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Tectonics and geochemical exploration for heavy metal deposits in the Southern Gulf of California

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Tectonics and geochemical exploration for heavy metal deposits in the Southern Gulf of California

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Content TECTONICS AND GEOCHEMICAL EXPLORATION FOR HEAVY METAL DEPOSITS IN THE SOUTHERN GULF OF CALIFORNIA by Jeffrey William Niemitz 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 (Geological Sciences) June 1977 UMI Number: DP28546 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publ shsng UMI DP28546 Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 U N IV E R S IT Y O F S O U T H E R N C A L IF O R N IA T H E G R A D U A T E S C H O O L U N IV E R S IT Y P A R K LO S A N G E L E S . C A L IF O R N IA 9 0 0 0 7 This dissertation, w ritten by Jeffrey William Niemitz under the direction of h.?:?... Dissertation C o m mittee, and approved by a ll its members, has been presented to and accepted by The Graduate School, in p artia l fu lfillm e n t of requirements of the degree of D O C T O R O F P H I L O S O P H Y Dean Date DISSERTATION COMMITTEE jhairman Pw.D. Git j / L -—-~ CONTENTS Page vlii List of* figures List of tables xi List of plates ACKNOWLEDGMENTS ABSTRACT INTRODUCTION Tectonic Elements of the Southern Gulf of PART I California 10 BACKGROUND History of exploration in the Gulf of 10 California 20 Previous work 21 Bathymetry Seismic reflection profiling and 28 sediment thickness 31 Magnetics Seismicity 35 Heat flow Origin of the Gulf of California 37 Discussion 39 ii Page DATA COLLECTION........................ 42 Navigation • • • * • • • • • • • • • • • 42 Bathymetry ........................... 43 Magnetics........................ 43 Seismic reflection profiles and sediment thickness .......................... 44 Other geophysical data presented .... 43 D A T A ................................. 46 Bathymetry........... 46 Carmen and Farallon b a s i n s . 46 Pescadero Basin Complex .•••••• 50 Ceralbo Island-Ceralbo Trough- Ceralbo Bank: ••••• • . 50 Mazatlan basin-Tres Marias Islands 33 region Alarcon Seamount region Seismic reflection and sediment thick nesses Magnetics Seismicity Heat flow Discussion of data TECTONIC INTERPRETATION 102 iii Page CONCLUSIONS........................ 107 PART II# Geochemical Exploration for Heavy Metal Deposits in the Southern Gulf of California........................ 109 INTRODUCTION..................... 110 BACKGROUND........................ 113 History of mining and ore deposits in Baja California........................ • • . 113 Pliocene ore deposits and their tectonic implications ......... ••••••••• 116 Boleo copper deposit ••••••••• 117 Lucifer and Punta Concepcion Mn i deposits...................... . • . 1^3 SOURCES OF METALS IN GULF OF CALIFORNIA SEDIMENTS........................ 123 j Source rocks and detrital phases ......... 125 I Source rocks and hydrothermal phases • « • 128 I | Seawater and metals in biogenous phases # # 132 i | Seawater and metals in hydrogenous phases • 137 I I Bacterial sulfate reduction and the ; formation of metal sulfides ............. 145 i | SEDIMENT DATA................................... 149 | Geologic sample collection •••••••• 149 Sediment lithologies ...................... 152 iv Page Sediment distribution patterns and sedimentation rates ............... • • • 15^ Distribution of* bedrock outcrop •••••• 15^ Anomalous sediments • •••••••••.. 153 DISTRIBUTION OF BIOGENOUS COMPONENTS IN GULF OF CALIFORNIA SEDIMENTS............. 160 Biogenic component analysis • ••••••• 160 Distribution of organic carbon ..•••• l6l Distribution of calcium carbonate • • • • • 163 Distribution of biogenous components in piston cores • ••••••• •••••• 163 GEOCHEMICAL PROSPECTING AND TECHNIQUES .... 172 Analytical methods ••••••••.... 17^j Acid leaching and trace element partitioning: previous work .... 176 Metal analyses of sediments in the Gulf of California •••••••.. 178 Reliability of HNO^ leaching technique 180 DISTRIBUTION OF LEACHABLE METALS IN GULF OF CALIFORNIA SEDIMENTS ........................ 186 Distribution of leachable metals in surface sediments •.....•••••. 188 Distribution of leachable copper . . . 188 Distribution of leachable nickel . . . 189 v page Distribution of* leachable zinc . . . . 190 Distribution of* leachable manganese • 192 Distribution of* leachable iron . . . . 192 Distribution of* metals with depth in piston cores • ••••• •••••• •• 195 Distribution of* leachable copper . . . 195 Distribution of* leachable nickel . . . 202 Distribution of* leachable zinc . • . • 202 Distribution of* leachable manganese • 202 Distribution of* leachable iron .... 205 Anomalous metal accumulations in indivi dual samples •• • • • • • • • • • • • • 208 Metal accumulation rates and sedimentation rates • • • • • • • • • • • • • • • • • 217 DISCUSSION: GEOCHEMICAL DATA . . . . . . . . 223 Correlation of* metal distributions with environmental factors ••••••••• 224 Metals and biogenic components • • • • 224 Metals and other environmental factors 233 Inter-element correlations with depth in piston cores • • • • • • • • • • • • • • 237 Correlation of metal distributions with tectonic elements ••••••••••• 254 Page Statistical analyses (factor analysis) . . ♦ 256 Theory.........*........................... 256 Data and discussion...................... 257 DISCUSSION: COMPARISON OP THE GULP OF CALI FORNIA AND THE RED S E A ........................ 263 Tectonic comparison of the Gulf of Cali fornia and the Red S e a .................... 