetmore et al., 2002; 2003), and the northern (Johnson et al., 1999a; b; 2003) and southern (Schmidt; 2000; Schmidt and Paterson, 2002; Schmidt et al., 2002) Sierra San Pedro Martir (SSPM). I also briefly summarize observations from the Sierra Calamajue study area, which are described in detail in Chapter 2. These descriptions are followed by description of the finite strain data from these areas. San Vicente area The following paragraphs are summaries of work completed by Dr. Paul Wetmore, who mapped in the San Vicente area as part of his Ph.D. dissertation at the University of Southern California (USC) (Wetmore, 2003). During my studies at USC, I accompanied Dr. Paul Wetmore for a total of about two weeks and have seen many of the structures described below. Many of the conclusions are based on those by Dr. Paul Wetmore and restated as I understand them. 116 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The structural geology of the San Vicente area is fundamentally defined by a broad (>20 km wide) brittle-ductile fold-thrust belt (Wetmore, 2003). The Late Cretaceous ancestral Agua Blanca fault (aABF), which is located within this fold- thrust belt, is a suture that divides the area into two segments and juxtaposes the Santiago Peak arc to the north with the Alisitos arc to the south (Fig. 4.3.). While both arcs are deformed in the fold-thrust belt, deformation is more extensive and of greater intensity in the Alisitos than in the Santiago Peak arc. Gentle to open folding continues to affect Alisitos arc strata southwest of this area, but does not contribute significantly to bulk shortening (see Strain Analyses section and discussion below). Santiago Peak arc The Santiago Peak Volcanics are deformed in a ~5 km wide zone north of the suture. Deformation is characterized by a large overturned, SSW-vergent, NNW- SSE-trending fold, several upright, tight folds, and a peculiar absence of faults. Tight folds are defined by deformed bedding and exhibit wavelengths that vary between one and three kilometers. The interaxial angles range between 20° and 50° and axial planes to these folds generally strike toward the northwest. With proximity to the active Agua Blanca fault, these folds exhibit a ~90° clockwise rotation to an orientation of approximately 030°, consistent with dextral shear observed across this active structure (Fig. 4.3.). A single moderate to intense bedding parallel foliation exhibits the same deflection as the folds. Additionally, the foliation exhibits an increase in intensity 117 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Santiago Peak Arc Piedra Rodada pluton 105,5 £ ,3.4 Ma t-S!- -- '... '"^..Balbuena n 7 io7.7°±"' Pluton g / 3 A M a K C A L A V tR A : rk SANDOVAL '105.0 i 3.4: Ma A lisitos Fm .; r e e f lim e s to n e s, v o lc an iclastic , v o lc an ic, ca lc- silicate, a n d argillitic ro c k s San Vicente pluton A lisitos Fm .; v o lc an ic a n d v o lc an iclastic ro ck s 5 km Figure 4.3. Generalized geologic map of the San Vicente area (after Wetmore, 2003). Shown are only main faults and folds, pluton ages, and strain sample locations with shortening in the Z direction (where X>Y>Z) in percent. 118 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. across the active Agua Blanca fault toward the aABF. However, unlike the Alisitos Formation to the south of the aABF (see below), the Santiago Peak Volcanics are not mylonitized along the structure and in fact retain primary depositional features such as accretionary lapilli and grading. Most units also contain a well-developed, moderately northeast-plunging stretching lineation. Asymmetries exhibited by breccia fragments and phenocrysts in planes perpendicular to the foliation and parallel to the lineation indicate a northeast side up, reverse sense of shear. Alisitos arc A brittle-ductile fold-thrust belt forms a ~15 km wide belt in the Alisitos arc. In this zone, packages of sediment- or volcanic-dominated arc strata are deformed by several brittle-ductile, dip-slip shear zones and multiple groups of subhorizontal folds of varying tightness and inclination (Fig. 4.3.). The most important faults are, from southwest to northeast, the El Ranchito fault, the El Tigre fault, and the aABF. While the El Ranchito fault has a brittle character, dips steeply to the northeast and gives NE-side up kinematics, the existence of the largely brittle El Tigre fault is supported only by local structural and stratigraphic relationships. Brittle structures described above differ from the aABF, which is a 50 to 100 m wide, WNW-trending, NNE-dipping mylonitic ductile shear zone (Wetmore et al., 2003). The shear zone preserves kinematic indicators in lineation parallel sections that support reverse (NE-side up) shear, but simultaneously show asymmetries in clast shapes and folds in lineation perpendicular section that support sinistral 119 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. displacement. The amount of sinistral displacement is unconstrained and could be of considerable magnitude, while reverse shear along the aABF and throughout the San Vicente area has to be minimal ( « 5 km) as rocks throughout the fold-thrust belt record similar greenschist facies metamorphic temperatures and pressures (Wetmore, 2003; Wetmore et al., 2003). In contrast to the limited number of faults, folds of bedding are abundant. Folds, whose axial traces are -300° (subparallel to the aABF), exhibit some moderate unit thickening in the hinge region, while showing continuous changes in tightness and dip of their axial surfaces from southwest to northeast (Fig. 4.3.). Southwest of the El Ranchito fault, two pairs of close to tight, upright and horizontal folds exist. Between the El Ranchito and El Tigre faults a single, overturned tight to isoclinal fold has an axial surface that dips steeply to the northeast. Much of the overturned limb of this fold is cut-out by the El Tigre fault. No less than five pairs of tight to isoclinal, commonly overturned folds are mapped northeast of the El Tigre fault. The axial surfaces for these folds typically dip steeply toward the northeast (-70-80°), but those closest to the El Tigre fault possess upright and even steeply southwest dipping axial surfaces. Most units contain a well-developed spaced to continuous cleavage that is axial planar to folds of bedding and subparallel to the trend of the aABF (Fig. 4.3.). In most instances, a true, steeply northeast-plunging stretching lineation is defined by the elongation of lithics or phenocrysts. A large number of kinematic indicators including asymmetric clasts and folds (cm- to km-scale) from lineation parallel- 120 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. foliation perpendicular sections indicate a northeast over southwest, reverse shear sense. Summary In summary, the fold-thrust belt in the San Vicente area is ~ 20 km wide, but is much narrower (5-km-wide zone) in the Santiago Peak arc than the Alisitos arc (15-km-wide zone). Gentle to open folding continues southwest of the Alisitos arc, but does not significantly contribute to bulk shortening. Regional kilometer-scale folds dominate the structural regime, accommodate most of the bulk shortening, and increase in tightness towards the aABF, which is the suture between these two arcs and preserves evidence for reverse and sinistral displacement of unconstrained magnitude. Based on outcrop observations, the metamorphic grade does not change dramatically throughout the area, which limits the total amount of fault-related vertical displacement is probably « 5 km. These constraints are poor, as neither detailed thin section work nor metamorphic petrology has been completed. Northern Sierra San Pedro Martir The following section below is based on work completed by Dr. Scott Johnson and coworkers (e.g., Johnson et al., 1999a; b; 2003), who mapped extensively in the northern Sierra San Pedro Martir (SSPM). I have done no actual field work in the area, but had the opportunity to accompany Dr. Johnson on a 3-day field trip in January of 2003. 121 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The northern SSPM area is located -80 km southeast of San Vicente (Fig. 4.2.). Johnson et al. (1999a) divided the Alisitos arc strata in this area into two major lithostratigraphic assemblages; volcanic-dominated strata to the west and sediment- dominated units to the east. The latter units lie adjacent to amphibolite-grade metasedimentary and metavolcanic units that are interpreted as basinal assemblages containing the remnants of a continental margin arc (Johnson et al., 1999a). Similar to the San Vicente area, the northern SSPM is characterized by a fold-thrust belt -20 to 25 km in width (Fig. 4.4.). However, this belt trends roughly NNW, which represents -50° of clockwise rotation with respect to structures in the San Vicente area (i.e. from -300° to -350°) and, while it affects the eastern edge of the Alisitos arc, it extends significantly into continental margin units to the east. Two major fault structures, the Rosarito fault and the Main Martir thrust, have been identified (Fig. 4.4.). The Rosarito fault, which separates the volcanic-rich from the sediment-rich section of the Alisitos arc, is a high angle, east-dipping brittle-ductile fault with rare kinematic indicators that suggest reverse motion (Johnson, 1999a). Since useful marker horizons are absent, the exact amount of displacement has not been determined. However, rocks on either side of the fault are reported to display similar metamorphic assemblages suggesting that displacement was limited to a few kilometers or less (Johnson et al., 1999a). In contrast, the Main Martir thrust is a major east-over-west, ductile shear zone that separates the Alisitos sediment-rich strata from continentally-derived units to the east (Johnson et al., 1999a). The metamorphic gradient across this fault structure indicates significant 122 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 4.4. On next page. Generalized geologic map of the northern Sierra San Pedro Martir (after Johnson et al., 1999a; 2003). Shown are only main faults and folds, pluton ages, and strain sample locations with shortening in the Z direction (where X>Y>Z) in percent. Note inset in the that lower left comer shows blow up of strain samples collected in the aureole of the Zarza Intmsive Complex (from Johnson et al., 1999b). 123 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 1 1 5 °5 0 ’W 1 1 5 °4 0 ’W K > 4 ^ M am M artir T h ru s t (S u tu re ) North American Continental margin C e rro d e C ostilla c o m p le x 1Q3±f .O M a 31 0 5 N o g n e is s ? 1 2 7 .8 ± 1 .6 M a /Alisitos arc O r th o a n e is s V o lc a n o g e m c * 11 4 .8 ± 1 .5 M a ’ n • ^ : p i 1 3 3 .6 ± 1 .9 M X R o s a rito fau t S ie rra S a n P e d ro M artir p lu to n 9 7 .4 ± 1 .0 M a B urro c o m p le x , 1.0 M a / Z a rz a c o m p le x t ’t y h 3 0 °5 5 'N — i s' A 116.2 ± 0 .9 M a I I Explanation C alc-silicate , v o lc an iclastic a n d s e d im e n ta ry ro c k s, tuffs, m ig m atite s, o rth o g n e is s e s , s h e e te d in tru sio n s, m y lo n ites U n d ifferen tiated C re ta c e o u s Intrusive C o m p le x e s A lisitos F m .; re e f lim e s to n e s, v o lc an iclastic , v o lc an ic, calc- silicate, a n d argillitic ro ck s A lisitos F m .; v o lc a n ic a n d v o lc an iclastic ro ck s M ain M artir T h ru s t s e p a ra tin g w e s te rn a n d e a s te r n p re b a th o - lithic ro ck s R o sarito C o n tra c tio n a l fault C re s ta l tr a c e s of s e le c te d fo ld s displacement as rocks metamorphosed at 2.3±0.6 kbar are now juxtaposed against mid-crustal rocks exhumed from depth between 15 and 18 km (5-6 kbar) (Kopf and Whitney, 1999; Kopf et al., 2000), which suggests significant displacement across this structure with a vertical component that may exceed 10 km. Furthermore, a dramatic deformation gradient exists towards the Main Martir thrust. Along the west side of the area, strata are gently folded with subhorizontal fold hinges (Johnson et al., 1999a). Approximately 200 m west of the Rosarito fault, folds become tighter and, with increasing proximity to the Main Martir thrust, folds become tight to isoclinal and hinge lines curve into subparallelism with the westerly thrust direction (Johnson et al., 1999a). According to Johnson et al. (1999a), a similar gradient can be seen in the development of foliation and lineation. Penetrative foliation and lineation are absent on the west side of the area mapped by Johnson et al. (1999a) and again start to be better developed just west of the Rosarito fault. Within a few hundred meters of the Main Martir thrust, fabrics become penetrative, whereas east of the thrust, rocks become mylonitic with strong east-side-up shear sense indicators and show strongly annealed fabrics (Johnson et al., 1999a). The Main Martir thrust, which is the suture between the Alisitos arc and continental margin units, is the dominant structure in the northern SSPM and accommodated a significant component of vertical displacement (possibly >10 km). Penetrative ductile structures (i.e. foliation and lineation) are rare along the southwest side of the area and folding accounts for limited shortening in volcanic- 125 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. dominated Alisitos arc strata. Ductile fabrics and fold tightness increase markedly in the sediment-rich strata ~10 km west of the Main Martir thrust and continue to contribute significantly to bulk shortening east of it (Johnson et al., 1999a). Southern Sierra San Pedro Martir Mapping in the southern SSPM was conducted by Dr. Keegan Schmidt during his Ph.D. studies at USC and the section below is based on his descriptions (Schmidt, 2000). I had the opportunity to visit this remote area by myself for three days during the summer of 2004, but only had the chance to visit a limited part of the area studied by Dr. Schmidt. Schmidt (2000) and Schmidt and Paterson (2002) describe an approximately 40 x 20 km segment, where the Alisitos arc is juxtaposed with North American continental margin strata in the southern SSPM (Fig. 4.5.). Litho-stratigraphic units are similar to those described in the northern part of the range by Johnson et al. (1999a; see above) with volcanic-rich strata to the west and sediment-rich Alisitos arc assemblages juxtaposed against abundant plutonic intrusions and their metasedimentary host units with North American affinity (Schmidt, 2000; Schmidt and Paterson, 2002). The area is a ~20-km-wide doubly-vergent fan structure marked by reverse metamorphic gradients and west-vergent reverse faults and mylonitic shear zones (including the Rosarito fault and Main Martir thrust) on the west side (Fig. 4.5.) and 126 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 101.3±0.6 La Suerter complex )/?. La Suerte 164.4 0 0 132±7 R. Rosarito Alisitos arc R. Nuevt E53 5 km Figure 4.5. Generalized geologic map of the western part of the fan structure in the southern Sierra San Pedro Martir (after Schmidt, 2000). Shown are only main faults and folds, pluton ages, and strain sample locations with shortening in the Z direction (where X>Y>Z) in percent. 127 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. east-vergent reverse ductile shear zones on the east side (Schmidt, 2000; Schmidt and Paterson, 2002). The three litho-stratigraphic sequences are separated by faults/shear zones that are interpreted to be continuous with structures in the northern Sierra San Pedro Martir area. The brittle-ductile Rosarito fault, which is characterized by steep, NE- dipping, spaced to locally penetrative cleavage, shear bands, and discrete chloritized faults with predominantly NE-over-SW shear sense, juxtaposes the two Alisitos arc assemblages. The equivalent to the Main Martir thrust is a mylonitic high strain zone that places continental margin strata over Alisitos arc strata and reflects a major metamorphic break similar to that observed to the north (Kopf and Whitney, 1999; Kopf et al., 2000). In addition to the metamorphic variations, dramatic contrasts in deformation style and intensity between the Alisitos arc rocks and the continental margin strata have been described (Schmidt, 2000). In the volcanic-rich assemblages of the footwall of the fan structure, west of the Rosarito fault, bedding is folded by map- scale open, upright folds with SE and NW shallowly-plunging hinges. Immediately east of the Rosarito fault, these folds tighten and plunge steeply. Deformation in the sedimentary-rich unit and adjacent continental margin strata are characterized by a mylonite fabric that increases in intensity eastward and structurally upward through this ~5 km thick sequence. Mylonitic lineations are dominantly NNE-trending. Kinematic indicators, including s-c fabrics, sigma-porphyroclasts, and extensional crenulations are common in the mylonites and show consistent NE-over-SW shear 128 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sense parallel to lineation. Structural relationships on the west side of the fan structure are similar to those observed in the northern SSPM (Schmidt, 2000), but a fan-like pattern of these structures has not been recognized to the north (Johnson et al., 1999a). In the southern SSPM, the suture (Main Martir thrust) accommodated significant amounts of collision-related vertical displacement (Schmidt and Paterson, 2002). Description by Schmidt and Paterson (2002) suggest that the volcanic- dominated section of the Alisitos arc is weakly deformed along the west side of the fan structure, and deformation was again concentrated in sediment-rich assemblages and continental margin units. Ductile fabrics are reported to get stronger at a distance of ~3 km west of thrust and are increasingly well-developed east of the thrust in the central part of the fan structure, where ductile deformation takes up much of the shortening (Schmidt, 2000; Schmidt and Paterson, 2002). Sierra Calamajue This area is located ~330 km south of the San Vicente area (Fig. 4.2.). My mapping in this area expands initial reconnaissance work by Hoobs (1985) and Griffith (1987; see also Griffith and Hoobs, 1993), who noted that deformation is concentrated in a narrow (<10-km-wide) zone with maximum deformation in Calamajue Canyon and suggested that this area represents the suture between North America and the Alisitos arc (Fig. 4.6.). It is possible that Quaternary basins to the north and south of the Calamajue Canyon area are responsible for the apparent 129 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. m m Explanation: Quaternary/ Tertiary Cretaceous Plutons C o T ai: Alisitos arc (volcanic-rich) Allochthonous Paleozoic units Molino fault Mesozoic Central zone Paleozoic units (Eastern zone) Albian-Aptian fossils Depositional contact Cretaceous thrust faults 100 MaU-\P Earlv Triassic Folds (upright overturned) 125 Ma am a ju e C a Strain sample locality Fossil locality : c r-;'i U-Pb age U-Pb detrital zircon age M ississippian fossils € W I ® S S S l t t ® l ., ^ ; ; Dalmag pluton - f - u J 1 5 km>^5 14 10 N 2 9 15 N Figure 4.6. Generalized map of Sierra Calamajue area. Shown are only main faults, folds, ages (after Griffith and Hoobs, 1993 and new ages presented in Chapters 3 and 5), and strain sample locations with shortening in the Z direction (where X>Y>Z) in percent. Detailed 1:50,000 scale map of the same area is in back pocket. 130 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. narrowness of the zone. Alternatively, the narrowness could be the result of deformation localization related to a rigid pluton to the southwest (see Chapter 3). Whatever the cause for the narrowness, the zone of deformation appears to widen to >10 km to the NW and SE of the canyon and can generally be described as a brittle- ductile, SW-vergent fold-thrust belt. Following initial mapping by Griffith and Hoobs (1993), I have divided this thrust belt into five units: (1) the Paleozoic Canon Calamajue unit; (2) the Cretaceous Alisitos Formation; (3) the Cretaceous Canon de los Frailes unit; (4) Early Triassic La Mision unit; and (5) Paleozoic La Josefina unit (Fig. 4.6.)(see Chapters 2 and 5 for details). The Alisitos formation and Canon Calamajue units lie on the southwest side of the area, the Canon de los Frailes and La Mision units occupy the central portion, and the La Josefina unit extends to the Gulf of California on the northeast side of the study area, where similar units have been described as the Canal de Las Ballenas group by Campbell and Crocker (1993). These units are juxtaposed by reverse faults and a large number of individual fault-bounded blocks exists (Fig. 4.6.). Correlations are possible between these units and basement assemblages described from the SSPM area (e.g., Johnson et al., 1999a; Schmidt and Paterson, 2002). The Alisitos Formation is the same units as Cretaceous volcanic-dominated arc assemblages farther north. The Canon de los Frailes and La Mision units correspond to central (or transitional) zone Triassic through mid-Cretaceous metasedimentary units, whereas the La Josefina unit 131 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. represents Paleozoic deep-water sediments, which are related to North American passive margin sequences (cf. Chapter 2). In spite of these correlations, differences are apparent between the two regions. First, the sediment-dominated Alisitos arc strata are not identified in the Sierra Calamajue. Second, Paleozoic units of the Canon Calamajue unit lie well to the west of similar strata in the SSPM. Paleozoic units underlying Cretaceous arc units have been identified in the El Marmol area (Buch and Delattre, 1993; Morgan et al., 2005) and I think these units represent large olistostromal blocks that formed as a result of mass wasting during the earlier phases of arc collision (see Chapter 5). The Alisitos arc strata are separated from the overlying sequences by the NW-SE striking, NE-dipping El Toro fault, which correspond to either the Main Martir thrust or the Rosarito fault. The strong brittle character and limited metamorphic gradient across this structure (all rocks are greenschist facies) suggest that the fault zone corresponds with the Rosarito fault. However, preservation of older ductile fabrics overprinted by brittle deformation suggests that the fault is the shallow crustal equivalent of the Main Martir thrust. Ductile shear zones with brittle overprints are common in the central part of the study area. These faults juxtapose different lithologies and may locally repeat sections, but the lack of marker horizons and limited metamorphic changes, does not allow quantification of vertical offset across individual faults. The top of the central zone is marked by the discrete El Molino fault, which separates the units from overlying, lower-amphibolite facies Paleozoic units and also has a ductile to brittle character. Both brittle and ductile 132 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. kinematic indicators, such as tension cracks locally filled with quartz, fractured clasts, deflection of foliation, s-c fabrics, and sigma clasts, suggest northeast-side up, reverse motion. Taking into account the overall change from sub-greenschist facies rocks in the southwest to lower amphibolite facies (3.2±0.5 kbar and 476±18°C; Rothstein and Manning, 2003) rocks to the northeast, the combined vertical displacement accommodated by these reverse faults does not exceed 5 or 6 km. The strata in the area display a deformation gradient from southwest to northeast that is similar to that observed in the SSPM. Depositional structures are preserved in the Alisitos arc to the southwest and gentle to open, outcrop-scale folds of bedding start to tighten within 3 to 4 km of the Main Martir thrust. Northeast of the thrust, folds become tight and several kilometer-scale folds with subhorizontal hinge lines are preserved near the structural top of the central zone. Across the El Molino fault at the bottom of the Paleozoic section, folds are still tight with subhorizontal hinge lines, but are overturned to the southwest (Fig. 4.6.). Similarly, where folding intensifies, ductile deformation increases and units pick up a NW-SE striking moderately to steeply NE-dipping foliation with a roughly downdip NE plunging mineral lineation (Chapter 2). The increase in deformation intensity is characterized by strong transposition of depositional features, which are only poorly preserved in the central zone and Paleozoic units. Deformation becomes more complex in Paleozoic units, which records at least one earlier phase of deformation unrelated to collision of the Alisitos arc (e.g., Goetz, 1993; Buch and Delattre, 1993; Schmidt, 2000; Alsleben and Paterson, 2002). 133 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. There are several key differences between the Sierra Calamajue area and the SSPM. In the Sierra Calamajue 1) Alisitos arc strata record only limited deformation, 2) sediment-rich Alisitos arc units are not recognized, 3) Paleozoic units, which were originally either thrust over arc units or displaced as olistostromal blocks, now structurally underlie Alisitos volcanics, 4) brittle deformation strongly overprints earlier ductile deformation, 4) the metamorphic gradient is less severe and maximum pressures are much lower than in the SSPM, 5) sheeted intrusions and Jurassic orthogneisses are not recognized, and 6) a fan structure did not develop Summary of qualitative structural observations Several observations are common to all study areas (Fig. 4.3. through 4.6.). Most notably, on the west side of the arc, outside the main fold-thrust belt, minimal shortening is accommodated by gentle to open, upright folds, which gradually become tighter towards the north and east as the ancestral Agua Blanca fault and Main Martir thrust/El Toro fault are approached, respectively. In the fold-thrust belt in the San Vicente area interaxial angles and spacing (wavelength) of now tight to isoclinal folds decrease with proximity to the ancestral Agua Blanca fault (Wetmore, 2003). Similarly, folding intensifies in the SSPM (Johnson et al., 1999a; Schmidt, 2000) and Sierra Calamajue. Another common observation is the lack of ductile structures such as foliation or lineation outside of plutonic aureoles in the western portion of the arc. Deformation slowly increases again towards the northern and eastern edges of the arc and spaced cleavage grades into a continuous cleavage. 134 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. However, several significant along-strike differences also exist between the four localities. One of the most striking is the significant amount of shear associated with the Main Martir thrust, which led to progressive rotation of fold hinges on kilometer-scale folds from gently plunging to down-dip parallel to the direction of thrusting and juxtaposition of shallow crustal with mid-crustal units (Johnson et al., 1999a; Schmidt and Paterson, 2002). Shear of this magnitude is not observed in the San Vicente area (Wetmore, 2003), where units of similar greenschist facies metamorphism are juxtaposed. Total vertical shear displacement is also less in the Sierra Calamajue, where the metamorphic gradient ranges from sub-greenschist to lower amphibolite facies (3.2±0.5 kbar; 476±18°C; Rothstein and Manning, 2003). In addition, the types of structures that accommodated shortening in the fold- thrust belt differ along strike. Folding dominates in the San Vicente area, whereas reverse faulting plays a lesser role (Wetmore, 2003). In contrast, reverse shear is dominant in the Sierra Calamajue and kilometer-scale folds are much rarer. In the SSPM, large amounts of contraction are taken up by the Main Martir thrust, but both folds and ductile shear zones are also abundant in the area (Johnson et al., 1999a; Schmidt, 2000; Schmidt and Paterson, 2002). Furthermore, the San Vicente area shows that strongest evidence for transcurrent deformation (Wetmore, 2003). Kinematic indicators along the aABF support sinistral motion (in addition to revere motion) along this structure. No direct evidence for transcurrent deformation (i.e. strike-slip faults with appropriate kinematic indicators) exists in the Sierra Calamajue or SSPM (Schmidt, 2000), 135 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. although Schmidt and Paterson (2002) could not rule out limited (few kilometers) sinistral, orogen-parallel shear. Another difference is the width of folding and faulting of the Alisitos arc strata. In the San Vicente area, the Alisitos arc strata are deformed in a -15 km wide zone. This zone narrows southward and reaches ~10 km in the northern SSPM, before narrowing further, to ~ 3 or 4 km in the southern SSPM and Sierra Calamajue. These observations support a gradational increase in the evolution and intensity of ductile structures from a little deformed western margin to intense deformation along the northern and eastern sides near the ancestral Agua Blanca fault and Main Martir thrust, respectively. Although these observations hold true for the entire fold-thrust belt, in detail, there are significant along-strike changes in the deformation of the belt. Strain analyses Introduction To characterize the strain component of deformation (see Appendix B for analytical procedure), I have compiled the available strain data from the Alisitos arc (Griffith and Hoobs, 1993; Chavez-Cabello, 1998; Johnson et al., 1999b; Schmidt, 2000, Wetmore, 2003) and have added 30 new strain analysis results (Table 4.1.). By focusing on polymictic, lithic-rich volcaniclastics to measure strain, I am able to compare my data with the existing dataset, as Theologically similar rock types were used in previous studies. 136 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table 4.1. Strain data collected from volcaniclastics throughout the Alisitos arc segment. BC and Chavez samples are from the northern Sierra San Pedro Martir study area (Johnson et al., 1999b; Chavez-Cabello, 1998). Griffith are from the Sierra Calamajue (Griffith and Hoobs, 1993). Areas are: SV=San Vicente (Fig.4.3.); N SSPM=Northem Sierra San Pedro Martir (Fig. 4.4.); S SSPM=Southem Sierra San Pedro Martir (Fig. 4.5.); SC=Sierra Calamajue (Fig. 4.6.); PP=Punta Prieta (not on map); ASJ=Arroyo San Jose (not on map). Elongations are apparent constant volume extensions assume that the final axial ratios (X>Y>Z) formed by constant volume strain of an initially perfectly uniform population o f markers with initial axial lengths equal to Lo. Natural strains are the natural logarithms o f the ratio for each axial length to the initial length. Strain Intensity (SI) is equal to I/a/3 [(E1-E 2 ) 2 + (E2-E 3 ) 2 + (Ej-E3 ) 2 ] /2 where Eb E2, and E3 are the principle natural strains (after Hossack, 1968). Symmetry is equivalent to the Lodes Parameter (LP) where negative numbers = prolate shapes, 0 . 0 = plane strain, and positive numbers = oblate shapes. Sample Area Lengths Elongations Natural Strains SI LP E1-E2 E2-E3 Distance to X Y Z Lo X Y Z el e2 e3 suture (km) PHW 2/24/01-A SV 1.29 1.21 1.00 1.16 11 4 -14 0.11 0.04 -0.15 0.19 0.49 0.07 0.19 25.0 PHW 2/24/01-B1 s v 1.12 1.03 1.00 1.05 7 -2 -4 0.06 -0.02 -0.05 0.08 -0.53 0.08 0.03 25.0 PHW 2/24/01-B2 SV 1.21 1.10 1.00 1.10 10 0 -9 0.09 0.00 -0.10 0.13 0.03 0.09 0.10 25.0 PHW 2/24/01-B3 s v 1.62 1.49 1.00 1.34 21 11 -25 0.19 0.11 -0.29 0.36 0.66 0.08 0.40 25.0 PHW 2/24/01-B4 s v 1.39 1.16 1.00 1.17 19 -1 -15 0.17 -0.01 -0.16 0.23 -0.09 0.18 0.15 25.0 PHW 2/24/01-B6 s v 1.19 1.13 1.00 1.10 8 2 -9 0.07 0.02 -0.10 0.12 0.40 0.05 0.12 25.0 PHW 2/24/01-C s v 1.36 1.24 1.00 1.19 14 4 -16 0.13 0.04 -0.18 0.22 0.40 0.09 0.22 25.0 PHW 2/24/01-Cl s v 1.18 1.14 1.00 1.10 7 3 -9 0.07 0.03 -0.10 0.12 0.55 0.04 0.13 25.0 PHW 5/17/01-P s v 1.57 1.29 1.00 1.27 24 2 -21 0.22 0.02 -0.24 0.32 0.11 0.20 0.25 7.0 PHW 5/21/00-C s v 2.30 1.44 1.00 1.49 54 -4 -33 0.43 -0.04 -0.40 0.59 -0.13 0.47 0.36 12.0 PHW 5/26/00-C s v 6.91 3.18 1.00 2.80 147 14 -64 0.90 0.13 -1.03 1.38 0.20 0.78 1.16 11.0 PHW 5/9/00-C s v 6.66 4.14 1.00 3.02 120 37 -67 0.79 0.32 -1.11 1.40 0.50 0.48 1.42 0.4 PHW 6/13/00-E s v 4.68 2.15 1.00 2.16 117 0 -54 0.77 0.00 -0.77 1.09 -0.01 0.78 0.77 8.4 PHW 6/13/00-F s v 9.92 3.04 1.00 3.11 219 -2 -68 1.16 -0.02 -1.14 1.62 -0.03 1.18 1.11 8.4 PHW 6/22/00-B s v 2.34 1.46 1.00 1.50 56 -3 -34 0.44 -0.03 -0.41 0.60 -0.12 0.47 0.38 12.0 PHW 6/22/00-M s v 6.16 4.30 1.00 2.98 107 44 -66 0.73 0.37 -1.09 1.36 0.60 0.36 1.46 12.0 PHW 6/24/01-J s v 3.18 2.32 1.00 1.95 63 19 -49 0.49 0.17 -0.67 0.85 0.45 0.32 0.84 1.2 PHW 6/6/01-N s v 2.96 2.26 1.00 1.88 57 20 -47 0.45 0.18 -0.63 0.80 0.50 0.27 0.81 4.2 PHW 6/7/00-C s v 4.09 3.59 1.00 2.45 67 47 -59 0.51 0.38 -0.90 1.10 0.82 0.13 1.28 9.7 PHW 6/9/00-D s v 1.55 1.35 1.00 1.28 21 5 -22 0.19 0.05 -0.25 0.32 0.36 0.14 0.30 9.4 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table 4.1. continued. Sample Area Lengths Elongations Natural Strains SI LP E1-E2 E2-E3 Distance to X Y Z Lo X Y Z el e2 e3 suture (km) PHW 6/9/00-1 SV 3.88 2.77 1.00 2.21 76 25 -55 0.56 0.23 -0.79 1.00 0.50 0.34 1.02 9.4 PHW 6/25/01-G SV 15.00 10.00 1.00 5.31 182 88 -81 1.04 0.63 -1.67 2.07 0.70 0.41 2.30 1.5 PHW 6/25/01-H s v 27.00 6.00 1.00 5.45 395 10 -82 1.60 0.10 -1.70 2.33 0.09 1.50 1.79 1.8 PHW 5/7/01-J s v 3.80 2.77 1.00 2.19 73 26 -54 0.55 0.23 -0.78 0.99 0.53 0.32 1.02 5.7 PHW 6/5/01-A s v 4.20 3.27 1.00 2.40 75 37 -58 0.56 0.31 -0.87 1.08 0.65 0.25 1.19 4.7 PHW 6/6/01-H s v 3.21 2.54 1.00 2.01 60 26 -50 0.47 0.23 -0.70 0.87 0.59 0.24 0.93 4.2 PHW 7/6/01-T s v 9.68 4.49 1.00 3.52 175 28 -72 1.01 0.24 -1.26 1.63 0.32 0.77 1.50 4.0 PWS 1-9-E s v 1.31 1.16 1.00 1.15 14 1 -13 0.13 0.01 -0.14 0.19 0.03 0.12 0.15 n/d PWS 2-24-E s v 1.54 1.38 1.00 1.29 20 7 -22 0.18 0.07 -0.25 0.32 0.39 0.11 0.32 n/d PWS 2-24-D s v 1.56 1.41 1.00 1.30 20 8 -23 0.18 0.08 -0.26 0.33 0.45 0.10 0.34 n/d PWS 2-24-B s v 1.65 1.26 1.00 1.28 29 -1 -22 0.26 -0.01 -0.24 0.35 -0.21 0.27 0.23 n/d PWS 2-23-C s v 1.63 1.44 1.00 1.33 23 8 -25 0.20 0.08 -0.28 0.36 0.40 0.12 0.37 n/d PWS 1-10-1 s v 1.14 1.06 1.00 1.06 7 -1 -6 0.07 -0.01 -0.06 0.09 -0.15 0.07 0.06 n/d PWS 9-23-H s v 1.54 1.38 1.00 1.29 20 7 -22 0.18 0.07 -0.25 0.32 0.40 0.11 0.32 n/d BC 472 N SSPM 6.48 6.33 1.00 3.45 88 84 -71 0.63 0.61 -1.24 1.52 0.97 0.02 1.85 n/a BC 209 N SSPM 7.12 3.53 1.00 2.93 143 21 -66 0.89 0.19 -1.07 1.41 0.29 0.70 1.26 n/a BC 208 N SSPM 3.56 2.96 1.00 2.19 62 35 -54 0.48 0.30 -0.78 0.97 0.71 0.18 1.09 n/a BC 506A N SSPM 4.45 2.63 1.00 2.27 96 16 -56 0.67 0.15 -0.82 1.07 0.30 0.53 0.97 n/a BC 207 N SSPM 2.19 1.90 1.00 1.61 36 18 -38 0.31 0.17 -0.48 0.59 0.64 0.14 0.64 n/a BC 220 N SSPM 1.46 1.26 1.00 1.23 19 3 -18 0.18 0.03 -0.20 0.27 0.22 0.15 0.23 n/a BC 387 N SSPM 2.33 2.00 1.00 1.67 39 20 -40 0.33 0.18 -0.51 0.64 0.64 0.15 0.69 n/a BC 413 N SSPM 1.48 1.11 1.00 1.18 25 -6 -15 0.23 -0.06 -0.17 0.29 -0.47 0.29 0.10 n/a BC 221 N SSPM 1.27 1.12 1.00 1.12 13 - 1 -11 0.12 -0.01 -0.12 0.17 -0.07 0.13 0.11 n/a Chavez PP-1 N SSPM 1.34 1.26 1.00 1.19 12 6 -16 0.12 0.06 -0.17 0.22 0.59 0.06 0.23 0.6 Chavez PP-2 N SSPM 3.77 2.42 1.00 2.09 80 16 -52 0.59 0.15 -0.74 0.95 0.33 0.44 0.88 0.6 Chavez PP-3 N SSPM 4.44 3.79 1.00 2.56 73 48 -61 0.55 0.39 -0.94 1.16 0.79 0.16 1.33 0.6 Chavez SPM-1 N SSPM 14.07 4.61 1.00 4.02 250 15 -75 1.25 0.14 -1.39 1.88 0.16 1.12 1.53 0.1 E3-43 N SSPM 5.79 4.95 1.00 3.06 89 62 -67 0.64 0.48 -1.12 1.37 0.82 0.16 1.60 0.2 E3-74 N SSPM 13.22 5.75 1.00 4.24 212 36 -76 1.14 0.31 -1.44 1.86 0.35 0.83 1.75 0.1 u > o o Table 4.1. continued. D i s t a n c e to 1 B a •w" u 3 3 Vi p d C O d p o in d O N d O N o O n O O n d C O d in d 'O ’ © (N © C O in © m d in © p 00 oo © in © 1 o e | 1 z-z 1 00 © C N © V O © p 1 -H E 2 - E 3 1 O n oo © 00 in d On C N o co C N d co Tj- d CO p C O rj- d o V O d 00 vo d -3- C O d o o cn p in © P © r - © © C O 00 © O N p <N 00 O N © O N © © ■3- vo © c-* © C N 00 © CN p P C N ’ 3 ’ cn © E 1 - E 2 co co © C O oo d p r - o d o in O n o d C N d ’ ' t d r~- © d o o o in d C O i n d © ■ O ’ © (N © 'O ’ C O © 00 O n © r - C N © © in © O N V O © r - 00 © 00 © vo vo © V O © CN 00 p cn C N © 00 oo a . hJ V O Tf © 00 d i (N V O d i in d V O m d i C O d On C N o vo d 00 d r - V O d C O C O d C O d in © 'O' oo © in C O © V O © © <N in © C N © in C O © 00 © C N © C N © C N © © 1 © © vo © © On © i 00 vo © r - cn © oo vo © 1 So O N 00 o p C N C N C N d co p o p 00 Tf o vo in d O n uo d ^H C O d 00 p in p V O © in r - © p 00 © V O p O N O N O N p p C N O n © in O N © O n p On 00 © r - C N m p N a t u r a l S t r a in s | C O a o r - © i r - V O d i O N in d i 00 d i 00 r-' d i in o d i p d i m rj- d i 00 ■ 3- o i in (N o i ti- 00 o i vo p i 'O ’ 00 © 1 n O N © 1 00 in © i V O © i V O © » On <N i C O O N © i 00 00 © 1 cs) © 1 vo O N © i ■3- V O © i O N V O © i C N C N i in p i O N 00 © i C N i co 00 © 1 O n d oo o d i C O d i in o o vo C O d i 00 o d vo o o m d o C N d O n o d r - d o cn d C N C N © <N © (N d " O ’ © © O n © © © O N © © © 00 © © 00 © © © © « ■3- © © in © © vo © i m © r - © O N rj- © i V C N d in r-* d o O n d C N d rj* r - 00 d o C O d o C O o t-' O N o vo d V O d On r - d CN V O © -O ’ in © vo 'O' © (N © in © O N C O r - © O N © *3’ O N © O N 00 © in vo © in V O © r - p V O in © ■3- P C N p E l o n g a t i o n s | SI IT ) I On Tf i in 1 vo i in i vo i C O 1 V O C O i 00 C O 1 C N C N i r - m i in vo i c— in i vo i 1 in vo i Tf 1 (N r - i © V O i O N n i V O i C N V O i 00 1 © in i r - i in O N I O N in > 00 00 1 V O in , C N oo 1 V O C N i V O o C O i 00 r - C O C N O 00 o C O " O ’ (N <N in co -O ’ <N © <N (N © O O 00 1 m in V O in C N O N m O N in On C O 1 X 00 V O <N V O Tf co C O C N o C O m C O m C O C N C O in O N CN vo 00 O n in 00 in © C O C N 00 © © (N V O in cn C N O N O N cn C N C N in O N in r - Tj- r - C N o J C N © C N in p ^H 00 ^H On O n C N o m C N ■ O ’ p r - in vq 00 p p C N 00 00 C N C O (N © V O (N On p 00 00 C N © p C O p C O (N p C N C N p C N vo p (N C N p C N p © © CN O N p cn 00 p rn cn p C N cn p 00 © p C N L e n g t h s S ] O © o p o p O O O O O O O O o o o p o p O p o p © © © © © © © © © © © © © © © © © © © © © © © © © © © © © © © © © © IT) C N On p co p VO p C O in 00 C N tJ - p C O 00 00 p ^H p C O r - C N in p C O V O 00 01 " O ’ P C O (N © n i © © C O © p n i © © ■3- © C O r - P r i 00 ON C N cn 00 C N ON O O rH ON © C N V O p cn in ON C N P cn © rn p On C O co co V O p -'t m p 00 vd O C N vd in p C N C N (N C N P p m C O vd O n <N " O ’ •O ’ p •O ' co 00 C N © © 00 © © C O © © <N ■ O ' p in <N p in 00 © 00 cn vd vo p cn cn oo cn in ON © T-H r - p p © p C N ■3- © p 00 A r e a 1 2 & C O C /3 Z 2 Q U co C O Z 2 C U C O C O Z 2 cu C O C O C O 2 a . C O C O C O 2 On C O C O C O 2 C L h C O C O C O 2 C U C O C O C O 2 cu C O C O C O 2 cu C O C O C O 2 cu C O C O C O s C O C O C O 2 C L h C O C O C O 2 cu C O C O C O s cu C O C O C O s cu C O C O C O 2 C L C O C O C O 2 C U C O C O C O O C O U C O U C O U C O U C O U C O u C O u C O U C O U C O U C O 1 S a m p l e 1 C N ON I C O m oo o r co PQ o C N i co W in C O C Q ON O n o C L , C O o o cu C O 3 r - C O C U C O C Q i C O C U C O r - C O cu C O C N O X ) r - C O cu C O C Q i 00 -0- in C U C O © 00 cu C O vo © 00 cu C O 00 <N 00 C U C O (N © O n C U C O C O I 00 £ C O C O hJ X in cu & C O C O i CO in i LC ■ * — * U -4 'C o 00 in « -C S p ‘u o < oo in ■ +-* s p ‘C a C N © i 00 ON © < X C N © i in vo < ffi C N © © < X C N © i © C N C N < C N © i © ON © < K CN © m C N < C N © i in CN CN < C N © i CO vo < X 139 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 4.1. continued. | Distance t o | £ a « U a a v in O ^ H (N L'Z 1 VI 1 C N p V O d C N d o C N O N © o in © O in O O | 40.0 | O O © © fO 1 c n 0.54 | 0.56 | 0.78 | 0.70 | 0.58 | O O O d 0.72 | 0.58 | O N O 0.36 | 0.29 | 0.44 | 0.30 I 0.97 | cn IN d 0.66 | C N E1-E2 0.14 0.56 6 1 0 0.22 C N C N d n m d cn N- d O N d 00 cn d C N O O N N - d m d 00 o d 91^0 0.29 9 1 0 0.22 a. O O in © 0 0 0 V O © cn in d 0.44 d in C N d ^ H in d 00 ti- o N p d i in ■ p d i 00 Tf d N in d in cn d cn N - d © vo © © N © lA in © 0.79 cn N d 0.67 0.59 00 O N d 0.82 0.57 oo p p 0.79 cn Tf o 0.28 p 0.74 vo © O N © N atural S train s cn a > N - © i V O in © i O N in © i in d i V O T j- d i cn d i C N V O d i in p d i in 00 d i 00 in d i V O d i -0.34 cn C N d i o 00 d i 00 in d i -0.49 00 00 © 1 <s cn o 0 0 0 o C N © 0.16 z r o 00 o d 0.09 cn d 0.24 -0.22 V O d i O d N - O d N ^ H d in d 9 1 0 cn cn © O 0.27 0.56 0.39 00 cn d 0.34 in vo d cn in d 0.32 0.62 o 00 d 0.62 m C N o in d cn vo d cn N - o cn cn © in in d E longations N C n cn i cn tJ - i T j- l C N 1 n cn i C N in i vo i V O cn i N in i N " N - i IN cn i O N C N i o C N i in in i N " 1 O N cn i 00 in i N - o C N C N N cn 00 o N " IN C N O C N i in i O O O 00 V O 00 ON cn X C M cn m in n N - vo T j- N - C N O N o n 00 cn in 00 C N C N vo 00 00 C N IN 00 00 ^ 1 - m o^ cn cn IN o o in in n o 00 IN ON in 2.07 V O 00 * — H IN in in cn C N O N IN 00 in in C N cn C N C N ON N N " p ovz Lengths N o p o p o o o o o p O O o p o o O O O O o o 1 — H O O o o O O O O © © © © > < N I 1 in 1 - H 61'3 1 - H p C N O N 2.24 in p C N O N IN 1 - H IN O S C N ■ * t cn in in in cn 2.64 2.07 cn O s in cn cn X 00 O n 00 p cn in p C N 2.49 2.24 V O O N cn VO cn LVZ in cn N- ’ N O N cn in O N C N o 00 vo p 4.20 2.76 2.27 4.16 Area 1 V c n U l A U in O l A u in O in U in V m U in U in U in • — » in < > — » m < cl CL a, C L , CL C . CL O h 1 Sam ple H A 100-02 H A 110-02 C N O i o in C N < X |H A 268A-02 |H A 269-02 CN o 1 C N in CN < K IH A 273-02 IH A 274-02 IH A 283-02 |H A 301-02 CN O t in cn < X |H A 0 11-04 |H A 012-04a IHA033-04 |H A 041-04 |H A 052-04 |H A 054-04 140 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Summary o f strain data Plotting all existing data on a modified Flinn diagram, which contains lines of potential volume loss (Fig. 4.7.), shows rather impressive scatter, which indicates a complex strain field in the Alisitos arc. Most data fall into the flattening field, which is typical for fold-thrust belts elsewhere (Hossack, 1968). Although small errors during the analyses contribute to the complexity of the pattern, those errors cannot account for the wide scatter in results. Below, I first summarize the data according to geographic location by plotting ductile shortening (in Z-direction) with respect to distance to the suture zone that bounds the arc and lies within the fold-thrust belt described above (Fig. 4.8. a-e). Furthermore, data from the structural aureole of the Zarza Intrusive Complex (Johnson et al., 1999b) allows evaluating the strain pattern with increased proximity to the margin of the plutonic complex (Fig. 4.8.fi). In the San Vicente area (Fig. 4.3.), Wetmore (2003) collected samples from a number of different localities including 1) hinges and limbs of folds, 2) structural aureoles of intrusive bodies, 3) hanging and footwalls of faults, and 4) areas distant to any of these structures. The intensities range from 0.08 (4.4% shortening in the Z- direction) to 2.3 (82% shortening in the Z-direction) (Table 4.1.). The range in intensities reflect the analyses of samples that did not record any finite ductile strain (primary fabrics, see below) and therefore produced low intensities, and those associated with large shear zones and pluton aureoles and exhibit the largest gradients. In general, the shapes of the strain ellipsoids exhibit a range from plane strain to oblate with only those with the smallest intensities exhibiting prolate shapes. 