263 Environmental comparison of the Gulf of California and the Red S e a ................ 271 CONCLUSIONS...................................... 276 REFERENCES............................................ 279 APPENDICES.............................................. 297 Appendix I# Sample locations, depth, metal and biogenic component analyses of surface sediments ............... 298 Appendix II. Sediment lithology, texture and color of sediments • • • ......... 319 Appendix III. Location, depth, metal and biogenic component analyses of sediments in piston cores .... 327 Appendix IV. Nitric acid leaching technique and procedure......................... 339 Appendix V. Statistical analyses (factor analysis)........................ 342 1 vii ILLUSTRATIONS Figures I ! 1. Physiographic map by Father Fernando Consag from 1746 expedition in the Gulf of Cali fornia ........................................ 1 | 2. Physiographic map of basins and continental shelves in the Gulf of California • . • • • 1 i j 3. Bathymetry of the Carmen and Farallon Basins . . .......... ........................ 4. Bathymetry of the Pescadero Basin Complex, Ceralbo trough, Mazatlan Basin, and Alarcon Rise region . ...................... 1 | Sediment thickness between the inferred | Alar9on Rise spreading center and the Mazatlan Basin......................... . . . j 6. Location of major ore deposits in Baja California ......... .... ... ......... 7. Effect of organic matter on Eh of sediments I and resulting deposition of Mn02 in dif- | ferent geochemical environments ............ 8. Schematic profiles of dissolved Mn in an ocean section........................ .. j i 9« Schematic drawing of sources, transport ! mechanisms, chemical environments and phases in which metals reside in the Gulf of I California ................................... | ! 10. Location map of piston cores . ............. t ! 11. Distribution of organic carbon in twelve j piston cores .................................. I 12. Distribution of calcium carbonate in twelve piston cores ................................. Page l4 18 47 51 83 1 ! I 118| l4l 143 147 165 167 169 viii Figures Page 196 13. Distribution of* Copper in twelve piston cores • • • • • • .................. . . 14. Distribution of Nickel in twelve piston cores • • • • • • • • • « • • • • • • • • • 198 1 1 15. Distribution of* Zinc in twelve piston cores 200 ! 16. Distribution of* Manganese in twelve piston cores 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 203 I 17• Distribution of* Iron in twelve piston cores 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 206 I 18. Plot of* Mn sediments, crusts and nodules I from the Gulf of California and other metal s' liferous sediments and hydrothermal crusts | from tectonic environments...........• • • 212 | 19# Organic carbon versus leachable Copper . . 226 ; 20. Organic carbon versus leachable Zinc . . . 230 1 21. Inter-metal and biogenous component trends in piston core 21967 ••••••••••• 238 i 22. Inter-metal and biogenous component trends ' in piston core 20397 ••••••••••• 240 I 23. Inter-metal and biogenous component trends i in piston core 21965 . . . . . . . . . . . 242 24. Inter-metal and biogenous component trends in piston core 21984 ••••••••••• 244 25. Inter-metal and biogenous component trends in piston core 21995 ••••••••••• 246 26. Inter-metal and biogenous component trends in piston core 22023 ••••••••••• 248 27* Diagrammatic bathymetry and features of the Gulf of Aden • • • • • • • ........... . . 266 28. Position of transform faults, spreading centers and magnetic anomaly lineations in the Gulf of Aden ...................... 268 IX Tables I. Average composition of* plankton, seawater, shale and sediment £*rom the East Equatorial Pacific and the Gulf of California . • . . . II. Organic carbon content (°/o) of sediments in the Gulf of California compared to other marine environments • ••••••.•••• III. Comparison of leached and total concentra tions of elements in a mid-ocean ridge red clay diatomaceous ooze, standard U.S.G.S. hemipelagic mud and two sediments from the Gulf of California • IV. Amount of SiOg, A^O^ and MnO leached by HNO^ leaching technique from a National Bureau of Standards plastic clay #98A from A. P. Green Fire Brick Company, Mexico, Missouri V. Comparison of concentrations of metals, Si, Al» Corg, CaCO^ in Mn crusts, nodules, sediments of inferred hydrogenous, hydro- thermal and diagenetic origin . • • * • • • VI. Comparison of Si/Al and Fe/Mn ratios in manganese sediments, crusts and nodules of inferred hydrothermal, hydrogenous and diagenetic origin VII. Metal accumulating rates and sedimentation rates for sediments of the Gulf of Cali fornia compared to metal accumulation rates I on the East Pacific Rise and the North | Pacific | VIII. Accumulation rates of Si and A1 and metal/ Si and metal A1 ratios for samples in Table VII Page 133 162 182 184 209 215 218 220 Plates 1. de Fleury physiographic map - 1864 (Northern Gulf of California) ......... 2. de Fleury physiographic map - 1864 (Southern Gulf of California) « • • . • 3. Tracklines of cruises in the Southern Gulf of California .................... 4. Sediment thicknesses and sediment distribution patterns (tenths of a second two-way travel time) ........... 5. Bathymetry (meters) .................... 6. Fault traces ........................... Seismic reflection profiles (locations)..................# • • • • 8. Magnetic anomalies with bathymetry • . 9. Earthquake seismicity with bathymetry . 10. Sediment thicknesses with fault traces 11. Heat flow measurements (HFU) with fault traces.......................... 12. Earthquake seismicity with fault traces 13. Magnetic anomalies . . 14. Schematic diagram of inferred tectonic elements ............................... 15. Sample locations ...................... 16. Sediment lithology distribution • • • • 17* Association of 0^ minimum with organic carbon content ........................ 18. Sedimentation rates with sediment thicknesses............................ Page In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket xi Plate 19. Distribution of* bedrock outcrop . . . . 20. 21. 22. 23. 24. 25. 26. 1 27. | 28. J 29. I j 30. | 31. 32. Distribution of organic carbon in sediments (percent) •••••••••• Distribution of CaCO^ in sediments (percent) . • • • • • • • • • • • • • • Distribution of leachable copper (ppm) in sediments • • *•• •••••• •• Distribution of leachable nickel (ppm) in sediments • • . • • • ••• •••• Distribution of leachable zinc (ppm) in sediments • • . • • • ••• •«•• Distribution of leachable manganese (ppm/lO) in sediments •••.••«•• Distribution of leachable iron (percent) in sediments minimum zone correlation correlation correlation correlation correlation of leachable Mn and 0^ in tectonic elements tectonic elements tectonic elements tectonic elements - tectonic elements Page In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket In pocket xii ACKNOWLEDGMENTS My sincerest thanks to Dr. James L. Bischoff, my benefactor, advisor and committee chairman over the past five years, to Drs. David Piper and Tom Henyey for their help with the trace metal chemistry and geophysics respectively, to Bob Rosenbauer, Rex Pilger, Kam Leong and Craig McHendrie for help with the inordinate amount of analytical work, geophysical data processing and computer analyses, to the officers and crew of the R/V Velero IV i i and Samuel P. Lee for their patience with an inexperienced i Chief Scientist. I would especially like to thank my wife, Tricia, for her unceasing love, support and faith through four years of struggles. This research was supported by grants GA-23495 and DES 7^-21152 from the National Science Foundation and a grant-in-aid from the Alcoa Foundation for which I am extremely grateful. ABSTRACT Detailed bathymetric, seismic reflection and mag- i netic surveys of the Southern Gulf of California (25.5 N- !21°N latitude) reveal complex structural trends inferred to be the active tectonic boundary between the North American and Pacific plates* This seismically active zone |appears to be a combination of short loci of sea floor | spreading (Alar^n Rise, Farallon Basin), oblique exten sion and rifting (Carmen Basin) and convergent and 'divergent transform faulting (Pescadero Basin Complex)* The sea floor spreading process in conjunction with rapid i 'imput of terrigenous and biogenous sediment (van Andel, I 1 1964; Calvert, 1966; this study) evident from high and [variable sedimentation rates, produce unique sediment dis- 1 I 'tribution patterns and thicknesses* The apparent periodic [readjustment of the plate boundary over the past 4 MY has ^deactivated fracture zones no longer an integral part of |the active diverging boundary* Sediment rapidly fills jthese abandoned tectonic elements producing distinct wedges jof sediment on both sides of the presently active tectonic I [zone * | Exploration for heavy metal deposits associated with ! 2 inferred divergent plate boundaries as in the Red Sea revealed no such deposits to exist in the Gulf of Cali fornia. Reconnaissance geochemical prospecting techniques were employed and resulted in the delineation of several i heavy metal anomalies (Fe, Mn, Cu, Ni and Zn) in the sedi- I ments. A compilation of environmental data for the Gulf j (biogenous sediment components, sediment type and grain t ' size, depth, redox potentials, areas of minima and river sediment discharge) was compared to the metal anomalies. Anomalies correlative with environmental factors were eliminated as evidence of possible hydro- thermal metallogenesis. The anomalies solely correlative with inferred tectonic elements remain as permissive i evidence of hydrothermal imput to the sediments. These j associations are most pronounced in the Mazatlan basin 1 region. Over the majority of the study area, however, : evidence of hydrothermal metallogenesis is lacking. This I may be due to either non-deposition of metalliferous sedi ments because of the plate boundary configuration and ifrequent readjustment or active deposition and simulta- |neous rapid dilution with terrigenous and biogenous sedi- i j ■ments. ! The Gulf of California is a young and rapidly evolv ing ocean basin tectonically, hydrographically and sedi- jmentologically similar not to the Red Sea but to the Gulf I ]of Aden. The lack of metalliferous sediments in new ocean basins may be the rule rather than the exception. Climatic and tectonic peculiarities in the Red Sea have allowed hot water brines and metalliferous sediment to survive in this environment through time despite the close proximity of continental land masses. No such processes appear to have occurred in the Gulf of California. i ! 