141 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2.00-r Modified Flinn diagram 1.80- 1 . 6 0 1.40 H i 0.80 0.60 0.40 Constriction All strain data (N=95) ♦ San Vicente AN SSPM • S SSPM ■ Sierra Calamajue P lan e Strain A Flattening A 20% possible volume loss 40% possible volume loss 60% possible volume loss 80% possible volume loss L00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 E 2 : E 3 Figure 4.7. Modified Flinn plot showing apparent volume loss lines and all strain data from the PRB (n=95). Data are from Chavez-Cabello (1998), Johnson et al. (1999b), Schmidt (2000), Wetmore (2003), and this study (Figures 4.3. through 4.6.). See Table 4.1. for data. 142 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. a. sw e -100 | -80 ) £ N D ) C 'c < D ■ c o . c C O b. c. c 0 t> ( D i_ T 3 1 N c D ) g " c C D t o . c c o - 2 0 -■ 04 El Ranchito El Tigre NE fault fault AABF « * ♦ ♦ ♦ # « « ► ♦ « ♦ 4 .................... ^ Primary fabric field 30 -1U0 sO -80 N c -Rn C 7 ) C c < 1 > -40 r o ,.c -?0 C O 0 25 w 20 15 10 Distance to suture (km) Main Martir thrust ■ ........................ ▲ ▲ ▲ ■ A A * A Primary fabric field -------------------i— r ..■ ■ ■ ■ ■ .,—— — r — 900 700 500 300 100 -100 -300 Distance from Main Martir thrust (m) W -100 -80) -60 -40) -20 0J Rosarito Main Martir E fault thrust Central Fan ‘ .................................! V ! • • • 1 Primary fabric field 2 1 0 Distance to suture (km) -1 Figure 4.8. Plots of strain intensity versus distance to the northern and eastern edges of the Alisitos arc. Note that horizontal scales vary between plots. Primary fabric field after Paterson et al. (1995), Wetmore and Paterson (2002), and Wetmore (2003). a. San Vicente area. b. Near Main Martir thrust in northern Sierra San Pedro Martir c. Southern Sierra San Pedro Martir. d. Sierra Calamajue. e. All data from all four study areas, f. Strain data with increased proximity to the Zarza Intrusive Complex in the structural aureole of the pluton suite in the northern Sierra San Pedro Martir (Fig. 4.4.). 143 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Shortening i n Z (%) Southwestern Northeastern ^ SW limit limit NE -100 0 s ■I -80 0 o > -60 1 N .£ -40 D ) C o -20 ■ e o O T 0 - ' " ■ ■ ■ ■ ■ ■ ■ # ■ ■ ■ ■ ■ Primary fabric field -l------------------------1 i - ------------------------------------ I - - - - - - - - - - - -1 - ------------ r- 3 2 1 0 -1 -2 -3 Distance to suture (km) -100 1 Pnmary fabric field -40 - 16 12 8 Distance to suture (km) f. N _c CD C 'c 0 } ■ c o -C C O -100 -80- -60- -40 -204 0 A A .......................... 'A '" Primary fabric field a a 0 200 400 600 800 1000 Distance from Zarza Intrusive Complex (m) Figure 4.8. continued. 144 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Low intensities (SI <0.23) are measured in samples that do not show evidence for any ductile deformation. Shortening and extension values remain low until -15 km from the aABF (Fig. 4.8.a). The main part of the fold-thrust belt is ~15-km-wide and simply averaging the strain values within this part of the belt, gives -55% shortening and 110% extension accommodated by ductile strain. In the northern SSPM area, Johnson et al (1999b) measured ductile strain in the aureole of the Zarza Intrusive Complex (ZIC). Their data show a steep strain gradient (Fig. 4.8.f) toward the margin of the pluton. Outside the pluton aureole, fabric intensities are generally low and values of 0.17 and 0.29 are well within the range of primary fabrics (Paterson and Yu, 1994; Paterson et al., 1995; Wetmore and Paterson, 2002). However, one sample outside the structural aureole showed unexpectedly high strains (SI=0.64) that were not explained. Strain increases dramatically near the edge of the intrusive complex, where strain intensity reaches 1.52, corresponding to -71% shortening (88% extension), which is interpreted to be related to emplacement of the intrusive complex. Strain ellipsoids are mostly oblate to plane strain with one sample showing constrictional fabrics and Lode’s parameters range from 0.71 to -0.41 (Table 4.1.) (Johnson et al., 1999b) In addition to the samples from the aureole of the ZIC, I calculated strain values for five samples proximal to the Main Martir thrust (distance <1000 m). These data in addition to those produced by Chavez-Cabello (1998) provide a limited dataset of ductile strain associated with the thrust. Strain intensities vary from 0.89 (51% shortening, 68% extension) to 1.88 (75% shortening, >200% extension) with 145 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. an average value of 1.33 (-60% shortening, 135% extension). Ellipsoid shapes range from oblate to prolate with Lode’s parameters between -0.61 and 0.82. Strain values from near the Main Martir thrust (Fig. 4.8.b) are similar to those near the aABF (see above). Strain data do not extend far enough from the thrust to constrain the extent of regional ductile shortening quantitatively, but qualitative field observations suggest that ductile deformation gradually decreases westward for -10 km toward the Rosarito fault (Fig. 4.4.), where it ceases -200 m west of the fault. Reconnaissance strain studies across the western side of the southern SSPM show good qualitative agreement with fabrics observed in the field (Schmidt, 2000). Higher strain intensities correspond with strong ductile fabrics, and constrictional fabric symmetries are associated with strong lineation. Within 1 km east and west of the Main Martir thrust, strain intensities are between 0.81 (48% shortening, 58% extension) and 1.76 (72% shortening, >200% extension) with an average strain value o f-60% ductile shortening (93% extension)(Fig. 4.8.c). Although based on sparse data, strain symmetry shows flattening fabrics (Lode’s parameter of 0.5-0.8) in rocks west of and within the Rosarito fault zone to more plane strain and constrictional fabrics (Lode’s parameter of -0.6) in rocks within the western fan (Table 4.1.). Strain intensities from samples near the Main Martir thrust are comparable to those measured in the northern part of the range. Near the Rosarito fault, -1 km west of the Main Martir thrust, strain appears to drop significantly reaching values between 0.31 (22% shortening) and 0.59 (38% shortening) and falling even lower just a short distance farther west (SI=0.22 or 16% shortening). The sharp drop off in strain is not 146 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. supported by qualitative structural observations. Field observations suggest a more gradational decrease in strain westwards, which could explain the strain intensity of 0.75 (44% shortening) ~3500 m west of the Main Martir thrust. Strain intensity estimates from the Sierra Calamajue represent the best quantitative example of a gradual strain increase towards the suture. Strain intensities in the area range from 0.51 to 2.71 (33 to 88% shortening, 32 to >200% extension) (Fig. 4.8.d; Table 4.1.). Strain ellipsoids are mostly oblate and plot in the flattening field or near plane strain and only two samples show apparent constrictional strains. Alisitos arc strata west of the suture record strains that increase towards the suture over a distance of ~3 km from 0.67 (42% shortening, 46% extension) to 1.1 (59% shortening, 75% extension) (average value of 45% shortening, 58% extension). East of the suture, strain intensities in Mesozoic volcanic and sedimentary units remain high, ranging from 0.79 (43% shortening, 75% extension) to 2.71 (88% shortening, >200% extension). Compared to Alisitos arc strata to the west, average ductile shortening increases dramatically to -60% (136% extension) in the central part of the fold-thrust belt. Combining all data on a distance vs. shortening plot (Fig. 4.8.e) reveals that shortening strains are low to the west and southwest of the suture. Strains increase with proximity to the suture as folding and faulting intensifies. However, strain increase is heterogeneous and samples in close proximity to the suture record some of the highest and lowest strain values measured in the study areas, which support strain partitioning towards the suture. 147 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Calculation of finite strain removal One of the general assumptions in many structural analyses is that strain axes are parallel to structural elements, so that the XY-plane of the strain ellipsoid is parallel to foliation and the X-axis parallel to lineation. Although this assumption is oversimplified (see Appendix B; also Ramsay, 1967; Bayly, 1974; Ghosh, 1975; Williams, 1976; Ramberg and Ghosh, 1977), several studies have shown this to be generally valid (e.g., Ghosh, 1975; Williams, 1977). Making this assumption for the Alisitos arc, I calculated how much arc perpendicular shortening and vertical extension by ductile strain occurred across the fold-thrust belt along the northern and eastern margin of the Alisitos arc. In order to complete this calculation, I averaged finite shortening and extension values from three areas with the best strain data coverage (San Vicente, southern SSPM, Sierra Calamajue) (Table 4.2.). Furthermore, I assumed that these average values apply over the entire width of strained Alisitos arc strata. The assumption that other volcanic and sedimentary units record similar amounts of strain is not unreasonable as all units display similarly developed ductile fabrics (foliation and lineation) and, in fact, sedimentary units often take up more finite ductile strain than volcanic units (e.g., Paterson et al., 1989). Using average foliation orientations (XY-plane of strain ellipsoid), which are parallel to the trend of the fold-thrust belt, and lineation values (X-axes of strain ellipsoid), which are on average downdip, I recalculated the average horizontal, arc perpendicular shortening and vertical extension (Table 4.2.; Fig. 4.9.). 148 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table 4.2. Recalculation of finite strain data to horizontal shortening and vertical extension assuming that average foliation is equal to XY-plane of strain ellipsoid and mean lineation value is equal to X-axes of strain ellipsoid. Shortening and extension values are then taken to ‘unstrain’ a volume of rock to pre-strain conditions.________________________________ San Vicente Southern SSPM Sierra Calamajue Alisitos Alisitos volcanics Alisitos sediments Alisitos volcanics Central zone Average X 1 1 0 % 32% 93% 58% 135% Average Y 2 2 % 1 2 % 31% 18% 23% Average Z -55% -31% -60% -45% -60% Avg. foliation 2 9 7 0 / 7 3 0 n/a 322°/35° 318770° 318776° Avg. lineation 72°/037° n/a 37°/037° 707037° 757100° Recalculation of strain to horizontal and vertical Average X 105% 32% 55% 55% 130% Average Y 2 2 % 1 2 % 31% 18% 23% Average Z 53% -31% -36% -42% -59% Current width o f FTB in arc strata | 15 km | 7 km 3 km | 3 km 3 km Width after removing strain in X 8 km 5 km 2 km 2 km 1 km Width after removing strain in Y 1 2 km 6 km 2 km 3 km 2 km Width after removing strain in Z 32 km 1 0 km 5 km 6 km 6 km Crustal thickening 7km 2 km 1 km 1 km 2 km Arc parallel extension 3km 1 km 1 km 0 km 1 km Arc perpendicular, horizontal shortening 17 km 3 km 2 km 3 km 3 km Extrapolation to 15 km wide zone* "Original" width after removing strain in X 8 km 1 1 km 1 0 km 9km 6 km "Original" width after removing strain in Y 1 2 km 13 km 1 1 km 13 km 1 2 km "Original" width after removing strain in Z 32 km 2 2 km 23 km 27 km 37 km Cmstal thickening 7 km 4 km 5 km 6 km 9 km Arc parallel extension 3km 2 km 4 km 2 km 3 km Arc perpendicular, horizontal shortening 17km 7km 8 km 1 2 km 2 2 km h - * In order to better compare values, the width o f the fold-thrust belt in each area is extrapolated to a width of 15 km 'O Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Southern Sierra San Pedro Martir 36% horizontal shortening Surface U 1 cn Figure 4.9. Diagram explaining recalculation of finite strain shortening and extension values to horizontal shortening and vertical extension. Calculations assume that average foliation is equal to XY-plane of strain ellipsoid and mean lineation value is equal to X-axes of strain ellipsoid. Example given from the southern SSPM, but equally applies to recalculation in San Vicente and Sierra Calamajue. See text for discussion. H — 4 C /i o Assuming pure shear and constant volume, I removed the strain component in the fold-thrust belt (Fig. 4.10.). To be able to better compare the results, I applied the known strain values from the San Vicente area (Wetmore, 2003), southern SSPM (Schmidt, 2000), and the Sierra Calamajue to a rock volume of 15 km3 (Table 4.2.). In this case, the new dimensions of this volume of rock after unstraining are 32 x 12 x 7 km3 for the San Vicente area (Fig. 4.10.b.) and ~11 x 12 x 23 km3 for the southern SSPM. Two different results are calculated for the Sierra Calamajue. The Alisitos Formation records less strain and a 15 km3 block would have had original dimensions of 9 x 13 x 27 km3 , whereas a block of the more strained units east of the Alisitos Formation would have had dimensions of 6 x 12 x 37 km (Table 4.2.) Discussion Causes of strain heterogeneity Variations in lithology In evaluating the strain field in the Alisitos arc, I have focused on analyses of lithic-rich volcanic rocks, similar to those analyzed by previous workers (Johnson et al., 1999b; Schmidt, 2000; Wetmore, 2003), thus trying to eliminate heterogeneity caused by varying lithologies (e.g., Ramsay, 1982; Bell et al., 1986; Paterson et al., 1989). However several additional factors affect finite strain and add to strain heterogeneity. For example, small variations in the matrix-lithic ratios from one location to the next, changes in the composition and original shape of lithic fragments, and different size distributions of lithic constituents contribute and 151 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. o o 7 V 12 km 15 km Figure 4.10. Example of ‘unstraining’ a volume of rock. a. Block diagram representing 15 km3 volume of rock in the San Vicente at present, b. Removing the average measured finite strain ('unstraining') assuming pure shear and constant volume results in an original block with dimensions of 32 x 12 x 8 km3 . See Table 4.2. for values for other areas and text for discussion. N > strongly affect the recorded strain (e.g., Hossack, 1968). Thus, even though only one rock type has been analyzed, heterogeneities are invariably introduced by these small, but significant variations. In addition, layering of units produces heterogeneity and competency contrasts between layers affect the amount of partitioning of ductile strain. Less competent units, for example, accumulate strain faster than more competent layers, which will lead to less finite ductile strain in the latter layers and require them to deform by brittle processes (e.g., Goodwin and Tikoff, 2002). Temperature, pressure, and strain rate Temperature, pressure and strain rate, which control deformation mechanisms, are not homogeneous throughout the arc. Sub- to lower greenschist facies metamorphism dominated the San Vicente and Sierra Calamajue areas, while lower to mid-amphibolite facies metamorphism dominated the Sierra San Pedro Martir domains, particularly in close proximity to and east of the Main Martir thrust (e.g., Johnson et al., 1999a; Schmidt, 2000). Thus, deformation mechanisms that operated while the rocks were being strained could have varied along strike in the arc. Thin section analyses would be helpful to document varying deformation mechanisms, but are not available. 153 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Primary fabrics Primary fabrics add another significant control on the finite strain magnitudes. A common assumption in many strain analyses is that the marker population began as a statistically even distribution. However, most rocks will acquire a primary fabric during deposition (Paterson and Yu, 1994; Paterson et al., 1995; Wetmore and Paterson, 2002, Wetmore, 2003). Initially, primary fabrics were presumed to be flattening fabrics with the XY-plane parallel to and greatest shortening (Z) perpendicular to bedding/layering. This general assumption, however, is incorrect (e.g., Paterson et al., 1995; Wetmore and Paterson, 2002, Wetmore, 2003). Thus, the superposition of primary fabric ellipsoids by tectonic strain introduces additional complications that will increase data scatter. The effect of primary fabric cannot simply be removed even if the average shape and magnitude of primary fabric ellipsoids are known because orientation of the primary fabric ellipsoid is unpredictable, precluding simply multiplying the inverse primary fabric ellipsoids with the tectonic strain ellipsoid to remove the primary fabric effects. However, the existing primary fabrics data allows bracketing the primary fabrics effects, which are usually small, particularly for lithic-rich rock samples (Paterson and Yu, 1994; Paterson et al., 1995; Wetmore and Paterson, 2002, Wetmore, 2003). Alisitos arc samples collected at distances >25 km from the suture record very low fabric intensities (Fig. 4.8.e; Table 4.1.). These samples fall within the primary fabric fields on a modified Flinn diagram (Paterson et al., 1995; Wetmore, 2003) and cannot be distinguished from undeformed rocks (Fig. 4.11.a.). Thus, the 154 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. M o d i f i e d F l i n n d i a g r a m P la n e 2.00 1 .8 0 20% 1 .6 0 4 0 % 1 .4 0 1.20 6 0 % C M 0 .8 0 0 .6 0 8 0 % 0 .4 0 0.20 0.00 1.00 1 .5 0 2.00 0.00 0 .5 0 E 2 :E 3 M o d i f i e d F l i n n d i a g r a m P la n e 2.00 1 .8 0 20% 1 .6 0 4 0 % 1 .4 0 1.20 6 0 % 0 .8 0 0 .6 0 8 0 % 0 .4 0 0.20 0.00 1.00 1 .5 0 2.00 0.00 0 .5 0 E 2 :E 3 Figure 4.11. Modified Flinn diagrams showing data subdivided according to local strain setting, a. Primary fabrics (all areas), b. Regional tectonic and folding strain. A=FIinges and limbs of regional folds (all areas); squares are from Sierra Calamajue (□=Alisitos Formation; ■=Central zone); 0 = San Vicente area; n =Punta Prieta area. 155 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. M o d i f i e d F l i n n d i a g r a m Plane 2.00 1 .8 0 20% 1 .6 0 4 0 % 1 .4 0 1.20 6 0 % ^ 1.00 0 .8 0 0 .6 0 8 0 % 0 .4 0 0.20 0.00 0.00 0 .5 0 1.00 1 .5 0 2.00 E 2 :E 3 M o d i f i e d F l i n n d i a g r a m Plane 2.00 1 .8 0 20% 1 .6 0 4 0 % 1 .4 0 1.20 6 0 % 0 .8 0 0 .6 0 8 0 % 0 .4 0 0.20 0.00 0.00 0 .5 0 1.00 1 .5 0 2.00 E 2 :E 3 Figure 4.11. (continued), c. Strain in shear zones. •= Main Martir thrust (southern SSPM); 0=Rosarito Fault (southern SSPM); A=Main Martir thrust (northern SSPM); ♦=ancestral Agua Blanca fault (San Vicente area); n=El Topo fault (Sierra Calamajue). d. Strain in pluton aureoles. San Vicente area (0=side; ♦=end); Northern SSPM (A=side; A=end); Sierra Calamajue (■=end). 156 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. fabric measured in these samples is probably related to formation of these units. This interpretation is supported by the absence of ductile fabrics and significant folding in these areas. Volume change The effect of differential volume change on the shape and magnitude of the strain ellipsoid also has to be considered. Volume changes caused by lithification, metamorphism, and strain can have significant effects on the interpretation of strain data because the plane strain line on the modified Flinn diagram will shift and the flattening and constriction fields change if the volume changes (Fig. 4.11.; e.g., Twiss and Moores, 1992). Two approaches have been used to evaluate volume changes (see Table 4.3. for reference list). Paterson et al. (1989) used geometric arguments after completing detailed strain analyses on a variety of rock types (volcanics, graywackes, conglomerates, and slates) in the Western Metamorphic Belt, Central Sierra Nevada, California. Their results show that strain intensities of volcanics plot near the constant volume plane strain boundary line, whereas all other rock types, particularly slates plot in the flattening field. The authors argued that it is unlikely that slates (igraywackes) have undergone large bedding-parallel extensions, while volcanics record plane strain. By decomposing the oblate strain ellipsoid into plane strain and pure flattening ellipsoids (Sanderson, 1976), they estimated volume losses depending on rock type ranging from 0 to 65% (Fig. 4.12.). Although this approach provides a 157 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table 4.3. Summary table of studies calculating volume changes during diagenesis, metamorphism, and strain in various rock # Rock type M etam orphic conditions Deformation/Environment Volume change Authors 1 Silicic ash Low grade Burial & diagenesis Volume loss o f about -35% Huff et al., 1996 2 Argillites Expulsion o f pore water Volume loss o f about -50% Sorby, 1853; Skempton, 1970 3 Chlorite mud Reduction o f pore volume Reduction in pore volume o f -45 to -60% Chen and Oertel, 1989 5 Slate Low grade Cleavage formation Volume change from +7 to - 81% Wright and Platt, 1982; Beutner and Charles, 1985; Waldron and Sandiford, 1988; Wright and Henderson, 1992; Goldstein et al., 1998 8 Carbonates Maximum temperature of ~220°C Folding and locally cleavage formation Volume loss: About -3% regionally; 0% in unstrained rocks; Between -2 and -12% in weakly deformed strata; Between - 20 and -50% in strongly deformed units Davidson et al., 1998 6 Argillite, sandstone, carbonates Chlorite grade regional metamorphism; Andalusite& cordierite and K-spar&sillimanite in pluton aureoles Pluton aureole Volume strain in aureole:12.5±8.3% Yoshinobu&Girty, 1999 Mudstone to slate Low grade; transition from mudstone to slate Metamorphism Ramsay&Wood, 1973 4 Pelites Greenschist to amphibolite Metamorphism Volume loss o f maximum -30% during prograde metamorphism; Medium grade rocks (-6 to -20%); High grade rocks (-20 to -30%); Shale&slate (stable) Ague, 1991 U \ 00 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table 4.3. continued Rock type M etam orphic conditions Deformation/Environment Volume change Authors 4 Aluminous metapelites Barrovian regional metamorphism Metamorphism Volume loss o f maximum -50% during prograde metamorphism; garnet (-12±10%); staurolite (- 19±6%); kyanite (-23±6%); chlorite and biotite (stable) Ague, 1994 Tuff Chlorite grade Volume loss after cleavage development Volume loss between -20 and - 26% Bell, 1985; Boulter, 1986 9 Andesites Lower to mid-greenschist facies Metasomatism Volume change between +25 and - 25% Khalaf, 1999 10 Basic volcanics Metamorphism Volume change from +4 to -1.6% Barr&Coward, 1974 16 Paragneiss Temperatures range from <200 to 300°C Reverse shear zones Volume loss: -13±3% (maximum - 42±19%) Zulauf et al., 1999 17 Paragneiss Amphibolite grade (>500°C) Mylonitic shear zone Volume loss between -50 and - 60% Ring, 1999 15 Granitic gneiss Temperatures « 450°C (greenschist facies) Mylonitic shear zone Volume change from +7 to -63% Bailey et al., 1994 13 Metabasite Temperatures range from <200 to 300°C Reverse shear zones Volume gain: +27±28%; 132+28% Zulauf et al., 1999 14 Metagabbros and amphibolite Temperatures ~800°C Shear zone/mylonite No volume change Bhattacharyya and Hudleston, 2001 7 Graywacke and Conglomerate Regional deformation Volume loss: 0 to -26% Paterson et al., 1989 11 Lapilli Tuff Regional deformation Volume loss: 0 to -11% Paterson et al., 1989 # refers to numbers given in Figure 4.12. so Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 100 80 60 40 \0 b 20 I -20 > -40 -60 -80 -100 Figure 4.12. Summary diagram for studies calculating volume changes during diagenesis, metamorphism, and strain in various rock types. See Table 4.3. for list of authors (numbers below figure refer to # in table) and see text for discussion. o\ o i Z F : ■ m _£2 jf f : I M H o o ^ ■ ■ < + - i ■■ O-.u- V ' S ' • d + * ■ ■ ■ ■ ■ o * C A .£ * :■ ■ ■Pi 3 ^ O x d :;S P - . d : > < : 'C L W. i o : * * I ..... 0 0 .. < L > ■ ' S P > : ■ g.; u i 0 1 ::e‘ ; p I ■ ■ ■ O '- a xg ‘5b < D P i o M.: ’’ O V* 1 3 .2 o > S i/3 i - s I . . . . . . . d < u Q i n a ‘ q g o 1 • o . - : PL,:: < u ••S3:: § ; t / > . ^ » :• x : :C 3 Q ■s u o O O 0 0 1 ■ ■ ■ x> : m m 13 m ■■■■o V i ‘ o : 05.*CS.. •S'S: C C A |- 8 -13 d n ^ < u S h a u ■ ■ ■ O ' : : o o c n i o O ' < N x V : o :'-d - X & O " C t f : ■ ■ c 3 :& ■ a : O o o A GO c d : : c 3 Q h I 4 4 4 Pelite 6 ■ 7 ■ 8 8 Carbonate Unconsolidated Graywacke & Conglomerate Volcanic 15 16 17 Plutonic (all from shear zones) powerful tool for estimating potential volume changes, it should be remembered that at least two different, juxtaposed rock types have to be evaluated in detail for these calculations to be obtained. The second approach to assess volume changes is geochemically, using mass balance calculations (Table 4.3.). Studies have been completed in a many rock types, under varying pressure-temperature conditions, and varying amounts of strain (Fig. 4.12.). Although the results of these studies are highly variable, some general constraints can be derived: (1) Burial and compaction result in significant loss of pore volume (35 to 60%); (2) Volume loss increases during prograde metamorphism of pelites (Ague, 1991; 1994); 3) Carbonates recording higher finite strain show greater volume loss than carbonates that experienced lower strains (Davidson et al., 1998); 4) Volume loss during cleavage formation in slates is controversial and estimates range from slight volume gain (Goldstein et al., 1995) to no volume change (Waldron and Sandiford, 1988) to >80% volume loss (Goldstein et al., 1995); (5) Few rocks in the surveyed studies showed significant volume gain (Fig. 4.12.). The data from the PRB are insufficient to make geometric arguments (e.g., Paterson et al., 1989) or geochemical mass balance calculations (e.g., Ague, 1991; 1994; Yoshinobu and Girty, 1999) to derive volume changes in these rocks. However, qualitative observations on a limited number of thin sections from Alisitos arc volcanics suggest little to no differential dissolution in these rocks (Scott Johnson, pers. comm., 2004), which suggests only limited volume loss. These observations are comparable to arguments put forward by Paterson et al. (1989), who 161 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. estimated a maximum of 11% of volume loss in lithic tuffs in the Western Metamorphic Belt of California. Regional tectonic strain and local strain effects Ideally, finite tectonic strain intensities should systematically increase towards the suture of the Alisitos arc. Furthermore, finite strain intensities and strain types (i.e. flattening, constrictional, plane strain) should closely correspond with the relative development of cleavage and stretching lineation, whose character and development should be a function of proximity to the suture as well as to local structures or high strain zones (i.e. folds, faults, structural pluton aureoles). In order to evaluate changes in finite strain intensities and types, I separated samples into regional strain samples, whose finite strain intensity should solely be controlled by proximity to the suture, and samples that record an additional component of strain because of their proximity to local high strain zones and, therefore are related to local strain gradients. The latter category has been further subdivided into folds, shear zones, and pluton aureoles (Fig. 4.11.). Samples are considered in close proximity to local structures, if they were located in the hinge or limb of regional folds or within 500 m of the edge of a pluton or shear zone, which appears to be the approximate extent of increased emplacement- or shear-related strain. Finite strains were not determined on individual outcrop-scale folds, where strains should vary in hinges and limbs according to the fold mechanism (e.g., 162 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ramsay, 1967; Ramsay and Huber, 1987). Seven samples analyzed from hinges and limbs of regional folds are not significantly different from samples that I interpret to record tectonic strain related to island arc collision (Fig. 4.1 l.b). Since the data overlap, I combined all data into a single plot (Fig. 4.1 l.b.). The overlap between the data allow several interpretations: (1) Samples from hinges and limbs of regional folds record strain associated with the folding process that is indistinguishable from regional strain or (2) all samples record fold-related strain that accumulated during development of the regional fold-thrust belt. More detailed work on regional and outcrop-scale folds is desirable to determine the strain effects of folding. Data for all but two samples that I interpret to record regional tectonic strain lie clearly outside the primary fabrics field (Fig. 4.1 l.b). This suggests that these samples truly record tectonic strain. Strain measured in Alisitos arc samples in the Sierra Calamajue record dominantly flattening strains that are lower than strains determined in the San Vicente area (Wetmore, 2003). Crossing the suture in the Sierra Calamajue, finite strain increases to similar values as in the San Vicente area and strain starts to approximate plane strain (Fig. 4.1 l.b). This suggests that greater strain was accommodated east of the suture in the Sierra Calamajue, whereas strain was dominantly concentrated in Alisitos arc strata in the San Vicente area (Wetmore, 2003). Figure 4.1 I.e. shows samples collected in close proximity (<500 m) to major shear zones in the study areas, samples collected in close proximity to the suture (i.e. ancestral Agua Blanca fault, Main Martir thrust, El Topo fault) by Chavez-Cabello 163 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (1998), Schmidt (2000), Wetmore (2003), and myself show significant scatter with strong flattening strain dominating, but overall range from strong flattening to highly constrictional (Fig. 4.1 I.e.). Constrictional fabrics have been measured in samples where field observations document strong linear fabrics (Schmidt, 2000), while at least two of the samples from the northern Sierra San Pedro Martir probably record strain related to both the shear zone and emplacement of the Potrero pluton (Fig. 4.4., Chavez-Cabello, 1998). The overall scatter suggests that the strain in these shear zones is rather complex or that complex interactions between regional and shear zone strain exist. In addition, four samples were collected from the Rosarito fault zone (Schmidt, 2000). Samples from the Rosarito fault show low flattening strains barely outside the primary fabrics field. Potentially, this reflects lithologic or rheologic variations (see above). Alternatively, the Rosarito fault records only limited ductile strain and acted mostly as a brittle structure. This is supported by field observations, which suggest that the fault is a relatively late regional, but mostly brittle structure (Johnson et al., 1999a; Schmidt, 2000; Schmidt and Paterson, 2002). Data from samples in pluton aureoles show similar scatter as data from shear zones (Fig. 4.1 l.c; d). Field studies and numerical models predict constrictional strains in cleavage triple points at the end of plutons (e.g., Brun and Pons, 1981; Brun, 1983). Only two samples from cleavage triple point show the expected constrictional strain (Fig. 4.1 l.d.), but this pattern is not consistent and most samples record flattening strains regardless of location (end or side). The lack of 164 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. constrictional strains at the end of plutons, where emplacement-related and regional shortening should be at high angles (e.g., Guglielmo, 1993; 1994), suggests that either regional strain or emplacement-related strains are insignificant. Johnson et al. (1999b) suggested that regional deformation in the aureole of the Zarza Intrusive Complex (ZIC) was negligible and most observed strain was emplacement-related. However, the ZIC lies outside the main suture zone and a greater component of regional strain is expected adjacent to plutons in the San Vicente area and Sierra Calamajue. I suggest that regional strain contributions are present in these latter areas and resulted in greater flattening strains in aureole samples when compared to regional strain samples (compare Fig. 4.1 l.b. and 4.1 l.d.). However, in most cases emplacement-related strain is dominant and, with the exception of the Sierra Calamajue samples, constrictional strain did not develop. Comparison between regional tectonic strain and either emplacement-related or shear zone strain (Fig. 4.1 l.b. through 4.1 l.d.) show greater flattening strains in the latter. One explanation is that greater flattening strains result from combining the regional flattening strain ellipsoid with a flattening ellipsoid caused by pluton emplacement and/or shear zone strain. However, locally (e.g., pluton ends) this should produce constrictional fabrics which are rare. The lack of a clear pattern suggests that lithologic effects, primary fabrics, variable temperature and pressure conditions, strain rate in combination with local and tectonic strain contributions factored into the strain heterogeneity observed in the study area. Additional heterogeneity could come from strain contributions by more than one local process 165 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (e.g., shear plus aureole strain). Lastly, the effects of volume changes need to be considered further. Although most studies on similar rock types and comparable deformational and metamorphic environments suggest that total volume loss in these strata do not exceed ~20% (Fig. 4.12.), differential volume loss between the different environments (regional strain, shear zone, pluton aureole) is possible and should be addressed in more detail in the future. Deformation gradient Below I address whether the increase in deformation, including strain increase from primary fabrics in the western part of the arc to heterogeneous but generally high strains in the eastern part of the arc is gradual or abrupt. Furthermore, I explore the possibilities of along-strike variations in deformation. A number of qualitative field observations are comparable along-strike of the fold-thrust belt and favor a steep deformation gradient across the fold-thrust belt (Johnson et al., 1999a; Schmidt, 2000; Wetmore, 2003; this study). From the west to the bounding structure in the east and northeast the observations include 1) increased tightening of folds from gentle/open to tight/isoclinal, 2) absence of ductile fabrics (i.e. foliation and lineation) to the west and a gradual development of spaced and finally continuous cleavage to the east and northeast, and 3) well-preserved primary depositional structure that are being obliterated and finally completely annealed near the bounding structure. 