4 1 INTRODUCTION ! i Exploration of the Gulf* of California coasts and exploitation of ore deposits in Baja California and I Sonoran Mexico have been recurring themes since the time of the Spanish conquistadors of early l6th century. It was not until 35 years ago, however, that the first oceano graphic expedition was mounted (E, ¥. Scripps cruise of 1939-^0) to explore the geology of the Gulf of California I proper. Anderson (1950) likened the shape of the Gulf to ' that of the Red Sea and the Persian Gulf. Shepard (1950) |noted from the first complete bathymetric chart of the 1 Gulf that the physiography was exceedingly irregular con sisting of alternating V-shaped and broad, flat floored troughs of great depth trending north-northwest. The inception of plate tectonic theory (McKenzie and Parker, 1967; Morgan, 1968; and Heirtzler jet al., 1968) !revolutionized thinking about earth processes and its 1 I implications for the Gulf of California (Moore and Buffing-j ton, 19685 Larson et, al., 1968) and the Red Sea (McKenzie et al., 1970) were soon realized. The suggestion that the Gulf of California was the tectonic link between the East Pacific Rise (EPR) and the San Andreas Fault strengthened the physiographic comparison with the Red Sea (Anderson, 1950), thought to be the link between the Carlsberg Ridge and the Dead Sea fault. Furthermore, the discovery of heavy metal deposits in the Red Sea (Miller et al,, 1966), on the EPR (Bostrom and Petterson, 1966) and associated | with volcanic vents in Indonesia (Zelenov, 1964) suggested 1 | j that submarine metallogenesis was also associated with 1 | processes of sea floor spreading and measured high heat flow along seismically active mid ocean ridges. Recognizing the similarities in physiography, structure and heat flow in the Gulf of California and the t | Red Sea, might not the Gulf also be an environment of j heavy metal deposition? The sediments of the Gulf contain ] I considerable organic carbon (van Andel, 1964) and H^S (Berner, 1964b) capable of mobilizing Cu, Ni and Zn and precipitating metal sulfides similar to phases found in the Red Sea (Bischoff, 1969)# In addition to this line of reasoning, evidence for submarine hydrothermal emplacement j exists in the Pliocene Boleo and Lucifer ore deposits of | Baja California (Wilson and Rocha, 1955? Wilson and Veytia, * . 1949)* If* submarine hydrothermal deposits were being deposited along active faults in Baja California in the past, could they not also be present along active struc tural trends in the Gulf of California today? 1 Xt is necessary to first be able to recognize the active structural trends or tectonic elements with which 6 ! heavy metal deposits might be associated. What criteria ! can be used to recognize tectonic elements and within what kind of tectonic framework can interpretations be made? Secondly, how does one find heavy metal deposits in sub- i | marine environments such as the Red Sea, the EPR or the j Gulf of California? The answer to the second question is ' somewhat easier than the answer to the first. One simply i I looks for metal concentrations in the sediments that are i i two or more orders of magnitude above the surrounding sedi ments, Submarine heavy metal deposits in the Red Sea and on the EPR were found by simply sampling the sediment column. If heavy metal deposits are found in association i with tectonic elements, then the area of search can be I confined. However, if not, geochemical prospecting | techniques can be employed to search all environments in a i | geographical area for evidence of metallogenesis usually in i i ; the form of high metal anomalies in the sediments, | Ultimately, the questions that must be answered in i i the exploration of the Gulf of California for heavy metal deposits are: ! 1, Are there heavy metal deposits in the Gulf as- 1 sociated with inferred tectonic elements, similar to the j ; Red Sea deposits? If not, are any heavy metal anomalies ; found from geochemical prospecting and are they associated I i with tectonic elements? i 2, If metal anomalies exist but are not associated ! 7 with tectonic elements, what factors contribute to the existence of the anomalies? What are the possible sources of the metals? 3* Xf there are no metal anomalies in the sediments, ! why not? It is the purpose of this study to explore the I Southern Gulf of California to clarify via detailed geo- l | physical surveys of the bathymetry and the structure, i i i tectonic elements inferred by previous workers and to * I i j search for heavy metal deposits in association with those I inferred tectonic elements* In the event no heavy metal i ! deposits exist, it is also the purpose of this study to geochemically prospect for evidence of submarine metal- i * f ! logenesis in the sediments* I i i PART I TECTONIC ELEMENTS OF THE SOUTHERN GULF OF CALIFORNIA BACKGROUND History of Exploration in the Gulf of California Conquistador Hernan Cortes first sent his lieuten- i jants to explore the northern part of the Mexican Pacific |coast in 1533 (Mathes, 1969)* The ill fated expedition of the Concepcion was plagued by mutiny and devastation at the |hands of hostile natives living in what is now the city of I I La Paz. The survivors chose to return to Jalisco to face 1 charges of mutiny rather than certain death at the hands of the natives, only to be captured by a rival of Cortes, / v Nuno de Guzman. The tales of the great wealth in pearls the natives possessed spurred more Spanish expeditions to Baja California. Xn 1534, Cortes himself led an expedi- I | tion to La Paz anchoring at a shallow cove on the east side I |of Ceralbo Island, claiming Baja for Spain (Weber, 1968). Xn 1539 Francisco de Ulloa sailed the length of the Gulf to the Colorado River delta, back around Cabo San jLucas and north to Cedros Island on the Pacific coast (Weber, 1968). Ulloa was followed shortly thereafter by Hernando de Alarcon who retraced Ulloa's route and ventured many miles up the Colorado River in 1540. Juan Rodriguez Cabrillo journeyed along the Pacific coast as far north as jCape Mendocino in 1542-43 (Leon-Portilla, 