166 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Despite the gradual increase in deformation, strain shows variable patterns (Figs. 4.8.a through 4.8.d.). The best example for a strain gradient comes from the Sierra Calamajue (Fig. 4.8.d.). Similar gradients are not seen in data from the Sierra San Pedro Martir (Fig. 4.8.b and 4.8.C.) (Chavez-Cabello, 1998; Schmidt, 2000; this study) or the San Vicente area (Fig. 4.8.a.) (Wetmore, 2003). It is possible that ductile strain in these latter areas is locally compensated by other aspects of deformation (e.g., rigid rotation by folding in San Vicente area) and therefore, despite the presence of a deformation gradient, an abrupt strain front exists. This indicates along-strike variations in the strain field and overall displacement field that are controlled by local factors (see below). Bulk shortening and crustal thickening estimates Constraining cumulative bulk shortening and crustal thickening in the arc using finite strain data in combination with constraints from folding and faulting is one of the goals of structural investigations in fold-thrust belts. Below I present initial speculations regarding the contributions by folding, faulting, and strain to overall shortening of the arc and thickening of the crust. Bulk shortening by folding is hard to estimate because continuous, folded stratigraphic layers have not been mapped and fold amplitudes are uncertain (Johnson et al., 1999a; Schmidt, 2000; Wetmore, 2003; this study). The best understood section with respect to folding is the San Vicente area, where folds are the dominant structures (Fig. 4.3.). Wetmore (2003) estimated an average fold 167 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. wavelength of ~1 km in the San Vicente area. Making the assumption that the amplitude of folds is -% of the wavelength on all folds in the area and using open to isoclinal fold morphologies (see above; also Wetmore, 2003), bulk shortening estimates by folding in Alisitos arc strata reach as much as 50% (-20 km). In contrast, making similar assumptions for openly folded volcanic-rich Alisitos arc strata in the southern SSPM (after Schmidt, 2000) fold-related shortening is as little as -15% (-1 km). These constraints show that folding is an important bulk shortening mechanism that potentially varies along-strike of the fold-thrust belt. The lack of marker horizons and questions about the original dip of fault structures and shear zones in the fold-thrust belt make fault displacement determinations ambiguous. Using petrologic observations and the limited amount of barometry and thermometry data provides some clues to overall vertical displacements in the fold-thrust belt (e.g., Johnson et al., 1999a; Kopf and Whitney, 1999; Kopf et al., 2000; Schmidt and Paterson, 2002; Wetmore, 2003). In the San Vicente area, Wetmore (2003) describes steady greenschist facies metamorphic conditions and suggests that the differences in exposed crustal levels are insignificant and vertical displacement are minimal ( « 5 km). Fault displacements in the Alisitos arc in the Sierra Calamajue are also limited, as all units record sub-greenschist to greenschist facies metamorphism. Gradual changes from greenschist to lower amphibolite (3.2±0.5 kbar, 476±18°C; Rothstein and Manning, 2003) facies strata east of the arc support exhumation of somewhat deeper crustal levels and cumulative vertical displacement between -5 and 6 km in the area. The greatest vertical 168 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. displacement is associated with the arc-bounding Main Martir thrust in the SSPM, where the distinct inverse metamorphic gradient indicates >10 km of vertical displacement (Kopf and Whitney, 1999; Kopf et al., 2000). Unless faults rotated into steeper dips from originally shallower orientations, overall bulk shortening associated with faulting does not have to be significant. Data presented above suggest that arc perpendicular shortening and crustal thickening by finite ductile strain in Alisitos arc strata is greatest in the San Vicente area, where back calculations across the now ~15 km-wide fold-thrust belt suggest up to 17 km shortening and 8 km of crustal thickening. Similar calculations across an assumed belt of similar width for the southern SSPM and Sierra Calamajue give only ~8 km of shortening and ~5 km of thickening and 12 km shortening and 6 km of thickening, respectively (Table 4.2.). However, the Alisitos arc strata affected by deformation actually narrows southward. In the southern SSPM, the belt of rocks is between 5 and 10 km wide (Fig. 4.5.), whereas a ~3-km-wide belt exists in the Sierra Calamajue (Fig. 4.6.). Thus, total cumulative arc perpendicular shortening by strain is only ~5 km in the southern SSPM and ~3 km in the Sierra Calamajue and crustal thickening in both areas is only about 1 to 2 km. Although Alisitos-related arc strata along the east side of the arc show less shortening and crustal thickening, continental margin strata east of the arc show very strong ductile deformation and in the Sierra Calamajue, where enough strain data is available, shortening and crustal thickening for a 15-km-wide belt exceed calculations from the San Vicente area by 5 and 2 km, respectively (Table 4.2.). 169 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Thus, along the east side of the arc, deformation was concentrated in the continental margin units and resulted in more crustal thickening in continental margin units than in Alisitos arc strata. Greater crustal thickening along the east side of the Alisitos arc is also supported by geochemical data. A >35 km deep crustal magma reservoir for plutonic rocks in the SSPM and Sierra Calamajue are inferred from rare earth element signatures (Tate et al., 1999; Tate and Johnson, 2000; Chapter 3). In contrast, data from intrusives in the San Vicente area suggest magma sources at shallower crustal levels (Wetmore et al., 2003b; 2005). These geochemical data also support greater crustal thickening along the east side of the arc (Wetmore et al., 2003b; 2005), where crustal thicknesses are thought to have reached >55 km in Cretaceous time (Schmidt, 2000; Whitney et al., 2004). In summary, the greatest amount of crustal shortening and thickening in the Alisitos arc occurred in the San Vicente area. Here, a total of up to 37 km of fold- related (up to 50% or -20 km) and strain-related crustal shortening (17 km) occurred and crustal thickening of -8 km is not unreasonable. Significantly less fold-related shortening (-15% or 1 km) is estimated for the southern SSPM and strain-related shortening in the SSPM and Sierra Calamajue are only - 5 and 3 km, respectively. Similarly, crustal thickening in Alisitos arc strata in the SSPM (1 to 2 km) is comparable to the Sierra Calamajue (1 km). Fault-related vertical displacements are limited in the Alisitos arc. Wetmore (2003) suggested little ( « 5 km) vertical displacement in the San Vicente area and 170 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. limited fault displacement is also suggested Alisitos arc units in the SSPM and Sierra Calamajue. Faulting is most dominant along the east side of the arc. Vertical displacement on the Main Martir thrust in the SSPM alone exceeded -10 km (Kopf and Whitney, 1999; Kopf et al., 2000) and ~5 to 6 km of cumulative vertical displacement occurred across the Sierra Calamajue. Although the zone of deformation that affected the Alisitos arc strata narrows southwards, crustal thickening and shortening was accommodated to the east in continental margin units away from the arc. Reasons for the strain/displacement transfer are discussed below. Factors controlling along-strike character of the fold-thrust belt Development of a fold-thrust belt along the northern and eastern edge of the Alisitos arc and significant concentration of deformation along those margins provides evidence that the arc did not behave as a rigid indenter, but accommodated significant internal deformation during collision. The most extensive involvement of the arc during collision occurred along a ~15 km wide northern margin. The width of significantly deformed arc strata narrows progressively to the south from -10 km in the northern to -5 km in the southern Sierra San Pedro Martir to <5 km in the Sierra Calamajue. Several factors control the along-strike variations in the character of the fold- thrust belt in the Alisitos arc. The controlling factors include: (1) changes in the tectonic setting, which changes from sinistral transpression in the north to normal 171 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. convergence along the eastern margin of the arc (Johnson et al., 1999a; Schmidt and Paterson, 2002; Wetmore et al., 2002; Wetmore, 2003); (2) the pre-existing geometry of the continental margin, including a promontory forming a rigid buttress at the latitude of the SSPM; and (3) rheologic changes caused by the transition from miogeoclinal units east of the SSPM to slope basin deposits east of the Sierra Calamajue and southward decrease of Cretaceous arc-related sedimentary basin deposits. Wetmore et al. (2002; 2003) and Wetmore (2003) recognized a component of sinistral transpression along the northern edge of the Alisitos arc and a counter clockwise rotation of structures with respect to structures along the east side. The sinistral component of deformation is accommodated along the ancestral Agua Blanca fault (Wetmore, 2003), whereas shortening is taken up in a -20 km wide fold-thrust belt. The majority (15 km) of this belt is located in the Alisitos arc and a belt of smaller width (-5 km) is in the Santiago Peak arc to the north. I suggest that this reflects variations in the lithologies between the arcs as the Alisitos arc is composed of a mix of submarine metasedimentary and metavolcanic strata that were weaker than dominantly subaerial metavolcanics with only minute amounts of metasedimentary material to the north. Transcurrent deformation is not recognized along the east side of the arc (Schmidt, 2000; Schmidt and Paterson, 2002; Chapter 2) and orthogonal convergence dominated. In the SSPM, convergence and associated deformation most strongly affected 1) Alisitos arc metasedimentary strata that formed in marine basins 172 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. along the east-side of the arc (e.g., Suarez-Vidal, 1987; 1993, 2) Cretaceous deep- marine metasediments, 3) Triassic-Jurassic accretionary prism units that formed along the continental margin, and 4) Jura-Cretaceous arc magmas (Johnson et al., 1999a; Schmidt and Paterson, 2002). These units are Theologically weaker than and trapped between volcanic-dominated Alisitos arc strata to the west and the promontory of miogeoclinal carbonate strata to the east, which acted as a rigid indenter (Fig. 4.1.). This resulted in 1) strong ductile deformation that was concentrated between these two entities, 2) exhumation of mid-crustal strata, 3) significant crustal thickening and ductile shortening (e.g., Johnson et al., 1999a; Tate and Johnson, 2000), and 4) formation of the doubly-vergent fan structure in the southern SSPM (Schmidt and Paterson, 2002). Farther south in the Sierra Calamajue, where the sediment-rich Alisitos arc strata are not recognized, deformation was mostly concentrated in continental margin units to the east of the arc as well. However, the bulk of the eastern strata in the Sierra Calamajue are comprised of deep-water, shale-dominated units (Campbell and Crocker, 1993; Alsleben and Paterson, 2002; Chapter 2) not the miogeoclinal strata exposed farther to the north. These deep-water units are Theologically weaker than the arc volcanics to the west and miogeoclinal units farther to the north and resulted in more distributed deformation in metasedimentary strata east of the arc and exhumation of shallower crustal levels than in the SSPM. 173 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Conclusions From the structural observations in the study areas and strain data I can deduce several conclusions about the strain field in the Alisitos arc. 1. The strain field of the Alisitos arc is very heterogeneous and significant variations of strain magnitudes and ellipsoid shapes exist with most data lying in the flattening field (oblate strain ellipsoid shapes). Several factors contribute to the heterogeneity of the strain field. These include rheologic variations between analyzed strain samples, possible volume change (most likely volume loss), strain contributions from primary fabrics, regional finite tectonic strain, and from strain gradients towards local structures such as faults or pluton margins. Subdividing strain samples according to strain contributions during formation of local structures does not produce unambiguous plots and scatter remains, indicating that several of the mentioned factors contribute to the finite strain in these samples. To address these issues, more detailed studies of one or more of these effects are desirable. 2. Strain increases qualitatively and quantitatively from the west side of the arc towards the northern and eastern edges, where a fold-thrust belt including major faults, which are interpreted as part of a suture zone, separate the Alisitos arc from the Santiago Peak arc to the north and continental margin strata to the east. Strain increases from zero, with strata exhibiting no evidence of ductile structures and only primary fabric preserved, on the west side to as high as 90% shortening in the Z- direction (where X>Y>Z) in the fault zones to the north and east. Averaging strain values in the main segments of the fold-thrust belt suggests that as much as 60% of 174 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ductile shortening perpendicular to the arc and significant vertical thickening of the crust occurred. 3. The fact that strain is concentrated along the northern and eastern edges of the Alisitos arc is in agreement with a collision model for the arc with North America. The ~E-W trending ancestral Agua Blanca fault accommodated accretion with sinistral transpressive motion along the northern margin of the arc, while the ~N-S trending Main Martir thrust and the fold-thrust belt in the Sierra Calamajue accommodated almost orthogonal convergence along the eastern edge of the Alisitos arc. 4. The arc did not behave as a rigid indenter, but shows abundant evidence for significant deformation associated with collision. The fold-thrust belt that formed in response to collision shows along strike variations whose characteristics are controlled by a) the tectonic setting, which changes from sinistral transpression in the north to normal convergence along the eastern margin of the arc and is responsible for the counterclockwise deflection of structures in the northern Alisitos arc, b) the pre-existing geometry of the continental margin, including an apparent promontory at the latitude of the SSPM, and c) rheologic changes caused by the transition from miogeoclinal units east of the SSPM to slope basin deposits east of the Sierra Calamajue and southward decrease of Cretaceous arc-related sedimentary basin deposits. 175 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 5: ALISITOS ARC AND SEDIMENT PROVENANCE Introduction Recent studies on the Mesozoic tectonic evolution of the PRB identified the different tectonic elements that comprise the PRB (e.g., Gastil et al., 1981; Todd et al., 1988; Johnson et al., 1999a; Schmidt, 2000; Schmidt and Paterson, 2002; Wetmore et al., 2002; 2003a; Wetmore, 2003) and, furthermore, started to address relationships between different arc processes such as deformation, magmatism, and orogeny (Schmidt, 2000; Wetmore et al., 2005). One outstanding question with respect to the tectonic evolution of the PRB is the distance at which the Alisitos arc formed from the North American continent. I am also interested in the evolution of the sedimentary system as it responds to island arc collision. This Chapter is designed to: 1) add constraints on how far from the North American continent the Alisitos arc formed and 2) determine changes in and provenance of sedimentary detritus in Paleozoic continental margin strata, Mesozoic accretionary prism deposits, Cretaceous marine basin sequences, and Cretaceous Alisitos intra-arc basin sediments. These constraints are established by using two well-known techniques: 1) detrital zircon geochronology (e.g., Gehrels, 1990; Ross et al., 1993; Gehrels et al., 1995; Roback and Walker, 1995; Gehrels and Ross, 1998; Gehrels and Stewart, 1998; Cawood et al., 1999; Soreghan and Gehrels, 2000; Gehrels et al., 2002) and 2) paleomagnetic analyses (e.g., Beck et al., 1981; Irving et al., 1985; Beck 1986, 176 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Butler, 1992). Detrital zircon studies in Mesozoic continental margin units and the Cretaceous Alisitos arc in the southwestern North American Cordillera are feasible because the general distribution of zircon sources in North America (Gehrels et al., 1995) and, more specifically, in the southwestern Cordillera (e.g., Gehrels and Stewart, 1998; Stewart et al., 2001) are known. Paleomagnetic analyses along the western North American margin and interpretations of the data have been very controversial. Magnetic inclinations are much shallower than expected for North America and therefore support large-scale northward translation (e.g., Beck et al., 1981; Irving et al., 1985; Beck 1986, Umhoefer, 1987; 2003). However, geologic evidence for translation of the suggested magnitude has not been found (e.g., Monger et al., 1994; Monger and Price, 1996; Dickinson and Butler, 1998). Below, I introduce both of these techniques and discuss the results of seven detrital zircon analyses from basement assemblages in the PRB and present some reconnaissance paleomagnetic analyses on Alisitos arc-related volcanic strata. I discuss the implications of the former, which provide insight into 1) depositional ages of units, 2) detrital zircon populations in the Alisitos arc and adjacent units, and 3) changes in sedimentary sources with time along the North American margin, whereas results of the latter are preliminary and do not yet allow regional interpretations and correlations with previous studies. However, I will discuss issues that have not been adequately determined in previous paleomagnetic studies in the PRB and point out some of the ambiguities with existing data. Despite some of the shortcomings of previous analyses and controversy surrounding the results, I 177 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. conclude that a new paleomagnetic study has great potential to significantly add to our understanding of the PRB. Detrital zircon provenance Introduction In the past decade refinements in geochronologic techniques (e.g., LA-MC- ICPMS, SHRIMP), have led to a virtual explosion in provenance studies using detrital zircons (e.g., Gehrels, 1990; Smith and Gehrels, 1991; 1994; Rainbird et al., 1992; 1997; Ross et al., 1993; Gehrels and Dickinson, 1995; Gehrels et al., 1995; Roback and Walker, 1995; Ross et al., 1997; Gehrels and Ross, 1998; Gehrels and Stewart, 1998; Cawood et al., 1999; Gehrels et al., 1999; Mahoney et al., 1999; Soreghan and Gehrels, 2000; Stewart et al., 2001; Gehrels et al., 2002; Premo et al., 2002; DeGraaf-Surpless et al., 2002; 2003; Barbeau et al., 2005). Fundamental to the use of detrital zircons for provenance studies is a correct understanding of the distribution of Archean and Proterozoic cratonal landmasses on the North American continent with a general younging from Northern Canada to the Southwestern United States (e.g., Hoffman, 1989; Ross, 1991). Recently, the southern extent of Proterozoic North American basement and first occurrences of accreted terranes have been delineated in northwestern Mexico (Valencia-Moreno et al., 2001; Iriondo et al., 2004). Thus, these studies provide a comprehensive picture of the distribution of Archean and Proterozoic rocks in western North America and ultimately helped to establish a reference frame for North American detrital zircons, which allows 178 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. evaluating provenance links between tectono-stratigraphic terranes along the western North American Cordillera. This reference frame was first established to constrain the allochthonous nature of pre-Jurassic terranes (e.g., Soreghan and Gehrels, 2000) and provide clues about whether strata formed and evolved 1) near its present position, 2) elsewhere along the Cordilleran margin, 3) in the Paleo-Pacific far from the continent, or 4) near a continent other than North America (e.g., Gehrels, 2000). However, DeGraaf- Surpless et al. (2002; 2003) have shown that the detrital zircon dataset provide an exceptional basis for determining sources of detrital material in younger (Mesozoic) strata. One of the interesting results of the study by DeGraaf-Surpless et al. (2002) on the Great Valley sequence is that depocenters receive detritus from local sediment sources for a prolonged period of time and that extensive sediment mixing and homogenization is not as effective as often assumed in active continental margin settings (e.g., Ingersoll, 1990). Furthermore, heterogeneous detrital zircon populations in deep-water turbidite sequences can show significant systematic and predictable variations thus aiding interpretations about the evolution of sedimentary basins (DeGraaf-Surpless et al., 2003). Results by DeGraaf-Surpless et al. (2002; 2003) bear interesting implications for other Mesozoic ‘suspect’ terranes (Coney et al., 1980) that have potentially been displaced long distances along the western North American margin (e.g., Burchfiel et al., 1992). In the following, I present detrital zircon analyses from the accreted, and potentially allochthonous Alisitos island arc and adjacent Mesozoic and Paleozoic sedimentary sequences of Baja California, Mexico (Fig. 5.1.). Comparison to similar 179 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Los AngelesV San Vicente San Quintin Explanation: Santiago Peak arc Alisitos arc Bedford Canyon Complex Mesozoic clastic sediments Undifferentiated L I Paleozoic passive margin strata Proterozoic basement SAF ABF MSM? Pm-Tr Detrital zircon locality Depositional contact Fault zontact (thrust, strike-slip) Gulf of California (incipient spreading centers and transform faults) San Andreas fault Agua Blanca fault Mojave-Sonora Megashear? Permo-Triassic U.S./Mexican highways Figure 5.1. Overview of the PRB including detrital zircon locatities discussed in the text. Locations 1 through 4 from this study [l=Canal de Las Ballenas Group; 2=Sierra Calamajue; 3=southem Sierra San Pedro Martir; 4=San Vicente area]. Locations 5 and 6 are from Gehrels et al. (2002)[5=Rancho San Marcos quartzite; 6=San Felipe quartzite]. Locations 7 through 12 are from Morgan et al. (2005)[7= Bedford Canyon formation; 8=French Valley formation; 9=Julian schist; 10=Vallecitos formation; 11=E1 Marmol area; 12=Bahia de Los Angeles area], 180 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. data from units that formed the continental margin prior to accretion and to the unique detrital zircon reference frame established for the North American continent (e.g., Gehrels et al., 1995) allowed me to constrain potential source regions for the detrital zircons and help establish provenance links for sedimentary strata in the Alisitos arc. Furthermore, the data provide insights into sedimentologic processes along the continental margin. These data provide a means of evaluating how sediment sources changed during island arc collision and at least partly enables tracking accretion of the arc to the North American continent. Below I describe four samples collected from the Sierra Calamajue study area, one sample from the southern Sierra San Pedro Martir, and two samples collected by Paul Wetmore in the San Vicente area (Wetmore, 2003). These samples span the southern basement assemblages (Fig. 5.1.) and depositional ages are in agreement with the general subdivisions. Furthermore, important information about sediment dispersal and sources, along-strike continuity of assemblages, and potentially the proximity of the Alisitos island arc can be interpreted from the data. All samples were analyzed using the LA-MC-ICPMS at the University of Arizona (see Appendix A for description of analytical procedures and Table A.2. for raw data). Each sample description is followed by a short interpretation about the significance of the data and regional implications of the data for the evolution of the PRB are discussed at the end. 181 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Regional setting After initially dividing the PRB into three tectono-stratigraphic basement units (e.g., Gastil et al., 1975, 1981; Gastil and Miller, 1984; Gastil, 1993), results from more recent studies suggest that five distinct, NW-trending litho-stratigraphic basement assemblages with separate geologic histories exist (Fig. 5.1.) (Wetmore et al., 2002; 2003a). In southern California and northern Baja California, the Cretaceous Santiago Peak arc represents the remnants of a continental margin arc (Herzig, 1991) built on and through Triassic-Jurassic accretionary prism units (Bedford Canyon Complex) (Sutherland et al., 2002; Wetmore et al., 2003a). Farther south, the accreted Alisitos oceanic island arc is faulted against Triassic through mid- Cretaceous sedimentary and volcanic units intruded by Jura-Cretaceous plutons that are interpreted to also represent remnants of a continental margin arc (e.g., Johnson et al., 1999a). Shallow and deeper-water Paleozoic passive margin sequences with North American affinities comprise most of the eastern PRB (e.g., Gastil et al. 1991; Gastil and Miller, 1993). Sierra Calamaiue and adjacent ranges Provenance o f Canal de Las Ballenas Group North of the Sierra Calamajue, Campbell and Crocker (1993) collected Devonian fossils with North American affinities and assigned a Devonian age to the Canal de Las Ballenas Group (CLB) (Fig. 5.1.). To substantiate the claim that the CLB is Paleozoic and shares provenance links with passive margin sequences in the southwestern Cordillera, I collected a coarse-grained sandstone sample for detrital 182 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. zircon U-Pb analysis. One hundred zircons were analyzed (Appendix A, Table A.2.). The projected ages for the zircons range from 1.75±0.02 to 3.01±0.02 Ga. Thus, all of the zircons yield Paleoproterozoic (1.6 to 2.5 Ga) to Archean (2.5 to 3.8 Ga) ages. The range of ages is almost continuous between the youngest and oldest grains, but on a probability plot several maxima can be identified at 1.81 Ga, 1.86 Ga, 1.96 Ga, 2.1 Ga, and 2.76 Ga (Fig. 5.2.). Comparison between probability curves from the CLB and Devonian miogeoclinal or deeper-water strata of North American origin shows that the mix of ages from the CLB is demonstrably different (Fig. 5.3.). This suggests that the sandstone unit is either not Devonian or is derived from different detritus than Devonian passive margin sequences in the southwestern Cordillera. Comparing the age distributions to quartzites from San Felipe and San Marcos, which are interpreted as Ordovician deep-water strata in the PRB (Gehrels et al., 2002), provides a good match, although 1.1 Ga (Grenville age) detrital grains, which are typical for strata elsewhere in Baja California, are absent (Fig. 5.4.). Based on fossils (Campbell and Crocker, 1993) and the detrital zircon age, the unit is Ordovician to Devonian in age. The exact tectonic setting (i.e. shallow vs. deep water) cannot be established from a detrital zircon sample, but I agree with Campbell and Crocker’s (1993) description of the lithologies, which suggest a deep water environment, most likely the Paleozoic North American passive margin. 183 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 3 X ) o < D ao 03 < U _> 0 3 T 3 Pi 12 10 8 6 4 2 0 0.6 3.0 1.0 1.8 2.6 1.4 2.2 Detrital zircon age (Ga) Fig. 5.2. Detrital zircon analyses probability plot for metasandstone sample (HA-5-28-01-1) collected from the Canal de Las Ballenas Group near the Gulf of California (Crocker and Campbell, 1993). See text for discussion. o o Devonian Alaska Reference y \ a L _ Devonian Northern British Columbia Reference Devonian Nevada Reference O h < 0 6 0 a j 0 ) > Devonian Sonora Reference Canal de Las Ballenas N=100 Canon Calamajue unit N=98 0.6 1.0 2.2 0 .4 .8 2.6 3 .0 1.4 Detrital zircon age (Ga) Figure 5.3. Comparison between detrital zircon probability plots from the Canal de Las Ballenas sample (HA-5-28-01-1), Canon Calamajue unit (HA-260-02), eastern PRB (San Felipe and San Marcos quartzites), Devonian detrital zircon populations from the western North American Cordillera (modified from Gehrels et al., 1995; 2002; Gehrels, 2000). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Paleozoic strata in Oaxaca terrane N =131 Cambrian miogeoclinal and cratonal cover strata N=101 “Lower” Ordovician eugeoclinal strata M=41 “Higher” Ordovician eugeoclinal strata » s r -— N=110 Ordovician miogeoclinal strata ^ „__________ San Felipe quartzite N=59 San Marcos quartzite Canal de Las Ballenas N=100 Canon Calamajue unit N=98 2.2 0.6 1.0 2.6 3.0 1.4 1.8 Detrital zircon age (Ga) Figure 5.4. Comparison between detrital zircon probability plots from the Canal de Las Ballenas sample, Canon Calamajue unit, eastern PRB, Cambrian and Ordovician detrital zircon populations from the Cordillera, and Oaxaca terrane of Mexico (modified from Gehrels et al., 1995; 2002; Gehrels, 2000). 186 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Provenance o f Canon Calamajue unit The structurally lower unit (Canon Calamajue unit of Griffith and Hoobs, 1993) in the Canyon Calamajue area (Fig. 5.5.) contains Mississippian conodont fossils near the top of the section (Griffith and Hoobs, 1993). The top of the section is composed of limestone blocks in a volcaniclastic matrix, which make the origin and location of the Mississippian fossils suspect. In order to determine whether the units in this section are Paleozoic or just contain inadvertently incorporated limestone blocks, I collected one medium grained sandstone sample (HA-260-02) from the middle of the Canon Calamajue unit (Fig. 5.5.). Ninety-eight zircons were analyzed (Appendix A, Table A.2.) from this sample. The ages for the zircons analyzed range from 706±7.4 Ma to 2946±11 Ma. Thus, the zircons ages range from Neoproterozoic to Archean with several distinct maxima at 706 Ma, 1.86 Ga, 1.96 Ga, and 2.72 Ga (Fig. 5.6.). Based on the absence of grains younger than Precambrian, deposition of the sample occurred in the Paleozoic. Comparing the probability plots from the CLB (described above) and the Canon Calamajue unit reveals significant similarities and suggests that these units could have been derived from similar sources. Furthermore, the unit stratigraphically underlies the Mississippian fossil-bearing limestone units, which indicates that the section is right-side up. Provenance of La Mision unit Griffith and Hoobs (1993) mapped the La Mision unit, but did not have any control on the depositional age. I collected one sample (HA-170-02) from a pebble 187 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. -12§M as Sierra Calamajue - - vMississippian © i fossils A 2 .5 k m 1 1 4 1 0 N I 2 9 1 5 N Explanation: Quaternary/ Tertiary Cretaceous Plutons Alisitos arc Canon Calamajue unit Central zone | Paleozoic units (Eastern zone) j Depositional — contact A Cretaceous thrust faults © Fossil locality O U-Pb age Figure 5.5. Simplified map of the Sierra Calamajue study area showing detrital zircon sample locations discussed in text. Detailed 1:50,000 scale map is in back pocket. A=Sample HA260-02; B=Sample HA-170-02; C=Sample HA-069-04. Fossil locality and identification and U-Pb ages reported by Griffith and Hoobs (1993). 188 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 14 -- HA-260-02 (N=98) O (“H C I h 400 800 1200 1600 2000 2400 3200 2800 Detrital zircon age (Ma) Figure 5.6. Detrital zircon analyses probability plot for medium-grained quartzite sample (HA-260-02) collected from the Canon ^ Calamajue unit (Griffith and Hoobs, 1993). See text for discussion. O O S O metaconglomerate unit just below the El Molino fault, which defines the contact with structurally overlying Paleozoic units (Fig. 5.5.). Mineral separation yielded abundant zircon of which ninety-nine were analyzed (Appendix A, Table A.2.). The projected ages for the zircons analyzed range from earliest Triassic (247±5 Ma) to Archean (3039±17 Ma) with distinct Permian (-290 Ma) and Grenvillian (-1200 to 1000 Ma) populations (Fig. 5.7.). Based on the youngest cluster of ages, the sample is earliest Triassic or younger in age. The zircon population resembles similar units described from the Sierra Calamajue to the northeast (Morgan et al., 2005). By inference (i.e. intrusion of -164 Ma orthogneisses) units with similar ages are also exposed in the southern SSPM. Furthermore, the detrital zircon population in sample HA-170-02 shares general characteristics, such as distinct populations of late Paleozoic, Grenvillian, and older (Paleoproterozoic to Archean) grains, with basement assemblages along-strike of the entire central part of the PRB (Morgan et al., 2005). Thus, a continuous belt of turbidite (sand/shale) clastic sedimentary units with similar provenance signatures extends from southern California (Bedford Canyon Formation, French Valley Schist) to Bahia de Los Angeles in central Baja California (Fig. 5.1.). Provenance o f the Canon de los Frailes unit Based on a U-Pb age from a deformed volcanic flow (-125 Ma), Griffith and Hoobs (1993) suggested that the Canon de los Frailes unit, which structurally overlies the Paleozoic Canon Calamajue unit and Alisitos Formation, is Cretaceous 190 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. *8 o 5 - h & 0 ) b O c b < U p4 HA-170-02 (N=99) 8 7 5 4 3 2 1 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 0 Detrital zircon age (Ma) Figure 5.7. Detrital zircon analyses probability plot for pebble conglomerate sample (HA-170-02) collected from the La Mision unit in the Sierra Calamajue. See text for discussion. VO in age. I collected a sample from a sequence of fine sand to shale units in the Sierra La Asamblea that I correlate with the Canon de los Frailes unit. Ninety-two zircons were analyzed in the sample (Appendix A, Table A.2.). The youngest grain is 105±4 Ma and the oldest is 2749±12 Ma (Fig. 5.8.). A distinct Cretaceous peak exists (-133 Ma) and numerous Precambrian and Proterozoic (n=28) and Archean (n=4) detrital grains are present. Using the youngest grain, the depositional age could be -105 Ma or younger. However, a single grain does not represent a statistically robust number to assign a depositional age and it is uncertain if the analyzed grain was a detrital zircon. In general, a depositional age is best determined from the youngest statistically significant cluster of grains (George Gehrels, personal communication 2005). The youngest cluster occurs between 112 and 118 Ma, which forms the basis for assigning an inferred depositional age of -115 Ma to this sample. A Cretaceous age for Sample HA-069-04 is consistent with the Cretaceous age assigned to the units by Griffith and Hoobs (1993). Similar Cretaceous turbidite units deposited in deeper water lying east of the suture with the Alisitos arc have been described from farther north in the northern and southern SSPM (Johnson et al., 1999a; Schmidt and Paterson, 20002). These units are interpreted as a Cretaceous marine basin of regional extent that lay between the Alisitos arc and the North American continent and received detritus from an arc source (younger grain population) as well as deposits that contained old continental detritus. 192 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 30 -- 25 • j s 2 0 cd J O o S - i C X < D 6 0 1 5 cd < u cd P 4 10 5 -- A 1 L 400 jL . D JjL HA-069-04 (N=92) 800 1200 1600 Detrital zircon age (Ma) 2000 2400 2800 Figure 5.8. Detrital zircon analyses probability plot for fine- to medium grained quartzite sample (HA-069-04) collected from Canon de los Frailes unit in the Sierra La Asamblea. See text for discussion. Southern Sierra San Pedro Martir Following work by Schmidt (2000) in the southern SSPM, where he identified a doubly-vergent fan structure spanning the width of the range (see Chapter 1), I collected two samples on the west side of the fan structure in the western domain. The mapping of Schmidt (2000) suggests that one sample is from Alisitos arc-related sediment-dominated sequences that lie between the Rosarito fault and Main Martir thrust (Fig. 4.5.) and that the second sample is from the structurally overlying volcanic-rich ‘flysch’ assemblage (Schmidt, 2000). Unfortunately, mineral separation on the sample from the Alisitos arc-related strata, a siltstone to very fine sandstone unit, did not yield any zircons. Sample HA-094-04, a well-sorted, medium-grained quartzite, from the overlying volcanic-sedimentary section contained a large number of very small zircons. Eighty-five zircons analyzed from sample HA-094-04 produced satisfactory results (Appendix A, Table A.2.). With the exception of one Jurassic grain (153±28 Ma) with very large uncertainties, all detrital grains are Cretaceous in age and the age probability shows an unusual normal Gaussian distribution (Fig. 5.9.). Based on the youngest cluster of ages, the sample has a depositional age of ~110 Ma. The detrital zircon population cannot be used to clearly link the unit to either the ‘flysch’-type assemblages in the transition zone of Schmidt (2000) or the Alisitos arc sediment-rich units to the west. The detritus in sample HA-094-04 is clearly not derived from an old continental source, which is typical for continent-derived accretionary prism assemblages or deep water turbidites elsewhere (see above; also Gastil and Girty, 1993; Morgan et al., 2005). A mid-Cretaceous depositional age and 194 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. x > s a 4 > bo C 3 < D > - * — » 0 3 1 3 Pi HA-094-04 (N=85) 45 40 35 25 20 15 10 5 0 60 100 140 180 Detrital zircon age (Ma) 220 Figure 5.9. Detrital zircon analyses probability plot for well-sorted, medium-grained quartzite sample (HA-094-04) collected from the southern Sierra San Pedro Martir (Schmidt, 2000). See text for discussion. 195 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the lack of grains older than Late Jurassic supports correlation with Alisitos arc sediments. The peculiar close range in zircon ages indicates a point source and a somewhat unusual depositional setting. San Vicente area Wetmore (2003) collected and described two detrital zircon samples from intra-arc Alisitos arc sediments. These samples represent the only available detrital zircon data that clearly comes from the Alisitos arc-related units. Two stratigraphic horizons were sampled in adjacent fault-bounded blocks separated by -1400 m of structural/stratigraphic section (Fig. 5.10.). The data represent reconnaissance analyses during the early stages of operation of the LA-MC-ICPMS at the University of Arizona and only a limited number ( « 100 grains) of zircons have been analyzed (Appendix A, Table A.2.). Below I describe these two samples following closely descriptions by Wetmore (2003). The stratigraphically lower sample is a coarse-grained sandstone (sample PHW-6-6-00-F) collected just below the El Ranchito fault (see Chapter 4). Twenty- two detrital zircons were analyzed and the interpreted ages range from 102.9±3.3 to 1550.1±61.7 Ma (Fig. 5.11.). Nearly all zircons analyzed from sample PHW-6-6-00- F (20 of 22) yield latest Late Jurassic through latest Early Cretaceous ages with an almost continuous range from -145 Ma to 115 Ma. In addition, two early Middle Proterozoic ages were also determined for zircons in this population. As mentioned above, a single crystal with an age of 102.9±3.3 Ma is insufficient to establish a depositional age. Deposition of the sample at that time is 196 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6000 5000 4000 2000 0 5 I 3000 1000 < ■ * . b .‘* /.*. N El Tigre fault El Ranchito fault Argillites and shales Volcaniclastic sandstones Limestones/marbles — 1 ; ■ Felsic ashes w/ accretionary lapilli Felsic ashes (dacites and rhyolites) Mafic volcanics (basalts and basaltic andesites) Pillow basalts 0 Detrital zircon sample Figure 5.10. Stratigraphic column for the Alisitos Formation in the central part of the San Vicente area (modifed from Wetmore, 2003). • denotes stratigraphic level of detrital zircon samples discussed in text. l=Sample PHW-6-6-00-F; 2=Sample PHW- 5-19-00-A. 197 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Detrital zircon age (Ma) Figure 5.11. Detrital zircon analyses probability plot for coarse-grained volcaniclastic metasandstone sample (PHW-6-6-00-F) collected from the San Vicente area (Wetmore, 2003). See text for discussion. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. precluded by observations in the San Vicente area that indicate that deformation of the Alisitos arc segment, including the sediments from which these detrital zircons were collected, mostly predates -108 Ma. A more probable age of deposition is determined from the youngest cluster of ages, which is defined by five zircons that yield ages between 115 and 120 Ma. Based on this cluster, Wetmore (2003) inferred that the deposition of the volcaniclastic sandstone unit occurred at or slightly after -117 Ma. The second coarse-grained sandstone sample from the stratigraphic section (Fig. 5.12.) comes from -800 m below the El Tigre fault (sample PHW-5-19-00-A). Fifty-five zircons yielded interpretable ages that range from 100±2.8 to 2758±16.9 Ma. Ages from sample PHW-5-19-00-A exhibit a continuous range from 131 Ma to 152 Ma, where typically less than a few million years separate any two consecutive ages. After -152 Ma age clusters are typically defined by only two grains until -1430 Ma where five (5) Mesoproterozoic ages form a distinct cluster and again at -1730 Ma where another five (5) grains form a cluster of Paleoproterozoic ages. These age distributions are in stark contrast to the stratigraphically lower sample (PHW-6-6-00-F). Only -60% of the zircons from sample PHW-5-19-00-A yield Mesozoic ages, while the remaining detrital grains yield Paleozoic (n=4), Proterozoic (n=16), and Archean (n=2) ages. Similar to the sample described above, the youngest grain (100±2.8 Ma) does not constitute a statistically significant proportion of the total sample size and a more probable age of deposition is again represented by the youngest cluster of ages. A weak cluster occurs at -110 Ma (three zircons between 109 and 111 Ma). This 199 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1, ; mil 0 400 800 1200 1600 2000 2400 2800 Detrital zircon age (Ma) Figure 5.12. Detrital zircon analyses probability plot for coarse-grained volcaniclastic metasandstone sample (PHW-5-19-00-A) collected from the San Vicente area (Wetmore, 2003). See text for discussion. 200 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cluster was used to infer a depositional for this volcaniclastic sandstone unit of ~110 Ma (Wetmore, 2003). The presence of zircons yielding Paleozoic and Precambrian ages in the volcaniclastic sandstone samples from Alisitos arc sedimentary assemblages clearly implies a source other than the Alisitos arc itself. Furthermore, the stratigraphically lower sample with an inferred older depositional age contains less detritus from a continental source, suggesting that continentally-derived sediments were being deposited on the Alisitos arc segment very late in its evolution. Discussion The above data allows correlation between the analyzed units and other strata described along the southwestern Cordillera (e.g., Gastil, 1993; Gastil and Girty, 1993; Gastil and Miller, 1993; Johnson et al., 1999a; Schmidt, 2000; Gehrels et al., 2002; Wetmore et al., 2003a; Morgan et al., 2005). These correlations help define regionally extensive basement assemblages, which have distinct depositional and tectonic histories and help constraining the tectonic evolution of the PRB. Paleozoic passive margin units The identification of Paleozoic fossils with North American affinities have originally led to assigning a Paleozoic age to the eastern PRB (e.g., Gastil et al., 1975; Miller and Dockum, 1983; Gastil and Miller, 1993 and references therein). The detrital zircon data presented here and data from Gehrels et al. (2002) provide further constraints on the age of the eastern PRB and of relationships of these units to 201 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. North America. Problems, like reworking of these detrital zircon-bearing units in olistostromal blocks notwithstanding (see below; also Lothringer, 1993), all detrital zircon samples strongly resemble Ordovician strata from elsewhere in the North American Cordillera (Fig. 5.4.), suggesting similar provenance and links to the North American continent (e.g., Gehrels et al., 2002). Widespread presence of Ordovician units in the eastern PRB suggests the existence of a continuous section of passive margin units deposited along the North American continental margin. The dispersed nature of these units and unknown structural relationships between them, leaves open the possibility that the Paleozoic strata in the eastern PRB are not continuous, but are fragments dispersed along the continental margin during Permian-Triassic truncation of the North American margin (e.g., Burchfiel et al., 1992; Barth et al., 1997). One of the puzzling observations is the presence of the Canon Calamajue unit, which covers a ~5 km2 area, structurally below Alisitos arc units. Griffith and Hoobs (1993) suggested that these units form the basement to the arc. However, this notion is hard to reconcile with several observations throughout the area and throughout the rest of the arc. First, the Canon Calamajue unit is not cut by dikes and only along its west side intruded out by the Calamajue pluton. Larger quantities of magmatic material should be expected if the unit forms the basement to an overlying arc. Second, the Canon Calamajue unit lacks deformation related to Phase 2 deformation (Chapter 2), which is observed in overlying volcanic and volcaniclastic rocks and would require that the section was tilted prior to Cretaceous deformation. Third, none of the geochemically and geochronologically analyzed plutonic and volcanic rocks in the Alisitos arc show any sort of contamination by continental 202 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sources, which would be expected if units with strong North American affinity underlie the arc (e.g., Johnson et al., 1999b; Wetmore et al., 2003b; 2005). In Chapter 2 ,1 proposed two alternative hypotheses for the presence of these units at the base of the structural section through Calamajue Canyon. I suggested that these units either represent a thrust slice or klippe displaced along a fault with a minimum displacement of ~7 km or a major olistostromal block that formed during mass wasting along the continental margin. Subsequent to displacement, the unit was incorporated at the base of the exposed section during final suturing of the arc to North America. I prefer the mass wasting interpretation, as olistostromes have been reported from the PRB (Lothringer, 1993) and additional blocks potentially exist in the El Marmol area, where Paleozoic rocks underlie Cretaceous strata (Buch and Delattre, 1993; Phillips, 1993; Morgan et al., 2005). Triassic-Jurassic accretionary prism units By latest Paleozoic or earliest Mesozoic, the tectonic setting along the North American continental margin switched to an active, Andean-type subduction zone (e.g., Burchfiel et al., 1992; Barth et al., 1997). Remnants of the Triassic through Jurassic accretionary prism complex that formed along the continental margin during subduction have been identified in southern California and northern Baja California (e.g., Gastil and Girty, 1993; Wetmore et al., 2003a). These units, called ‘flysch’- type strata by Gastil et al. (1975) are generally younging progressively westward as expected if younger sediments are scraped off with time as oceanic lithosphere is 203 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. continuously subducted below the North American continent (Wetmore et al., 2003a). Although the overall lithologies (turbidite sand/shale sequences) are continuous southward past the latitude of the Agua Blanca fault (Fig. 5.1.), identification of the setting of these units has been obscured by amphibolite facies metamorphism and intense deformation related to collision and accretion of the Alisitos arc (Johnson et al., 1999a; Schmidt, 2000). Data from the La Mision units above and recent work by Morgan et al. (2005) on detrital zircons in units ranging geographically from southern California to Bahia de Los Angeles (Fig. 5.1.) suggests the existence of units that share similar detrital zircon sources. Although the lithologies are similar and detritus shares the same general provenance, the tectonic setting cannot be properly constrained by these data alone and additional structural and geochronologic studies in these units are necessary to constrain the tectonic setting. I suggest that these units are early accretionary prism deposits that formed during initiation of a subduction zone complex, which began to form in the Triassic and was well established by the Jurassic along the North American continental margin (e.g., Miller and Busby, 1995; Barth et al., 1997). An interesting observation is the existence of Permian grains in sample HA- 170-02, which are also seen in samples throughout the belt of same age rocks (Morgan et al., 2005, and J.R. Morgan, personal communication, 2005). Sources for Permian igneous zircons are not abundant in the southwestern Cordillera. The nearest known sources in the southwestern United States that contain Permian 204 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. volcanic or plutonic detritus are in the Shoo Fly complex in the western metamorphic belt of the Sierra Nevada (e.g., Saleeby et al., 1987; Hanson et al., 1988) and in the sedimentary Havallah assemblage in western Nevada (Murchey, 1990; Harwood and Murchey, 1990), which received detritus from an outboard, western arc during the time of formation. Another known source for Permian detritus lies in eastern Mexico, where Permo-Triassic arc granitoids are known to exist in the subsurface (Torres et al., 1999) and volcanic rocks of similar age crop out locally (Bartolini et al., 1999). Erosion and dispersal of these units as far as the Colorado plateau have been suggested (e.g., Fox et al., 2005; Hurd and Schmidt, 2005). A third alternative is reworking of Permian sediments exposed at the base of the Antimonio Formation in Sonora (e.g., Stanley and Gonzalez-Leon, 1995; Lucas and Estep, 1999). Cretaceous marine deposits Depositional patterns become a little more complex in Cretaceous sediments. Approximately 110 Ma sediments in the southern SSPM and a -114 Ma volcanogenic metasedimentary sample from the northern SSPM are dominated by Cretaceous zircons and do not show any sign of continentally derived zircons (Johnson et al., 2003). Rocks of comparable age (-117 Ma) in the San Vicente area (Sample PHW-6-6-00-F) also remain dominated by Cretaceous detritus, but show minor influx (two grains) of continental detritus. In contrast, coeval units in the Sierra Calamajue (-115 Ma) and younger units in the San Vicente area (-110 Ma) are loaded with sediment that had a continental source, as old (Paleozoic to Archean) detrital zircon grains are increasingly abundant. 205 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. These older grains preclude derivation of the sediment from the arc itself, the probably proximal Santiago Peak arc, or Jurassic intrusions that are now known to be more extensive and have been described in southern California (Shaw et al., 2003) and the southern SSPM (Schmidt, 2000). One possible source for the older grains is the accretionary prism complex (Bedford Canyon Complex) that defines basement assemblages in the core of the PRB. Another source are Paleozoic passive margin strata (described above) that contain a large variety of Precambrian zircons and now comprise much of the eastern PRB. The mix of ages in the detrital grains in these younger Cretaceous strata supports reworking of nearby sediment rather than erosion of cratonal basement complexes, in which case a dominant age peak for a particular cratonal source should exist. These observations suggest the existence of two coeval basins that received sediment from different sources. A moderate to deep water basin (or basins) (Suarez- Vidal, 1987; 1993) lying immediately to the north and east of the Alisitos arc received only very limited influx from continental sources and between 117 and 110 Ma were either too distant or somehow shielded from North American detritus (Fig. 5.13.). Farther to the east, a deep marine basin, whose remnants are exposed in the Sierra Calamajue (Sample HA-069-04 with a depositional age of ~115 Ma) and in the along the west side of the transitional zone in the southern SSPM (Schmidt, 2000; Schmidt and Paterson, 2002), received detritus from the North American continent. At or shortly after -110 Ma, far greater influx of continental detritus is recognized in the San Vicente, which indicates that the Alisitos arc and associated 206 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. depositional centers were close enough to receive significant input from continental, most likely North American, sources (Fig. 5.13.). It is possible that not all basins received continental detritus simultaneously, which explains the presence of large numbers of Precambrian zircons in the San Vicente area and a lack of these grains in the SSPM. Summary and implications All available detrital zircon data from the eastern PRB (Gehrels et al., 2002; this study) suggest deposition during the Ordovician and strong similarities to Ordovician strata along the southwestern North American Cordillera. These observations in conjunction with the presence of various fossils that range in age from Ordovician to Permian and have strong North American affinities (e.g., Miller and Dockum, 1983; Buch and Delattre, 1993; Campbell and Crocker, 1993; Griffith and Hoobs, 1993; Leier-Engelhardt, 1993) suggest that these units formed as part of the Paleozoic passive margin of North America. This implies that these units cannot have formed too far south of there current location as continental margin units and their southward extent are well constraint in mainland Mexico and do not exist south of ~27°N latitude (e.g., Stewart et al., 1990; Valencia-Moreno et al., 2001; Iriondo et al., 2004). The tectonic setting along the southwestern North American margin changed to an active subduction zone in the Early Triassic (Barth et al., 1997) and remnants of the Triassic-Jurassic arc are exposed throughout the Mojave province in southeastern California and in northwestern Mexico (e.g., Anderson and Silver, 207 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PHW-5-19-00A (N=22) Western Zone (Alisitos arc) PHW-6-6-00F (N -55) Western Zone (Alisitos arc) Western zone (Alisitos sediment-rich assemblages) HA-094-04 (N=85) HA-069-04 (N=92) Western zone (Alisitos sediment-rich assemblages) Central/Transitional zone Early Mesozoic sedimentary assemblages) HA-170-02 (N=99) HA-260-02 (N=98) Eastern zone (Paleozoic passive margin sequences) Eastern zone (Paleozoic passive margin sequences) HA-5-28-01-1 (N=100) 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 0 Detrrital zircon age (Ma) Figure 5.13. Comparison between the populations of all detrital zircon sample collected from the basement assemblages in the San Vicente area (PHW-5-19-00-A and PHW-6-6-00-F from Wetmore, 2003), the southern Sierra San Pedro Martir (HA- 094-04), the Canal de Las Ballenas group (HA-5-28-01-1), and the Sierra Calamajue area (HA-170-02, HA-260-02, and HA-069-04). Note that the different basement assemblages are clearly discemable. 208 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1978; Burchfiel et al., 1992; Saleeby et al., 1992; Moran-Zenteno, 1994; Barth et al., 1997). The accretionary prism units to this continental margin arc are preserved in a long belt that extends from southern California to at least Bahia de Los Angeles. Accretion continued at least until the Jurassic (Gastil and Girty, 1993; Morgan et al., 2005). The limited width of the accretionary prism belt suggests that accretion was periodic. Alternatively, south of the ancestral Agua Blanca fault (Wetmore et al., 2002), a significant part of the belt could have been tectonically removed (i.e. thrust beneath the continental margin) during Cretaceous collision of the Alisitos arc (Wetmore et al., 2003a). During the mid-Cretaceous either two different depositional centers or, since depositional ages overlap, a single basin with proximal and distal sources existed between the approaching Alisitos arc and the continental margin. Strata just to the north and east of the arc, and generally associated with it, are dominated by arc detritus (i.e. Cretaceous detrital zircons). In contrast, deep-water units farther east show significant influx of continental detritus and a clear link to continental sources existed. As the basin was closed, continental sources reached intra-arc depositional centers establishing clear ties to the continent by ~110 Ma (Wetmore, 2003). Paleomagnetism Introduction A multitude of studies on allochthonous or ‘suspect’ terranes in the North American Cordillera have shown that magnetic inclinations in Cretaceous and Tertiary strata are much shallower than expected for strata of stable North America 209 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (e.g., Beck et al., 1981; Irving et al., 1985; 1996; Beck 1986). Thus, interpretation of these data supports paleopositions significantly farther south than the North American continent (e.g., Gordon et al., 1985; Enkin et al., 2004). This has led to the postulation of the “Baja - B.C. hypothesis”, which predicts northward translation of suspect terranes ranging from 1140 ± 640 to 3100 ± 600 km (Cowan et al., 1997) and clockwise rotations of terranes with respect to western North America between the Late Cretaceous and early Tertiary (e.g., Beck et al., 1981; Irving et al., 1985; Beck 1986, Umhoefer, 1987; 2003). Large-scale northward translation has been questioned because of the lack of appropriate structures on which to accommodate thousands of kilometers of displacement in Late to post-Cretaceous time (e.g., Monger et al., 1994; Monger and Price, 1996). Thus, to account for the shallow magnetic inclinations in terranes accreted to the North American continent, alternative interpretations have been proposed. Since the correct identification of paleohorizontal is required for any paleomagnetic study, a favored interpretation for paleomagnetic data from plutonic intrusions is the tilting of batholiths or individual plutons (e.g., Ague and Brandon, 1992; Bohnel et al., 2002). And to explain shallow magnetic inclinations in sedimentary strata, compaction-related processes during lithification of the sediments have been proposed (Dickinson and Butler, 1998; Yule and Herzig, 1994; Li et al., 2004; Vaughn et al., 2005). Large amounts of paleomagnetic data are also available for the PRB (Fig. 5.14., Table 5.1.) and interpretations of these data from Baja California are similarly controversial. Most of the data have been interpreted to support northward 210 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Explanation: Santiago Peak arc Alisitos arc Bedford Canyon Complex Inter/Back-arc sediments Undifferentiated Paleozoic&Proterozoic strata Mexican accreted terranes Depositional contact Fault zontact (thrust, strike-slip) Gulf of California (incipient spreading centers and transform faults) San Andreas fault ABF Agua Blanca fault Sedimentary strata Volcanic strata Plutonic strata Figure 5.14. Generalized geologic map of the PRB showing locations where paleo magnetic studies have been completed (see Table 5.1. for references). 211 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Tal to N J # Unit Age Northward Transport Rotation Authors 1 Silverado Formation 60±2 1 2 ± 6 -18±10 Morris et al. (1986) 1 Silverado Formation 64±3 11±5 -2 0 ± 8 Lund et al. (1991) 1 Ladd and Williams Formations 82±8 1 1 ± 6 -29±9 Fry et al. (1985); Morris et al. (1986) 2 Santiago Peak Volcanics 124±4 3±8 13±13 Yule and Herzig (1994) 3 Southern California 110±5 13±4 25±6 Hagstrum et al. (1985); Tessiere and Beck (1973) 4 Poway Group 42±1 4±4 5±7 Lund et al. (1991) 4 La Jolla Group 49.5±2 6±3 17±5 Lund et al. (1991) 5 Point Loma Formation 72±2 14±5 35±8 Bannon et al. (1989) 5 Point Loma Formation 72±2 17±10 42±17 Bannon et al. (1989) 6 La Posta pluton 94 1±5 4±7 Symons et al (2003) 7 El Testerazo pluton 1 0 0 -1 1 0 ? 8±5 18±6 Bohnel et al. (2002) 7 San Marcos dike swarm 1 2 0 ± 1 8±5 18±6 Bohnel et al. (2002) 8 Rosario Formation (Punta San Jose) 77±3 11±5 1 1 ± 6 Filmer and Kershvink (1989) 9 San Telmo batholith 90-100 6±5 -1±7 Bohnel and Delgado-Argote (2000) 1 0 Punta Baja Formation 70±3 5±11 10±19 Filmer and Kershvink (1989) 1 0 Rosario Formation (Punta Baja) 74±6 8±7 1 1 ± 1 1 Morris et al. (1986) 1 1 San Ignacito 95±5 4±4 24±6 Hagstrum et al. (1985) 1 2 Las Tetas de Cabra Formation 55±1 -3±4 -5±6 Flynn et al. (1989) 1 2 Bateque Formation 55±1 5±5 -19±9 Flynn et al. (1989) 13 Valle Formation (Cedros Island) 90±2 15±5 6 ± 8 Patterson (1984) Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Ta D ie 5.1. continued. # Unit Age Northward Transport Rotation Authors 13 Valle Group (Cedros Island) 95±5 16±4 14±6 Smith and Busby (1993) 14 Valle Formation (Malarrimo) 85±1 13±8 25±13 Patterson (1984) 14 Valle Formation (Malarrimo) 87±1 16±5 33±9 Patterson (1984) 14 Valle Formation (Malarrimo) 90±2 11±5 32±7 Patterson (1984) 14 Valle Formation (El Plallon) 90±2 4±6 -22±9 Patterson (1984) 14 Valle Formation (Vizcaino Peninsula) 94±8 12±10 28±9 Hagstrum et al. (1985) 15 Valle Formation (San Lorenzo) 90±2 9±4 11±5 Patterson (1984) 15 Valle Formation (La Pitahaya) 94±2 14±3 14±4 Patterson (1984) 16 Magdalena/Santa Margarita Islands Remagnetized n/a n/a Hagstrum and Sedlock (1998) 17 San Bartolo 105±5 -1±11 25±18 Hagstrum et al. (1985) #=number corresponding to numbers on Fig. 5.14.; Unit=Unit name; Age=Approximate age o f formation o f unit; lat/long current approximate latitude and longitude; plat=paleolatitude as estimated from paleomagnetic results; Northward transport=estimated amount translation (positive=northward; negative=southward); Rotation=vertical axes rotation (positive=clockwise; negative=counterclockwise); Authors=authors of original work. to I — - translation (14°±3°) and clockwise rotation (29°±8°) of the Baja peninsula with respect to North America between the Late Cretaceous and Late Miocene (e.g., Teissere and Beck, 1973; Patterson, 1984; Hagstrum et al., 1985; Beck, 1991; Lund and Bottjer, 1991; Hagstrum and Sedlock, 1998). While the opening of the Gulf of California contributed ~2° of translation and 8 ° of rotation (e.g., Sedlock et al., 1993), most of the displacement is proposed to be related to dextral shear linked to right oblique convergence between the Pacific and North American plates as predicted by plate motion models (Engebretson et al., 1985; Stock and Molnar, 1988, Atwater and Stock, 1998). If these interpretations are correct, Baja California would have been located near present-day southern Mexico and could be the northward continuation of the margin truncated along the Northern Middle America trench (e.g., Karig et al., 1978). These interpretations have been challenged because 1) not all paleomagnetic data support large-scale northward translation (Fig. 5.15.; Table 5.1.; e.g., Yule and Herzig, 1994; Bohnel and Delgado-Argote, 2000; Bohnel et al., 2002; Symons et al., 2003) and 2) the paleomagnetic data is not easily reconciled with the observed geology (e.g., Gastil et al., 1991). Gastil et al. (1991) suggest ties between the Paleozoic strata of eastern Baja California and Sonora, which could not be established with strata farther south (e.g., Bohnel et al., 1992; Schaaf et al., 1994, 2000). These conclusions are consistent with detrital zircon data, which support provenance links between Paleozoic strata in the eastern PRB and strata in southwestern North America (see above; also Gehrels et al., 2002). In addition to lithologic similarities between the PRB and North American strata, the peculiar 214 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 12±10 - 1+11 160 km Explanation: Santiago Peak arc Alisitos arc Bedford Canyon Complex Inter/Back-arc sediments Undifferentiated Paleozoic&Proterozoic strata Mexican accreted terranes Depositional contact Fault zontact (thrust, strike-slip) Gulf of California (incipient spreading centers and transform faults) San Andreas fault ABF Agua Blanca fault Figure 5.15. Generalized map of the PRB showing average values for suggested latitudinal translation of the PRB (see table 5.1. for references). Positive values= northward translations; negative values =southward translation. 215 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. absence of and sometimes evidence against appropriate structures (Schmidt, 2000; Schmidt and Paterson, 2002) that could accommodate right-lateral strike-slip displacement of the proposed magnitudes during Cretaceous and Tertiary time constitute major problems for the northward translation hypothesis of the PRB. Ortega-Rivera et al. (1997) and Dickinson and Butler (1998) used geochronologic and geologic data, respectively and suggested that their data support post-magnetization 15-20° northeast side up tilt of the PRB about an -330-340° axis. This tilt is comparable to a calculated tilt of 21 ±5° about an axis of 320°±10° that would be needed to account for the observed paleomagnetic data (Dickinson and Butler, 1998). Albeit without much evidence, another alternative interpretation suggested both by supporters and opponents of large-scale translations involves pre-mid- Cretaceous southward and almost identical subsequent Late Cretaceous-early Tertiary northward transport of the Baja peninsula (see above; also Sedlock et al., 1993; Sedlock, 1994; Gehrels et al., 2002). Aside from the problems with Late Cretaceous - early Tertiary large scale translations described above, the tectonic model of Wetmore et al. (2002; 2003a) suggests the existence of two separate arc segments along the southwest North American Cordilleran continental margin. The Alisitos oceanic island arc formed at an unknown distance from the North American continent (e.g., Todd et al., 1988; Johnson et al., 1999a), whereas the Santiago Peak arc was built in situ on the North American continental margin (Wetmore et al., 2003a). If the Alisitos arc was located significantly north or south of the Santiago Peak arc and both arcs were once 216 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. separated by several degrees of latitude, paleomagnetic inclinations should show statistical differences. Furthermore, vertical axes rotations, which are common in collisional environments (e.g., Stevens et al., 1999; Marshak, 2004; Sussmann and Weil, 2004) and are evident from the existing declination data for the PRB (Fig. 5.16.), resulted from the collision of the Alisitos arc. While both, latitudinal displacement and vertical axis rotations are possible, one shortcoming of paleomagnetic data is that purely latitudinal (east-west) motion (whether large or small) of the Alisitos arc is undetectable by paleomagnetic data. Santiago Peak arc Preliminary data is available from the Santiago Peak arc (Yule and Herzig, 1994). These authors sampled 15 primary volcanic flows and tuffs, which are suggested to produce the most reliable data sets (Butler et al., 1991), and 13 volcanogenic sands and silts. Using standard demagnetization techniques (alternating field and thermal demagnetization), a good high temperature (>450°C) component that is considered to represent the primary characteristic remanent magnetization was isolated in nine volcanic flows and seven sedimentary samples. Correcting for sample and bedding orientations, volcanic and sedimentary samples give average declinations/inclinations of 354.0°/58.4° and 345.9746.6°, respectively. The declination/inclination results from the volcanic flows are indistinguishable from the expected values for cratonal North America (e.g., Enkin, 2004) suggesting in-situ formation of these units. In contrast, the sediments have significantly shallower inclinations, which could be interpreted as northward translation. While it is 217 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Explanation: -18±10 - 20±8 -29±9 Santiago Peak arc 13± 13] ±8 Alisitos arc 42±17 ) Bedford Canyon Complex Inter/Back-arc sediments 8 11 ± 6^ ; Undifferentiated Paleozoic&Proterozoic strata Mexican accreted terranes 10±19 11+11 Depositional contact Fault zontact (thrust, strike-slip) 5±6 -19+5 Gulf of California (incipient spreading centers and transform faults) 25±13 San Andreas fault -22±9 ABF Agua Blanca fault V 25±18 0 80 160 km Figure 5.16. Generalized map of the PRB showing average values for suggested rotations in the PRB (see table 5.1. for references). Positive values=clockwise; negative values counterclockwise. 218 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. prohibitive to have part of the stratigraphically continuous section to be translated northward and parts having formed in place, the alternative interpretation is that sediments record shallower inclinations as a result of compaction. Inclination differences of 12° between volcanic and sedimentary strata in the Santiago Peak arc are comparable to values of up to ~14° shallowing between compacted and uncompacted sediments in the Valle Group (e.g., Vaughn et al., 2005). Assuming that inclination shallowing occurred in sedimentary units, the paleopole derived from the volcanic Santiago Peak strata is indistinguishable from the North American paleopole. This led Yule and Herzig (1994) to conclude that the Santiago Peak arc formed in situ in the mid-Cretaceous without significant translation or rotation of the arc with respect to North America. Alisitos arc The study by Yule and Herzig (1994) in the Santiago Peak arc represents the only dataset from volcanic units in the PRB. Although paleomagnetic data from several plutonic intrusions and sedimentary strata have been published from units within or on top of the Alisitos arc (e.g., Lund and Bottjer, 1991, Bohnel et al., 2002), no paleomagnetic data exists for the Alisitos arc volcanics. Methodology Two sections of Alisitos arc related strata were sampled for paleomagnetic analyses (Fig. 5.17. and 5.18.). The northern section near Erindera (Fig. 5.17.) is dominated by primary volcanic flows interlayered with minor volcanogenic 219 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. USA Mexico Pacific Ocean La P a 2 HW-ti H W-6-18-02- HA-025-04 24 22 28 .y u A_ 028-04 HA 030^04^ 500m Explanation Q u atern ary Alluvium Tertiary(?) te rra c e d ep o sits V olcaniclastic sa n d sto n e /a re n ite S h ale/siltsto n e locally brecciated & interlayered with volcanic flows Plag-pheric, lithic-rich volcanic flows an d tuffs(basaltic to andesitic) P eb b le-co b b le cong lo m erate locally s a n d sto n e dom inated Bedding Contact (dashed where inferred) Fold hinge lines (with plunge direction) Road Paleomagnetic sample locality t o t o o Figure 5.17. Generalized geologic map of the Erindera area sampled for paleomagnetic analyses. 115°W USA Mexico Map" Pacific O cean 29°2j)’ N ' ; ■ ' \ V A rro y o El C uerv fto La Paz P acific O c e a n S a n J o s e d e la P ie d ra 5 0 0 1 0 0 0 1 5 0 0 m Figure 5.18. Generalized geologic map of the Arroyo San Jose section sampled for paleomagnetic analyses (modified from Wack, 1988). 221 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sedimentary units continuously exposed in a road cut for ~2 km. Bedding is gently to openly folded without the development of a new axial planar cleavage or evidence for ductile deformation. Similarly, ductile deformation is absent in the southern section near Arroyo San Jose (Fig. 5.18.) located on the west side of the Alisitos arc ~270 km south of the Erindera section. Here, sedimentary strata (mostly shale and siltstone) dominate over volcanic units and all units are dipping homoclinally to the southwest. Oriented samples were collected from 11 volcanic flow units and two sedimentary beds in the Erindera area and from eight sedimentary units and two volcanic flows in the Arroyo San Jose section. A minimum of five specimens from each rock sample were either drilled in the field or in the lab facilities at USC and oriented using a standard Brunton compass. Prior to demagnetization, initial natural remanent magnetization (NRM) was measured at room temperature (20°C) and bulk magnetic susceptibility measurements were completed (Appendix D; Table D.l. and D.2.). Since all samples were well-behaved during initial measurements (i.e., gave consistent orientations), several specimen (total of 15) with initial NRM greater than 150 SI were selected for reconnaissance thermal demagnetization. All samples came from the Erindera section, since volcanic samples generally have higher initial NRM than sedimentary samples. Two specimens from five volcanic flow sites (10 specimens) were chosen with two volcanic flow sites located on opposite limbs of a regional anticline allowing for a fold test (e.g., Butler, 1992). Demagnetization was also completed on five specimens from three volcanic pebbles and boulders in a 222 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. pebble-boulder conglomerate that lies on top of the Erindera section (Fig. 5.17.). Demagnetization of these specimens allows for a conglomerate test; both the fold and conglomerate tests, can be used to establish whether the characteristic NRM is primary or not (e.g., Butler, 1992). Thermal demagnetization was completed in the magnetic-field shielded room in the paleomagnetism laboratory at USC. Following measurement of initial NRM, samples were heated in 50°C steps up to 500°C to remove any low temperature viscous remanence. Above 500°C, samples were heated at 25°C steps to 600°C, since this temperature range covers much of the blocking temperature spectra for single domain magnetite. If any remanence was left after heating to 600°C, which supports the presence of hematite, heating was continued in 10°C steps to 680°C at which temperature hematite loses its remaining remanence (Appendix D; Table D.I.). After each temperature step, NRM (Appendix D, Fig. D.l.) and bulk susceptibility (Appendix D, Fig. D.2.) were measured in each sample. After demagnetization was complete, sample and tectonic corrections were applied to determine site directions using an Excel Macro written by John Yu (University of Southern California) (Appendix D; Table D.3.). Preliminary Results The preliminary paleomagnetic data from volcanic units in the Alisitos arc give reproducible and internally consistent directions (Appendix D). Normalized NRM versus temperature plots (Appendix D, Fig. D.l.) show that most samples have a low temperature, viscous overprint that is removed at temperatures between ~250 223 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and 300°C. After removal of this overprint, three samples (HA-028-04A; PHW-6 - 18-02-H; PHW-6-18-02-1) show magnetic behavior that is consistent with magnetite as the main carrier of the magnetization and samples are demagnetized after heating to ~580°C. However, remanence remained in the other samples (HA-025-04B; HA- 030-04; PHW-6-19-02-D) even after heating to 580°C. This is indicative of hematite in these samples, but whether hematite is the primary magnetic carrier, resulted from secondary alteration, or was produced during thermal demagnetization remains speculative at present and needs to be further investigated in future analyses. In order to evaluate whether the high temperature magnetic remanence in these samples is primary or secondary, a preliminary fold test was completed on samples PHW-6-18-02-H and PHW-6-18-02-1, which were collected from opposite limbs of a regional, kilometer-scale fold (see Butler, 1992 for explanation of fold test). Statistics (declination=D, inclination^, and 0195) for four specimens were calculated before and after bedding corrections. Before bedding correction, D= 327.6°, 1=37.6°, and 0195=3 1 .6 . After applying bedding corrections, D=328.4°, 1=49.4°, and 0 1 9 5 = 11.3. The decrease in the 0195-value after bedding correction indicates that these samples pass a fold test and that remanence was acquired prior to folding and is most likely primary. Another standard test to assess whether magnetic remanence is primary or secondary is a conglomerate test (Butler, 1992). Five specimens from three different pebbles were used to calculate statistics. To pass a conglomerate test, statistics are expected to be poor as this would indicate that pebbles are randomly oriented after erosion and deposition. In contrast, good statistics would produce a failed 224 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. conglomerate test. The statistics (D=311.5°, 1=49.4°, 95=6 . 4 after field correction) are good (small 9. 5) and in close agreement with values obtained from the fold test (see above). Thus, the data would constitute a failed conglomerate test. Based on the preliminary data, the fold test passes, whereas the conglomerate test fails. Since the conglomerate depositionally overlies the volcanic strata, it is hard to imagine that the underlying volcanics were hot enough to cause remagnetization in the overlying sedimentary unit. One possibility is that thick, but now eroded, volcanic successions were originally deposited on top of the conglomerate resulting in reheating of the conglomerate and obliteration of the primary NRM. Alternatively, it is possible that the number of data points is insufficient to unambiguously establish a passed or failed conglomerate test. The sample orientations (inclination, declination) for all samples have been corrected for in situ and bedding orientations (Appendix D.l.). The expected inclinations for stable North America during the Cretaceous are ~ 59° (Lund, pers. comm., 2005). Inclinations for three samples (HA-025-04B; PHW-6 - 18-02-H; PHW- 6-19-02-D) are similar to those expected from North America (Enkin, 2004; Lund, pers. comm., 2005), whereas the other three samples (HA-028-04A; HA-030-04; PHW-6-18-02-1) show shallower than expected inclinations. Most samples also show a counterclockwise rotation with respect to stable North America. However, the limited number of analyses does not allow determining average site inclinations and declinations that could be properly compared to the North American Polar Wander Path. 225 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Discussion Results form reconnaissance paleomagnetic work Because these preliminary data are not sufficient to calculate average site inclinations and declinations, the data cannot be used to answer questions about paleolatitude of the Alisitos arc or its position with respect to the Santiago Peak arc. However, several initial observations regarding these preliminary data can be made: 1) The results are internally consistent enough to continue the study in the Alisitos arc and produce a high precision dataset that can eventually be compared to similar data from the Santiago Peak arc and the North American Polar Wander Path. 2) Problems with the conglomerate test and the presence of hematite must be carefully evaluated and the primary nature of the characteristic magnetic remanence needs to be established. 3) Initial data from the strata at Erindera (Fig. 5.17.) support counterclockwise rotations. These rotations are in agreement with counterclockwise structural trends in the San Vicente area (see Chapter 4) and are expected if the Alisitos arc collided against an irregular margin (Wetmore, 2003). Value of future paleomagnetic investigations I think that by continuing the paleomagnetic work several geologic issues in the PRB can be addressed that were previously ignored or not known and results will elucidate some of the ambiguities with the existing paleomagnetic data. 226 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1. Most paleomagnetic studies have treated the PRB as a single entity, although paleomagnetic inclinations and the inferred northward translation with respect to North America are clearly larger in the western than in the central part of the batholith (Fig. 5.19.a.) and rotations are variable (Fig. 5.19.b.). Sedlock (2003) pointed out that the current view of the PRB is oversimplified and Wetmore et al. (2002) showed that a larger than previously recognized number of lithostratigraphic domains exists. These tectonic domains need to be evaluated separately and one way to discriminate between them is by using paleomagnetic techniques. 2. Although a minimum of 8 ° of clockwise rotations are required by the opening of the Gulf of California during the Neogene (e.g., Hagstrum et al., 1985; Sedlock et al., 1993), much larger (up to 30° clockwise rotations) and opposing (up to 30° counterclockwise) rotations are recorded throughout the PRB (Fig. 5.16. and 5.19.b.; see Table 5.1. for references). Counterclockwise rotations are also suggested by the preliminary data provided above. Detecting different magnitudes of vertical axis rotations within distinct blocks support the presence of different tectonics domains with independent displacement histories (Wetmore et al., 2002; Sedlock, 2003). 3. Surprisingly, with the exception of a limited study by Yule and Herzig (1994), paleomagnetic analyses on widespread volcanic strata, which are generally regarded as the most reliable dataset (e.g., Dickinson and Butler; 1998), are absent. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. W Translations E 3000 2500 2000 1500 1000 * 500 0 -500 -1000 -1500 b W Rotations E 60 50 40 30 O W 20 0) o g> 10 Q 0 -10 -20 -30 Figure 5.19. a. Diagram showing that paleomagnetic data generally support greater northward translation in the western part than in the central part of the PRB. b. Diagram showing that paleomagnetic data show greater variations in possible vertical axis rotations in the western part than in the central part of the PRB. 228 t ■ Sedimentary A Volcanic ♦ Plutonic f ■ Sedimentary A Volcanic ♦ Plutonic f Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4. Only a limited number of studies have been completed on intrusive suites (Teissere and Beck, 1973; Hagstrum et al., 1985; Bohnel and Delgado- Axgote, 2000; Bohnel et al., 2002; Symons et al., 2003). Earlier studies, which were generally regional in scope and are based on very few sample sites per pluton (Teissere and Beck, 1973; Hagstrum et al., 1985) support large northward translations (or tilt) of similar magnitude as inferred from sedimentary units. In contrast, results from more recent studies with greater sampling density on individual intrusions or intrusive complexes are more consistent with very limited or no translation (Bohnel and Delgado-Argote, 2000; Bohnel et al., 2002; Symons et al., 2003), although locally tilt of individual plutons has to be considered (Bohnel et al., 2002). The observations suggest that better spatial resolution on individual plutons in conjunction with good control on magnetic mineralogy, overall geochemistry, and geochronology (including U-Pb zircon age and Ar-Ar hornblende and biotite cooling ages) is needed. These additional controls are needed because individual plutons can be very complex (e.g. Mt Stuart batholith; Paterson et al., 1994). In addition, plutons locally intrude subhorizontal bedding (e.g., San Telmo batholith; Bohnel and Delgado-Argote, 2000) and the use of Al-in-homblende barometry (Hammarstrom and Zen, 1986; Anderson and Smith, 1995) allows constraining paleohorizontal, which is generally missing from earlier studies. Moreover, plutons represent the only possibility to apply paleomagnetic techniques to the central and eastern parts of the PRB 229 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. because host rocks are greatly deformed and metamorphosed, which severely limits paleomagnetic analyses. 5. Paleomagnetic data from sedimentary strata produce much shallower inclinations (and therefore suggest greater translation) than data from igneous rocks (Fig. 5.19.a.). Recent results from sedimentary units addressed the possibility of compaction-related shallowing (e.g., Kodama and Davi, 1995; Tan and Kodama, 1998; Li et al., 2004; Vaughn et al., 2005), but detailed work in strongly interleaved volcanic and sedimentary rocks should provide additional insight into this problem and add further constraints to this controversial subject. 6 . Another way to address possible compaction-related and/or strain-related shallowing of magnetic inclinations is by detailed fabric analyses. This is a very valuable tool since it allows quantifying fabric or strain intensities and determining the affects of compaction or strain on sedimentary and volcanic units and magnetic inclinations. I think that combining several approaches will help address many of the above mentioned controversies surrounding the paleomagnetic data. First of all, it is necessary to pair paleomagnetic analyses with extensive geochronologic and geologic (i.e. structural) constraints, which is an often-overlooked necessity for any paleomagnetic study. Second, combining paleomagnetic analyses with detailed detrital zircon analyses and geochemistry, which will all provide independent datasets with their own unique constraints, will lead to a very valuable dataset that is 230 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. both precise and reliable and justifies a renewed effort to produce a high quality paleomagnetic dataset for the PRB. Linking paleomagnetic results and detrital zircon geochronology Paleomagnetic and detrital zircon analyses each are valuable tools to constrain tectonic provenance and also address questions about processes in tectonic environments such as vertical axis rotations of smaller domains and the evolution of the depositional system over time. I think that applying both of these tools in the PRB in conjunction with detailed stratigraphy, mapping, and structural analyses will significantly add to the understanding of this part of the southwestern North American Cordillera and below I list several hypotheses that can be addressed tested using these approaches. Hypothesis 1: Northward translation is only possible if southward translation occurred prior to the Cretaceous. The detrital zircon data show clear links between the North American continent and the Paleozoic passive margin and Mesozoic accretionary prism units in Baja California that extend to at least 28.5°N (Gastil and Girty, 1993; Gehrels et al., 2002; Morgan et al., 2005; this study). Furthermore, we know that the North American continent does not extend significantly south of ~27°N latitude (Stewart et al., 1990; Valencia-Moreno et al., 2001; Iriondo et al., 2004). Thus, the units that comprise the PRB could not have originated significantly farther south as suggested by paleomagnetic analyses (e.g., Teissere and Beck, 1973; Hagstrum et al., 1985; 231 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Beck, 1991) and would have had to be transported southward prior to northward translation. This hypothesis can be discarded if the Alisitos arc, which is one of several litho-stratigraphic domains, was the only tectonic element that was translated. However, this would require a right-lateral shear zone between the arc and the continental strata to accommodate significant translation of the arc. Such a shear zone has not been documented even where the contact between the arc and continental margin strata is well-exposed. Furthermore, the displacement of only the Alisitos arc and the existence of such as shear zone are precluded by Miocene paleomagnetic data, which support show comparable results between analyses from Baja California sur and Sonora/Sinaloa across the Gulf of California. This suggests that these units must have moved together and that the structure responsible for displacement is in Sonora, Mexico (Hagstrum et al., 1987; Gastil, 1991). Hypothesis 2: Paleomagnetic and detrital zircon data from the Santiago Peak arc will reveal no translation and continuous links to the North American continent. The Santiago Peak arc is built on top of and is in depositional contact with an accretionary prism complex that is clearly linked to North America (Herzig, 1991; Sutherland et al., 2002; Wetmore et al., 2003a). Thus, detrital zircon analyses on suitable rocks in the arc and more extensive paleomagnetic analyses should reveal continuous links to the North American continent and no statistical difference in paleolatitude, respectively. 232 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. If rock types in the Santiago Peak arc are not appropriate for detrital zircon analyses more extensive sampling of the underlying basement (Bedford Canyon Complex) will constrain the location of the arc itself. Furthermore, the exact sources for sedimentary detritus can be established by detailed sampling similar to studies presented by DeGraaf-Surpless et al. (2002; 2003). Hypothesis 3: Paleomagnetic data from the Alisitos arc are indistinguishable from the Santiago Peak arc. This hypothesis is based on the presence of detrital zircons in intra-arc strata of the Alisitos arc, which support links between the arc and a source for continentally derived zircons. If statistically differences between the paleomagnetic data exist, the arc could not have moved across a wide ocean basin and motion should have been dominantly north-south again requiring the existence of transcurrent faults between the arc and Mesozoic accretionary prism units (see Hypothesis 1). Hypothesis 4: Up to 50° o f counterclockwise rotations will be detected along the northern end o f the Alisitos arc Structural studies along the northern margin of the Alisitos arc show structural trends that deviate by up to 50° in a counterclockwise sense from observations along the east side of the arc (Johnson et al., 1999a; Schmidt, 2000; Schmidt and Paterson, 2002; Wetmore, 2003; see Chapter 2). Wetmore (2003) attributed these rotations to the accretion of the arc against an irregular margin and I predict that paleomagnetic studies will reveal this interpretation to be true. 233 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Hypothesis 5: Other domains with unique displacement histories will be found. Structural studies along the northern and eastern margin show that the displacement field changes between different locations (Johnson et al., 1999a; Schmidt, 2000; Schmidt and Paterson, 2002; Wetmore, 2003; see Chapter 2 and 4). I think that paleomagnetic studies in these domains will show local vertical axes rotations of these domains. Potentially other, as yet unmapped domains (e.g., the southern margin of the arc) also show large rotations. Hypothesis 6: Detrital zircon analyses can be used to differentiate between Alisitos arc-related sedimentary strata and marine sediments with North American affinities. Cretaceous Alisitos-related sediments do not contain continentally-derived detritus, whereas Cretaceous deeper-water sediments farther to the east include a distinct zircon population of continental origin (see above). I think this pattern will be more clearly defined by additional analyses and a clear distinction between the different marine basins (or proximal and distal basin facies) on the basis of their detrital zircon population is possible. Units that are 110 Ma and younger will contain a distinct older population of grains as the marine basins were close enough to receive North American detritus at this time. 234 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Hypothesis 7: It is possible to distinguish whether Cretaceous zircons were derived from the east or the west. I think it is possible to distinguish between western and eastern sources for Cretaceous detrital zircon grains as those derived from the Alisitos arc will show little complexity and no inheritance, whereas those derived form the continental margin arc to the east will show greater complexity including older cores (Jurassic, Paleozoic, or Precambrian). It is probably necessary to use SHRIMP rather than LA- MC-ICPMS techniques since the grains are mostly too small for analyses using the LA-MC-ICPMS. 235 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 6: REGIONAL SYNTHESIS AND CONCLUSIONS Introduction The existence of the collided Alisitos island arc in the PRB makes it an ideal field laboratory to evaluate how collision changes processes along the continental margin system. Accretion of this arc completely changed the configuration of the continental margin. Marine basins, which formed between the arc and the continental margin, and older continental margin features, such as the accretionary prism, fore arc basin, and the continental margin arc itself are incorporated into the collision zone. During collapse of these basins complex deformation, which is reflected in along-strike differences in the character of the collision zone, caused changes in 1 ) the geochemistry of the evolving continental margin arc as crust thickened and magmatic material encountered different host rock strata during ascent and 2 ) depositional patterns as sedimentary detritus with different sources was carried into new and existing depositional basins. The collision zone has recently been studied in several areas including detailed investigations in the San Vicente area (Wetmore et al., 2002; 2003a; b; 2005; Wetmore; 2003) and the northern and southern Sierra San Pedro Martir (Johnson et al., 1999a; b; Schmidt, 2000; Tate and Johnson, 2000; Schmidt and Paterson, 2002; Schmidt et al., 2002). My contribution to characterizing the variability of the collision zone and evolving processes during collision include the following: ( 1 ) a description of lithologies and structural history of the arc-continent transition zone in the Sierra Calamajue (Chapter 2); (2) new geochemical and 236 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. geochronologic data to constrain changes in and timing of magmatism and place limits on timing of pre and syn-accretion deformation (Chapter 3); (3) new finite strain data from the Sierra Calamajue and a regional synthesis of the strain/displacement fields of the collision zone (Chapter 4); and (4) detrital zircon analyses, which, in conjunction with reconnaissance paleomagnetic analyses, place constraints on the provenance of sediments in the Alisitos arc and adjacent continental margin units (Chapter 5). Below, I integrate observations presented in previous chapters, give a brief overview of the Paleozoic and Mesozoic tectonic evolution of the PRB, and suggest future research avenues needed in the PRB. Geology, geochemistry, and geochronology of the arc-continent collision zone in the Sierra Calamajue Structural geology Five litho-stratigraphic basement assemblages, which can be correlated with assemblages throughout the PRB, comprise the Sierra Calamajue study area. The area marks the collision zone between the Alisitos island arc and the North American continent and is characterized by a southwest-vergent, brittle-ductile fold-thrust belt that extends from the eastern edge of the Alisitos arc well into Paleozoic, fine grained, deep-water strata. In the Calamajue Canyon, the collision zone is narrow (<10 km), but widens to the northwest and southeast. The narrowness is interpreted to result from either the presence of a Theologically stronger pluton and its homfelsed aureole, which lie to the southwest and acted as a rigid indenter, or differential erosion, which led to formation of a Quaternary basin to the north of the area. 237 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Field observations support four (4) phase of deformation in the study area. Phase 1 is recorded only in Paleozoic continental margin units and is characterized by isoclinal folding of bedding and formation of a largely incipient transposition foliation and compositional layering. Based on ages derived from fossils (Griffith and Hoobs, 1993) and detrital zircon analyses, deformation occurred between the Mississippian and Permian. Phase 2 is recorded by all units in the study area and is associated with a steep deformation gradient from no foliation in the aureole of the Calamajue pluton to well-developed continuous cleavage near and northeast of the arc-bounding El Toro fault. Northeast of the El Toro fault, all units are open to tightly folded (or refolded) and display a well-developed, generally northwest-southeast-trending foliation and moderately to steeply plunging stretching lineation. The style of Phase 2 structures is similar in all units and formation is attributed to Cretaceous collision of the Alisitos arc. Phase 3 deformation resulted in a sinistral flexure or ‘megakink’ that deforms the entire Sierra Calamajue, but also caused widespread outcrop-scale kink folding. The kink folds deform all previous structures and therefore formed after Phase 2 deformation had ceased. Phase 3 deformation is interpreted to represent an increment of Cretaceous tectonic strain related to elastic relaxation following regional Phase 2 deformation. Phase 4 deformation is very restricted in nature and related to pluton emplacement. The best example occurs in the narrow structural aureole of the Las 238 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Palmas pluton, where foliation is locally deflected into a margin parallel fabric and folds of foliation have axial planes parallel to the pluton margins. Geochemistry and geochronology Two deformed plutons, the Piedra Blanca orthogneiss in the Sierra Calamajue and the Chapala Ring Complex in the Alisitos arc west of the main study area, were recognized. Samples collected from these intrusions did not yield enough zircons for determination of U-Pb crystallization ages and were considered too altered for geochemical analyses. Based on field observations and general petrologic and structural characteristics, the Piedra Blanca orthogneiss is suggested to be Jurassic in age as similar orthogneisses have been described from the southern SSPM (Schmidt and Paterson, 2002), southern California (Shaw et al., 2003), and southern Baja California (Grove et al., 2005). A mid-Cretaceous age is inferred for the Chapala Ring Complex as similar ring complex structures have been reported from the Alisitos arc (Johnson et al., 1999b; Tate et al., 1999). Undeformed plutons in the Sierra Calamajue include the Calamajue, Corral, and Las Palmas plutons, which were processed for whole rock and trace element geochemistry. All plutons are medium- to high-K, metaluminous, tholeiitic to calc- alkaline plutons and, based on their major element geochemistry, are indistinguishable from one another and comparable to reconnaissance analyses presented by Goldfarb (1996). These results are misleading, as trace elements geochemistry show different trends and geochronology reveals different crystallization ages. The Calamajue 239 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. pluton is -144 Ma in age and shows a flat REE pattern with a weak Europium- anomaly, which suggests derivation from a plagioclase-bearing source. In contrast, the -95 Ma Las Palmas pluton and the undated Corral plutons show slight enrichment in light REE and depletion in heavy REE suggesting a garnet-bearing magma source. Comparison between REE data from the Sierra Calamajue, the northern SSPM (Tate et al., 1999), and the San Vicente area (Wetmore et al., 2005) shows that the data from the Sierra Calamajue study area support a crustal thickening event, resulting in deeper source regions for melting along the east side of the arc as a result of arc-continent collision (Wetmore et al., 2003b; 2005). Complex displacement fields in the island arc-continent collision zone Over the past decade four studies have focused on the structural and tectonic evolution of the suture zone between the Alisitos arc and North American continental margin units (Johnson et al., 1999a; Schmidt, 2000; Wetmore, 2003; this study). Although all of these studies provided evidence for an arc accretion event between -115 and 100 Ma, significant differences exist in how this collision was accommodated. A deformation gradient from the west side towards the northern and eastern edges of the arc exists in all areas (Johnson et al., 1999a; Schmidt, 2000; Wetmore, 2003; Chapters 2 and 4). Qualitatively, this deformation gradient is expressed by gradual changes in the intensity of structural features. On the west side of the arc bedding is preserved, ductile structures are mostly absent, gentle to open, upright 240 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. folds dominate, and brittle faults accommodate minimal offset. In contrast, as the northern and eastern edges of the arc are approached, a spaced cleavage develops that quickly grades into a continuous cleavage, folds tighten and become isoclinal and overturned, and faults, which preserve evidence for brittle and ductile deformation, locally have significant displacements. Finite strain analyses provide some quantitative constraints on the deformation gradient. Fabrics intensities measured in rocks on the west side of the arc are indistinguishable from primary fabrics (e.g., Paterson and Yu, 1994; Paterson et al., 1995; Wetmore, 2003) and rocks are interpreted to record no tectonic strain. Finite strain increases to 90% shortening in the Z-direction (where X>Y>Z) near the arc-bounding structures. Average strain values in the fold-thrust belt along the edges of the arc suggest as much as 60% of ductile shortening perpendicular to the arc and significant vertical crustal thickening. Within the arc, ductile shortening and thickening estimates are variable as the deformed arc strata changes in width from a ~15-km-wide zone in the north to a 5 to 10-km-wide zone in the SSPM to a <5 km-wide zone in the Sierra Calamajue. As the zone of affected arc strata narrows southward, the continental margin units take up increasing amounts of deformation and overall ductile shortening: crustal thickening is greatest in continental margin units immediately east of the arc. Other along strike differences include: 1) significant shear associated with the Main Martir thrust, progressive rotation of fold hinges from gently plunging to down-dip parallel to the direction of thrusting, and juxtaposition of shallow crustal with mid-crustal units in the SSPM (Johnson et al., 1999a; Kopf and Whitney, 1999; 241 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Kopf et al., 2000; Schmidt and Paterson, 2002), which are not seen to north (Wetmore, 2003) or south; 2) evidence for sinistral transcurrent deformation in the San Vicente area (Wetmore, 2003), but no evidence for strike-slip deformation along the east side of the arc (Johnson et al., 1999a; Schmidt and Paterson, 2002); and 3) different structures that accommodate contraction, with folds being the dominant structures in the San Vicente area (Wetmore, 2003), brittle faults, ductile shear zones, and folds being abundant in the SSPM (Johnson et al., 1999a; Schmidt and Paterson, 2002), and reverse faults dominating in the Sierra Calamajue. The overall development of a deformation gradient is consistent with collision of the Alisitos arc with North America. During collision, the arc did not behave as a rigid indenter, but records internal deformation. Intensity of internal deformation changes along-strike and is controlled by: 1 ) changes in the tectonic setting with sinistral transpression in the north and normal convergence in the east; 2 ) the pre-existing geometry of the continental margin, including an apparent promontory at the latitude of the SSPM, and 3) rheologic changes caused by the transition from miogeoclinal units east of the SSPM to slope basin deposits east of the Sierra Calamajue and southward decrease of Cretaceous arc-related sedimentary basin deposits. Although most strain data in the collision zone lie in the flattening field (oblate strain ellipsoid shapes), local variations of strain magnitudes and ellipsoid shapes are significant and finite strain is heterogeneous. The heterogeneity is controlled by rheologic variations between analyzed strain samples, possible volume loss, changes in metamorphic conditions and strain rate, and strain contributions 242 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. from primary fabrics, regional finite tectonic strain, and local strain gradients caused by faulting or pluton emplacement. Evolution of the sedimentary system: Lessons learned from detrital zircon provenance Detrital zircon data from the Sierra Calamajue, southern SSPM, and San Vicente area provide constraints on: 1) depositional ages of the sedimentary units; 2) provenance of detrital grains; 3) changes in the depositional environments over time; and 4) mass wasting processes. The inferred depositional ages from samples collected in the western, central, and eastern zones correlate well with the subdivision of basement units into: 1) a western Cretaceous Alisitos arc; 2) central Triassic(?)-mid Cretaceous volcanic and clastic assemblages; and 3) eastern Paleozoic passive margin sequences (e.g., Gastil et al., 1981; Gastil, 1993; Wetmore et al., 2003a). More specifically, eastern belt units in the Sierra Calamajue can be linked to the Ordovician passive margin sequences of North America extending the age of known Paleozoic units in that area from Ordovician to Mississippian (Campbell and Crocker, 1993; Griffith and Hoobs, 1993), whereas units in the central belt can be further subdivided into Triassic-Jurassic accretionary prism units (e.g., Gastil and Girty, 1993; Morgan et al., 2005) and Cretaceous deep water sequences, which have clear links to continental detritus. Cretaceous Alisitos arc-related sediments are largely composed of Cretaceous arc detritus with only very limited links to continental sources until ~110 Ma. By ~110 Ma, detritus from continental sources is 243 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. abundant and sedimentary links between depositional basin(s) in the Alisitos arc and North American are established. The existence of large (several square kilometers) olistostromal slide blocks, which are composed of Paleozoic passive margin strata, near Rancho San Marcos (Lothringer, 1993), in the Sierra Calamajue, and possibly near El Marmol (Buch and Delattre, 1993) suggests that passive margin units were eroded and deposited in local deep water basins between the early Mesozoic and Cretaceous. Paleomagnetic data from the PRB: another look at an old controversy Although the reconnaissance nature of the paleomagnetic data from the Alisitos arc presented in this dissertation restrict interpretations of those data (Chapter 5), a large number of studies on sedimentary, plutonic, and, to a far lesser degree, volcanic rocks have provided meaningful paleomagnetic data (e.g., Teissere and Beck, 1973; Patterson, 1984; Hagstrum et al., 1985; Beck, 1991; Lund and Bottjer, 1991; Yule and Herzig, 1994; Hagstrum and Sedlock, 1998; Bohnel and Delgado-Argote, 2000; Bohnel et al., 2002; Symons et al., 2003). Most data show shallower than expected magnetic inclinations, which are interpreted to indicate either northward translation of the PRB between the Late Cretaceous and Late Miocene (e.g., Teissere and Beck, 1973; Patterson, 1984; Hagstrum et al., 1985; Beck, 1991; Lund and Bottjer, 1991; Hagstrum and Sedlock, 1998) or geologic processes such as compaction and/or tilting of plutonic bodies (Yule and Herzig, 1994; Bohnel and Delgado-Argote, 2000; Bohnel et al., 2002; Symons et al., 2003). 244 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Inclination data from sedimentary strata studied along the west side of the PRB support the largest translations, although northward latitudinal transport ranges from as little as 4° (Patterson, 1984; Lund et al., 1991) to as much as 17° (Patterson, 1984; Bannon et al., 1989; Smith and Busby, 1993). Similar variations are seen in results from plutonic rocks (Teissere and Beck, 1973; Hagstrum et al., 1985; Bohnel and Delgado-Argote, 2000; Bohnel et al., 2002; Symons et al., 2003). However, shallower inclinations are dominant in the earlier, more regional studies (Teissere and Beck, 1973; Hagstrum et al., 1985), while later studies with higher sampling density show steeper inclinations suggesting less or no northward translation (Bohnel and Delgado-Argote, 2000; Bohnel et al., 2002; Symons et al., 2003). The analyses of volcanic strata in the Santiago Peak arc do not support northward translation either (Yule and Herzig, 1994). Furthermore, results from intimately interlayered volcanic and sedimentary rocks suggest that compaction- related inclination shallowing of up to -12° accounts for the shallow inclinations in the sedimentary strata (Yule and Herzig, 1994). If all sediments undergo compaction-related shallowing of comparable magnitude, northward translation is not required. Therefore, the possibility of compaction-related shallowing needs to better understood (e.g., Kodama and Davi, 1995; Li et al., 2004; Vaughn et al., 2005). Furthermore, more detailed studies on all available rock types in conjunction with good geologic, geochronologic, and geochemical constraints and a good understanding of the magnetic mineralogy are needed to better understand and interpret the results of paleomagnetic analyses in the PRB (see below). 245 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A speculative tectonic model for the Paleozoic and Mesozoic evolution of the PRB Ordovician through Permian Remnants of the Paleozoic North American passive margin are preserved in the eastern zone of the PRB. Both shallow and deep water sections, whose boundary runs roughly north-south through southern California and northern Baja California and changes abruptly into an east-west trend at ~30.5° N latitude, have been recognized (Gastil and Miller, 1993 and references therein). The changing trend suggests that the Paleozoic units in Baja California represent either the actual southwestern comer of the North American passive margin sequence or, alternatively, an embayment along the continental margin. The oldest units presently identified are Ordovician sandstone (metaquartzite) units in the Sierra Calamajue, near San Felipe and Rancho San Marcos (Lothringer, 1993; Gehrels et al., 2002), and marble units near Coyote Mountains in Southern California (Miller and Dockum, 1983). In addition, younger (Devonian through Permian) units, interpreted as passive margin sequences, have been identified (Gastil and Miller, 1993 and references therein). Ordovician and Mississippian strata in the Sierra Calamajue record deformation that is not recognized in younger (Triassic) strata in the same mountain range. These observations support the interpretation that deformation occurred between the Mississippian and Permian. Stewart (1988) and Stewart et al. (1990) describe Permo-Triassic contractional deformation along the southern margin of North America preceding 246 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. collision between South and North America. I interpret east-west trending structures such as foliation and fold hinge lines east of the SSPM (Schmidt, 2000) and near San Felipe (Anderson, 1993) and structures recognized in deep-water strata in the Sierra Calamajue (Chapter 2) to be related to this tectonic event along the southern margin of North America, which resulted in deep-water units being thrust over miogeoclinal strata (Stewart, 1988; Stewart et al., 1990). Truncation of the southwestern North American margin, which led to sinistral (southward) translation of passive margin sequences into northwestern Mexico (including Baja California), probably followed contractional tectonism, although the exact timing remains speculative (e.g., Burchfiel and Davis, 1972; Davis et al., 1978; Burchfiel et al., 1992; Barth et al., 1997; Dickinson, 2000; Dickinson and Lawton, 2001) and alternative interpretations have been proposed (e.g., Hamilton and Myers, 1966; Schweickert, 1976; Dickinson, 1981). If sinistral translation at the end of the Paleozoic occurred along several strike-slip zones instead of one major shear zone, different blocks of passive margin sequences (micro-continents) could have been widely dispersed along the modified continental margin and account for southward translation of Paleozoic units as required by Hypothesis 1 presented in Chapter 5. This interpretation is weakened by the fact that accretionary prism units that currently lie west of passive margin sequences have clear cratonal provenance links. This requires that: 1) the accretionary prism units did not form along the North American continental margin (see below) and that detritus is derived from an unknown, potentially South American cratonal source or 2) the contact between the accretionary prism units and 247 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. passive margin strata in the PRB is a major strike-slip fault. Neither of these hypotheses appears feasible and significant southward translation beyond the proposed truncation of the continental margin at the end of the Paleozoic is not supported by currently available data. Triassic through middle Jurassic (>164 Ma) An active, Andean-type subduction zone complex initiated along the western North American margin in the Triassic (Barth et al., 1997). Remnants of the continental margin arc are preserved in southeastern California and northwestern Mexico (e.g., Saleeby et al., 1992; Moran-Zenteno, 1994; Barth et al., 1997). The accretionary prism (‘flysch’ belt of Gastil et al., 1975) to this continental margin arc is preserved along the axis of the PRB (Wetmore et al., 2003a; Morgan et al., 2005). These deposits are best preserved in southern California, where they are composed of turbidites combined with serpentinite blocks and olistostromes that are internally deformed and young progressively westward as expected in an accretionary prism (Wetmore et al., 2003a). Correlation with units south of the ancestral Agua Blanca fault (Wetmore et al., 2002) is based on similar lithologies and similar detrital zircon populations (Morgan et al., 2005; Chapter 5). Cretaceous deformation and metamorphism (see below) strongly overprinted original structures obscuring better identification. However, present constraints suggest that the belt of accretionary prism units is continuous from southern California to at least as for south as Bahia de Los Angeles. 248 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Middle Jurassic to Early Cretaceous During the middle Jurassic, arc magmatism was well established in the continental margin arc (e.g., Saleeby et al., 1992; Miller and Busby, 1995) and sedimentation continued along the western margin of the continent with detritus from cratonal North America as well as proximal volcanic arc sources (Morgan et al., 2005). An apparently short-lived, middle Jurassic (~164 Ma) magmatic event is recognized in the accretionary prism and possibly in Paleozoic passive margin units in the PRB (Schmidt, 2000; Schmidt and Paterson, 2002; Shaw et al., 2003; Grove et al., 2005). Many sheet-shaped plutons intruded in an apparent short-lived pulse in a narrow belt between southern California (Shaw et al., 2003) and the tip of the Baja California peninsula (Grove et al., 2005). The setting for this magmatism remains unknown, but could be related to underplating of hot magma and melting of accretionary prism sediments during spreading ridge subduction or short-lived, but widespread extension (or transtension) in the accretionary prism. However, this interpretation is complicated by a lack of contemporaneous mafic magmatism, which is commonly expected in these settings (e.g., Lytwyn et al., 2000; Bradley et al., 2003). Schmidt (2000) and Schmidt et al. (2002) describe contractional deformation (folding and cleavage development) from the southern SSPM during this time period, although the cause for this event is uncertain. Since it follows the Jurassic magmatic event, it is possible that the strain field switched from extensional to 249 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. contractional related to either subduction of younger crust or a slight velocity increase in plate convergence. Based on the oldest presently recognized plutonic material in the Alisitos arc (-144 Ma Calamajue pluton; Chapter 3), the arc was evolving at least by the Early Cretaceous. The identification o f-164 Ma (Re-Os and U-Pb ages) oceanic lithosphere, which could represent the basement of the Alisitos arc, in the El Arco area indicates that the arc could have started to form even earlier (Victor Valencia, written comm., 2005; see also Barthelmy, 1979). If the arc started to evolve this early, a second subduction zone beneath the Alisitos arc is needed. Instead of a second subduction zone, I think the possibility that the basement to the Alisitos arc is an oceanic plateau that moved towards North America during this time needs to be considered in future investigations (Paul Wetmore, pers. comm., 2003). This time period marks another possibility for sinistral translation along the continental margin related to the enigmatic Mojave-Sonora megashear (e.g., Anderson and Silver, 1979; Campbell and Anderson, 2003). This proposed structure is interpreted to be a transcontinental transform fault related to opening of the Gulf of Mexico and a mylonitic shear zone with sinistral kinematics has been reported from Sonora, Mexico (Campbell and Anderson, 2003). The location of this structure in Sonora is consistent with Hypothesis 1 presented in Chapter 5. However, Jurassic sinistral displacement of the proposed magnitude has been challenged in northwest Mexico (e.g., Molina-Garza and Geissman, 1998; 1999; Iriondo et al., 2004) and the Mojave province (Dickinson, 2000; Dickinson and Lawton, 2001), where Triassic and Jurassic strata are continuous (e.g., Busby-Spera, 1988). At present large 250 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. magnitude sinistral displacement, particularly in the Mojave desert region, remains ambiguous. Detailed field studies in Sonora are necessary to further elucidate the potential and timing of sinistral translation. Early to mid-Cretaceous In the early Cretaceous continental margin magmatism had shifted westward and is now represented by the 128 and 116 Ma Santiago Peak arc, which is clearly recognized in southern California (e.g., Anderson, 1991; Herzig, 1991; Meeth, 1993; Carrasco et al., 1995) and whose remnants are preserved in the central zone in the northern and southern SSPM and the Sierra Calamajue (Johnson et al., 1999a; Schmidt, 2000; Chapter 2). Structural studies in the Alisitos island arc support the interpretation that the arc collided with and accreted to the continent during this time interval (Griffith and Hoobs, 1993; Johnson et al., 1999a; Schmidt, 2000; Wetmore, 2003; Chapter 2). The main collisional phase occurred between -115 and 108 Ma and resulted in the development of an arc-bounding fold thrust belt including the doubly-vergent fan structure in the southern SSPM (Schmidt and Paterson, 2002) that juxtaposes the arc with collapsed basin deposits (see below) and continental margin units along its northern and eastern edges (Johnson et al., 1999a; Schmidt, 2000; Wetmore, 2003; this study). Based on finite strain data (Chapter 4) and geochemical pluton signatures (Tate et al., 1999; Tate and Johnson, 2000; Wetmore et al., 2003b; 2005), accretion was also accompanied by significant (up to 10 km) crustal thickening, particularly 251 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. along the east side of the arc, probably accommodated by lower crustal ductile flow between -115 and 110 Ma. Cretaceous moderate to deep water basinal assemblages were trapped between the arc and continental margin. Their presence in the collision zone supports the closure and collapse of one or more marine basin(s). Prior to accretion, sedimentation into a deep water marine environment still continued west of the continental margin arc. The detritus came dominantly from local arc sources, but also from older detritus, which was probably added by erosion of Paleozoic passive margin strata in the eastern PRB. Simultaneously, moderate to deep water basins adjacent to the approaching Alisitos arc received dominantly arc-related detritus suggesting that continental sources could not yet reach basins associated with the Alisitos arc. Basins in the Alisitos arc were receiving sediment from cratonal sources by-110 Ma. Although structural studies are consistent with collision (Johnson et al., 1999a; Schmidt, 2000; Wetmore, 2003; this study), debate continues about the fate of fore-arc and accretionary prism sediments that must have existed along the continental margin arc and have not yet been identified. Wetmore et al. (2002) suggested removal by subduction of these sediments and preferred that interpretation to strike-slip translation because structural observations such as moderate to steep lineations and reverse (NE-side up) kinematics along the east side of the arc (e.g., Johnson et al., 1999a) are more consistent with the former than the latter. Normal subduction of oceanic lithosphere beneath the continental margin at the latitude of the Alisitos ceased as a result of collision and lithospheric plates had 252 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. to adjust to the new conditions, while convergence between the Farallon and North American plates continued (e.g., Engebretson et al., 1985). Subduction to the north of the Alisitos arc, beneath the Santiago Peak arc probably continued while a new subduction zone complex and continental margin arc formed to the south. Alternatively, if two subduction zones were present prior to accretion (Johnson et al., 1999a), subduction continued beneath the Alisitos arc, which now formed part of the continental margin. With the main phase of collision ending — 108 Ma (Johnson et al., 1999a; 2003; Wetmore, 2003), more localized intra-arc deformation continued and discrete faults continued to be active until at least 103 Ma in the San Vicente area (Wetmore, 2003) and northern SSPM (Johnson et al., 1999a; 2003) and -85 Ma in the southern SSPM (Schmidt, 2000; Schmidt et al., 2002). Mid- to Late Cretaceous During and following accretion of the Alisitos arc and crustal thickening mostly east of the arc, magmatism continued in the PRB (e.g., Silver et al., 1979). Some of the most voluminous plutonism in the PRB (so-called La Posta suite) occurred between 99 and 92 Ma (Walawender et al., 1990; 1991; Kimbrough et al., 2001) including intrusion of the -95 Ma Las Palmas and possibly the Corral plutons in the Sierra Calamajue (Chapter 3). The cause for the voluminous nature of this magmatism, the brief interval of intrusion, and somewhat unusual composition that resembles tonalite-trondhjemite-granodiorite plutons in Archean gneiss terrains (Kimbrough et al., 1998; 2001) remains to be investigated. One possible 253 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. interpretation is that the underthrusting of fore-arc and accretionary prism sediments during collision of the Alisitos arc beneath the continental margin provided the material that triggered the magmatic flare-up after the arc geotherm had re equilibrated (e.g., Ducea, 2001; Wetmore et al., 2003). Intrusion of the La Posta-suite was accompanied by rapid exhumation of the central and eastern zones of the PRB, which continued until ~85 Ma (Schmidt, 2000; Schmidt et al., 2002). Denudation of these zones occurred along the entire length of the PRB and postdates collision, which occurred only along one stretch of the PRB, by ~10 Ma (Schmidt, 2000). This suggests that collision was not the controlling factor for exhumation. Instead, a change in relative plate motions and/or crustal delamination could have triggered rapid exhumation (Schmidt, 2000; Schmidt et al., 2002). Erosion of these rapidly exhuming units shed abundant detritus into the newly formed fore-arc basin along the west side of the peninsula, while the developing orogen shielded the fore-arc from significant cratonal detritus as only small numbers of older detrital grains are recognized in these deposits (Kimbrough et al., 2001). This observation is puzzling since the exhumed plutons intruded Triassic- Jurassic accretionary prism units, which contain abundant cratonal material and should have been eroded as well. The lack of observed detritus of cratonal origin is probably related to the small sampling size (one sample) presented by Kimbrough et al. (2001) and I think that more detailed studies will find greater proportions of cratonal material. 