1973). Until the 1 1 10 time of* Ulloa, Baja California was considered to be an island. Ulloa and Alarcon seemed to have proved otherwise yet their evidence for Baja being a peninsula was generally ignored. I The need for trade to the Philippines and the 1 presence of pirates along the Pacific coast forced the | colonial government to proceed with more expeditions. \ Navigator Sebastian Vizcaino was commissioned in 1595 to I j explore the Gulf (Mathes, 1969)* Vizcaino sailed to 27°N | latitude and returned neither confirming nor denying the existence of Baja as an island. Xn 1602, Vizcaino set | forth again to chart the Pacific coast, sounding the gulfs | and bays with the greatest precision possible. On this ‘ expedition he sailed to 42°N latitude discovering the port j of Monterey and finding no north passage into the Gulf. | I | I All of this evidence still did not change the misconceptionj ! 1 I of Baja being an island (Leon-Portilla, 1973)• Exploration languished because of lack of money from Spain and it was ; not until 1615 that a wealthy Spaniard, Tomas de Cardona, sent, at his own expense, his nephew, Nicholas, to explore the Gulf and fish for pearls. Cardon (1632) made crude ; maps of the coast of the Southern Gulf of California show ing harbors and towns but little physiographic detail. Three extensive voyages were made by Captain Don Francisco de Ortega between 1632-1636 (Leon-Portilla, 1 I 1973)* The purpose of the expeditions were ”. . . to sail on a straight course to said Californias, to discover and reconnoiter the ports and inlets of the islands and coasts, observing the navigational bearings, routes and latitudes • . • ” according to the license received from the Viceroy of New Spain, Marquis de Cerralvo, Ortega was well i prepared, his equipment included a wooden diving bell of : his invention. It is unclear whether or not the bell was I I ! used but certainly the invention must be considered a first i attempt at undersea exploration in the Gulf of California, Ortega*s first voyage in 1632 followed the Mexican main land coast to about 25°N latitude, then crossed the Gulf to Ceralbo Island, named for the Viceroy, south to Cabo San Lucas and back north again to La Paz bay. Descriptions of the coastline were quite accurate including the stacks and j arches at the tip of Cabo San Lucas, The second voyage of !1633-3^ traced the coast of Baja from La Paz bay to Punta jConcepcion, Soundings and descriptions of the coastlines, |bays and islands were made, A number of islands along the jBaja coast were named (San Diego, Santa Cruz, Monserrate, |Carmen) and still bear those names. The third and last I |voyage in 1636 retraced the second and extended the region jexplored to 28,5°N latitude (San Sebastian Island). | With the multiple commercial (pearl fishing) jfailures in Baja California, exploration and colonization ;ceased until the time of the Jesuit missions. One hundred sixty-three years after Cortes claimed Baja California for Spain, Father Juan Maria de Salvatierra with Admiral Otando took possession and colonized the peninsula, found ing the first permanent mission at Loreto in 1697 (Weber, 1968). The misconception of Baja California being an is- j land had not yet been resolved and it was not until 1702 ! that Father Eusebio Kino established the true geography. 1 ! Kino proved Baja to be a peninsula by remapping the North- ; west part of Baja and finding no northern passage from the ! Gulf to the Pacific Ocean. However, both Father Kino and Father Juan de Ugarte who in 1721 also proved Baja to be a peninsula, apparently could not prove such to the author- l ities responsible for changing official maps, for the maps still showed Baja as an island until Father Fernando j ! Consag's voyage of 17^6 finally put the ’ ’island” theory to rest (Servin, 1968). i The 17^-6 voyage of Consag was considered the most important event of the period (Servin, 1968). Consag and a small party of Indians and soldiers plied the coastline from Carmen Island reaching the Colorado River Delta in l July 17^-6. An attempt was made to explore the Colorado 1 itself, however, the plan was frustrated by strong cur- ! rents which caused the loss of one boat. A detailed diary was kept which described the coastal physiography of the , east coast of Baja and resulted in a map (fig. l). A 1751 i overland expedition crossed the mountains to the Pacific, Figure 1 Physiographic map by Father Fernando Consag from 17^6 expedition in the Gulf* of California. C « £ j / * * U 0 L , y j v a j f a c n ta i y * g p i t i * * h ! k %/& A (* *$ < / A u j Wry»*tA ty fo -/tJta*rtttn*.y**i*J' j rfRi-o GA*r*A> «r» [J+Jfxv <V / I ’ SerdmaarcJn Coru*^- J r fa t I Cmtj? ^£§5,Wj£**f mlaCdfirni*J Jj&r t l AMt HLmA. ' ' K i p v £ J k J U f . F f M E R J j * v 3 - J ^ ^ - T ^ f e S s s r - w “ ' * l k Z l c A a c i o r t ' d e & i l o f * ^ ' Q > e h i m t e j . wi.tjr.jw,. SQJSTORA <)«iij. f,' “ M A I > 1 \ D E I . i f U R tfo fa p g p M A f a V * ^ 15 turned inland travelling northwest and reached the Pacific again north of* what is now Sebastian Vizcaino Bay. Con- sag's descriptions of* the Pacific coastline were poor, however his accounts of the mountains and his knowledge of the region were invaluable for choosing sites for later 1 missions. I ' Not much is known of any physiographic mapping of 1 the coasts of the Gulf of California until 1864 when i | Colonel E. de Fleury published a map of the entire Gulf j region (plates 1 and 2) , probably the result of time spent t in Mexico during the Mexican-American War of 1846-48. By today*s standards the maps are crude, yet they contain