254 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Subsequent to intrusion of the La Posta-type intrusions, magmatism migrated eastward into present day Sonora and Sinaloa, where latest Cretaceous-earliest Tertiary plutons are widespread (e.g., Henry, 2003; Valencia-Moreno et al., 2003). The latest Cretaceous to early Tertiary marks the time period of suggested northward translation of the PRB (e.g., Teissere and Beck, 1973; Patterson, 1984; Hagstrum et al., 1985; Beck, 1991; Lund and Bottjer, 1991; Hagstrum and Sedlock, 1998). Although detailed structural investigations in Sonora are still needed to explore the possible presence of dextral shear zones that could have accommodated northward translation of the proposed magnitude, the current data are inconsistent with the hypothesis of northward translation during this time as most strata in the PRB with the exception of the Alisitos arc, show clear links to North America during the Mesozoic and Paleozoic. Future research directions During the course of this project several questions remained unanswered and addressing the problems mentioned below would significantly improve our understanding of the evolution of the PRB. Paleomagnetism The reconnaissance data from the Alisitos arc suggest that it is worthwhile to pursue a paleomagnetic study in the arc as internally consistent results have been obtained and an in-depth study would probably provide satisfactory data. A more extensive dataset would be useful to evaluate the potentially disparate evolution of 255 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the Alisitos arc and the Santiago Peak arc and will aid in assessing tectonic models for the evolution of this part of the North American continent (e.g., Thomson and Girty, 1994; Johnson et al., 1999a; Wetmore et al., 2002; 2003a). Moreover, detailed data from various domains in the PRB could help to identify tectonic elements that have experienced independent displacement histories including possible vertical axes rotations. If vertical axes rotations occurred, structures that accommodated these rotations have to be present in the PRB. Moreover, I think the Alisitos arc represents an ideal location to address fundamental process-oriented questions with respect to compaction-related shallowing of magnetic inclinations in sedimentary rocks and tilting of plutonic bodies. Addressing these key problems with paleomagnetic data in the Alisitos arc is facilitated by the existence of (1) a wide variety of rock types including sediment, volcanics, and plutons and intimately interlayered sedimentary and volcanic strata; (2) techniques such as Aluminum-in-homblende thermobarometry (Hammarstrom and Zen, 1986; Anderson and Smith, 1995) to constrain paleohorizontal in plutons; (3) plutons that intrude subhorizontal bedding in host rock strata; (4) great markers (lithic fragments, phenocrysts) that can be employed to quantify primary and strain fabric intensities, which can be compared to inclination values; (5) a deformation gradient that developed under low to moderate metamorphic conditions (subgreenschist to greenschist facies) that allows to assess potential changes in inclinations with increased deformation; and (6) conglomerates and gentle to open folds, which allow application of standard paleomagnetic field tests (conglomerate and fold test) to characterize paleomagnetic stability. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Strain studies and characterization of overall displacement field A more comprehensive picture of the strain field in the Alisitos arc as a result of arc-continent collision can be established by continuing to conduct strain studies in the arc and adjacent continental margin. Moreover, detailed strain studies could help constraining our understanding of finite strain related to structural processes such as folding, shearing, and pluton emplacement as strain markers are found in and near folds, fault zones, and pluton aureoles. In addition to finite strain determinations, the Alisitos arc offers the opportunity to address the remaining aspects of deformation (i.e. translation, rotation, and volume change). Translation and rotation can be addressed in two ways. First, large-scale tectonic motions can be detected using paleomagnetic analyses briefly outlined above. Second, detailed structural analyses of the fold-thrust belt that rims the Alisitos arc would give insight into folding and faulting processes that contribute to overall translation and rotation. Volume changes can be addressed by focusing strain analyses on other rock types in the deformed part of the arc in addition to analyses of lithic-rich volcanic rocks presented in Chapter 4. Comparison between finite strain values from volcanic rocks and other rock types (shale, sandstone, conglomerate) can be used to infer volume changes (e.g., Paterson et al., 1989). Furthermore, detailed geochemistry on deformed and undeformed and mildly to moderately metamorphosed strata is a viable approach to determine volume changes (e.g., Ague, 1991; 1994). Ultimately, these detailed studies will help constraining the total bulk shortening and crustal thickening associated with collision of the Alisitos arc. 257 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Detrital zircon studies I think that the detrital zircon study presented in Chapter 5 needs to be extended. A general picture regarding the evolution of sedimentary basins starts to emerge, but detailed structural and stratigraphic studies in conjunction with detrital zircon analyses should ultimately provide a clear pattern on how sediment sources change, which sequences were eroded and (re-)deposited, and when deposition stopped. Thus, these data will provide a long-term record on the evolution of the sedimentary system as it changes from a subduction-dominated environment to a collisional environment and will help tie the Alisitos arc to the North American continent. Regional studies Several regional aspects of the evolution of the PRB still remain poorly understood and a full understanding of the tectonic evolution of the PRB will not be achieved without completing additional regional studies and mapping. Eastern zone basement assemblages are probably still the least understood part of the PRB. As described by previous workers (e.g., Campbell and Crocker, 1993; Buch and Delattre, 2993; Lothringer, 1993; Schmidt, 2000) and also described in Chapter 2 (see above), these Paleozoic sequences preserve structural evidence for protracted deformation that predates collision of the Alisitos arc and is not seen in early Mesozoic strata. Furthermore, structural records differ between Paleozoic shallow-water and deep-water strata. Better constraints on the significance and age of this deformation, differences between the structural styles in Paleozoic units, and 258 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. relationships to deformational events elsewhere in the southwestern Cordillera are desirable. In addition, the overall continuity (i.e. continuous sequence or dispersed blocks) of Paleozoic units and their relationships to units in Sonora, Mexico and other Paleozoic North American passive margin sequences needs to be investigated in greater detail than presently available. Another regional aspect that remains to be addressed is the along-strike character and tectonic setting of central zone (‘flysch’ belt of Gastil et al., 1975; transition zone of Schmidt, 2000) sedimentary assemblages. Sedimentary basement assemblages that share similar lithologies, depositional ages, and detrital zircon population extend from southern California to at least the Sierra Calamajue and possibly the Bahia de Los Angeles area. However, whether these units were deposited in a similar tectonic setting or formed in different settings and simply received detrims from similar sources has not been examined in detail. Finally, the geochemical and geochronologic evolution of the Alisitos arc itself needs to be better understood. While some effort has been put forward in southern California to complete geochemistry and geochronology on the Santiago Peak volcanics (e.g., Herzig, 1991) and related Cretaceous intrusions (e.g., Walawender et al., 1991), age determinations and geochemistry on the Alisitos arc volcanics and associated intrusive bodies remains inadequate. Furthermore, understanding the setting, stratigraphy, and evolution of sedimentary basins that formed contemporaneously with the Alisitos arc would greatly improve our understanding of the tectonic evolution of PRB and answer some of the long- 259 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. standing controversies with respect to the Mesozoic tectonic evolution of the PRB and the southwestern Cordillera in general. 260 Reproduced with permission of the copyright owner. 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B., eds., Geological Excursions in southern California and Mexico, p. 297-318. Waldron, H. M., and Sandiford, M., 1988, Deformation volume and cleavage development in metasedimentary rocks from the Ballarat slate belt: Journal of Structural Geology, v. 10, no. 1, p. 53-62. Wetmore, P. H., 2003, Investigation into the tectonic significance of along strike variations of the Peninsular Ranges batholith, southern and Baja California [PhD dissertation thesis]: University of Southern California, 199 p. Wetmore, P. H., Alsleben, H., Paterson, S. R., Ducea, M. N., Gehrels, G. E., and Valencia, V. A., 2005, Field trip to the northern Alisitos arc segment: Ancestral Agua Blanca fault region, Field Conference Guidebook for the VII International Meeting of the Peninsular Geological Society: Ensenada, Baja California, MX, 39 p. 287 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Wetmore, P. H., Ducea, M. N., Gehrels, G. E., Schmidt, K. L., and Paterson, S. R., 2003b, Magmatic response to differential crustal thickening; geochemical constraints on the tectonic evolution of the Alisitos Arc segment of Baja California, Mexico: Geological Society of America Annual Meeting Abstracts with Programs, v. 35, no. 6 , p. 114-115. Wetmore, P. H., Herzig, C., Alsleben, H., Sutherland, M., Schmidt, K. L., Schultz, P. W., and Paterson, S. R., 2003a, Mesozoic tectonic evolution of the Peninsular Ranges of southern and Baja California, in Johnson, S. E., Paterson, S. R., Fletcher, J. M., Girty, G. H., Kimbrough, D. L., and Martin-Barajas, A., eds., Tectonic Evolution of Northwestern Mexico and the Southwestern United States: Geological Society of America Special Paper 374, p. 93-116. Wetmore, P. H., and Paterson, S. R., 2002, Primary grain shapes and grain preferred orientations: Why no analysis of finite strain is complete without their incorporation: EOS Transactions AGU, p. 613. Wetmore, P. H., Schmidt, K. L., Paterson, S. R., and Herzig, C., 2002, Tectonic implications for the along-strike variation of the Peninsular Ranges Batholith, Southern and Baja California: Geology, v. 30, no. 3, p. 247-250. Whitney, D. L., Paterson, S. R., Schmidt, K. L., Glazner, A. F., and Kopf, C., 2004, Growth and demise of continental arcs and orogenic plateaux in the North American Cordillera: from Baja to British Columbia, in Grocott, J., Tikoff, B., McCaffrey, K. J. W., and Taylor, G., eds., Vertical Coupling and Decoupling in the Lithosphere, Geological Society of London Special Publication, 227, p. 167- 176. Williams, P. F., 1976, Relationship between axial plane foliations and strain: Tectonophysics, v. 30, p. 181-196. Williams, P. F., 1977, Foliation: a review and discussion: Tectonophysics, v. 39, p. 305-328. Windh, J., Griffith, R. C., and Girty, G. H., 1989, Tectonic significance of kink bands in Arroyo Calamajue, Baja California, Mexico, in Abbott, P. L., ed., Geologic studies in Baja California: Society of Economic Paleontologists and Mineralogists, Pacific Section, p. 75-78. Woodward, N. B., Boyer, S. E., and Suppe, J., 1985, An outline of balanced cross- sections: Knoxville, TN, University of Tennessee Department of Geological Sciences, 170 p. Wright, T. O., and Henderson, J. R., 1992, Volume loss during cleavage formation in the Meguma group, Nova Scotia, Canada: Journal of Structural Geology, v. 14, no. 3, p. 281-290. 288 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Wright, T. O., and Platt, L. B., 1982, Pressure dissolution and cleavage in the Martinsburg shale: American Journal of Science, v. 282, p. 122-135. Yoshinobu, A. S., and Girty, G. H., 1999, Measuring host rock volume changes during magma emplacement: Journal of Structural Geology, v. 21, p. 111-116. Yule, J. D., and Herzig, C., 1994, Paleomagnetic evidence for no large-scale northward translation of the Southern California Peninsular Ranges, Geological Society of America Annual Meeting Abstracts with Program, A-461 p. Zulauf, G., Palm, S., Petschick, R., and Spies, O., 1999, Element mobility and volumetric strain in brittle and brittle-viscous shear zones of the superdeep well KTB (Germany): Chemical Geology, v. 156, no. 1-4, p. 135-149. 289 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX A: U-PB GEOCHRONOLOGIC ANALYTICAL PROCEDURE OF ZIRCONS U-Pb geochronologic analyses of zircon U-Pb geochronology of zircons was conducted by laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS). The analyses involve ablation of zircon with a New Wave DUV193 Excimer laser (operating at a wavelength of 193 nm) using a spot diameter of 25 to 50 microns. The ablated material is carried in argon gas into the plasma source of a Micromass Isoprobe, which is equipped with a flight tube of sufficient width that U, Th, and Pb isotopes are measured simultaneously. All measurements are made in static mode, using Faraday detectors for 238U, 23 2Th, 2 08‘ 20 6Pb, and an ion-counting channel for 204Pb. Ion yields are ~1 mv per ppm. Each analysis consists of one 20-second integration on peaks with the laser off (for backgrounds), 2 0 one-second integrations with the laser firing, and a 30 second delay to purge the previous sample and prepare for the next analysis. The ablation pit is ~20 microns in depth, with vertical walls and a nearly flat floor. For each analysis, the errors in determining 206Pb/2 3 8 U and 20 6Pb/2 0 4 Pb result in a 9 o a 9 r measurement error of ~l-2% (at 2-sigma level) in the Pb/ U age. The errors in 9 0 A 9 0 7 9 0 7 measurement of Pb/ Pb are much larger due to the low intensity of the Pb signal. Age interpretations in this study are accordingly based entirely on 206Pb/2 3 8 U ages. Common Pb correction is made by using the measured 2 0 4 Pb and assuming an 290 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. initial Pb composition from Stacey and Kramers (1975) (with uncertainties of 1.0 for 2°6pb/2 °4 pb and 0 . 3 for 20 7Pb/2 0 4Pb). Measurement of 2 0 4 Pb is unaffected by the presence of 2 0 4 Hg because backgrounds are measured on peaks (thereby subtracting any background 2 0 4 Hg and 2 0 4Pb), and because very little Hg is present in the argon gas. Inter-element fractionation of Pb/U is generally <20%, whereas fractionation of Pb isotopes is generally <5%. In-run analysis of fragments of a large zircon crystal (generally every fifth measurement) with known age of 564 ± 4 Ma (2-sigma error) (G. Gehrels, unpublished data) is used to correct for this fractionation. The uncertainty resulting from the calibration correction (together with the uncertainty from decay constants and common Pb composition) is generally 3% (2-sigma) for 9 0 f \ 9TR the Pb/ U ages. Fractionation also increases with depth into the laser pit. The accepted isotope ratios are accordingly determined by least-squares projection through the measured values back to the initial determination. For each sample, Tera-Wasserburg diagrams are plotted (Fig. A.I.) and the 9 0 6 9T8 Pb/ U ages are determined with 1-sigma error bars that reflect only the error in determining 206Pb/2 3 8 U and 20 6Pb/2 0 4Pb. These ages and their errors are reported in Appendix A Table A.I. The weighted mean of the individual analyses is calculated according to Ludwig (2001), which is reported for each sample. The age of each sample, however, has additional uncertainty from the calibration correction, decay constants, and composition of common Pb. These systematic errors are added quadratically to the measurement errors to yield the larger uncertainty for the age of each sample. 291 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. a. data-point error ellipses are 68.3% conf. 0.6 - - 2800 2400 0.4 -- 00 oo C M 2000 A CL to o CM 1600 0.2 -1200 0.0 0 4 8 12 16 20 2 0 7 Pb/2 3 5 u Figure A. 1. Tera-Wasserburg concordia diagrams for single zircon grains analyzed for detrital zircon geochronology (Chapter 5) and plutons geochronology (Chapter 3). a. Sample HA-170-02; b. Sample HA-069-04; c. HA-260-02; d. HA-094-04; e. HA-5- 28-01-1; f. PHW-5-19-00-A; g. PHW-6-6-00-F; h. HA-068-04; i. HA-070-04. K ) K > o o o o CM o o c o C O Q i O O O CM o o " O c o o o o CM O O CD O ! o CM o o ■ ' 3 - c o o C M d o d o D in co C M n CL s- o CM d 293 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure A.I. continued. o c o c o CO C O a a C M ■ o O O C M O O o C M O CD O o C M O C O o M " o C M O d 3 If) CO cm n C L N - o C M n8 £ Z /qd 90Z 294 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure A.I. continued. T 3 295 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure A.I. continued. o o CN co co o o c o c o o 00 C M CN O o ■ 'f r CN 00 o o o CN O O CD O O CN o CD o CN d o o o D m co CN n CL N - O CN ^803^ ^ 903 296 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure A.I. continued. LO O ^8 0 3 ^ ^ 9 0 3 < 4 - 3 297 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure A.I. continued. ab 298 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure A.I. continued. C O C O 4 4 O 0 0 C O C> C M O 3 i n co C N n CL o CN 00 C O IT) C O C M T ” T “ T " T " T ” o o o o o o o d o o o o o o o o n C L to o CN 3 00 CO CN • £ 4 299 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure A . 1 . continued. 300 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure A.I. continued. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.I. Laser-Ablation IC-PMS zircon analyses results of pluton samples from the Sierra Calamajue area. Sample Las Palmas pluton=HA068-04; Calamajue pluton=HA070-04. Analyses were completed at the University of Arizona. sam ple U (ppm ) 206pb/2 04pb U/Th 207Pb/235U ±(% ) 2°6pb/238U ±(% ) e rrc o rr 206Pb/207Pb M% ) 206Pb/238U age ±(M a) 2 07Pb/235U age ±(M a) 206Pb/207Pb age ±(M a) Sampl e HA068-04 (Las Palm as pluton) pxa 448 33862 4 0.74146 1.10 0.09118 0.70 0.638 16.95616 0.85 562.5 3.8 563.3 4.7 566 18 pxb 486 41677 3 0.75654 1.85 0.09186 0.70 0.379 16.74121 1.71 566.5 3.8 572.0 8.1 594 37 HA068-01 275 3013 3 0.10186 19.49 0.01505 1.90 0.097 20.36696 19.40 96.3 1.8 98.5 18.3 153 458 HA068-02 345 6860 2 0.10270 7.28 0.01492 1.05 0.145 20.03560 7.21 95.5 1.0 99.3 6.9 191 168 HA068-03 276 2132 2 0.11032 15.09 0.01488 1.04 0.069 18.60233 15.05 95.2 1.0 106.3 15.2 361 341 HA068-04 329 4220 2 0.10156 19.12 0.01440 2.47 0.129 19.54680 18.96 92.2 2.3 98.2 17.9 248 440 pxc 475 17028 4 0.73076 1.95 0.09131 0.71 0.362 17.22865 1.81 563.3 3.8 557.0 8.3 531 40 HA068-05 416 444 3 0.16358 35.31 0.01551 4.47 0.127 13.06925 35.02 99.2 4.4 153.8 50.4 1109 722 HA068-06 293 3160 2 0.11506 11.86 0.01548 1.02 0.086 18.54445 11.82 99.0 1.0 110.6 12.4 368 267 HA068-07 243 800 2 0.12174 26.61 0.01470 3.75 0.141 16.65101 26.35 94.1 3.5 116.7 29.3 606 579 HA068-08 246 2422 2 0.10827 16.30 0.01430 1.53 0.094 18.21311 16.23 91.5 1.4 104.4 16.2 408 365 HA068-09 215 1173 2 0.12380 27.60 0.01537 6.71 0.243 17.11733 26.78 98.3 6.5 118.5 30.9 546 595 HA068-10 320 2681 2 0.10002 10.77 0.01464 0.98 0.091 20.18309 10.72 93.7 0.9 96.8 9.9 174 251 pxd 491 97408 4 0.75035 2.04 0.09171 0.70 0.343 16.85181 1.92 565.6 3.8 568.4 8.9 580 42 pxe 512 20661 4 0.73305 1.83 0.09092 0.70 0.384 17.10185 1.69 561.0 3.8 558.3 7.9 548 37 P*f 480 31280 4 0.74537 1.16 0.09172 0.70 0.605 16.96718 0.92 565.7 3.8 565.5 5.0 565 20 U > o Sam ple HA070-04 (C alam ajue pluton) pxa 491 97408 4 0.75035 2.04 0.09171 0.70 0.343 16.85181 1.92 565.6 3.8 568.4 8.9 580 42 pxb 512 20661 4 0.73305 1.83 0.09092 0.70 0.384 17.10185 1.69 561.0 3.8 558.3 7.9 548 37 pxc 480 31280 4 0.74537 1.16 0.09172 0.70 0.605 16.96718 0.92 565.7 3.8 565.5 5.0 565 20 HA070-01 229 5446 1 0.15789 12.06 0.02273 0.94 0.078 19.85152 12.02 144.9 1.3 148.9 16.7 212 279 HA070-02 146 2767 2 0.15509 17.54 0.02297 1.96 0.112 20.42332 17.44 146.4 2.8 146.4 23.9 146 412 HA070-03 123 3591 1 0.16109 15.04 0.02362 1.34 0.089 20.21779 14.98 150.5 2.0 151.7 21.2 170 352 HA070-04 91 2421 2 0.20273 13.78 0.02342 2.09 0.152 15.93007 13.62 149.3 3.1 187.4 23.6 701 291 HA070-05 282 5037 1 0.15677 18.06 0.02270 1.31 0.072 19.96489 18.02 144.7 1.9 147.9 24.9 199 421 pcd 497 29876 4 0.72695 1.80 0.09000 0.70 0.389 17.06947 1.66 555.5 3.7 554.8 7.7 552 36 HA070-06 146 3641 2 0.15041 18.51 0.02252 1.83 0.099 20.64079 18.42 143.5 2.6 142.3 24.6 121 437 HA070-07 107 1928 1 0.17540 26.31 0.02310 3.06 0.116 18.16052 26.13 147.2 4.5 164.1 39.9 415 593 HA070-08 129 2765 1 0.18248 21.41 0.02304 1.42 0.066 17.41248 21.36 146.9 2.1 170.2 33.6 508 475 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.I. continued sam ple U (ppm ) 20r,pb/2°4pb LTI’h 2 07Pb/235U ±(% ) 206Pb/238U ±(% ) errc o rr 2M Pb/207Pb ±(% ) 206Pb/238U age ±(M a) 207pb/235u age ±(M a) 206p b /207pb age ±(M a) Sam ple HA 170-04 (C alam ajue pluton) - continued HA070-09 259 5411 1 0.17135 8.28 0.02211 1.10 0.133 17.78852 8.21 141.0 1.5 160.6 12.3 461 182 pxe 466 14280 3 0.73710 2.20 0.09076 0.71 0.322 16.97714 2.08 560.0 3.8 560.7 9.5 563 45 p x f 474 5310 4 0.74254 4.42 0.09253 0.77 0.174 17.18246 4.35 570.5 4.2 563.9 19.1 537 95 H A070-10 88 2996 2 0.13633 40.20 0.02305 3.27 0.081 23.30971 40.07 146.9 4.7 129.8 49.0 -173 1035 HA070-11 149 1118 1 0.14895 24.99 0.02223 2.25 0.090 20.57682 24.89 141.7 3.2 141.0 32.9 128 594 PXg 445 15584 3 0.75510 2.43 0.09278 0.71 0.291 16.94192 2.32 572.0 3.9 571.2 10.6 568 51 HA070-12 131 841 1 0.10528 39.50 0.02272 2.95 0.075 29.75224 39.39 144.8 4.2 101.6 38.2 -823 1160 HA070-13 144 2113 2 0.16529 17.18 0.02259 1.78 0.104 18.84815 17.09 144.0 2.5 155.3 24.8 331 390 HA070-14 194 2725 1 0.14922 12.70 0.02165 1.24 0.098 20.00537 12.64 138.1 1.7 141.2 16.7 194 295 HA070-15 197 7837 1 0.13641 10.73 0.02157 1.23 0.115 21.80173 10.66 137.6 1.7 129.8 13.1 -9 258 pxh 481 58236 3 0.73756 1.41 0.09073 0.70 0.497 16.96109 1.22 559.9 3.8 561.0 6.1 566 27 HA070-16 88 1541 2 0.15991 29.99 0.02310 2.00 0.067 19.91537 29.92 147.2 2.9 150.6 42.0 205 708 HA070-17 99 2484 1 0.16759 31.89 0.02256 2.59 0.081 18.56154 31.79 143.8 3.7 157.3 46.5 366 733 HA070-18 94 7376 2 0.20465 15.76 0.02286 2.54 0.161 15.40482 15.55 145.7 3.7 189.1 27.2 772 329 pxi 461 70769 4 0.75333 1.86 0.09145 1.34 0.722 16.73783 1.28 564.1 7.2 570.2 8.1 594 28 o to Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.2. Laser-Ablation IC-PMS detrital zircon analyses results. Analyses were completed at the University of Arizona. Sam ple HA-170-02 206Pb/2 38U 207Pb/235U 2 06Pb/207Pb sam ple U (ppm ) 206Pb/204Pb 2 07Pb/235U ± (% ) 206Pb/238U ± (% ) errc o rr 206Pb/207Pb ±(% ) age ±(M a) age ±(M a) age ±(M a) pxa 643 16890 0.75213 1.72 0.09315 0.96 0.559 17.07638 1.42 574.1 5.3 569.5 7.5 551 31 pxb 589 21441 0.75226 1.95 0.09212 0.77 0.396 16.88521 1.79 568.1 4.2 569.5 8.5 575 39 pxc 579 21283 0.73993 1.76 0.09090 1.13 0.641 16.93907 1.35 560.9 6.1 562.4 7.6 568 29 pxd 615 22626 0.73712 1.82 0.09030 0.75 0.411 16.89134 1.66 557.3 4.0 560.7 7.9 575 36 pxe 557 25376 0.73611 1.80 0.09125 1.14 0.634 17.09185 1.39 562.9 6.1 560.1 7.7 549 30 1 254 19632 2.10830 1.54 0.19133 1.17 0.761 12.51270 1.00 1128.6 12.1 1151.5 10.6 1195 20 2 228 17819 2.07377 1.76 0.18974 0.75 0.427 12.61564 1.59 1120.0 7.7 1140.2 12.0 1179 31 3 433 33182 1.82963 2.98 0.16289 2.70 0.906 12.27524 1.26 972.8 24.4 1056.1 19.6 1233 25 4 181 6329 1.58529 2.94 0.15812 0.70 0.239 13.75229 2.85 946.3 6.2 964.4 18.3 1006 58 5 493 43752 2.97584 2.04 0.22307 1.43 0.702 10.33567 1.45 1298.1 16.8 1401.5 15.5 1562 27 pxf 626 36633 0.73990 1.70 0.09111 0.81 0.477 16.97889 1.49 562.1 4.4 562.3 7.3 563 32 6 342 28894 2.03623 1.53 0.18474 0.70 0.457 12.50910 1.36 1092.8 7.0 1127.7 10.4 1196 27 7 112 9770 1.95192 1.93 0.18266 0.90 0.466 12.90261 1.71 1081.5 9.0 1099.1 13.0 1134 34 8 76 12057 2.11778 4.76 0.20105 1.21 0.254 13.08924 4.60 1180.9 13.1 1154.6 32.8 1106 92 9 143 13614 2.04853 2.37 0.19257 1.73 0.731 12.96122 1.61 1135.3 18.0 1131.8 16.1 1125 32 10 185 18648 2.12865 2.60 0.19560 1.42 0.546 12.66939 2.18 1151.6 15.0 1158.1 18.0 1170 43 pxg 555 39515 0.74337 1.77 0.09097 0.70 0.396 16.87368 1.62 561.3 3.8 564.4 7.7 577 35 11 138 7514 1.59749 4.41 0.15337 2.29 0.520 13.23758 3.77 919.8 19.6 969.2 27.5 1083 76 12 326 40976 1.67672 1.51 0.16641 1.03 0.683 13.68431 1.10 992.3 9.5 999.7 9.6 1016 22 13 118 13621 1.55279 4.52 0.16086 1.15 0.255 14.28327 4.37 961.5 10.3 951.6 27.9 929 90 14 252 20282 1.36399 2.73 0.14801 2.03 0.745 14.96210 1.82 889.8 16.9 873.6 16.0 833 38 15 274 30136 1.65457 1.84 0.16410 0.94 0.512 13.67461 1.58 979.5 8.5 991.3 11.6 1017 32 pxh 584 42276 0.74600 1.74 0.09151 1.24 0.715 16.91293 1.21 564.4 6.7 565.9 7.5 572 26 16 581 66796 2.13763 2.45 0.19246 2.23 0.910 12.41425 1.01 1134.7 23.2 1161.1 16.9 1211 20 17 244 22283 2.05512 3.34 0.18890 3.00 0.897 12.67344 1.48 1115.4 30.7 1134.0 22.9 1170 29 18 184 9535 1.39173 4.53 0.14112 1.33 0.294 13.98082 4.33 851.0 10.6 885.4 26.8 972 88 19 521 16907 0.54910 2.89 0.07231 0.70 0.243 18.15849 2.80 450.1 3.0 444.4 10.4 415 63 20 49 828 0.19669 35.87 0.03977 3.84 0.107 27.88066 35.66 251.4 9.5 182.3 59.9 -641 1004 pxi 530 32362 0.73789 1.84 0.09237 0.73 0.396 17.25912 1.69 569.5 4.0 561.2 7.9 527 37 21 276 26290 1.61429 1.98 0.16013 0.97 0.490 13.67668 1.73 957.5 8.6 975.8 12.4 1017 35 22 570 50426 1.76131 1.74 0.16812 1.28 0.735 13.16111 1.18 1001.8 11.9 1031.3 11.3 1095 24 23 76 4068 1.73197 4.50 0.16515 1.82 0.404 13.14757 4.12 985.3 16.6 1020.5 29.0 1097 82 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.2. continued u > o 4 ^ Sam ple HA-170-02 (continued) sam ple U (ppm ) 20 6 p b / 2 0 4 p b 207Pb/235U ±(% ) 206p b /23«u ±(% ) e rrc o rr 206 p b /207p b ±(% ) 206p b /238u age ±(M a) 207Pb/2 35U age ±(M a) 206Pb/207Pb age ±(M a) 24 75 13172 1.69316 4.61 0.16270 0.70 0.152 13.24941 4.56 971.8 6.3 1006.0 29.4 1081 91 25 233 36093 1.85824 2.20 0.17517 1.09 0.496 12.99749 1.91 1040.5 10.5 1066.4 14.5 1120 38 pxj 592 38926 0.73051 1.95 0.09050 1.36 0.696 17.08156 1.40 558.5 7.3 556.8 8.4 550 31 26 350 57330 2.13610 1.13 0.19196 0.84 0.744 12.39037 0.75 1132.0 8.7 1160.6 7.8 1214 15 27 156 13444 1.69739 4.02 0.16639 1.36 0.338 13.51603 3.78 992.2 12.5 1007.5 25.7 1041 76 28 700 20906 1.98591 1.22 0.18080 0.95 0.781 12.55276 0.76 1071.3 9.4 1110.7 8.2 1189 15 29 73 7818 0.81006 5.61 0.09747 0.97 0.173 16.59092 5.53 599.6 5.6 602.5 25.5 613 120 30 86 3202 0.36926 22.05 0.05015 1.58 0.072 18.72560 21.99 315.4 4.9 319.1 60.4 346 503 pxk 630 43921 0.75705 2.02 0.09106 1.38 0.684 16.58516 1.47 561.8 7.4 572.3 8.8 614 32 31 92 10711 1.96246 4.03 0.18693 0.77 0.191 13.13319 3.95 1104.7 7.8 1102.7 27.1 1099 79 32 302 36510 1.57153 1.99 0.15732 0.91 0.457 13.80298 1.77 941.9 8.0 959.0 12.4 999 36 33 153 22060 2.34170 1.90 0.20916 1.24 0.653 12.31553 1.44 1224.4 13.8 1225.0 13.5 1226 28 34 45 7303 1.59122 9.73 0.15938 0.89 0.092 13.81013 9.69 953.3 7.9 966.8 60.7 997 197 35 334 49675 2.21292 1.98 0.19643 1.70 0.861 12.23922 1.01 1156.1 18.0 1185.1 13.8 1238 20 pxl 555 82640 0.75048 2.07 0.09184 0.80 0.386 16.87303 1.91 566.4 4.3 568.5 9.0 577 42 36 53 20743 1.86363 5.32 0.17761 1.41 0.265 13.14029 5.13 1053.9 13.7 1068.3 35.2 1098 103 37 178 16441 1.53121 2.37 0.15700 0.70 0.295 14.13707 2.27 940.1 6.1 943.0 14.6 950 46 38 374 43668 2.03423 5.13 0.18384 5.03 0.981 12.46040 0.99 1087.9 50.4 1127.0 34.9 1203 20 39 275 45361 2.07396 1.50 0.18948 1.25 0.831 12.59689 0.84 1118.6 12.8 1140.2 10.3 1182 17 40 198 38616 3.20959 2.77 0.24681 2.66 0.959 10.60273 0.78 1422.0 33.9 1459.5 21.5 1514 15 pxm 575 43914 0.76538 2.01 0.09362 0.79 0.394 16.86598 1.84 576.9 4.4 577.1 8.8 578 40 41 399 39518 2.14649 3.23 0.19422 3.15 0.976 12.47593 0.70 1144.2 33.0 1163.9 22.4 1201 14 42 85 13737 1.70747 4.55 0.16800 2.32 0.509 13.56603 3.92 1001.1 21.5 1011.3 29.2 1034 79 43 373 52800 1.78102 2.08 0.17183 1.69 0.812 13.30236 1.21 1022.2 16.0 1038.6 13.5 1073 24 44 74 7596 1.59145 5.81 0.16639 1.69 0.291 14.41589 5.56 992.2 15.5 966.9 36.2 910 115 pxn 614 36539 0.72859 2.46 0.09056 1.59 0.647 17.13852 1.87 558.9 8.5 555.7 10.5 543 41 45 77 9546 1.68142 6.22 0.16580 0.70 0.113 13.59560 6.18 988.9 6.4 1001.5 39.6 1029 125 46 668 17005 2.11324 3.62 0.18697 1.61 0.445 12.19902 3.24 1104.9 16.4 1153.1 24.9 1245 63 47 207 26185 2.27862 3.56 0.20333 3.15 0.885 12.30349 1.66 1193.2 34.3 1205.7 25.1 1228 32 48 82 8512 1.54704 4.81 0.16102 1.58 0.329 14.35104 4.54 962.4 14.1 949.3 29.7 919 93 49 69 3771 2.02592 6.44 0.16647 2.40 0.373 11.32946 5.97 992.6 22.1 1124.2 43.8 1388 115 pxo 519 19994 0.75180 1.97 0.09240 1.02 0.520 16.94574 1.68 569.7 5.6 569.3 8.6 568 37 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.2. continued Sam ple HA-170-02 (continued) sam ple U (ppm ) 206p b /204pb M7Pb/235U ±(% ) 2 06Pb/2 38U ±(% ) e rrc o rr 206Pb/207Pb ±(% ) 2 n6Pb/238U age ±(M a) 207Pb/2 35U age ±(M a) 2 “ pb/207Pb age ±(M a) 50 368 24520 1.63366 5.55 0.15846 4.15 0.748 13.37360 3.69 948.2 36.6 983.3 35.0 1062 74 51 94 2773 0.34474 9.68 0.04636 2.32 0.239 18.54159 9.40 292.1 6.6 300.8 25.2 368 212 52 128 10738 1.91707 3.72 0.17903 0.70 0.188 12.87659 3.65 1061.7 6.9 1087.0 24.8 1138 73 53 46 5167 1.44239 9.05 0.15125 1.24 0.137 14.45812 8.96 908.0 10.5 906.7 54.3 904 185 54 145 21955 1.76244 3.00 0.16883 0.70 0.233 13.20795 2.92 1005.7 6.5 1031.7 19.5 1087 59 pxp 434 32518 0.72639 1.60 0.09031 0.70 0.437 17.14160 1.44 557.4 3.7 554.4 6.9 542 32 55 121 38231 16.64494 2.12 0.52907 1.85 0.874 4.38259 1.03 2737.5 41.3 2914.6 20.3 3039 17 56 107 15048 2.26043 3.78 0.20000 1.32 0.349 12.19942 3.55 1175.3 14.2 1200.0 26.6 1245 69 57 226 9225 0.27233 10.63 0.03905 2.10 0.198 19.77189 10.42 247.0 5.1 244.6 23.1 222 242 58 461 18430 1.49772 3.96 0.14567 3.68 0.929 13.41003 1.46 876.6 30.2 929.5 24.1 1057 29 59 258 52453 1.46719 2.44 0.15229 1.11 0.454 14.31145 2.18 913.8 9.5 917.0 14.8 925 45 pxq 564 45908 0.75459 1.41 0.09274 0.80 0.567 16.94600 1.16 571.7 4.4 570.9 6.2 567 25 60 150 22910 1.71179 1.86 0.16692 0.93 0.501 13.44533 1.61 995.1 8.6 1013.0 11.9 1052 32 61 1230 4414 0.96383 6.92 0.09432 6.85 0.990 13.49246 0.95 581.0 38.1 685.3 34.5 1045 19 62 103 15166 2.10245 3.15 0.19379 1.21 0.384 12.70908 2.91 1141.9 12.7 1149.6 21.7 1164 58 63 49 1318 0.26046 38.10 0.04234 2.45 0.064 22.41495 38.02 267.3 6.4 235.0 80.1 -77 960 64 302 30706 1.84270 1.56 0.18021 0.95 0.608 13.48452 1.24 1068.1 9.4 1060.8 10.3 1046 25 pxr 591 41911 0.74841 2.64 0.09210 0.83 0.314 16.96750 2.51 567.9 4.5 567.3. 11.5 565 55 65 65 11351 2.07088 6.82 0.18813 2.24 0.328 12.52570 6.45 1111.2 22.9 1139.2 46.8 1193 127 66 101 24949 2.16269 3.57 0.19840 1.00 0.280 12.64894 3.43 1166.7 10.7 1169.1 24.8 1174 68 67 158 64708 1.75656 3.18 0.16969 1.50 0.472 13.31989 2.80 1010.4 14.0 1029.6 20.6 1071 56 68 181 27322 1.54577 2.97 0.15741 2.10 0.706 14.04038 2.11 942.3 18.4 948.8 18.3 964 43 69 46 1144 1.38235 16.92 0.15872 1.90 0.112 15.83139 16.81 949.7 16.7 881.4 100.0 714 360 pxs 571 46736 0.74004 1.95 0.09081 1.02 0.524 16.91925 1.66 560.3 5.5 562.4 8.4 571 36 70 635 37063 1.81281 1.22 0.17556 1.00 0.817 13.35316 0.70 1042.7 9.6 1050.1 8.0 1065 14 71 168 24368 1.75404 3.02 0.17718 1.74 0.575 13.92769 2.47 1051.6 16.9 1028.7 19.6 980 50 72 89 16122 1.69090 4.59 0.16619 4.00 0.871 13.55152 2.26 991.1 36.7 1005.1 29.3 1036 46 73 295 30707 2.30866 3.09 0.20355 2.81 0.911 12.15638 1.27 1194.3 30.6 1214.9 21.9 1252 25 74 1312 147122 2.00866 1.94 0.18831 1.72 0.886 12.92617 0.90 1112.2 17.6 1118.4 13.2 1131 18 pxt 607 44341 0.73876 1.70 0.09125 1.23 0.723 17.03083 1.18 562.9 6.6 561.7 7.3 557 26 75 77 17817 1.71444 3.50 0.17693 1.59 0.454 14.22939 3.12 1050.2 15.4 1013.9 22.5 936 64 76 63 8634 1.93799 4.89 0.18901 1.58 0.323 13.44749 4.63 1116.0 16.2 1094.3 32.8 1051 93 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.2. continued Sam ple HA-170-02 (continued) sam ple U (ppm ) 2°6p b /204pb 207Pb/235U ±(% ) 206Pb/238U ±(% ) e rrc o rr 206Pb/2 07Pb ±(% ) 2 0 < ’ Pb/238U age ±(M a) 207Pb/235U age ±(M a) 206Pb/2 l)7 Pb age ±(M a) 77 270 46407 1.57315 3.48 0.15838 3.02 0.867 13.88112 1.74 947.8 26.6 959.7 21.6 987 35 78 329 13696 1.65675 2.89 0.16446 2.67 0.923 13.68697 1.11 981.5 24.3 992.1 18.3 1016 23 79 48 8610 2.01442 7.74 0.18800 1.05 0.136 12.86816 7.67 1110.5 10.7 1120.4 52.6 1139 153 pxu 657 40695 0.75620 1.47 0.09308 0.70 0.477 16.97093 1.29 573.7 3.8 571.8 6.4 564 28 80 103 3693 0.41057 14.10 0.04905 1.71 0.122 16.47167 13.99 308.7 5.2 349.3 41.7 629 303 81 108 7266 0.32072 11.82 0.04101 2.00 0.170 17.63019 11.64 259.1 5.1 282.5 29.1 481 258 82 108 6929 1.20133 6.39 0.13503 5.33 0.835 15.49801 3.52 816.5 40.9 801.2 35.4 759 74 83 195 12637 1.70898 2.41 0.17256 1.20 0.498 13.92220 2.09 1026.2 11.4 1011.9 15.4 981 43 84 47 6699 1.70440 5.04 0.16552 1.46 0.290 13.39025 4.83 987.4 13.4 1010.2 32.3 1060 97 pxv 572 58621 0.72017 2.43 0.08914 1.27 0.524 17.06646 2.07 550.5 6.7 550.8 10.3 552 45 85 55 4916 1.48576 8.55 0.16122 2.97 0.348 14.96153 8.02 963.6 26.6 924.6 51.9 833 167 86 46 2232 0.82157 9.75 0.08535 4.26 0.437 14.32440 8.77 528.0 21.6 608.9 44.7 923 181 87 119 10920 2.01436 3.19 0.18333 1.89 0.592 12.54842 2.57 1085.1 18.9 1120.4 21.7 1189 51 88 96 8123 1.56222 5.29 0.16037 1.58 0.299 14.15420 5.05 958.8 14.1 955.3 32.8 947 103 89 114 9900 1.36986 4.53 0.14587 0.70 0.155 14.68178 4.48 877.7 5.8 876.1 26.6 872 93 pxw 569 53060 0.75164 1.49 0.09200 0.91 0.612 16.87623 1.18 567.3 4.9 569.2 6.5 576 26 90 256 41502 1.59695 3.02 0.16227 2.13 0.706 14.00999 2.13 969.4 19.2 969.0 18.8 968 44 91 120 23766 2.10923 2.89 0.19576 0.77 0.267 12.79658 2.79 1152.5 8.1 1151.8 19.9 1151 55 92 1804 54702 1.56542 1.11 0.15208 0.86 0.775 13.39479 0.70 912.6 7.3 956.6 6.9 1059 14 93 91 12877 1.75781 3.07 0.17306 1.17 0.382 13.57430 2.83 1028.9 11.1 1030.0 19.8 1032 57 94 45 4882 0.93404 11.53 0.10452 1.21 0.105 15.42886 11.46 640.8 7.4 669.8 56.6 768 242 pxx 572 61931 0.76240 1.66 0.09299 1.01 0.608 16.81684 1.32 573.2 5.5 575.4 7.3 584 29 95 75 20347 1.58794 5.25 0.16120 1.11 0.211 13.99703 5.13 963.4 9.9 965.5 32.7 970 105 96 132 2657 0.33900 10.12 0.04505 1.55 0.153 18.32157 10.00 284.0 4.3 296.4 26.0 395 225 97 258 7864 0.34081 7.24 0.04618 1.76 0.243 18.68470 7.02 291.1 5.0 297.8 18.7 351 159 98 181 13738 2.05546 2.97 0.18933 0.95 0.320 12.70021 2.82 1117.7 9.8 1134.1 20.3 1166 56 99 117 523 0.42514 28.10 0.04773 6.23 0.222 15.48077 27.40 300.6 18.3 359.7 85.3 761 588 pxy 573 130969 0.74162 2.01 0.09184 1.07 0.532 17.07541 1.70 566.4 5.8 563.3 8.7 551 37 u > o C \ Table A.2. continued © O n V© o < EC “ a £ Uj ±(Ma) m o- 1 1 Tf ON CO CO o- o CO OO 04 04 1 2 0 | 1 2 2 5 1 1 3 1 9 | 1 4 3 0 1 O ^t cn | 8 3 9 | | 2 2 7 | © O' ■ ^ t in 04 © © "t ^t m VO ■ *t 04 cn Tf 1 3 9 3 | | 9ZZ | in o o 1 Oi | in 04 04 cn 04 in cn in vo o ■ ^ ^ Ml o a 5. oo cs 04 On 04 o ON 04 o o CO o- vo m o> ON VO VO VO o On in O n in cn o "t O' in ■t O' in o VO 04 ■ * t in in 04 04 Tf O' VO vo O' in On cn O' O' cn oo vo O' in in m cn cn O n O cn o 04 O n 't in © ON © o> cn 04 cn rr VO 04 © vo cn •n O' m •t m 'o ' s ¥ q VO VO oo o O n © Tf CO 00 CO o- o 04 q oi 04 in 04 T j- oi in d q cd cn On in q o^ O' 04 vo (N cn vd q vd 04 04 04 q q o O n q in © in o d cn cn d q ■d 04 q oi q d cn o © oo q •t 00 in cn 04 in tj- ‘ in 00 co 04 04 On co q oi VO in <N 00 CO q 00 T j - in o o^ Tt q in O' 0 01 04 04 d vo in 00 m n- d O' q On On q cn vo O O VO q ■ 't 04 q -t m cn © 04 Tt On VO cn oi oo in q O n VO in q o^ © in vd in in d © q 00 in in q d oo © © © VO q in © vo 04 © oi ON 04 cn vd vo in O' d in s ¥ q cd q q oi q oi o^ vq cd o co q q 04 *t 00 q ON vo vd q q cn vd 00 © q ■ ^ t q -t in vd q On q vd q q cd q cd © vd © © q © in q cd 04 oo q in L « ^ Sp ?" ¥ ■ q r o- s © 6m im u o V u u 4> £ ¥ X M A & n © o ¥ s i n n £ £ 0* o A f t . > © ? 