considerable detail with regard to the location of active i mining ventures of the time. The first bathymetric sound- j t ; ! ings in the Gulf were made on U. S. Navy surveys between 1 1873 and 1901 and are included on the present U. S. Hydro- 1 ' graphic Office navigation charts used in this study. I 1 Coastal surveys were done without triangulation cor- I * rections or aerial photographs, hence discrepancies of 1.5-2.0 miles for the islands in the northern Gulf and up j to 4 miles in the southern Gulf are not uncommon (Rusnak, 1 !Fisher and Shepard, 1964). Though soundings were sparse j and probably somewhat inaccurate, the outlines of some of ,the deep basins can be seen. Oceanographic research expeditions to the Gulf of California did not begin until the 1920*s. The California 16 Academy of Science*s 1921 cruise as well as the Templeton- Crocker Expedition of 1935 and the 1936-40 Allan Hancock Expeditions were all mounted for the collection of bio- 1 logical specimens in the water column and the sediments. The first marine geological expedition was the E. ¥. !Scripps cruise of 1939-40 (Anderson, 1950). The evolution I jof bathymetric mapping in the Gulf began at this time with I IF, P, Shepard, Shepard (1950)* using a crude fathometer t !and sextant produced a bathymetric map which delineated i jmany of the basins in the Gulf trough, Shepard is respons ible for naming the Carmen and Farallon basins as well as the Ceralbo trough. The extent of knowledge of the marine geology of the Gulf remained at this level for nearly twenty years juntil the 1957-1962 cruises of the Scripps Institution of i jOceanography (S10) highlighted by the Vermillion Sea Ex pedition of 1959* An ambitious undertaking, this series of cruises collected 23,000 miles of soundings over the entire I I iGulf as well as seismic refraction, magnetics, gravity, jphysical oceanography, micro- and macropaleontology and detailed descriptions of the sediments. The bathymetry i map compiled by Rusnak, Fisher and Shepard (1964) was a ;vast improvement over the Shepard (1950) version. Figure 2 j i shows the extent and location of the major basins and i jshelf areas as delineated from their work. They also com— i piled the inferred faulting in the Gulf leading to the 17 Figure 2 Physiographic map of basins and continental shelves in the Gulf* of California (after van Andel, 1964)* 7 Colorado / RIVER CLOSED B A S I N ROUND SH ELF EDGE S H ARP S H E LF EDGE 50 DEPTH (fm s ) OF S H E LF EDGE SMOOTH UPPER S LO P E ROUGH UPPER S LO PE FELIPE RIO CONCEPCION SAL 51 PUEDES TIBURON TIBURON I . > KIN O BAY SAN PEDRO MART IR 50 STA_ROSALIA & ' GUAYM AS GUAYMAS RIO YAQUI 55 RIO MAYO CARMEN FAR ALL ON RIO FU ERTE \ LA PAZ PESCADERO M AZATLAN interpretation that the Gulf was the result of strike slip faulting and gravity tectonics* The inception of plate tectonic theory allowed previous work done in the Gulf of California to he seen in a different context and also the need to look more closely j at inferred structural trends* Moore and Buffington (1968) 1 | and Larson, Menard and Smith (1968) applying tectonic i theory suggested that the Gulf was the result of sea floor I spreading and strike slip motion over the past k million 1 1 years* More recently, Henyey and Bischoff (1973) and ! Bischoff and Henyey (197^0 and Sharman (1976a) have cora- i | pleted detailed bathymetric and seismic surveys in the 1 1 Northern and Central Gulf provinces, respectively* Henyey j and Bischoff (1973) and Bischoff and Henyey (197^-) have I “ mapped inferred fault traces in and between the deep 1 basins* Sharman has mapped the Guaymas, Carmen and Faral- | Ion basins in detail, speculating on the plate tectonic implication for evidence of jumping spreading centers seen in seismic profiles and changes in the strike of fault plane solutions with increasing latitude along the inferred 1 j plate boundary* Previous Work I The advanced state of marine geological and geo physical knowledge which has evolved over the past 35 j years and particularly in the last decade with the incep- tion of plate tectonic theory is an indication of the complexity of the inferred tectonic boundary between the North American and Pacific plates in the Gulf of Cali fornia. At this time the geologic picture is still in complete and only more detailed surveys will resolve the I [problems that exist. Xt is the purpose of this section to i tcritically review the geological and geophysical literature of the past 35 years which pertains to the tectonic frame work of the Gulf and to raise problems not dealt with by previous workers leading toward the presentation of new i data which may shed new light on these problems. Bathymetry i The first oceanographic expedition to the Gulf of I California for strictly geological purposes was the E. ¥. I (Scripps cruise of 1939—19^0 (Anderson, 1950)• From the i |more than 25,000 soundings made by Shepard (1950), the I jfirst bathymetric chart of the Gulf was produced. The I shortcomings of depth measurements and positioning were i iknown even then. Wire soundings or crude fathometers were [usedj the errors in depth increasing with increasing depth. (Positioning was done solely by sextant. The relatively i jsmall number of depths obtained could only lead to the iproduction of a general picture of the bathymetry. Yet, ,the relative errors in positioning the basins did not pre clude the recognition of alternating north and northwest ■ _______________________________________________________________ 2jl trending basins some of* which, were V—shaped, others broad and f*lat floored. Shepard was also impressed with the depth of* these basins and the steep escarpments which en closed them. From evidence of* recent faulting on Baja i ■ California, Carmen Island, Monserrate Island and Ceralbo !Island, he surmised that the irregularity of the bathymetry i i |was also due to diastrophism of some sort. However, at i I first the processes of erosion, deposition and warping were j not ruled out as means for forming the observed features. I I From the data collected Shepard systematically eliminated all other possible processes except faulting. He used the following criteria to deduce the faulting origin: I I 1. Relatively high slopes on the escarpments. i ' 2. The escarpments were linear. j I 3* There were depressions at the base of slopes of ! the trench-rift valley type and elongate basins | I i similar to Death Valley and the Dead Sea. I 4. Volcanic rocks rather than muds were dredged from the escarpments, an indication that the I ! slopes were not of deltaic origin. 5» A distinct absence of submarine valleys or canyons in the escarpments. 6. Continuation of the submarine scarps onto land. Shepard also noted that recent faulting could be recognized by: | 1. The absence of wave cut terraces. I 22 2. Earthquake seismicity. 3. Angular contact of the escarpments with the basin floors indicating little sediment ac- j cumulation in active fault traces. I The suggestion that strike slip motion was the major ; component of faulting was also advanced by Shepard. He surmised that the association of the San Andreas Fault with i the Gulf and the alternating V-shaped and broad floored t j troughs might be indicators of major horizontal forces I ! producing strike slip motion and some sort of oblique rift— | ing to form rhomboid basins. These were astute observa- | tions for the paucity of data. A series of cruises sponsored by S10 between 1957- ; 1962 climaxed with the Vermillion Sea expedition of 1959# ! From that work came the AAPG memoir of the Marine Geology 1 | of the Gulf of California (van Andel and Shor, 1964). From data collected on these cruises, Rusnak, Fisher and ; Shepard (1964) produced an improved bathymetric chart which i delineated the basins and escarpments and continental shelf i areas with greater accuracy (fig. 2). Physiographic i features not previously known were named, particularly the t j Pescadero and Mazatlan basins. The linearity of the ! northwest-southeast trending escarpments and intervening | northeast-southwest trending troughs was thoroughly docu- ! i mented. The continental shelf along the Mexican coast and 1 . the islands and banks along the Baja California coast were 23 dredged and determined to be of granitic composition while seamounts in the central Gulf trough were found to be of basaltic character* Shepard (1964) contributed detailed surveys of the submarine canyons off the tip of Baja and I along the continental shelf off the Fuerte River delta, j The area from 24°N latitude south to the Tres Marias Is- i |lands, however, still lacked adequate bathymetric cover- j age. I While Rusnak, Fisher and Shepard (1964) recognized ! the right lateral strike slip faulting and intervening basins, their work did not have the benefit of plate tectonic theory to aid in interpretation. The next step to recognizing a rhomboid basin as a possible center of |crustal upwelling and an escarpment as a transform fault !was not taken. i 1 Larson (1972) added bathymetric information to the iSouthern Gulf of California and at the mouth of the Gulf. JHis bathymetry shows the connection between the East ]Pacific Rise (EPR) and the Mazatlan basin. The linearity I of the EPR as it enters the Gulf is striking and the low i |yet rugged relief was different from anything observed in I |the Gulf up to this time. ^ With the advent of the theory of plate tectonics and :the concepts of sea floor spreading and transform fault 'motion, it was suggested that the structure of the Gulf i jcould be explained within the plate tectonic framework. Two studies, one in the Northern Gulf province (Henyey and Bischoff*, 1973) (29°-32°N lat.), and the other in the Central Gulf province (Bischoff and Henyey, 197*0 (27°- 29.5°N lat.) proposed to do detailed bathymetric and !seismic reflection studies in order to better delineate i heretofore inferred tectonic elements. They surmised that i the juxtaposition of the continental and oceanic crusts at I significantly different elevations and the accompanying 1 high sedimentation rates (van Andel, 1964) obscured the detailed features necessary in order to recognize the | inferred plate boundary. Xn order to maximize control on 1 j the positions of inferred fault traces orientation of track t jlines was perpendicular to the known escarpments. Even ' 1 I with detailed surveys delineation of inferred spreading j ;centers was difficult because of the discontinuous thicken- ;ing of sediment prisms on the flanks of some troughs and the abundance of fault traces cutting through others. Sharman (1976a), using the latest navigation ,techniques (satellite navigation with computer generated I !track lines) was able to make detailed surveys of the Guaymas, Carmen and Farallon basins and further refine the 1 bathymetry. From bathymetric, seismic and heat flow data (Lawver, 1973* 1975* 1976), Sharman proposed that these basins were the result of episodic sea floor spreading, a process whereby oceanic crustal material is upwelled at i discrete but separate locations at different times. The 25_ evidence Tor these so-called jumping spreading centers indicated to Sharman that realignment of tectonic elements was occurring. ! For purposes of this study, the