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Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.2. continued Sam ple HA-069-04 (continued) sam ple U (ppm ) 206pb/204pb 207Pb/235U ±(% ) 206Pb/238U ±(% ) errc o rr 2 (l6 Pb/207Pb ±(% ) 206Pb/238U age ±(M a) 207Pb/235(j age ±(M a) 206Pb/207Pb age ±(M a) 28 937 5407 0.12177 5.10 0.01757 1.14 0.224 19.89190 4.97 112.3 1.3 116.7 5.6 208 115 29 312 4675 0.12973 18.51 0.01934 2.47 0.134 20.55135 18.34 123.5 3.0 123.9 21.6 131 434 30 187 2028 0.15700 19.72 0.02262 1.49 0.076 19.86816 19.66 144.2 2.1 148.1 27.2 210 460 31 881 10874 0.12948 7.09 0.01919 1.30 0.183 20.43506 6.97 122.5 1.6 123.6 8.3 145 164 32 199 1243 0.14107 23.52 0.01963 1.64 0.070 19.19081 23.46 125.3 2.0 134.0 29.5 290 543 33 578 3439 0.13097 8.23 0.01991 1.19 0.145 20.96352 8.14 127.1 1.5 125.0 9.7 84 193 34 51 14497 4.66526 3.57 0.33746 1.98 0.554 9.97342 2.97 1874.4 32.2 1761.0 29.9 1629 55 35 135 4797 1.96789 3.16 0.18804 1.46 0.462 13.17491 2.80 1110.7 14.9 1104.6 21.3 1092 56 36 188 29226 4.24166 4.94 0.29486 4.76 0.964 9.58489 1.32 1665.8 69.9 1682.1 40.6 1703 24 pxf 554 61670 0.75418 1.72 0.09365 0.88 0.511 17.12165 1.48 577.1 4.9 570.6 7.5 545 32 37 291 4852 0.19680 9.28 0.02520 0.98 0.105 17.65748 9.23 160.5 1.6 182.4 15.5 477 204 38 242 4810 0.19666 16.06 0.02864 1.32 0.082 20.07928 16.01 182.0 2.4 182.3 26.8 186 375 39 95 1871 0.17411 18.82 0.01893 2.69 0.143 14.99400 18.63 120.9 3.2 163.0 28.3 828 392 PXg 549 63731 0.73620 2.26 0.09054 2.03 0.900 16.95776 0.99 558.8 10.9 560.2 9.7 566 21 40 69 17250 5.39763 2.10 0.34543 1.02 0.486 8.82376 1.83 1912.7 16.9 1884.5 18.0 1853 33 41 392 3606 0.14011 7.80 0.02110 1.74 0.224 20.76733 7.61 134.6 2.3 133.1 9.7 107 180 42 462 1474 0.11942 12.36 0.01728 1.17 0.094 19.95167 12.30 110.4 1.3 114.5 13.4 201 287 43 198 27033 2.48330 1.20 0.21961 0.82 0.682 12.19364 0.88 1279.8 9.5 1267.2 8.7 1246 17 pxh 525 49894 0.75230 2.64 0.09165 1.44 0.545 16.79727 2.21 565.3 7.8 569.6 11.5 587 48 44 235 4757 0.13349 28.27 0.01790 1.54 0.055 18.49234 28.22 114.4 1.8 127.2 33.8 374 647 45 141 4565 0.68336 6.69 0.08400 0.94 0.140 16.94760 6.62 519.9 4.7 528.8 27.6 567 144 46 130 359 0.14299 40.20 0.02230 4.72 0.117 21.50590 39.92 142.2 6.6 135.7 51.1 24 993 47 184 5480 0.15713 18.58 0.02157 1.25 0.067 18.92357 18.54 137.5 1.7 148.2 25.6 322 424 48 1584 5571 0.11140 5.50 0.01640 3.87 0.704 20.30344 3.91 104.9 4.0 107.2 5.6 160 91 pxi 577 72774 0.74697 1.87 0.09207 1.05 0.562 16.99457 1.55 567.8 5.7 566.5 8.1 561 34 49 497 1705 0.12176 11.61 0.01814 1.05 0.090 20.53745 11.57 115.9 1.2 116.7 12.8 133 273 50 447 13222 0.15082 14.18 0.02472 0.70 0.050 22.59796 14.17 157.4 1.1 142.6 18.9 -97 349 51 344 6809 0.14728 10.70 0.02067 1.50 0.140 19.35356 10.59 131.9 2.0 139.5 13.9 271 243 52 379 9925 7.54671 1.34 0.28682 1.11 0.827 5.24017 0.75 1625.6 16.0 2178.6 12.0 2749 12 53 61 1052 4.52634 9.57 0.31603 1.68 0.176 9.62689 9.42 1770.3 26.0 1735.8 79.7 1694 174 pxj 557 39576 0.73816 2.65 0.09094 1.83 0.690 16.98695 1.92 561.1 9.8 561.3 11.4 562 42 54 528 9952 0.16078 7.12 0.02419 1.13 0.159 20.74565 7.03 154.1 1.7 151.4 10.0 109 166 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.2. continued o Sam ple HA-069-04 (continued) sam ple U (ppm ) 206pb/204pb 207Pb/235U ±(% ) 2 0 6 p b / 238u ±(% ) e rrc o rr 2 0 S Pb/207Pb ±(% ) 206Pb/238U age ±(M a) 2 07Pb/23 S U age ±(M a) 206Pb/207Pb age ±(M a) 55 458 10980 0.15215 7.48 0.02287 1.46 0.195 20.72292 7.33 145.8 2.1 143.8 10.0 112 173 56 455 4859 0.18815 9.46 0.02492 1.50 0.159 18.25851 9.34 158.6 2.4 175.0 15.2 403 210 57 461 95335 6.37409 2.09 0.37416 1.97 0.942 8.09350 0.70 2048.9 34.6 2028.7 18.4 2008 12 58 50 6473 1.76988 11.85 0.18775 1.09 0.092 14.62621 11.80 1109.2 11.1 1034.5 77.0 880 245 pxk 554 27559 0.73131 2.83 0.09078 1.59 0.563 17.11552 2.34 560.1 8.5 557.3 12.1 546 51 59 180 3217 0.09218 50.50 0.02142 2.56 0.051 32.04222 50.43 136.6 3.5 89.5 43.3 -1039 1592 60 220 5903 0.17126 19.24 0.02290 1.80 0.094 18.43807 19.15 146.0 2.6 160.5 28.6 381 434 61 300 3066 0.14205 20.88 0.02140 2.92 0.140 20.77377 20.68 136.5 3.9 134.9 26.4 106 493 62 227 67741 4.64239 1.55 0.31742 0.85 0.550 9.42755 1.29 1777.1 13.2 1756.9 12.9 1733 24 pxl 393 235195 0.74520 3.18 0.09145 1.00 0.314 16.92056 3.02 564.1 5.4 565.4 13.8 571 66 63 245 2252 0.12978 17.28 0.01826 1.52 0.088 19.39992 17.21 116.6 1.8 123.9 20.2 265 398 64 48 11353 3.09772 3.87 0.25714 1.11 0.287 11.44529 3.71 1475.2 14.7 1432.1 29.7 1369 71 65 84 18705 2.67249 3.24 0.22727 1.00 0.308 11.72560 3.09 1320.2 11.9 1320.9 24.0 1322 60 66 170 1967 0.13225 26.01 0.02299 0.98 0.038 23.97212 25.99 146.5 1.4 126.1 30.9 -244 666 67 343 2380 0.14179 11.86 0.02085 1.15 0.097 20.27797 11.80 133.0 1.5 134.6 15.0 163 277 pxm 566 124873 0.74540 1.84 0.09145 0.70 0.380 16.91600 1.70 564.1 3.8 565.5 8.0 571 37 68 214 1567 0.16578 12.60 0.01916 2.21 0.175 15.93173 12.40 122.3 2.7 155.8 18.2 700 265 69 162 10865 2.71192 1.91 0.22018 1.30 0.680 11.19433 1.40 1282.8 15.1 1331.7 14.2 1411 27 70 139 507 0.20870 21.44 0.02230 2.96 0.138 14.73108 21.23 142.2 4.2 192.5 37.6 865 445 71 503 44569 2.33004 5.95 0.17094 5.91 0.993 10.11533 0.70 1017.3 55.6 1221.5 42.3 1603 13 72 162 39315 3.42622 1.06 0.26817 0.76 0.718 10.79172 0.74 1531.5 10.4 1510.4 8.3 1481 14 73 719 49534 4.56454 4.35 0.29828 4.29 0.987 9.01002 0.70 1682.8 63.5 1742.8 36.2 1816 13 74 1142 15924 1.82687 3.38 0.17081 3.31 0.978 12.89157 0.71 1016.6 31.1 1055.2 22.2 1136 14 75 2097 17277 0.13251 2.60 0.01973 0.70 0.269 20.53365 2.51 126.0 0.9 126.3 3.1 133 59 76 392 3687 0.13331 12.25 0.01972 2.35 0.192 20.39475 12.02 125.9 2.9 127.1 14.6 149 283 77 206 59902 11.91659 2.30 0.49405 2.19 0.952 5.71636 0.70 2588.2 46.7 2597.9 21.5 2605 12 pxn 594 20836 0.75003 1.84 0.09262 0.70 0.383 17.02582 1.70 571.0 3.8 568.2 8.0 557 37 78 68 21503 4.53319 1.96 0.31154 1.32 0.674 9.47565 1.45 1748.3 20.2 1737.1 16.3 1724 27 79 344 5063 0.14251 23.30 0.01917 2.31 0.099 18.54243 23.18 122.4 2.8 135.3 29.5 368 529 80 365 6894 0.13972 13.91 0.02033 2.31 0.166 20.06657 13.72 129.8 3.0 132.8 17.3 187 321 81 107 20439 1.90474 4.12 0.18992 1.70 0.413 13.74820 3.75 1121.0 17.5 1082.7 27.4 1007 76 82 110 14470 1.96886 2.81 0.19241 2.15 0.765 13.47432 1.81 1134.4 22.4 1104.9 18.9 1047 36 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.2. continued Sam ple HA-069-04 (continued) 2 06Pb/2 38U 207Pb/235U 206Pb/207Pb sam ple U (ppm ) 206pb/2°4pb 2(,7Pb/235U ±(% ) 2 06Pb/2 38U ±(% ) e rrc o rr 206Pb/207Pb ±(% ) age ±(M a) age ±(M a) age ±(M a) pxo 577 59513 0.72906 1.90 0.09087 1.28 0.673 17.18618 1.41 560.7 6.9 556.0 8.1 537 31 83 226 1866 0.19091 14.82 0.02135 1.49 0.101 15.41893 14.74 136.2 2.0 177.4 24.1 770 312 84 472 10400 0.32824 5.41 0.04502 1.26 0.233 18.91231 5.26 283.9 3.5 288.2 13.6 323 120 85 328 61429 5.21131 3.34 0.34238 3.27 0.978 9.05860 0.70 1898.1 53.8 1854.5 28.5 1806 13 86 34 13411 8.37548 3.80 0.35395 0.85 0.224 5.82688 3.70 1953.4 14.3 2272.5 34.5 2573 62 87 430 2705 0.13137 8.11 0.02080 1.32 0.163 21.82738 8.00 132.7 1.7 125.3 9.6 -12 193 pxp 556 59878 0.75478 1.91 0.09127 1.19 0.623 16.67275 1.50 563.0 6.4 571.0 8.3 603 32 88 373 9478 0.13811 12.17 0.01990 2.51 0.206 19.86239 11.91 127.0 3.2 131.4 15.0 211 277 89 339 5746 0.22093 8.17 0.03214 0.93 0.114 20.05779 8.12 203.9 1.9 202.7 15.0 188 189 90 63 8427 3.31646 3.25 0.25635 1.44 0.444 10.65770 2.91 1471.2 18.9 1484.9 25.3 1505 55 91 180 849 0.17339 16.58 0.02155 2.18 0.132 17.13820 16.43 137.5 3.0 162.4 24.9 543 361 92 629 4923 0.15137 6.81 0.02234 1.01 0.148 20.34610 6.73 142.4 1.4 143.1 9.1 155 158 pxq 585 67387 0.76361 1.92 0.09387 0.70 0.365 16.94909 1.79 578.4 3.9 576.1 8.4 567 39 pxr 643 78926 0.78386 1.61 0.09483 0.70 0.434 16.68031 1.45 584.0 3.9 587.7 7.2 602 31 pxs 540 74244 0.73730 1.61 0.09119 1.33 0.826 17.05234 0.91 562.5 7.2 560.8 6.9 554 20 Sam ple HA-260-02 206Pb/238U 2 < l7 Pb/235U 206Pb/207Pb sam ple U (ppm ) 206Pb/204Pb 2 07Pb/235U ± (% ) 2 06Pb/2 38U ± (% ) e rrc o rr 206Pb/207Pb ±(% ) age ±(M a) age ±(M a) age ±(M a) pxa 608 11773 0.73607 1.63 0.09195 0.72 0.442 17.22367 1.46 567.1 3.9 560.1 7.0 532 32 pxb 579 15026 0.73865 2.07 0.09065 1.84 0.890 16.92041 0.94 559.4 9.9 561.6 8.9 571 21 pxc 531 15063 0.71668 1.58 0.08884 0.80 0.505 17.09269 1.37 548.7 4.2 548.7 6.7 549 30 pxd 592 19433 0.73572 1.79 0.08993 0.70 0.391 16.85373 1.65 555.1 3.7 559.9 7.7 579 36 pxe 557 19587 0.74222 1.75 0.09178 0.73 0.418 17.04980 1.59 566.1 4.0 563.7 7.6 554 35 1 47 3905 1.90010 9.69 0.17859 0.71 0.073 12.95906 9.66 1059.3 6.9 1081.1 64.5 1125 193 2 292 34593 5.74864 1.03 0.34475 0.70 0.677 8.26864 0.76 1909.5 11.6 1938.7 8.9 1970 14 3 328 34367 4.35035 2.62 0.28497 2.52 0.960 9.03189 0.73 1616.4 36.0 1703.0 21.7 1811 13 pxf 584 26494 0.74843 1.15 0.09155 0.70 0.611 16.86647 0.91 564.7 3.8 567.3 5.0 578 20 4 129 31242 17.01768 0.99 0.57324 0.70 0.707 4.64450 0.70 2921.1 16.4 2935.8 9.5 2946 11 5 96 11238 5.19195 2.64 0.33279 0.70 0.265 8.83774 2.55 1851.9 11.3 1851.3 22.5 1851 46 6 170 31951 12.24450 0.99 0.49472 0.70 0.706 5.57088 0.70 2591.1 14.9 2623.3 9.3 2648 12 Table A.2. continued S ¥ <N cn 1 20 | © b cn cn m cn 1 20 | © b © cn cn b~ cn CN cn cn 'b CN b- CN © © 00 cn On cn ON cn 00 CN 1 09 | cn CN On CN 1 3 0 1 00 cn oo in 1 oe | b- CN © © b cn © [C- © 9 9 9 O X 9 b in oo cn b 00 © «n cn CN 00 On O n On O n © O O b cn On cn © CN 00 in in CN CN O n 00 b- cn b- © CN b - O n b- b- b- in in b 00 cn 00 On CN b- 00 cn © oo b- © O n b b ~~ in © cn 00 CN cn 00 © b— oo On © © b in b- © On in © b- O n b 00 b On in CN © CN in CN ON On b- On © in 'e? 5 ¥ oo © b cn On © CN m O n 00 oo b b CN ON b in CN 00 00 oo in © n © r -; © b- cn cn CN © CN © On b © © cn 00 oo b © On CN © oo CN CN © in b 00 00 00 CN n © b © b 00 b cn © O n P N © a. i - © 9 M 9 vo b b oo SO cn so 00 © in b in CN b © CN O n b in in oo cn b CN b b b © © CN in cn © in ON b CN On cn CN © 00 b ~ ; in b- © CN oo in cn 00 00 b^ © in CN cn © 00 *n b CN © cn On © 00 © in b b- b © © ON in b © in b On cn 00 © in © 00 cn CN b b^ b © CN © © b 00 b- CN 00 b- in O n O n b O n in © CN b- «n CN «n © CN in mi On b CN On b oo O n On in in /9 ‘ s 4f b b CN b cn © © cn CN cn in cn n CN oo in b b b CN in cn © CN CN -b in in © CN CN b^ b^ © b b^ On © 00 cn © cn in b^ b b b- © oo cn CN CN © © On b^ b; cn CN © © Q C A 0. 9 e 9 O X 9 On 00 cn 00 sq 00 00 cn b in in © cn CN © CN 00 b 00 b cn b 00 ON O n in in b 00 On © CN b b © in in cn cn O n © CN OO in 00 b» © CN rb © b~ OO ■b in © in © On b~ OO CN b b © b © © 00 CN © © b~ © b in O n CN CN © in © 00 b 00 b b On 00 On CN cn © in b cn © © 00 © cn b- in © cn O n ON b in © CN © cn b- CN oo b in b CN CN b cn 00 00 b in in 5 s ¥ so b CN © cn © b © cn b © in On © CN © CN © so © CN © CN cn 00 O n b^ © in © On b cn CN CN On © © ON b^ b in CN cn cn O n CN b © © b~ b^ b CN cn cn © b CN © b CN b © cn On © s .5 e 9 9 e © c- r - 9 3 e- 9 ® in o 00 00 b b CN b 00 oo m © © b b CN b b On 00 cn b b cn 00 © in © in b 00 © in in CN b oo © CN O n 00 On b cn © b © b b b b O n b oo b- rb 'b 00 On in CN © 00 b^ cn cn cn © On © On O n © OO © © O n CN © 00 oo OO © On cn © b cn b ~ ; 00 00 cn b b^ b n CN 00 CN 00 00 cn oo o oo © b~ © b O n OO CN b- CN O n 00 b b- cn b^ oo 00 © cn b^ cn © s CN cn On cn in b CN b ~; © ON CN O n © CN 00 On CN © © On cn cn © in in © in cn O n O n in CN On © On © b © cn On © © N i < X 9 a L . f c - 9 9 L . b . 9 © b b © b L T t © © cn © cn © ON © b b b © in ON cn © un cn © © On cn © CN b © in On •n © © cn Tb © 00 Tb Tb © Tb © © © © © © CN b © © b cn © in cn b © ON © 00 00 © b © cn © in © b © © © CN © cn CN O n © in b b © On 00 cn © oo s o cn © © CN CN © cn b ' in © © cn © 00 b- © On OO © 00 OO in © S 9 CO g tT 00 00 © 00 b © © b © in CN CN 00 © b 00 © © On © 00 00 © in b © © 00 © © On © CN O n © in r - © On O n © © CN oo b^ cn © © © © © b- © 00 © © b- © © cn © b- © © b- © © b- © cn b- © b cn CN cn in in © b © cn CN 9 0 P I ra X ! C u 9 f H © cn cn © in ON 00 cn cn © 00 b ON 00 © © © cn © 00 CN © cn © CN cn cn © Os © cn cn © © b cn i> CN © in b b 00 cn © © in On © © b b O n b cn © cn 'b © CN cn © b- 'b © 00 cn © © © cn cn © b- © On © © CN b 00 cn cn © cn oo n b- © 00 b- in cn cn © OO b- in © b- © b in cn © CN O © © On On cn cn © © b cn © oo CN OO 00 CN © b- © b b~ © © cn b CN cn © © © cn O n © © in CN ON b cn © 00 © CN On CN © b cn t CN m © in b © b © b On CN cn © b cn © ON © © ¥ b On b cn cn CN © CN © cn CN CN b © b CN CN 00 in b cn CN CN in © CN cn CN b^ O n b © On CN CN in b~ cn CN b~ CN On CN CN CN On b b^ © b cn © cn cn b~ in © 00 © On cn cn cn On On b b- © 00 O n b cn On © CN s V ) H 3 tD- 9 fS in O , v© m > 00 b © CN in cn b b © b 00 ON cn b ON in CN © in cn O n © CN in b © © 00 b b © © b © © © 00 b b © in CN b- b- © in © © On 'b © n- cn CN b~ © O n cn 00 On © n in CN O n b b- © b b- b © CN in b^ CN b b^ b b CN © cn in in b- CN 00 © CN CN b On 00 in CN in cn b b- © © © CN in cn © r-~ CN mi © b © in b O n OO b- b b^ b b oo O n b~ b b CN b- © b- © in CN cn CN 00 in © b- in b- b b cn cn © bi b © b- b- © © oo 00 ON On b b b in cn b © © B n 9 a- 9 n © On in © CN cn 00 © b in ti c s cn 00 b cn cn 00 cn On b oo On © cn b b b CN in CN © © © © © b b^ cn in b~ ON © © Tb 00 © cn CN b~ in b- b cn 00 in b © b - O n © b *- cn cn in b in © © 00 in 00 © 00 in cn 00 o b in On © O n © b- 00 © CN b 00 00 oo ON CN b b» © © CN O n © CN cn b in cn O n b b* b b 00 On in b in O n © b b © in in ? a 3 O n 00 On in m cn b b © b CN © m © in b b oo in b- On cn in © b- cn CN © © cn b- © in oo © cn b- cn 00 in b- in cn b b * - CN b cn CN in b- © b in 00 cn © © b 00 ON CN in b 00 •n 9 ' a S 9 «5 b 00 O f l X & On © CN cn © X a . 'b in © b~ 'x 00 On © CN CN CN CN ’ >? Q. cn CN b CN in CN © CN b~ CN -X X a 00 CN On CN © cn cn CN cn X a 311 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.2. continued Sam ple HA-260-02 (continued) sam ple U (ppm ) 2°6pb/204pb 207Pb/235U ±(% ) 206p b/238u ±(% ) e rrc o rr 2 06Pb/207Pb ±(% ) 2 0 6 p b / 238u age ±(M a) 207Pb/235U age ±(M a) 206p b / 20 7 p b age ±(M a) 33 149 20094 5.88071 1.17 0.35386 0.70 0.600 8.29668 0.93 1953.0 11.8 1958.4 10.1 1964 17 34 55 14695 5.29188 2.61 0.34301 1.45 0.555 8.93719 2.17 1901.1 23.9 1867.6 22.3 1830 39 35 105 18246 5.89601 1.57 0.36160 0.92 0.585 8.45611 1.28 1989.7 15.8 1960.6 13.7 1930 23 36 107 8056 4.96128 2.15 0.32639 1.24 0.577 9.07083 1.76 1820.9 19.7 1812.7 18.2 1803 32 pxm 581 40120 0.72162 2.99 0.09065 1.98 0.663 17.31999 2.24 559.4 10.6 551.6 12.7 520 49 37 88 21048 5.25407 1.61 0.33580 0.83 0.516 8.81221 1.38 1866.4 13.5 1861.4 13.7 1856 25 38 112 31295 13.20308 1.27 0.52822 1.02 0.801 5.51625 0.76 2734.0 22.7 2694.3 12.0 2665 13 39 155 25830 4.67190 1.63 0.29802 1.47 0.902 8.79536 0.70 1681.5 21.8 1762.2 13.6 1859 13 40 125 24270 5.40409 1.42 0.33984 0.95 0.669 8.67073 1.06 1885.9 15.5 1885.5 12.2 1885 19 41 294 28089 4.69025 2.13 0.29840 2.01 0.943 8.77200 0.71 1683.4 29.8 1765.5 17.8 1864 13 pxn 608 37640 0.74866 1.71 0.09196 0.70 0.410 16.93570 1.56 567.1 3.8 567.4 7.4 569 34 42 116 30757 11.40780 1.09 0.43880 0.83 0.764 5.30350 0.70 2345.3 16.3 2557.1 10.1 2730 12 43 68 13315 6.62270 2.59 0.37614 1.79 0.691 7.83093 1.87 2058.2 31.5 2062.4 22.9 2067 33 44 92 22447 5.54851 2.69 0.33334 1.90 0.708 8.28342 1.90 1854.5 30.6 1908.1 23.1 1967 34 45 44 10126 5.03182 3.70 0.33341 0.92 0.249 9.13585 3.59 1854.9 14.8 1824.7 31.4 1790 65 46 55 11202 5.31342 2.10 0.33678 0.74 0.352 8.73931 1.97 1871.2 12.0 1871.0 18.0 1871 36 pxo 514 49748 0.73257 2.49 0.09132 0.85 0.341 17.18709 2.34 563.3 4.6 558.1 10.7 537 51 47 160 4753 1.82882 4.26 0.17509 1.03 0.242 13.20039 4.13 1040.1 9.9 1055.9 27.9 1089 83 48 152 35908 5.78859 1.15 0.34987 0.91 0.791 8.33352 0.70 1934.0 15.2 1944.7 10.0 1956 13 49 37 6029 5.05943 4.11 0.32907 1.34 0.327 8.96792 3.88 1833.9 21.4 1829.3 34.8 1824 70 50 81 10507 5.19714 2.95 0.33467 2.28 0.772 8.87889 1.87 1861.0 36.9 1852.1 25.1 1842 34 51 113 34751 5.27410 1.59 0.33620 0.70 0.439 8.78927 1.43 1868.4 11.4 1864.7 13.6 1861 26 pxp 590 46870 0.75037 1.60 0.09249 0.70 0.437 16.99434 1.44 570.2 3.8 568.4 7.0 561 31 52 48 14371 5.25423 4.63 0.33897 0.91 0.197 8.89524 4.54 1881.7 14.9 1861.5 39.6 1839 82 53 425 113124 11.46269 1.26 0.47249 1.05 0.832 5.68344 0.70 2494.5 21.7 2561.5 11.8 2615 12 54 75 29328 5.11857 2.66 0.33627 0.70 0.263 9.05817 - 2.57 1868.7 11.4 1839.2 22.6 1806 47 55 110 21740 4.91395 1.77 0.31708 0.71 0.401 8.89700 1.62 1775.5 11.0 1804.7 14.9 1839 29 56 7 2620 8.27989 10.37 0.39511 2.23 0.216 6.57950 10.12 2146.5 40.8 2262.1 94.2 2368 173 p x q 604 48752 0.73500 1.63 0.08977 0.70 0.428 16.83982 1.48 554.2 3.7 559.5 7.0 581 .32 57 126 43714 5.19314 1.09 0.32932 0.78 0.715 8.74349 0.76 1835.1 12.5 1851.5 9.3 1870 14 58 98 31197 5.12305 1.35 0.33048 0.85 0.631 8.89442 1.05 1840.7 13.6 1839.9 11.5 1839 19 59 75 22287 7.54144 6.87 0.38062 5.65 0.822 6.95887 3.91 2079.2 100.4 2177.9 61.7 2272 67 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.2. continued Sam ple HA-260-02 (continued) sam ple U (ppm ) 206Pb/204Pb 2 07Pb/235U ±(% ) 206Pb/23S U ±(% ) errc o rr 206Pb/207Pb ±(% ) 206Pb/238U age ±(M a) 207Pb/235U age ±(M a) 206Pb/207Pb age ±(M a) 60 39 9803 5.12305 3.81 0.33333 0.70 0.184 8.97105 3.75 1854.5 11.3 1839.9 32.4 1823 68 pxr 518 33584 0.75289 1.87 0.09107 0.70 0.373 16.67841 1.74 561.9 3.8 569.9 8.2 602 38 61 55 35463 14.32371 1.42 0.55751 1.18 0.833 5.36659 0.78 2856.3 27.2 2771.4 13.5 2710 13 62 285 58149 5.89712 1.00 0.35863 0.72 0.717 8.38500 0.70 1975.7 12.3 1960.8 8.7 1945 13 63 496 4053 2.79523 4.33 0.18031 4.02 0.929 8.89401 1.60 1068.7 39.6 1354.3 32.4 1839 29 64 80 18313 5.33501 2.24 0.33965 1.25 0.558 8.77797 1.86 1885.0 20.4 1874.5 19.1 1863 34 65 276 4354 1.86369 16.89 0.13297 16.27 0.963 9.83729 4.55 804.8 123.1 1068.3 112.1 1655 84 pxs 593 59815 0.75123 2.29 0.09264 1.08 0.471 17.00343 2.02 571.1 5.9 568.9 10.0 560 44 66 390 82646 12.71411 1.56 0.52005 1.39 0.893 5.63978 0.70 2699.4 30.7 2658.7 14.7 2628 12 67 66 11737 4.59159 3.67 0.30616 2.57 0.701 9.19351 2.62 1721.8 38.8 1747.7 30.6 1779 48 68 50 15844 5.74280 1.28 0.36106 0.77 0.604 8.66885 1.02 1987.2 13.2 1937.8 11.0 1885 18 69 171 43502 5.41974 1.61 0.34476 0.74 0.461 8.77079 1.42 1909.5 12.2 1888.0 13.8 1864 26 70 105 11955 2.36486 3.71 0.20358 2.12 0.572 11.86929 3.04 1194.5 23.1 1232.1 26.5 1298 59 pxt 560 5054 0.70643 4.95 0.09098 0.98 0.198 17.75759 4.86 561.3 5.3 542.6 20.8 465 108 71 58 14447 3.39558 3.38 0.26944 1.16 0.343 10.94084 3.18 1538.0 15.9 1503.4 26.6 1455 60 72 293 11143 4.29563 3.69 0.27275 3.62 0.981 8.75460 0.71 1554.7 50.0 1692.5 30.4 1868 13 73 138 18033 5.42388 1.98 0.34548 1.10 0.555 8.78253 1.65 1913.0 18.2 1888.6 17.0 1862 30 74 418 5412 7.27367 12.70 0.29446 12.64 0.996 5.58184 1.18 1663.8 185.4 2145.6 113.8 2645 20 75 98 33176 12.08504 1.27 0.51312 1.06 0.834 5.85431 0.70 2670.0 23.2 2611.0 11.9 2566 12 pxu 600 50059 0.75032 1.81 0.09192 0.70 0.387 16.89163 1.67 566.9 3.8 568.4 7.9 574 36 76 77 20285 14.45951 1.33 0.55804 1.11 0.837 5.32129 0.73 2858.5 25.6 2780.3 12.6 2724 12 77 174 45249 6.09516 1.93 0.36695 1.80 0.932 8.30080 0.70 2015.0 31.1 1989.6 16.9 1963 13 78 1510 2821 0.95844 7.60 0.06924 6.18 0.813 9.96062 4.43 431.6 25.8 682.5 37.8 1631 82 79 525 97650 4.90289 1.25 0.32261 1.04 0.829 9.07242 0.70 1802.5 16.4 1802.8 10.6 1803 13 80 74 29029 7.20273 2.33 0.40422 0.73 0.313 7.73792 2.21 2188.5 13.5 2136.8 20.8 2088 39 pxv 556 4552 0.69225 5.83 0.09042 0.80 0.137 18.00997 5.77 558.0 4.3 534.1 24.2 433 129 81 103 48501 5.60736 1.52 0.34912 0.70 0.462 8.58449 1.35 1930.4 11.7 1917.2 13.1 1903 24 82 56 14997 5.79586 3.42 0.36258 1.04 0.304 8.62549 3.26 1994.4 17.8 1945.8 29.6 1894 59 83 131 40843 5.79952 1.37 0.35502 0.94 0.687 8.44044 0.99 1958.5 15.9 1946.3 11.8 1933 18 84 250 70284 12.65861 1.66 0.49210 1.51 0.907 5.36000 0.70 2579.7 32.1 2654.6 15.7 2712 12 85 149 101862 8.52170 1.36 0.42463 1.03 0.760 6.87040 0.88 2281.4 19.8 2288.2 12.3 2294 15 pxw 531 49677 0.72697 1.61 0.08934 0.70 0.435 16.94422 1.45 551.6 3.7 554.8 6.9 568 32 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.2. continued Sam ple HA-260-02 (continued) 2 06Pb/238U 207Pb/235U 206pb/2 07p b sam ple U (ppm ) 2°6pb/204pb 207Pb/235U ±(% ) 206Pb/238U ±(% ) e rrc o rr 2°6pb /2°7pb ±(% ) age ±(M a) age ±(M a) age ±(M a) 86 107 19495 4.66306 3.24 0.30072 2.58 0.795 8.89195 1.97 1694.9 38.5 1760.6 27.1 1840 36 87 42 11533 10.62276 3.80 0.47555 2.20 0.578 6.17245 3.10 2507.8 45.7 2490.7 35.3 2477 52 88 73 14608 5.25474 1.79 0.34106 0.99 0.552 8.94907 1.50 1891.8 16.3 1861.5 15.3 1828 27 89 31 9525 5.14009 4.34 0.34173 1.64 0.378 9.16673 4.02 1895.0 26.9 1842.8 36.9 1784 73 pxx 604 43328 0.74706 2.00 0.09227 0.70 0.349 17.03007 1.88 569.0 3.8 566.5 8.7 557 41 90 65 16408 5.36839 2.36 0.34704 1.34 0.569 8.91338 1.94 1920.5 22.3 1879.8 20.2 1835 35 91 29 4179 5.60811 6.73 0.35171 1.99 0.296 8.64712 6.43 1942.8 33.5 1917.3 58.1 1890 116 92 61 4294 5.84884 3.31 0.35487 1.08 0.327 8.36563 3.12 1957.8 18.3 1953.7 28.7 1949 56 93 247 43440 4.82709 3.30 0.26671 2.85 0.863 7.61835 1.67 1524.1 38.7 1789.6 27.8 2115 29 pxy 563 74323 0.74150 1.80 0.09084 1.39 0.773 16.89175 1.14 560.5 7.5 563.3 7.8 574 25 94 193 52977 4.58853 1.27 0.30083 0.70 0.550 9.03972 1.06 1695.4 10.4 1747.2 10.6 1810 19 95 103 49826 13.48376 0.99 0.52304 0.70 0.707 5.34837 0.70 2712.0 15.5 2714.1 9.4 2716 12 96 53 20492 8.52795 2.24 0.42159 1.39 0.619 6.81627 1.76 2267.7 26.6 2288.9 20.4 2308 30 97 163 63854 5.86447 1.37 0.35061 0.97 0.710 8.24331 0.96 1937.5 16.2 1956.0 11.8 1976 17 98 358 70059 4.65850 1.09 0.30707 0.83 0.763 9.08841 0.70 1726.3 12.6 1759.8 9.1 1800 13 pxz 577 46814 0.73290 1.58 0.09107 0.89 0.563 17.13355 1.31 561.9 4.8 558.3 6.8 543 29 pxaa 577 74999 0.75360 1.51 0.09207 1.05 0.694 16.84604 1.09 567.8 5.7 570.3 6.6 580 24 pxab 601 47634 0.74325 1.68 0.09183 1.16 0.690 17.03541 1.22 566.4 6.3 564.3 7.3 556 27 Sam ple HA-094-04 2 0 7 p b / 235u 206Pb/2°7Pb sam ple U (ppm ) 2 06Pb/204Pb 207Pb/235U ±(% ) 206Pb/238U ±(% ) e rrc o rr 206Pb/207Pb ± (% ) age ±(M a) age ±(M a) age ±(M a) pxa 674 37169 0.75002 3.77 0.09119 1.47 0.390 16.76334 3.47 562.6 7.9 568.2 16.4 591 75 pxb 643 18384 0.73935 3.24 0.09073 2.04 0.630 16.92075 2.51 559.9 10.9 562.0 14.0 571 55 pxc 477 15417 0.71453 4.78 0.08820 2.04 0.427 17.01982 4.33 544.9 10.7 547.4 20.2 558 94 pxd 574 26129 0.75026 1.72 0.09277 1.05 0.610 17.04861 1.36 571.9 5.7 568.4 7.5 554 30 pxe 483 25952 0.76302 2.96 0.09413 0.71 0.240 17.00928 2.87 579.9 3.9 575.8 13.0 559 63 1 382 1719 0.11025 32.43 0.01965 2.24 0.069 24.57004 32.35 125.4 2.8 106.2 32.7 -306 846 2 380 2288 0.14116 15.34 0.01966 1.75 0.114 19.20613 15.24 125.5 2.2 134.1 19.3 288 350 3 327 2136 0.12235 15.80 0.01966 1.53 0.097 22.15289 15.72 125.5 1.9 117.2 17.5 -48 384 4 297 2691 0.16253 20.20 0.01829 3.46 0.171 15.51317 19.90 116.8 4.0 152.9 28.7 757 424 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.2. continued Sam ple HA-094-04 (continued) sam ple U (ppm ) 206pb/2Mpb 207pb/23Su ±(% ) 206Pb/238U ±(% ) errc o rr 206Pb/2 < l7 Pb ±(% ) 206Pb/2 38U age ±(M a) 2 07Pb/23 S U age ±(M a) M 6Pb/207Pb age ±(M a) p x f 552 22958 0.73130 4.19 0.09146 1.43 0.341 17.24318 3.94 564.1 7.7 557.3 18.0 530 86 5 467 3283 0.15665 13.33 0.01929 2.19 0.165 16.98145 13.15 123.2 2.7 147.8 18.3 563 288 6 227 730 0.09461 38.51 0.01900 4.11 0.107 27.69190 38.29 121.3 4.9 91.8 33.8 -622 1078 7 430 6326 0.16218 12.19 0.01903 2.90 0.238 16.17659 11.84 121.5 3.5 152.6 17.3 668 254 PXg 613 12737 0.75244 3.16 0.09288 1.66 0.527 17.01882 2.69 572.5 9.1 569.6 13.8 558 59 8 285 3497 0.14562 35.18 0.02058 2.77 0.079 19.48798 35.07 131.3 3.6 138.0 45.4 255 829 9 211 1367 0.12394 29.61 0.01913 3.47 0.117 21.28644 29.40 122.2 4.2 118.6 33.2 48 716 10 338 3425 0.12600 28.81 0.01927 2.09 0.072 21.09029 28.73 123.1 2.5 120.5 32.7 70 696 11 314 2610 0.11535 24.78 0.01920 1.65 0.067 22.95627 24.72 122.6 2.0 110.8 26.0 -135 620 pxh 616 36825 0.76819 3.30 0.09297 2.76 0.836 16.68681 1.81 573.1 15.1 578.7 14.6 601 39 12 375 2081 0.14762 21.89 0.01851 3.36 0.153 17.29141 21.63 118.3 3.9 139.8 28.6 523 480 13 195 1335 0.18427 29.45 0.01982 4.76 0.162 14.82830 29.06 126.5 6.0 171.7 46.6 851 617 14 498 4249 0.13093 16.23 0.01817 1.36 0.084 19.13150 16.17 116.1 1.6 124.9 19.1 297 371 15 431 2532 0.12265 20.45 0.01965 1.45 0.071 22.09051 20.39 125.5 1.8 117.5 22.7 -41 500 pxi 651 57650 0.72816 3.25 0.08920 2.43 0.748 16.89109 2.15 550.8 12.8 555.5 13.9 575 47 16 331 2273 0.12899 22.50 0.01913 4.45 0.198 20.45062 22.06 122.2 5.4 123.2 26.1 143 523 17 509 3451 0.13666 15.78 0.02075 2.20 0.140 20.93137 15.63 132.4 2.9 130.1 19.3 88 372 18 459 3874 0.13612 13.55 0.02008 1.67 0.124 20.34082 13.44 128.2 2.1 129.6 16.5 156 316 19 588 4564 0.13885 14.70 0.01899 1.88 0.128 18.86161 14.58 121.3 2.3 132.0 18.2 330 332 pxj 654 26956 0.74441 3.52 0.09190 2.39 0.678 17.02259 2.59 566.8 13.0 565.0 15.3 558 56 20 349 2866 0.15571 19.44 0.01868 2.53 0.130 16.54283 19.28 119.3 3.0 146.9 26.6 620 420 21 61 213 0.03488 92.69 0.01892 11.25 0.121 74.78468 92.00 120.8 13.5 34.8 31.7 0 1265 22 605 6562 0.13271 13.71 0.02105 1.97 0.144 21.87402 13.57 134.3 2.6 126.5 16.3 -17 329 pxk 644 38252 0.72032 2.67 0.09022 1.12 0.420 17.26917 2.42 556.8 6.0 550.9 11.3 526 53 23 277 983 0.16683 17.78 0.01970 2.75 0.155 16.27916 17.57 125.7 3.4 156.7 25.8 654 380 24 486 2725 0.14417 10.67 0.01957 1.65 0.154 18.71474 10.54 124.9 2.0 136.8 13.7 347 239 25 180 258 0.03753 65.26 0.01645 12.05 0.185 60.44112 64.14 105.2 12.6 37.4 24.0 -3571 2 26 1495 11483 0.14135 4.83 0.02110 2.67 0.553 20.58445 4.03 134.6 3.6 134.2 6.1 128 95 pxl 568 93030 0.77755 2.17 0.09156 1.06 0.489 16.23630 1.89 564.8 5.7 584.1 9.6 660 41 27 377 2493 0.11539 15.48 0.01870 1.73 0.112 22.34195 15.38 119.4 2.0 110.9 16.3 -69 378 28 473 4501 0.15254 21.20 0.01665 3.62 0.171 15.05231 20.88 106.5 3.8 144.2 28.5 820 441 29 321 3396 0.16965 19.09 0.01973 2.80 0.147 16.03310 18.88 125.9 3.5 159.1 28.1 687 406 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.2. continued Sam ple HA-094-04 (continued) sam ple U (ppm ) 206pb/2°4pb 207Pb/2,5U =fc(%) 206pb/238u ±(% ) e rrc o rr 206pb/2°7p b ±(% ) 206pb/238l j age ±(M a) 207Pb/23sU age ±(M a) 206p b /207pb age ±(M a) 30 355 2072 0.16217 34.59 0.01804 13.17 0.381 15.33560 31.98 115.2 15.0 152.6 49.0 781 689 pxm 640 61906 0.74828 3.01 0.09175 1.76 0.584 16.90523 2.45 565.9 9.5 567.2 13.1 573 53 31 345 1904 0.12333 20.39 0.01773 6.62 0.325 19.81596 19.28 113.3 1A 118.1 22.7 216 450 32 325 2357 0.16258 29.99 0.02086 3.81 0.127 17.69140 29.74 133.1 5.0 153.0 42.6 473 672 33 70 205 0.12745 120.54 0.02105 10.77 0.089 22.77356 120.06 134.3 14.3 121.8 139.2 -116 1323 pxn 677 44231 0.74373 2.22 0.09148 0.70 0.315 16.95988 2.11 564.3 3.8 564.6 9.6 566 46 34 317 7386 0.13702 18.95 0.01925 1.83 0.097 19.37321 18.86 122.9 2.2 130.4 23.2 268 436 35 511 4286 0.13207 19.25 0.01980 1.29 0.067 20.67626 19.21 126.4 1.6 126.0 22.8 117 457 36 165 1010 0.22241 50.28 0.01877 6.71 0.133 11.63553 49.83 119.9 8.0 203.9 93.2 1337 1033 37 543 4049 0.11518 16.75 0.01704 5.65 0.337 20.40161 15.77 108.9 6.1 110.7 17.6 149 372 38 246 1694 0.14929 26.97 0.01982 2.87 0.106 18.30195 26.82 126.5 3.6 141.3 35.6 397 611 pxo 613 92764 0.74481 4.67 0.09145 1.64 0.351 16.92935 4.37 564.1 8.9 565.2 20.2 570 95 39 417 4100 0.14733 15.79 0.01795 2.50 0.159 16.79804 15.59 114.7 2.8 139.6 20.6 587 340 40 494 6331 0.13713 17.94 0.01915 2.04 0.114 19.26000 17.82 122.3 2.5 130.5 22.0 282 411 41 532 1446 0.08815 26.38 0.01906 2.09 0.079 29.81126 26.30 121.7 2.5 85.8 21.7 -828 761 42 365 6824 0.15305 15.06 0.01801 2.20 0.146 16.22098 14.89 115.0 2.5 144.6 20.3 662 321 pxp 660 30181 0.71741 3.71 0.08963 2.93 0.790 17.22532 2.27 553.3 15.5 549.1 15.7 532 50 43 323 2660 0.17234 33.70 0.01964 5.03 0.149 15.71545 33.32 125.4 6.3 161.4 50.3 729 725 44 281 4404 0.18252 21.97 0.02003 2.84 0.129 15.13498 21.79 127.9 3.6 170.2 34.5 809 461 45 294 1959 0.15684 25.25 0.01992 2.42 0.096 17.50973 25.13 127.1 3.0 147.9 34.8 496 562 46 568 2353 0.13127 14.09 0.01956 1.62 0.115 20.55051 14.00 124.9 2.0 125.2 16.6 131 331 47 111 2363 0.10642 16.69 0.01754 13.39 0.803 22.72358 9.95 112.1 14.9 102.7 16.3 -110 246 48 2442 14600 0.12883 5.46 0.01810 2.30 0.421 19.37267 4.95 115.6 2.6 123.0 6.3 269 114 49 473 4461 0.15653 27.14 0.01811 3.71 0.137 15.95086 26.88 115.7 4.3 147.7 37.3 698 583 50 152 1324 0.09548 73.74 0.02088 4.80 0.065 30.15374 73.59 133.2 6.3 92.6 65.4 -861 2439 51 308 2513 0.10844 33.55 0.02116 3.43 0.102 26.89910 33.37 135.0 4.6 104.5 33.3 -544 917 52 619 4253 0.15012 11.64 0.01985 1.48 0.127 18.23215 11.54 126.7 1.9 142.0 15.4 406 259 pxq 617 88936 0.75371 2.59 0.09145 2.13 0.821 16.72936 1.48 564.1 11.5 570.4 11.3 595 32 53 265 722 0.08284 60.65 0.01952 4.52 0.075 32.48745 60.48 124.6 5.6 80.8 47.1 -1081 1984 54 351 2056 0.12385 22.15 0.01946 2.83 0.128 21.66356 21.97 124.2 3.5 118.6 24.8 6 534 55 317 2796 0.14885 25.06 0.01872 3.05 0.122 17.34487 24.88 119.6 3.6 140.9 33.0 517 554 56 305 2613 0.10917 40.56 0.01963 4.10 0.101 24.78937 40.35 125.3 5.1 105.2 40.6 -329 1075 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.2. continued Sam ple HA-094-04 (continued) sam ple U (ppm ) 2 06Pb/204Pb 2 07Pb/235U ±(% ) 206Pb/238U ±(% ) e rrc o rr 206Pb/207Pb ±(% ) 206Pb/238U age ±(M a) 2 07Pb/235U age ±(M a) 2 06Pb/207Pb age ±(M a) pxr 502 51084 0.73446 3.28 0.09104 1.58 0.481 17.09045 2.88 561.7 8.5 559.2 14.1 549 63 57 414 4247 0.16353 9.69 0.01941 1.80 0.186 16.36644 9.52 123.9 2.2 153.8 13.8 643 205 58 529 4749 0.12017 11.21 0.01870 3.20 0.286 21.45140 10.75 119.4 3.8 115.2 12.2 30 258 59 324 637 0.10551 40.08 0.01834 3.91 0.098 23.96536 39.89 117.2 4.5 101.9 38.9 -243 1044 60 376 424 0.05375 66.39 0.01792 4.89 0.074 45.97582 66.21 114.5 5.5 53.2 34.4 -2283 377 61 1388 14129 0.13144 8.19 0.01911 1.50 0.183 20.04315 8.05 122.0 1.8 125.4 9.7 190 188 pxs 659 44660 0.74923 2.30 0.09213 1.44 0.625 16.95368 1.80 568.1 7.8 567.8 10.0 566 39 62 302 2268 0.14868 28.07 0.02018 2.03 0.072 18.71765 28.00 128.8 2.6 140.7 36.9 347 645 63 328 4296 0.13791 19.91 0.02089 2.41 0.121 20.88864 19.77 133.3 3.2 131.2 24.5 93 472 64 432 4443 0.12758 19.48 0.02063 2.46 0.126 22.29441 19.33 131.6 3.2 121.9 22.4 -64 475 65 287 5569 0.16762 22.65 0.02080 2.16 0.095 17.11321 22.55 132.7 2.8 157.3 33.0 546 498 pxt 485 11641 0.73250 4.18 0.09117 1.47 0.353 17.16098 3.91 562.4 7.9 558.0 18.0 540 86 66 326 2769 0.12221 22.43 0.01869 4.76 0.212 21.08032 21.92 119.3 5.6 117.1 24.8 71 527 61 385 6625 0.12851 23.72 0.01959 2.55 0.108 21.02045 23.58 125.1 3.2 122.8 27.4 78 567 68 45 443 0.28606 96.91 0.02205 16.54 0.171 10.62780 95.49 140.6 23.0 255.5 222.4 1510 n/a 69 278 4133 0.13661 31.56 0.01982 3.14 0.100 20.00720 31.40 126.5 3.9 130.0 38.5 194 746 pxu 629 13371 0.72424 3.62 0.08961 2.54 0.703 17.06052 2.57 553.3 13.5 553.2 15.4 553 56 70 264 5456 0.12902 36.81 0.02095 3.57 0.097 22.39212 36.64 133.7 4.7 123.2 42.7 -74 923 71 314 3730 0.17138 23.28 0.02014 3.69 0.158 16.20502 22.99 128.6 4.7 160.6 34.6 664 498 72 493 5384 0.13772 13.75 0.01985 1.93 0.140 19.86761 13.62 126.7 2.4 131.0 16.9 210 317 73 493 468 0.05196 64.90 0.01946 4.17 0.064 51.64810 64.77 124.3 5.1 51.4 32.6 -2781 205 74 319 1711 0.14363 20.79 0.02064 2.84 0.137 19.81473 20.60 131.7 3.7 136.3 26.5 217 481 pxv 605 54591 0.75815 3.10 0.09232 1.27 0.410 16.78957 2.82 569.2 6.9 572.9 13.6 588 61 75 343 3511 0.14381 24.50 0.02077 2.65 0.108 19.91846 24.35 132.5 3.5 136.4 31.3 204 573 76 303 3076 0.16066 35.21 0.02076 3.21 0.091 17.81655 35.06 132.5 4.2 151.3 49.5 457 800 77 368 1436 0.15232 17.32 0.01993 2.07 0.119 18.03732 17.19 127.2 2.6 144.0 23.2 430 386 78 390 4206 0.16238 14.28 0.02125 1.72 0.121 18.04089 14.18 135.5 2.3 152.8 20.3 430 318 79 512 5039 0.11971 13.53 0.01866 2.65 0.196 21.48924 13.27 119.2 3.1 114.8 14.7 25 320 pxw 634 70051 0.74104 3.21 0.09082 2.29 0.714 16.89735 2.24 560.4 12.3 563.0 13.9 574 49 80 389 3981 0.18515 15.14 0.01982 2.11 0.139 14.75630 14.99 126.5 2.6 172.5 24.0 861 313 81 535 2614 0.12643 20.74 0.02012 2.98 0.144 21.93975 20.53 128.4 3.8 120.9 23.6 -25 502 82 269 2439 0.16582 22.78 0.02156 6.88 0.302 17.92915 21.72 137.5 9.4 155.8 32.9 443 488 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table A.2. continued Sam ple HA-094-04 (continued) 2 06Pb/238U 207Pb/235U 2» ( ,p b /207p b sam ple U (ppm ) 206p b /2 °4p b 207Pb/235U ±(% ) 206Pb/238U ±(% ) errc o rr 20 6 p b /2 0 7 p b ±(% ) age ±(M a) age ±(M a) age ±(M a) 83 386 4409 0.15309 14.33 0.02081 2.13 0.149 18.74116 14.17 132.8 2.8 144.6 19.3 344 322 84 437 1418 0.12650 26.64 0.01880 3.92 0.147 20.49572 26.35 120.1 4.7 121.0 30.4 138 629 pxx 594 28685 0.77557 2.30 0.09484 1.52 0.660 16.86050 1.73 584.1 8.5 583.0 10.2 578 38 pxy 606 27522 0.72993 3.10 0.09155 1.68 0.542 17.29297 2.60 564.7 9.1 556.5 13.3 523 57 pxz 552 25005 0.73582 3.01 0.08940 1.74 0.579 16.75130 2.45 552.0 9.2 560.0 12.9 593 53 Sam ple HA-5-28-01-1 2(^1^238^ 2 U 7 pb/235u 206Pb/2 U 7 Pb sam ple U (ppm ) 206Pb/204Pb 207Pb/235U ±(% ) 206Pb/238U ±(% ) e rrc o rr 206Pb/207Pb ± (% ) age ±(M a) age ±(M a) age ±(M a) pxi 142 1381 0.75263 3.12 0.09603 2.17 0.695 17.593 2.24 591.1 13.4 569.8 23.6 485 25 1 73 10123 7.29621 3.06 0.36276 2.31 0.755 6.855 2.01 1995.2 53.8 2148.3 204.6 2298 17 2 55 58106 9.11221 3.23 0.40605 2.52 0.782 6.144 2.01 2196.8 65.7 2349.3 261.6 2485 17 3 54 11718 8.83789 3.03 0.40251 2.26 0.747 6.28 2.01 2180.6 58.4 2321.4 240.8 2448 17 4 123 26628 11.69306 2.99 0.44002 2.21 0.741 5.189 2.01 2350.7 62.5 2580.1 304.2 2766 17 5 117 14000 6.26025 3.51 0.33224 2.88 0.821 7.318 2.01 1849.2 61.5 2012.9 201.9 2185 18 pxj 198 1721 0.73541 3.1 0.08918 2.24 0.722 16.721 2.14 550.7 12.8 559.7 22.9 597 23 6 58 10621 8.41714 3.09 0.39766 2.34 0.756 6.514 2.02 2158.2 59.7 2277 234.9 2386 17 7 46 4877 6.16254 3.08 0.33923 2.31 0.751 7.59 2.03 1882.9 50.3 1999.2 176.3 2122 18 8 46 14641 8.19308 3.49 0.39464 2.85 0.816 6.641 2.02 2144.3 72.1 2252.6 255.6 2352 17 9 40 8532 5.77207 3.02 0.32765 2.23 0.738 7.827 2.04 1827 47 1942.2 163.3 2068 18 10 58 3449 13.4377 3.78 0.45742 3.2 0.847 4.693 2.01 2428.2 93.7 2710.9 416.8 2929 16 pxk 165 1797 0.70877 3.36 0.08978 2.52 0.748 17.465 2.23 554.2 14.5 544 23.9 501 25 11 44 14354 7.12304 3.15 0.35879 2.41 0.765 6.945 2.03 1976.4 55.5 2126.9 205.8 2276 18 12 32 16695 6.34308 3.24 0.33951 2.49 0.769 7.38 2.07 1884.3 54.3 2024.4 189.7 2171 18 13 59 12982 5.45806 3.06 0.32115 2.29 0.748 8.113 2.03 1795.4 47.2 1894 156.8 2004 18 14 37 50855 11.73471 3.22 0.4703 2.5 0.776 5.526 2.03 2484.9 75.3 2583.5 325.5 2662 17 15 31 148179 7.42788 2.99 0.38115 2.14 0.714 7.075 2.09 2081.6 52.3 2164.3 203.9 2244 18 pxl 135 4018 0.74738 3.31 0.09246 2.56 0.772 17.057 2.11 570 15.2 566.7 24.8 553 23 16 28 9459 5.52755 3.19 0.3368 2.44 0.764 8.401 2.06 1871.3 52.7 1904.9 164.9 1942 18 17 41 23286 14.18274 2.89 0.51438 2.06 0.715 5.001 2.02 2675.3 68.1 2762 348.4 2826 17 18 114 14251 5.15015 3.77 0.31704 3.18 0.845 8.488 2.01 1775.3 64.8 1844.4 180.1 1923 18 Table A.2. continued 'e? s 4f 1 oz | ON 2 5 On oo in CN 00 oo 1 27 | 00 e ' Os C" e- 'O <N O CN CN e- e- <N 00 00 oo e ' oo tv «N © CN r- © CN © CN ON Xi a , x f t . s o N 44 WD Cl CN 00 oo CN 00 • » > p NO r- NO OO r- ON OO cn NO r- NO CN CN SO CN tv tv in CN Tf CN en NO e- CN Os CN Os in so CN 00 in e- CN oo n in 00 NO 00 cn ON ON r - ~ in Os e - - rf r ^ - CN CN in e^ CN NO in cn o © 00 oo cn in Os en Tf in CN CN cn cn CN S in in in r- © so e- CN in © oo in SO 00 in ON 00 IT s ON ON 00 NO in Tt »n <N ON CN rf r- Os Tf t- NO 00 o Os 00 CN On d NO Os NO cn ■p - r f - e^ in © cn cn p 00 cn <N <N CN in p in On in CN 00 cn NO cn © e ' en in <N <N p in p 00 in SO SO p e^ © cn NO CN in CN ON © Tf © r- cn p •n T j- cn On in cn cn o jP N A f t . r ~ r j 4 4 M 0 1 CN NO 00 p © 00 tV tv tv •n d oo ON OO 00 OO e- Os r- t "- NO cn 00 © CN P NO CN CN ®o R in cn 00 CN T t; cn r- CN in Os cn so CN 00 cn cn c- CN <N NO ■n 0© cn o 00 p cn cn On SC cn On CN On © r- CN in NO CN r- CN oo p lO in p 00 •n r- oo OO OS p 00 © ■n- CN ON On ON CN CN VO •n CN O e- SO CN CN SO 00 r- e^ p 00 CN 00 p 00 00 s r - - oo NO cn K T j - cn <n p in N- NO Tf p cn in P Tf in so <N d "V p in in CN 0 0* CN e^ in SO in r- Os OO On <N cn © in p NO in p in in p 00 p cn 00 i© <N p CN in p CN in n- © in ■** d 00 00 NO <N 00 NO TT sq CN oo oo T l - p CN in ON cn in £ o e n £ On « o f S 44 b£ a • * ¥ ■ t} - 00 p Tf e- d cn "n OO d NO r - ~ Os 00 00 p Tf Os r- in © CN T j - © Os © CN Os E2 in ■p ON © CN p e^ r- CN © Os in © CN SO CN p © r- CN fn •n n e^ ON SO 00 r- 00 Os cn o in Os •n NO CN oo ON NO CN fn ?o © in VO 00 e^ C" e- © e^ 00 e -- 00 © © CN p- CN in CN CN Tf NO CN CN 5 in p e^ so V" o On Tf SO CN NO in e -> cn NO ON e- CN On so 00 44 g 4f cn CN e- p CN cn <N r- o CN cn p CN P CN cn © CN cn © CN •n N CN © CN © CN CN CN cn © CN © CN <N N r- © CN in sq CN 00 p <N CN © CN © CN in "V CN © CN CN © CN © CN C" © CN 00 © CN in <N p CN SO © CN r- CN CN CN r- © CN S a © i © i pO ia- x f t . S O r - » Tf 00 NO OO cn cn p 00 <5 cn NO •V NO >n P 00 NO NO 00 r ~~ e- CN ON Tf © SO Tf e^ "V tv oo d “ V cn © in 00 On in NO p OO 00 in in CN in cn 05 tv "V cn in p 00 in NO OO cn p 00 © p n cn CN in tv •v "V tv O cn in 0 0 * NO O sq oo in p oo in cn ON in CN CN e - ~ NO tv tv Os d Ti en ON e - - © p in CN SO © ON 00 o r - - oo in CN SO 00 cn i in 1 < X a k. L . o 4 4 f c . k . 44 e - ~ CN 00 © cn cn r- © On 05 tv d NO cn r- d CN fa d ON © o NO n- e- © Os OO e - - © oo R d cn r - - d e- in e- d SO r- e ^« d e -- m c- d o o e- © * * v tv 'O d r * - cn i - - © e- d cn CN r- © t i— t — d oo d d e- 00 r* © Os NO e - - © cn e- d Tf CN 00 © CN c- e -- d <N p d d in CN e - - © e- e - - e- © Tf e -> © in in e^ © Os SO e- © a S c a CO ¥ p cn t -~ cn CN cn N wn CN CN CN Os in CN r- CN CN SO CN "V <N •n ne CN CN cn cn CN so CN in cn CN r- NO CN On "V <N NO p CN NO CN o CN o CN CN in CN fN "V CN r- P CN cn p CN n CN cn cn m CN in 05 CN p CN tT P CN On p CN Tt P CN p CN s 9 0 N © f t . > o o 00 cn cn d cn © cn d “V NO 05 Os 05 d Os O cn o s Os cn cn o t -- O n O CN cn d cn NO N" e- cn © cn © cn 00 cn © Os £ Os 05 d Os 00 cn oo cn d OO CN CN in d cn cn © NO in © m © so © CN in d 'n fn “ v Os 05 d CN n- NO n- cn © cn cn 00 cn cn d e- NO in rf cn © r- NO © in © NO CN 00 in d © <N ©s d CN r - ~ e- m © oo NO SO cn cn © NO in NO cn d cn CN 00 p* d ON © CN T j - d N- N* “ V On O d in in cn © O cn 00 © in © cn cn cn d Tt cn CN cn © oo cn so cn cn © ¥ ON cn cn cn •n <N cn NO p cn cn Os CN in p cn m © cn cn cn tv © > CN © cn e- © cn in cn cn cn in p cn No p n e - - © cn p cn cn p cn CN p cn © fn e^ P cn so cn Os CN Tf sq cn p cn N- CN fn ON cn r- P cn cn p cn SO p cn Tf P cn J? N -O a. ® N CN 00 in CN in e- Os NO Os 00 Tt «o fn NO NO tv d in 00 in Os •*t in cn in CN • n - in 00 rf o r- P r- e ' en 00 e- vo SO CN r - * ‘ in in Os R d tT tj- m © r - » ‘ r *- NO NO © Os cn NO SO CN Os *n in 00 in oo p CN © CN NO NO P cn oo oo On R d n- r- NO in p in in n- cn p in n- CN p in o e- cn p cn © NO NO cn fn «n <N d o 00 cn in n- 00 cn p «n e^ NO cn © d in r- NO P OS in cn cn sq 00 NO <N S: d o © e- o Tf e - - so p cn oo CN Tf SO P in ON CN in © in cn r- e^ P in -C f t . 1 © 0. < o o Tf Tf NO NO o e ' en oo oo > cn CN O nh cn r- n r- ■n cn in o CN CN © © cn © SO Os SO NO <N •n CN so 00 S SO © NO m cn m CN cn © Os © CN S oo oo n- e^ NO n- 00 e - > o 00 e - ~ - n- NO NO O © CN CN © o N- fN oo in in © 00 o oo cn © NO in © in in CN V© in <N N- P VO in in © CN On e- so Os cn 00 SO 00 cn cn © cn © ? a a cn "V <N «n cn oo in 00 in cn cn *n “ V NO Tf © CN Os CN cn cn "V oo cn CN in SO CN cn *? cn © fn ON 00 in e -* © © oo cn in CN © CN e- © CN e -- CN © T j - 44 ’ a S C 4 Os o CN s s. CN CN CN cn CN tj- CN m CN S s. NO CN e- - CN 00 CN O CN © cn O s. cn CN cn cn cn rf cn in cn 1 NO cn r - cn 0 0 cn On cn © p - 1 Tt CN Tf cn Tf Tt Tf in tT 319 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table A . 2 . continued /c? s ■ /" » < N o - O s V O © C N oo 1 91 o~ fx- o © C N 00 Os C N 00 Os as o> O' in <N © oo 00 00 © C N oo < N O' O' © © V O C N > <N 00 .£ fi. r- © a . © e «s u M A *x, ■ O © nr O' C N C N © O O 00 © © cn © "it Os n r m Os § < N o- nr O' C N in O' C N © C N O- C N cn C N 00 C N vo Os in in oo O' as V O nr 00 C N O' oo O' C N O' C N V O O' C N n r O) in © O' 00 © V O 00 cn nr o C N V O 00 O' 00 O' <n fn m nr © m C N m n r C N n r 00 O' nr 00 oo O' in o- O v vo © 'S ' 4T fn fn <N in m vq S Os in in nr O' C N O O txx vd n r in cd < N Os O O cn cn o- mi o- cn © O' cn vo © in O' O' n r vo <N C N vd o - C N o i ■ ^ r cn cn V O O- o i © nr Os © nr cn t \ <N C N o i in cn O ^ m O S mi V O C N n f in C N Os cn m nf C N C N txi 00 C N Os 00 C N nr vq o i O' nr cd O' < N 00 oo vo rj a * ® W a oo t< m in cn n r o* OI in © 00 cn cn fx. Os C N 00 cn oo Os nT C N 00 00 C N Oi os nr cn vd o C N O S cd 00 O ' C N t-~ mi nr O' C N V O V O 00 O; cn Os Os V O C5 00 in C N O Os 00 o i in oo O' 00 00 nr C N O ' C N Os vo C N <N © in in O' © nr 00 C N Os O s O O oo O cn O s nr cn vo 00 m © 00 m m m O' © C N in C N in o^ m nr C N cn cn 00 cn o- © cn vd in 00 3 m in cd © C N 'S ' £ ¥ <N fn x», cn cn h> 00 mi nr n t Os txx «n in C N cn n r 00 «n " X , cn © O' vq o i 00 00 mi nT vd in n fn V O in vq cn nr oo n f m 00 oo Os nT oo O' v < 5 o i •x, n r as nr C N m 00 o i m oo © m nr cn nr o . o i nr n f vo n r o i O' O; n f nr m in vq O' nT t \ fn X X , in © in s 9 9 A 0 . S © © < s a> Ml a m oo 'O m Os in cn O' C N oo oo oo C N C N Os C N © C N © C N n t 00 oo C N in in in in o- vo C N cn o i C N 00 C N 00 © 00 O' C N mi © Os vq n f C N © C N <N oo oo in C N n f V O Os vo 00 m 00 © Os C N nf O' C N Os a s o- nr C N in vd ■n in mi 00 m cn O s cn cn o in n f V O O O oo < © C N 00 nr S m cn nr C N © 0 0 * © in C N cn vd O' 00 C N Os m © C N o^ V O nT © Vo 05 vo C N Os in © C N g 4 f t \ < N < N 25 C N © © C N C N © C N nT C N C N C N © o i «n C N oi © o i C N © o i o i cn C N C N © o i fN vo o i C N © o i V O © o i in © o i cn © o i C N © o i o . O) o i O s © o i cn © o i C N cn © o i V O o i m m o i o t © o i cn © o i © © o i o i 00 o i <N o i © o i -O fi. h O A fi. © 'O fn t< "X . n r C N >n Os r~ x © Oi O' Tt Tj- O O cn 00 in Tf cn oo oo oo Os " » « . o- nr C N mi in cn C N in Tt cn cn mi in O' Os 00 o - © cn 00 £ © K X X , cn C N oo’ as in 00 00 in cn o 00 C N cn mi oo nr cn mj © ®o Oj o i in ? 