present knowledge of ! * the bathymetry of the Southern Gulf of California can be ' summarized as follows. j The trough axis in the Southern Gulf of California | province is dominated by deep, narrow and enclosed basins i bounded by steep escarpments and a broad continental shelf along the Mexican mainland (fig. 2). The Pescadero basin as well as the Carmen basin and Ceralbo trough trend northwest-southeast. The Mazatlan and Farallon basins trend northeast-southwest. All basins are bounded by steep i ; j escarpments trending northwest-southeast, the basins being | j situated en echelon with respect to each other. A shallow I ! continental shelf area is observed along the Mexican main- i ; land and is thought to be a remnant of an early epiric sea i t : or protogulf (Karig and Jensky, 1972; Moore, 1973)• The : recent shelf sediments are thought to be underlain by Early Pliocene, lithified marine sediments, however, a I j study by Anderson (1969) suggests that protogulf sediments 1 as old as late Miocene may be exposed in the San Felipe 1 ' area in northwestern Baja California. These lithified sediments are in turn underlain by continental crust of granitic or granodioritic composition. The shelf widens j from approximately 20 km in the northwest at Guaymas to 75 km in ike southeast near the Tres Marlas Islands* Two breaks in slope have been recognized in cross- sections from the Mexican mainland to the Gulf* trough axis. One slope break at approximately 200 m delineates i the "active" shelf* area; that part of* the shelf* which I experiences nearshore transport of* sediments and has been i 1 effected by deltaic progradation of Pleistocene continental i terraces during eustatic sea level changes (Curray and Moore, 1964). The second shelf break generally occurs at 1400-1600 m and is thought to be caused by extensive fault ing resulting in slope changes from 10° in the Mazatlan basin to 45° in the Farallon basin (Sharman, 1976a). These scarps may be remnants of the zone of weakness and initial rifting of the continental crust and consequently show con-j i 1 ! siderable bathymetric expression in the form of uplift : along the shelf break edge. i i | The Carmen basin, in the northern part of the study ; area, shows bathymetry which drops off suddenly from the i | shelf area into a narrow, deep trough. The trough is I ; bounded by inward facing escarpments. Rusnak, Fisher and ; Shepard (1964) mapped one deep basin in the northwest end of the trough. Sharman (1976a) delineates three basins : each separated by a basement high. The Farallon basin is a i ; rhomboid basin with steep escarpments bounding it on the j northwest and southeast flanks* The Pescadero basin ap- j pears as an attenuated backward nSn %vith three small but i 27 deep basins within the narrow trough. Further to the south the amount of sea floor below shelf depth (1500 m) increases and the enclosed basins become less distinct when compared to the surrounding sea ! floor bathymetry. The Mazatlan basin region is predominant- i ly below shelf break depth and the basin itself has been j mapped as a small, narrow, U—shaped trough with a small | ridge trending northeast-southwest into the , f U” (Rusnak, Fisher and Shepard, 1964)• From the tip of Baja Cali fornia south, the sea floor appears to be broadly undula— tory, however, track lines are apparently sparse because of the lack of detail on the EPR trend. Several abrupt penetrations of the deep ocean floor sediments appear to i be recently active seamounts, some of which have risen as 1 I ' much as 1200 m above the sea floor (Rusnak, Fisher and I Shepard, 1964)• i ! Seismic Reflection Profiling I I and Sediment Thickness ! ! Moore and Buffington (1968) were the first to use ! seismic reflection profiling to delineate inferred tectonic j j elements in the Gulf of California. A profile across the EPR at the mouth of the Gulf showed increasing sediment thickness to the northwest away from the crest of the rise ! I indicating an actively accreting mid ocean ridge. Profiles i 1 | of the southwestern flank, however, showed non—uniform I 28 thicknesses of undisturbed, well stratified sediments. They interpreted these sediments to be turbidites. Other profiles taken from the shelf region across escarpments and into the deep basins revealed thick sequences of sedi- | ments on the shelves which abruptly terminated at the es- | carpments. Moore and Buffington (1968) interpreted this j 1 abrupt change in sediment thickness to be the result of a I j period of tectonic quiescence lasting approximately 6 mil- 1 lion years (MY). The profiles showed numerous offsets in the bathymetry inferred to be the result of faulting. In the context of plate tectonics, Moore and Buffington (1968) mapped an inferred plate boundary as a series of long, sub- 1 parallel, northwest-southeast trending, strike slip faults 1 with short, intervening northeast-southwest trending i | troughs thought to be loci of sea floor spreading. ! Moore (1973)> in an expanded analysis of the Moore ' and Buffington (1968) profiles, also mapped the inferred i I j transform faults using the bathymetry of Rusnak, Fisher and i ; Shepard (1964) as a base map. The paucity of seismic 1 profiles used in both analyses produced, as is now known, an overly simplistic representation of the inferred plate boundary. j With increased track line coverage, Henyey and jBischoff (1973) and Bischoff and Henyey (1974) were able to 1 map the fault traces in the Northern and Central Gulf I provinces with considerably greater detail. Many of the faults delineated were indeed long with smaller faults subparallel and/