00 o O; 00 V O o cn 00 oo O' oo nr in o i V O X ". 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Table A.2. continued S 321 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. e s s ¥ X i O n 0\ « ¥ ■ a a > S < X H i a £ * 0 < u | - C 3 a o o ( N <i < u H X l C u N Os 'O 'O < N N ¥ X e u s a D a E « I Os Os Os K * s-i <N X C - X P m X C m 'a S X O n < s C N Os cn Tf < N O s < N Os £ T f © > © I •n < N < N S s o s.- Tf S O ! Q N c n C N O § S © S © * ■ > 5 05 > S © f N * N 322 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table A.2. continued CN r- os © r- C N *1 > K c n -O fi* © C u OS CN © 0 0 (N 0 0 NO CO © N * . N O N © <N © fi. © oo 0 0 CN K* OS > • C - J ¥ © fi. s fi. O a £ © c u © «ri 00 C O > < * > JO «0 < N R *o 0*1 2 * ■ > C O § : N O N O 3 'O O S © \ < N “ > t <N 323 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table A . 2 . continued A Q m -O 0- ‘ n c n s c 5S O — C N — f i . X f i . o " S . 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Further reproduction prohibited without permission. < D | O a < N < < D 1 H ±(M a) v o 0 0 & O s T f w o S O c o | 3 7 7 1 S O w o 0 0 0 4 C O C O v o v o v o 1 1 7 9 1 0 0 0 4 0 4 | 2 2 2 1 c n © 0 4 © O s W - s O s O s > £ ® O i -a « a. f S o o 0 4 a * n 0 0 o C O s o s o O s O ' o 0 0 0 4 © v o T t V o v o o o C O C M T t © O O T t c n © O s V S O s O s V S v - > O ' T f © © ±(M a) T f 0 0 O s o 5 o s o o w o 0 0 C O O ' s d C O C O c o 0 4 O S c o < N C O 0 0 O ' 0 ^ 0 4 O O c n 0 4 © v o T t 0 4 c n 0 4 o ^ P v s 0 4 O S o s N * 0 0 < N S V ^ S P f t . * 0 4 O s * N S o o s o ^ 0 4 w o K T f O s o i w o T f C O T t o . o . V o s o o - ^ 0 4 0 4 O ' 0 4 O s c n O ^ 0 0 0 0 O s v " i 0 4 V , 0 4 0 5 T f V S © c n v - s 'c ? s V O s o i O s » o T f C O o s C O T t T t C O 0 0 C O v o K © C O O s C O O s 0 4 O s 0 4 p T f s o © s o T t 0 0 O s s ^ 8 P f t . 8 8 ® ¥ la f t . o N im L . O W u & g ¥ X S f t . v e O g 4 f £ t f l f * s r j - Q f t . r ~ ® N .f i f t . V S !a f t . 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O ' C O w o 0 4 c n © O s V O c n v o T t © T t © 0 4 0 4 v s © c n © c n T t v - > O ' 0 0 © © T f 0 4 0 0 £ 9 s O s s o c o 0 4 § 0 4 S O C O o > T f O ' o © 0 4 0 4 0 0 K s © c o O ' T t O s 0 4 0 4 0 4 © c n © V > c n T t c n T f O s © c n O s O s o 1 o - 0 4 C O T t * m S O O ' 0 0 O s © 0 4 0 4 0 4 0 4 1 325 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX B: STRAIN ANALYSES METHODOLOGY AND RELATIONSHIP BETWEEN FOLIATION AND THE XY-PLANE OF THE STRAIN ELLIPSOID Introduction Deformation in its strict sense encompasses four components, which are 1) translation, 2) rotation, 3) strain, and 4) volume change (e.g., Davis, 1996). The common practice of using ‘deformation’ and ‘strain’ synonymously should be avoided, as the latter only refers to one component of deformation, namely the change in shape, which is the aspect of deformation I am concerned with in the following. Methodology To measure strain, I collected oriented lithic-rich volcanic samples. Three mutually perpendicular, but otherwise arbitrary, cuts were made of each sample and an XYZ coordinate system was set up using the intersections of faces as axes. On each face the length of the longest and shortest (in a direction perpendicular to that of the long dimension) axes and the orientation of the long axis relative to the XYZ reference frame was measured for 30 to 100 markers (i.e. deformed clasts, lithic fragments). I avoided the inadvertent inclusion of measurements of pumice clasts, which tend to exhibit extreme syn- to post-depositional compactions and therefore are prone to strong and highly variable primary shapes (Wetmore and Paterson, 2002, Wetmore, 2003). Using the 3-D strain technique of Miller and Oertel (1979), 326 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. two dimensional strain ellipses were calculated for each face from which a three dimensional fabric ellipsoids was determined using a Macintosh program called ‘Strain’ written by Dr. Scott Paterson. For each sample, assuming initial spherical shapes, I calculated the original length of the long (X), intermediate (Y), and short (Z) axes and the initial length (1 0 ), which equals (X*Y*Z) /3 (Table 4.1.). From these values, I calculated elongations in percent (positive = lengthening, negative = shortening) and natural strains, which are the natural logarithms of the ratio for each axial length to the initial length [Ei=ln(X/l0 ); E2=ln(Y/l0 ); E3=ln(Z/l0 ]. Strain Intensity (SI) is equal to 1 /V 3 [(E1-E 2 ) 2 + (E2-E 3 ) 2 + (Ei-E3) 2 ] ’ /2 where Ei, E2, and E3 are the principle natural strains (after Hossack, 1968). Symmetry is equivalent to the Lodes Parameter (LP) calculated from [2(E2)-Ei-E3]/[Ei-E3 ] where negative numbers are prolate shapes, zero equals plane strain, and positive numbers represent oblate shapes. Relationship between foliation and XY-plane o f strain ellipsoid Numerous studies show that foliation and the XY-plane of the strain ellipsoid need not be parallel. Parallelism is achieved if the foliation behaves and rotates as a passive material plane during deformation (e.g., Ramsay, 1967; Bayly, 1974; Ghosh, 1975; Williams, 1976; Ramberg and Ghosh, 1977). Furthermore, high strains and/or recrystallization of minerals will result in <5° deviation between foliations and the XY-plane of the strain ellipsoid and can be considered subparallel for most purposes (e.g., Ghosh, 1975; Williams, 1977). However, if the foliation does not rotate 327 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. passively, strains are low, or two or more deformation episodes are completed, the XY-plane may deviate from the foliation (e.g., Ramsay, 1967; Bayly, 1974). To assess relationships between the strain ellipsoids and field foliation and lineation, I have reoriented strain samples and the reoriented strain ellipsoids into geographic coordinates (Fig. B.I.). I subdivided the data by regional transects and plotted poles to XY planes and foliation and plunges of X-axes and lineation in separate plots. Foliation and/or lineation were not equally developed at all field stations and discrepancies in the number of data points for each area exist. Stereoplots of the data generally show consistent field measurements, but wide scatter in the orientations of the strain ellipsoid data (Fig. B.I.). The closest match between field and strain ellipsoid data exists in the northern Sierra San Pedro Martir on samples collected from within 500 m of the Main Martir thrust. However, deviations between foliation planes and XY-planes of strain ellipsoids exist and in general, there is a very poor match between field and strain ellipsoid data and subparallelism is achieved in very few instances (see Table B.I.). Several explanations can account for the deviations between the strain ellipsoid and field data. 1. The first problem that has to be considered is measurement errors. I think that several errors are introduced during the strain calculation process. These include errors during measurement of foliation and sample orientations in the field (a few to 5-6 degrees), inaccuracies of the magnetic compass (-5°), errors during the calculation of strain intensity and the strain ellipsoid shape, which are generally small, errors during reorientation 328 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. D a xi 4 - Figure B.l. Stereoplots showing field data and strain ellipsoid orientation data. a. Poles to foliation (closed symbols) and poles to XY plane of strain ellipsoid (open symbols). Triangle =Northem Sierra San Pedro Martir; Circles= Southern Sierra San Pedro Martir; squares= Sierra Calamajue. b. Plunge of lineation (closed symbols) and X-axes of strain ellipsoid (open symbols). 329 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table B.l. Orientation data for geographically reoriented strain ellipsoid and field data. XY plane Foliation X axis Lineation Area Sample strain ellipsoid Strike Dip Trend Plunge Trend Plunge N SSPM E3-43 267 86 290 78 83 46 — — N SSPM E3-74 — — 293 77 — — 73 334 N SSPM E3-92 273 50 285 66 58 34 — — N SSPM E3-108 341 50 330 55 66 49 55 60 N SSPM E3-120 308 66 287 68 64 64 64 53 S SSPM B 135 198 46 — — 278 46 — — S SSPM SP 099 37 57 308 50 61 32 55 50 S SSPM SP 100 340 35 308 50 19 24 55 50 S SSPM SP 137a 177 80 332 59 351 72 — — S SSPM SP 137-B 140 66 150 88 211 68 — — S SSPM SP 317e 135 76 332 59 137 8 — — S SSPM SP 317g2 358 84 332 59 101 84 — — S SSPM SP 548-B 39 56 345 17 169 49 45 17 S SSPM SP 801 311 44 307 41 57 43 37 41 S SSPM SP 806 306 19 302 17 46 18 46 17 S SSPM SP 828 71 31 338 40 71 0 41 37 SC HA 098-02 160 86 160 84 231 86 244 81 SC HA 100-02 265 66 294 65 301 53 72 55 SC HA 110-02 293 34 318 78 32 34 79 76 SC HA 163-02 266 49 266 49 36 49 36 49 sc HA 165-02 230 84 257 55 44 44 47 35 sc HA 170-02 68 79 325 76 200 75 113 65 sc HA 220-02 172 84 168 86 260 84 250 81 sc HA 225-02 322 78 322 78 38 78 38 78 sc HA 250-02 313 50 307 82 60 48 104 70 sc HA 268A-02 284 13 306 34 41 11 29 34 sc HA 269-02 110 51 318 74 195 51 356 46 sc HA 272-02 2 81 328 65 38 74 63 65 sc HA 273-02 134 83 118 71 256 82 241 68 sc HA 274-02 254 60 317 65 40 44 16 62 sc HA 275-02 258 23 302 55 51 11 4 52 sc HA 283-02 325 72 325 72 98 66 98 66 sc HA 301-02 173 81 206 81 214 26 320 80 sc HA 315-02 49 61 34 78 211 26 64 67 Area: N SSPM=Northern Sierra San Pedro Martir from Johnson et al. (1999a; b; Fig. 4.4.); S SSPM=Southern Sierra San Pedro Martir (from Schmidt, 2000; Fig. 4.5.); SC=Sierra Calamajue (Fig. 4.6.). 330 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of the sample into geographic coordinates in the laboratory, which are potentially large and again requires the use of a magnetic compass, and errors during the calculation of the strain ellipsoid orientation, which are generally small. 2. In places the foliation is a weakly-developed spaced cleavage. This cleavage was not always developed and measured exactly at the location where the strain sample was collected. This produces three possible problems. First, the mineral fabric represented by the spaced cleavage need not have the same orientation as the ellipsoid calculated from the aligned clasts. Both represent independent material planes that respond differently to the imposed strain. Second, calculated fabrics are in places very small and the resulting ellipsoid is the product of a small tectonic strain component and a primary fabrics component, which control the orientation of the ellipsoid. Third, grid mapping in the North Cascades crystalline core has shown that structural elements such as foliation and lineation can vary significantly over the scale of just a few centimeters (Paterson et al., 2001). 3. A third complication that may have an effect on the orientation of the strain ellipsoid with respect to the orientation of field data is the shape and size of the primary fabrics ellipsoid (Paterson and Yu, 1994; Paterson et al., 1995; Wetmore and Paterson, 2002, Wetmore, 2003). A statistically even distribution as assumed by most strain analyses (including the Rf/Phi method and its algebraic solutions; Shimamoto and Ikeda, 1976; Miller and Oertel, 1979) is not realistic and any rock will have a primary fabric. If the 331 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. primary fabric ellipsoids are interpreted as strain ellipsoids, they show an equivalent of up to 20% shortening in Z (where X>Y>Z). However, the orientations of these ellipsoids are not parallel to primary structures such as bedding, but display angles from parallel to perpendicular. Thus, simple matrix multiplications are precluded and it is not straight forward to correct for primary fabrics. Depending on the orientation of the primary ellipsoid in samples measured for the above study, the orientation of the strain ellipsoid may significantly vary from the orientation of the mineral fabric generally measured as the foliation. 4. The dominance of flattening strains may produce large errors in calculating the orientation of the X-axes of the strain ellipsoids with respect to the plunge of lineations and may explain the scatter in the orientation of the X- axes and the deviation from lineation orientations. 332 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX C: GEOLOGY OF CANYON LAS PALMAS AREA Introduction In addition to the 1:50,000 scale map of the Sierra Calamajue area (Map in back pocket), I also mapped in significant detail (scale of 1: 25,000) in the Canyon Las Palmas area east-southeast of Calamajue Canyon, where the zone of deformation widens to > 1 0 km and structural relationships are well-preserved. Las Palmas Canyon Section Detailed mapping was conducted east-southeast of Calamajue Canyon in the Canyon Las Palmas area (Fig. C.I.), where the fold-thrust belt in the Sierra Calamajue area widens to >10 km. While all units in this area are assigned to the Mesozoic volcano-sedimentary central zone, a large number of folds and brittle faults and intricate structural relationships in the fold-thrust belt are well-preserved. In places, faults splay and form horse structures or thrust duplexes repeating weakly metamorphosed sedimentary units. I divided the map area into three structural sections dominated by different lithologies and separated by major fault zones. Based on structural position, I describe these three sections below going from structurally lowest to highest. 333 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Faults (thrust, normal); d ash e d w here inferred, dotted w here covered Strike and Dip of bedding Strike and Dip of foliation Trend and Plunge of mineral or stretching lineation Q al A lu v iu m , Q u a te rn a r y E x P - ^ a t i ° - n - Ks1 M e s o z o ic m e ta s e d im e n ta r y s h a le , s a n d s to n e ,a rg illite in te rla y e r e d w ith m in o r v o lc a n ic s ( C r e t a c e o u s ? ) L a s P a lm a s T o n a lite (C r e ta c e o u s ) Kv M e s o z o ic m e ta v o lc a n ic s in te rla y e re d w ith m in o r s e d im e n ts ( C r e t a c e o u s ? ) M e s o z o ic m e ta s e d im e n ta r y s h a le , s a n d s to n e ,a rg illite in te rla y e re d w ith s u b s e q u e n t v o lc a n ic s ( C r e ta c e o u s ? ) K s2 K sl M e s o z o ic ( C r e t a c e o u s ? ) lim e s to n e un it Figure C.l. Generalized geologic map of the Canyon Las Palmas area. 334 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Lower plate: The lower plate is best exposed in small drainages, which most likely reflects the compositional make up of the strata. The fault-bounded block is dominantly composed of sand-shale units locally interleaved with volcaniclastic deposits and rare limestone and plagioclase-pheric, lithic-rich volcanic units metamorphosed at greenschist facies conditions. Chlorite dominates, but biotite is locally developed. Shales have been metamorphosed to slates and show a well-developed layer-parallel foliation. The northwest-southeast-trending, moderately northeast-dipping foliation (average 340°/49°; (n=25); Fig. C.2.) contains a moderately plunging mineral lineation (mean 52°/l 10°; (n=21); Fig. C.3.) defined by aligned chlorite, biotite, and locally lithic-volcanic fragments. Rarely exposed fold hinges suggest that the layer- parallel foliation may in fact be an axial planar foliation to tight to isoclinal folds of original bedding. Several intra-formational, reverse faults contain top-to-west and top-to- southwest kinematic indicator such as sigma clasts, s-c fabrics, tension gashes, and asymmetric cracks that are best-developed parallel to the mineral lineation. These faults tend to be layer-parallel and lack displaced markers that could be used to estimate the magnitude of displacement. However, limited compositional variations and a rather uniform metamorphic grade suggest that displacement does probably not exceed a few hundred meters at most. The top of the lower plate is truncated by the brittle Las Palmas fault, which contains a 1 to 2 meter zone of intense brecciation (Fig. C.4.) with locally developed fault gouge (Fig. C.5.). Similar to faults elsewhere 335 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. L ow er H em . Q O Total D a ta : 2 5 E q u al A rea Figure C.2. Stereoplot showing poles to foliation in the lower plate of the Canyon Las Palmas area. Average orientation = 340°/49°; (n=25) L ow er H em . 0© 0 E q u al A rea Total D a ta : 21 Figure C.3. Stereoplot showing plunges of stretching lineations in the lower plate of the Canyon Las Palmas area. Mean orientation = 52°/110°; (n=21). 336 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Figure C.4. Picture of the Las Palmas fault zone. Note the brittle character of the fault zone and fault gouge development with zone of intense brecciation. Box shows approximate area of picture shown in Figure C.5. u > u > Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure C.5. Close-up picture o f th e L as Palmas fault zone showing fault gouge a n d zone o f intense brecciation. in the lower plate, kinematic indicators, albeit rare, also support top-to-west displacement. Middle Plate: The hanging wall units above the Las Palmas fault are composed of volcanic and volcaniclastic rocks interlayered with significantly less abundant shale, limestone, and arkosic sandstone. Metamorphism does not exceed greenschist facies conditions reflected in the development of chlorite-rich zones. The volcanic protoliths apparently were more resistant to deformation, which resulted in better preservation of bedding and only open to tight folding. Folded bedding (average 136°/84°; (n=38); Fig. C.6 .) defines several roughly northwest-southeast-trending folds (Fig. C.I.). A well-developed foliation is steeply dipping (average 352771°; (n=72); Fig. C.7.), contains a moderately to steeply plunging lineation defined dominantly by lithic fragments [mean 667110°; (n=34); Fig. C.8 .], and is in many places bedding parallel. A true axial planar cleavage is only developed in rare, Theologically weaker shale layers. Faults are mostly observed near the Las Palmas fault, where several fault splay with reverse kinematics are probably coeval with the Las Palmas fault. Thus, the faults may represent the larger Las Palmas fault zone that is related to west- directed thrusting of the middle over the lower plate (Fig. C. 1.). The top of the middle plate is bounded by the La Equis thrust, which is best exposed in a steep, 339 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. L ow er H em . E q u al A rea Total D a ta : 37 Figure C.6 . Stereoplot showing poles to bedding in the middle plate of the Canyon Las Palmas area. Average orientation = 136°/84°; (n=37). L ow er H em . A a Total D a ta : 71 E q u al A re a Figure C.7. Stereoplot showing poles to foliation in the middle plate of the Canyon Las Palmas area. Average orientation = 352771°; (n=71). L ow er H em . v V Total D a ta : 34 E q u al A rea Figure C.8 . Stereoplot showing plunges of stretching lineations in the middle plate of the Canyon Las Palmas area. Mean orientation = 667110°; (n=34). 340 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. inaccessible cliff (Fig. C.9.), but clearly places sediment-dominated rocks over middle plate units. Upper Plate: The upper plate is dominantly composed of weakly metamorphosed limestone and shale units and rare volcanic flow units. While the limestone crops out reasonably well, the section is again best exposed in small drainages throughout the area. Bedding (n=10; Fig. C.10.) is strongly overprinted by a mostly bedding-parallel foliation (average 298°/51°; (n=48); Fig. C .ll.) with a moderately northeast- plunging mineral lineation (mean 517065°; (n-26); Fig. C.12.). Folding of upper plate units is not obvious. If folds were once present, they were probably strongly disrupted by faulting that dominates the outcrop-scale structure (Fig. C.I.). Distinct duplication of stratigraphy with limestone overlain by fine-grained shale units bounded at the top and bottom by faults with reverse kinematics suggests that the units are repeated in duplex structures (see cross-section on map in back pocket). Thus, the La Equis thrust forms the floor thrust, which utilized the apparent weakness of the limestone units to propagate through the section leading to duplex formation. The top of the upper plate is defined by another moderately to steeply northeast- to north-northeast-dipping reverse fault that is part of the greater northwest-southeast-trending fold-thrust belt (Fig. C.I.). 341 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Figure C.9. Regional view of the La Equis thrust in steep cliff face showing upper plate units overlying middle plate units in the Canyon Las Palmas area. Contact is outlined for clarification. Dashed lines mark the top of small ridges in the foreground of the picture. View is to the north. u > N J L o w er H em . Total D a ta : 10 E q u al A re a Figure C.10. Stereoplot showing poles to bedding in the upper plate of the Canyon Las Palmas area (n=10). Note that too few and scattered data have been measured to determine an average orientation. L ow er H em . E q u al A re a Total D a ta : 47 Figure C. 11. Stereoplot showing poles to foliation in the upper plate of the Canyon Las Palmas area. Average orientation = 298°/51° (n=47). L ow er H em . O O Total D a ta : 26 E q u al A re a Figure C.12. Stereoplot showing plunges of stretching lineations in the upper plate of the Canyon Las Palmas area. Mean orientation =51°/065° (n=26). 343 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX D: RAW DATA FOR PALEOMAGNETIC ANALYSES Introduction The data presented in the following tables represent the raw data from measurements of the natural remanent magnetization (NRM) and magnetic susceptibility at room temperature and after each temperature step (Figs. D.l. and D.2.) during thermal demagnetization using a MolSpin spinner magnetometer (Table D.l.) and a KLY-4S AGICO Kappabridge (Table D.2.), respectively. Inclination and declination data was corrected for in situ and bedding orientations using an Excel Macro written by John Yu (University of Southern California) and the converted data are presented in Table D.3. 344 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. a. J/J20 vs. Temperature 1.2 HA-025-04B-D HA-025-04B-E 1.0 0.8 0.6 0.4 0.2 0.0 0 200 600 800 400 Temperature (°C) b. J/J20 vs. Temperature 1.2 HA-028-04A-A HA-028-04A-E 1.0 0.8 0.6 0.4 0.2 0.0 0 200 400 600 800 Temperature (°C) Figure D.L Normalized NRM versus temperature plots for all sites analyzed in the Erindera study area (Fig. 5.17.). a. Site HA-025-04B; b. Site FIA-028-04A; c. Site PHW-061802-1; d. Site PHW-061802-H; e. Site PHW-061902-D; f. Site HA-030-04 345 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. c. J/J20 vs. Temperature PH W -061802-l-G -A PH W -061802-l-G -G 0.8 § 0.6 0.4 0.2 0.0 800 600 400 Temperature (°C) 200 0 d. J/J20 vs. Temperature PH W -061802-H -A -A PH W -061802-H -B-B 0.8 § 0.6 0.4 0.2 0.0 600 800 400 Temperature (0 | 200 0 Figure D.l. continued. 346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. e. J/J20 vs. Temperature PH W -061902-D-H-A PH W -061902-D -l-A 0.8 ^ 0,6 0.4 0.2 0.0 200 400 Temperature (°C) 600 0 800 f. J/J20 vs. Temperature 1.2 HA-030-04C-A HA-030-04C-B HA-030-04E-A H A -030-04E-B HA-030-04A-A 1.0 0.8 0.6 0.4 0.2 0.0 0 200 400 600 800 Temperature (°C) Figure D.l. continued. 347 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. a. Magnetic Susceptibility versus Temperature 0.003 — HA-025-04B-D — O - H A -0 2 5 - 0 4 B -E 0.002 . c O 0.001 400 600 200 0 Temperature (°C) b. Magnetic Susceptibility versus Temperature -J k— H A -0 2 8 -0 4 A -A ■ V — H A -0 2 8 - 0 4 A -E 0.04 0.03 -C O 0.02 0.01 0.00 400 600 0 200 Temperature (°C) Figure D.2. Bulk susceptibility versus temperature plots for all sites analyzed in the Erindera study area (Fig. 5.17.). a. Site HA-025-04B; b. Site HA-028-04A; c. Site PHW-061802-1; d. Site PHW-061802-H; e. Site PHW-061902-D; f. HA-030-04-A; g. HA-030-04-C; h. HA-030-04-E. 348 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Magnetic Susceptibility versus Temperature •* — P H W - 0 6 1 8 0 2 - l- G - A P H W - 0 6 1 8 0 2 - l- G - G 0.016 0.012 — 0.008 0.004 0 . 0 0 0 400 600 200 0 Temperature (°C) d. Magnetic Susceptibility versus Temperature 0.04 P H W -0 6 1 8 0 2 - H -A - A -O — P H W -0 6 1 8 0 2 - H - B -B 0.03 02 0.01 0.00 400 600 200 0 Temperature (°C) Figure D.2. continued. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. e. Magnetic Susceptibility versus Temperature P H W - 0 6 1 9 0 2 -D -H -A P H W -0 6 1 9 0 2 -D -l-A 0.0008 JZ O 0.0004 0.0000 600 400 200 Temperature (°C) f. Magnetic Susceptibility versus Temperature H A -0 3 0 -0 4 A -A 0.03 0.01 0.00 400 600 200 Temperature (°C) Figure D.2. continued. 350 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. g- Magnetic Susceptibility versus Temperature + — H A -0 3 0 -0 4 C -A -O— H A -0 3 0 -0 4 C - B 0.02 0.01 0.00 400 600 200 0 Temperature (°C) h. Magnetic Susceptibility versus Temperature 0.016 H A - 0 3 0 -0 4 E - A H A - 0 3 0 -0 4 E -B 0.012 6 0.008 0.004 0.000 400 600 200 0 Temperature (°C) Figure D.2. continued. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table D.l. Bulk natural remanent magnetization (NRM) measurements of samples analyzed during reconnaissance paleomagnetic study in the Alisitos arc strata near Erindera. Temp. Sample (°C) HA-025-04B-D HA-025-04B-E HA-028-04A-A HA-028-04A-E HA-030-04C-A HA-030-04C-B 20 181.5 180.8 546.3 697.5 1443.7 1428.0 50 180.5 177.8 500.3 668.6 1433.9 1417.2 100 178.6 178.4 470.0 588.7 1428.2 1386.3 150 171.2 170.0 425.2 442.1 1273.7 1236.9 200 166.1 164.6 393.7 414.3 1159.7 1111.8 250 156.6 157.4 321.5 304.0 726.9 664.6 300 143.7 142.4 329.1 276.2 602.1 561.8 350 121.6 124.8 243.5 192.5 520.3 486.3 400 123.5 123.5 267.2 173.9 470.1 428.0 450 100.9 100.8 228.9 149.1 449.4 406.5 500 74.0 77.8 175.3 113.1 373.1 329.3 525 62.8 69.3 144.9 94.6 331.1 289.2 550 45.5 51.8 92.3 60.1 278.0 240.9 575 31.1 35.4 6.1 6.4 99.7 93.4 600 12.5 6.4 5.0 11.2 33.9 15.7 610 12.5 6.5 9.9 6.3 27.6 13.7 620 12.8 6.7 17.5 11.0 16.2 12.0 630 12.6 6.7 21.0 15.9 8.4 5.6 640 12.3 6.8 9.4 9.9 5.6 4.1 650 8.7 6.7 7.4 7.5 4.5 3.6 660 5.0 6.0 12.5 12.1 4.1 3.4 670 3.9 5.9 nd nd 3.1 2.5 680 0.6 2.0 nd nd 1.4 1.1 Table D.l. continued. i < i e i CM O 2 < NO o 1 £ a Pi 551.0 | 543.2 | 465.6 | 292.0 | 248.8 | 1 5 8 .2 | 57.1 | 4 6 .4 | 4 5 .4 | 3 7 .8 | 3 1 .7 | 2 8 .2 | 2 3 .0 | 1 5 .2 | O n t o C O t o CM 3 .0 | 2 .3 | 0 .5 | a n d | Sample PHW-061902-D-I- A 158.6 150.9 154.5 145.6 144.5 127.8 124.4 111.8 113.3 86.6 68.7 59.4 46.9 37.5 32.1 29.4 23.8 21.9 17.9 15.9 Z’9 CM © £ 0 PHW-061902-D-H- A 158.5 156.5 153.0 147.0 140.4 135.1 123.5 111.5 116.7 006 73.1 62.1 50.5 40.4 34.7 34.5 28.5 24.8 20.7 19.6 15.6 0.3 0.4 HA-030-04A-A 13669.5 13771.8 13783.6 13611.0 12716.0 00 r- o 9868.0 8695.0 8332.7 7280.2 5104.5 2549.2 1127.8 80.2 00 n o 2.6 2.9 60 2.0 3.7 CO nd nd HA-030-04E-B 3556.9 3456.6 3422.9 3286.1 3242.8 2490.1 2364.8 2199.6 9‘Z60Z 2038.1 00 t o c - * - 00 1719.3 1495.7 820.2 429.2 309.1 185.7 55.3 VIZ o oo 16.9 6.6 o HA-030-04E-A 3365.3 3252.6 3250.8 3165.2 3088.0 2454.5 2308.7 2115.7 2034.1 1989.2 1870.5 1745.8 1524.9 833.2 464.3 311.5 172.1 65.5 r o z 15.6 13.7 601 S'S £ o o o O O o o O o t o O t o O O o o O O o o © o to o t o O t o o t o o CM t o r- O i-H CM C O ^|- t o NO r-- 0 0 Q H CM CM CO CO t o t o t o NO NO NO NO NO NO NO NO NO 353 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table D.l. continued. PHW-061802-I-G- G 1144.9 | 1105.8 | 1068.3 | 1107.4 | 1109.1 | 444.1 | 284.7 | 1 9 6 .5 | 1 7 3 .9 | 1 2 5 .5 | 8 7 .7 | 68.0 | 3 9 .8 | 2 0 .9 | 00 00 1 1 .3 | 6 .9 | fO | 90 t o | 90 n d | n d | Sample PHW-061802-I-G- A VLL6 958.5 925.6 965.4 946.6 370.0 230.2 156.3 140.5 103.9 76.2 59.9 36.0 20.3 16.5 11.3 9.3 2.8 2.3 p CN nd nd PHW-061802-H-B- B 694.4 647.7 553.1 313.2 296.2 175.5 51.8 38.5 37.3 30.1 24.2 VOZ 00 t o 7.9 £'S 3.5 2.6 0.8 0.5 0.4 nd nd d, o o O o o o o O o lO o t o O O O O o O o O o S U o t o O lO o t o o tO o f N t o r- o i-H (N C O t o t o r- 00 < D H <N (N m t o t o t o t o t o t o t o t o t o t o t o t o t o 354 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table D.2. Bulk magnetic susceptibilty measurements of samples analyzed during reconnaissance paleomagnetic study in the Alisitos arc strata near Erindera. ____________________ ___ Temp. Sample (°C) HA-025-04B-D HA-025-04B-E HA-028-04A-A HA-028-04A-E HA-030-04C-A HA-030-04C-B 20 0.001995 0.001960 0.033025 0.035055 0.012940 0.012485 50 0.001990 0.001970 0.033250 0.034870 0.012950 0.012580 100 0.002010 0.001970 0.033070 0.036030 0.013330 0.012690 150 0.002253 0.002208 0.036420 0.041020 0.019160 0.018530 200 0.002099 0.002058 0.033790 0.038120 0.018320 0.017550 250 0.002278 0.002238 0.036610 0.041620 0.014580 0.013720 300 0.002027 0.002010 0.036480 0.038820 0.011400 0.011300 350 0.001640 0.001670 0.036100 0.032600 0.010000 0.010200 400 0.001594 0.001622 0.035630 0.032090 0.009621 0.009727 450 0.001533 0.001568 0.035310 0.031730 0.008915 0.008994 500 0.001402 0.001439 0.034610 0.030900 0.007348 0.007521 525 0.001303 0.001366 0.034230 0.030450 0.006453 0.006658 550 0.001213 0.001278 0.033750 0.029970 0.005802 0.006001 575 0.001083 0.001143 0.032800 0.028760 0.004871 0.005095 600 0.000746 0.000758 0.030450 0.026390 0.003735 0.003810 610 0.000761 0.000772 0.029980 0.025670 0.003441 0.003547 620 0.000745 0.000756 0.028870 0.024320 0.003069 0.003194 630 0.000670 0.000717 0.027230 0.022470 0.002667 0.002802 640 0.000697 0.000676 0.025850 0.020910 0.002427 0.002602 650 0.000704 0.000676 0.023680 0.018800 0.002106 0.002214 660 0.000749 0.000686 0.021910 0.017120 0.001856 0.002012 670 0.000795 0.000714 nd nd 0.001635 0.001768 680 0.000813 0.000736 nd nd 0.001451 0.001568 Table D.2. continued. PH W -061802-H -A - A 0.021800 | o o C N o © 0.023640 1 0.030230 1 0.030070 | 0.030580 | © r- C N © © 0.009220 | | 1 8 0 8 0 0 0 0.007169 | 0.006359 | 0.005523 | 0.004677 | 0.003234 | 0.002460 | 0.001975 | 0.001621 | 0.001248 | 0.001136 | 0.000987 | 0.000925 | n d | ’d c 1 H H Q C N o o O fN V O c-- in 0 0 OS C N 0 0 i — i r- C N C N i — i C N C N V O C N V O o 0 0 V O V O Os V O in C N © r- C N © t-* in © C N i — i C N m i- H i-H O s r-* r-- O O r- 0 0 0 0 0 0 0 0 r* - r- r- V O vo V O V O vo in in in in in in d <£ o o o o © © © © © © © © © © © © © © © © © © © V O o o o o © © © © © © © © © © © © © © © © © © © o o o © o © © © © © © © © © © © © © © © © © © © 1 o © © d © © © © © © © © © © © © © © © © © © © a P h i a Q i > / " ) o © c-- m in (N in 0 0 i — H 0 0 0 0 Tf vo in r- i- H vo 0 0 © in C N C T v C N o i — i © r- in i- H V O C N Os in © C N © i — * in i — * © O s vo O r-~ 0 0 oo O n 0 0 Os Os 0 0 0 0 0 0 V O V O V O vo vo m in in in 2 <! o o © O © © © © © © © © © © © © © © © © © © © 1 — H "S o o © o © © © © © © © © © © © © © © © © © © © V O o o © o © © © © © © © © © © © © © © © © © © © i d © © o © © © © © © © © © © © © © © © © © © © £ o X o « a P h 0 0 < 3 i c o o © o © © © © © © © © C N co CO ^ H © © V O in o o s © C N in © © i-H V O V O 0 0 C N in r-* O s © C N C N © o i-H 0 0 Os m C N © 0 0 © r-*- i-H r-- Os © C N © © Os O s O s i V O V O V O ro C N © vo vo CO t"- i — H r* - ^ r ^ r CO CO CO C N C N C N © T 3 l w> C N C N < N m m CO CO C N C N (N i-H *-H © © © © © © © © © c C o O o © © © © © © © © © © © © © © © © © © © I < l* o © © o © © © © © © © © © © © © © © © © © X m i a o © o © © V O © C O co V O co —i O s © co in OS 0 0 ''3 " in in vo C N V O © Os 1 -H Os © C O C O C N in r-* r* - in c -» o m in O s N " vo Os 0 0 in © C O r-* oo C O i-H O s vo in C O C N i —i © 0 0 0 0 0 0 rr> C N Os c - * * V O vo V O in C O C O C O C N C N C N C N C N C N C N cn o o © © © © © © © © © © © © © © © © © © © o o o © o © © © © © © © © © © © © © © © © © © © I <- © © © d © © © © © © © © © © © © © © © © © © © X < i a in o © o © Os in © c o CN vo CO —H ^H c o CN CN © CN 0 0 Os Tj- ■ '3- Os 0 0 CO CO © © i-H Os © CO r ^ Os VO 0 0 CO r- r - VO 0 0 o m CN © CO CO 0 0 Os vo CN t-- CO © in © 0 0 vo CO CN © Os 0 0 r- r- r- © 0 0 vo in in in CO CO CN CN CN CN CN i-H i-H i-H o o © © © © © © © © © © © © © © © © © © © I ’ 1 o o o © o © © © © © © © © © © © © © © © © © © © 1 <1 © © © d © © © © © © © © © © © © © © © © © © © a d rl t \ / • “V © o © © © © © © © in © in © © © © © © © © © S /v .1 u ■ ^ © in © in © in © in © CN in C - * © i-H CN c o in vo r-« 0 0 0> H o (N V J r-H CN CN CO CO in in in in vo VO vo vo VO vo vo vo vo 356 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table D.2. continued. P H W - 0 6 1 8 0 2 - I - G - G 0 . 0 1 1 9 6 5 | 0 . 0 1 1 7 2 0 | 0 . 0 1 2 6 1 0 | 0 . 0 1 5 9 4 0 | 0 . 0 1 5 1 4 0 | 0 . 0 1 3 6 3 0 | 0 . 0 1 1 1 1 0 1 0 . 0 1 0 2 0 0 | | 9 9 6 6 0 0 0 0 . 0 0 9 4 8 9 | 0 . 0 0 8 6 4 2 | 0 . 0 0 7 9 5 4 | 0 . 0 0 7 1 7 9 | 0 . 0 0 5 6 6 1 | 0 . 0 0 5 1 2 1 | 0 . 0 0 4 3 0 3 | 0 . 0 0 3 8 7 7 | 0 . 0 0 3 4 4 9 | 0 . 0 0 3 1 3 3 | 0 . 0 0 2 8 2 3 | 0 . 0 0 2 5 6 5 | nd | £ 1 O 1 —4 CN IT ) O o O O O O o NO - t ON CN i-H O CN 0 0 O n c o O o o ON o 1 — 1 CN r-* r - O n NO c o 0 0 CN ON 0 0 c o NO r* - NO 0 0 • n 0 0 r - - r-** i n i n r-* i n CN c o i-H 0 0 o r - ^1- 0 0 r » CN o r - i n & 5 2 C o o w -H c o CN O ON O n 0 0 0 0 r - NO i n c o c o CO CN CN s 'sO ^ H i-H f-H i-H F —1 i-H o O o o o o o o o o o o o o £ £ £ o o o o o o o © o O o o o o o o o o o o o o X fl 1 > : © o d d d d d d © d o d d d d d d d d d d a P h i 0 5 1 i n o o o o o o o o * —i CO NO r ^ i n r - O n c o i n 0 0 CN ON ''i - c o i n ON o o o > o F— H o c o r - o r-* i n c o NO i n CN ON c o o i n o NO l > .-H 0 0 NO CN NO 0 0 CN 0 0 CO i-H O . 2 m r - 0 0 o r - r - i n NO F —1 o 0 0 r - NO i n c o CN CN i-H F-H i-H i-H ^ H H n CN CN c o c o c o c o h h 1-H o o o o o O O o o o o o £ £ NO o o O o o o o o o o o o o o o o o o o o o o 1 > © d o d d d d d o d o d o d d d d d d d d a C n & f \ c — , f—> i o o o o o o o o o i n o i n o o o o o o o O O £ o i n o m o i n o i n o CN i n c ^ o i-H CN c o i n NO r - 0 0 < 0 H o CN ^ H CN CN c o CO m i n i n i n NO NO NO NO NO NO NO NO NO 357 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table D.3. In situ and bedding corrected declinations (Dec) and inclinations (Inc) determined from samples analyzed from the Erindera section (see Fig. 5.17.)._______________________________ __ Sample HA-025-04B-D HA-025-04B-E HA-028-04A-A HA-028-04A-E PHW-061902-D-H-A (°C) Dec Inc Dec Inc Dec Inc Dec Inc Dec Inc Initial -45.3 57.0 -42.5 56.7 -37.1 39.3 -23.0 37.6 -21.9 55.8 50 -45.2 56.9 -41.6 56.3 -31.3 36.2 -23.0 37.7 -21.7 56.3 100 -44.5 58.7 -40.5 58.9 -31.8 38.5 -23.4 37.3 -24.8 56.5 150 -44.5 58.5 -38.6 57.4 -31.9 38.0 -20.7 31.6 -21.9 54.3 200 -46.7 59.0 -41.2 58.8 -33.0 41.4 -24.5 37.9 -24.0 54.5 250 -39.7 55.9 -31.8 53.3 -14.9 39.7 -5.3 29.9 -24.4 56.2 300 -41.8 58.3 -44.1 57.4 -30.3 39.5 -22.1 36.7 -20.7 53.8 350 -39.3 60.2 -49.8 60.1 -36.1 42.9 -31.3 37.0 -22.3 51.1 400 -37.4 56.4 -43.6 56.6 -27.9 40.6 -22.1 36.4 -25.0 50.2 450 -38.3 57.8 -47.8 57.6 -34.9 41.5 -32.7 37.1 -23.6 51.8 500 -40.9 57.6 -52.8 57.1 -26.0 43.4 -27.3 39.7 -22.0 52.4 525 -41.3 60.5 -52.0 60.9 -32.7 42.1 -28.6 37.8 -21.5 52.7 550 -38.1 56.8 -45.4 56.3 -18.8 35.3 -13.8 28.8 -24.7 53.1 575 -43.0 60.3 -53.4 59.0 -36.6 46.6 -8.4 62.3 -22.7 54.0 600 -40.5 68.0 -154.2 71.1 -55.6 3.9 2.9 5.6 -23.1 51.9 610 -39.4 67.4 -154.1 71.5 -41.9 2.0 -24.9 4.1 -23.6 55.1 620 -37.5 66.7 -152.7 69.5 -20.3 24.8 -30.0 5.7 -19.5 53.3 630 -41.3 70.1 -163.2 74.5 -6.0 41.9 -0.2 40.8 -15.5 51.6 640 -35.4 70.2 -155.5 73.4 33.0 38.5 19.6 30.3 -14.4 51.5 650 -45.4 73.3 -153.0 74.6 5.1 16.9 4.6 -1.6 -18.3 54.0 660 -24.8 63.9 -138.2 70.2 33.6 -15.8 29.6 10.8 -18.0 55.1 670 -47.3 71.7 -138.2 70.2 n/a n/a n/a n/a -76.1 -14.5 680 -179.6 68.3 -128.4 55.8 n/a n/a n/a n/a -71.2 -5.3 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table D.3. continued. Sample PHW-061902-D-I-A PHW-061802-H-A-A PHW-061802-H-B-B PHW-061802-I-G-A PHW-061802-I-G-G (°C) Dec Inc Dec Inc Dec Inc Dec Inc Dec Inc Initial -22.7 58.0 -25.3 63.2 -26.3 61.9 -35.3 48.7 -37.6 49.2 50 -22.6 57.0 -20.7 63.9 -24.2 64.9 -36.8 46.2 -36.9 48.5 100 -29.1 57.0 -19.5 63.0 -18.4 64.1 -34.3 44.4 -37.6 45.7 150 -25.0 55.7 -19.9 61.0 12.0 58.4 -41.7 46.5 -43.8 44.2 200 -24.7 54.9 -28.1 57.9 -22.6 58.8 -45.0 45.7 -46.7 46.7 250 -26.7 58.8 -18.9 61.9 -16.7 62.4 -39.2 43.1 -38.7 43.6 300 -23.8 57.1 -31.8 51.8 -19.3 56.5 -44.1 46.1 -42.6 43.9 350 -23.3 56.7 -29.5 50.6 -25.8 55.7 -46.5 47.9 -45.9 44.2 400 -24.8 56.3 -21.2 54.2 -22.7 61.0 -40.5 45.0 -42.1 42.0 450 -22.5 59.3 -31.5 47.5 -28.6 53.5 -45.3 47.0 -43.7 46.3 500 -24.4 59.2 -21.0 51.9 -23.9 58.6 -39.8 44.9 -38.0 41.1 525 -22.8 60.3 -23.6 48.8 -27.6 54.4 -43.8 43.2 -43.1 40.8 550 -29.1 58.4 -19.4 53.1 -20.0 53.6 -41.3 41.4 -42.4 38.8 575 -27.8 60.1 -25.4 45.7 -19.3 47.3 -42.3 44.0 -45.3 43.2 600 -27.7 58.0 -21.7 48.8 -19.8 59.6 -35.4 43.4 -43.1 45.8 610 -26.1 61.7 5.2 68.3 -18.4 53.6 -38.4 37.9 -44.7 39.1 620 -19.9 59.6 -17.0 56.3 -15.5 60.7 -34.2 43.5 -41.6 41.3 630 -22.1 62.1 -11.1 65.8 86.8 65.8 -14.8 48.9 4.1 35.2 640 -18.4 57.8 -31.0 54.9 -2.5 47.5 -21.2 46.0 49.8 14.5 650 -23.5 56.8 -42.7 64.9 -72.4 45.7 10.2 6.7 53.9 -35.6 660 -22.2 68.3 -3.5 50.7 -26.8 4.0 57.4 -19.9 -1.1 -25.0 670 -170.2 20.2 n/a n/a n/a n/a n/a n/a n/a n/a 680 -67.7 -42.3 n/a n/a n/a n/a n/a n/a n/a n/a 'O Table D.3. continued. P O 1 w O i o a I - H 25.0 | 25.6 1 25.6 | 26.3 | 24.3 | 25.5 1 25.7 | 23.6 | 23.5 | 24.3 | 23.4 | 23.7 | 23.2 | CN CN 23.5 | 23.1 | CN CN 21.5 | | VZ\ 1 2 .0 | | 6 0 1 5 .5 | 14.3 | m o i Dec -55.1 -51.2 -53.5 o in i -55.6 0 0 " 3 - i -59.2 -61.7 -55.2 -58.3 -57.4 -58.4 0 0 © in i -56.7 -55.6 -49.4 -53.6 -54.2 -49.7 -52.2 -53.4 -40.3 001 H A -030-04E -A o c s I-H 69Z V9Z 26.3 25.8 25.7 26.5 25.2 24.6 23.9 24.7 23.6 24.3 24.0 27.0 26.0 25.1 25.3 23.8 19.2 20.2 18.6 14.0 -2.7 D ec -55.3 -52.2 -52.8 0 0 ■ n in i -55.7 s o 0 0 ''t i -59.3 © O s in 1 -52.6 -56.9 -58.0 -60.3 -52.7 -54.7 -57.5 -51.6 -55.2 -57.8 -54.4 -56.5 -55.8 -55.2 -62.9 H A -030-04C -B O d I-H 30.9 31.0 30.7 28.0 L'LZ 29.1 28.9 29.0 29.1 28.1 30.0 29.2 30.0 30.6 28.6 30.3 39.4 30.3 0 0 in 19.8 28.6 18.7 0 0 D ec -54.1 -52.2 -53.9 -54.4 -56.0 -46.7 -60.1 -62.3 -51.2 -64.4 -56.5 -59.3 -53.1 © »n i -38.8 -30.1 -25.0 -22.3 -23.0 -25.7 voz- -40.7 -52.6 H A -030-04C -A o c HH 1 28.7 30.9 29.5 28.5 28.4 29.5 28.3 27.7 28.9 27.5 28.5 29.0 9'6£ 29.6 31.6 31.4 m 34.5 33.4 39.6 39.5 33.2 48.0 D ec -52.5 -51.7 -53.7 -54.0 -56.6 -48.0 -54.4 -57.4 -56.2 -65.5 -58.4 6 0 9 - -53.4 -54.6 -53.2 -43.0 -52.1 -33.3 -39.0 -37.0 -26.4 -38.6 -26.8 H A -030-04A -A o c HH 1 15.5 15.5 15.7 14.6 14.9 14.4 14.4 14.7 12.3 14.2 14.7 15.4 14.0 14.6 14.9 2.3 -29.7 12.1 33.9 64.4 3.0 n/a n/a Dec -49.6 -50.2 -50.0 -52.1 -51.5 © m i -48.2 -49.6 -49.8 -52.3 -49.2 -53.8 -48.7 -45.9 -50.5 -34.9 -21.2 -18.9 56.4 0 0 1 vzz- n/a n/a 1 Sam ple (°C) 1 Initial O in o o O ID 1 20 0 o in < N o o m © in C O | 400 | 450 | 500 | 525 | 550 | 575 | 600 | 610 | 620 | 630 | 640 | 650 | 660 | 670 | 680 360 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

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Asset Metadata

Creator Alsleben, Helge (author)

Core Title Changing characteristics of deformation, sedimentation, and magmatism as a result of island arc -continent collision

School Graduate School

Degree Doctor of Philosophy

Degree Program Earth Sciences

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag Geology,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Advisor Paterson, Scott (committee chair), Davis, Gregory (committee member), McCann, Edwin (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c16-597977

Unique identifier UC11336607

Identifier 3219867.pdf (filename),usctheses-c16-597977 (legacy record id)

Legacy Identifier 3219867.pdf

Dmrecord 597977

Document Type Dissertation

Rights Alsleben, Helge

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA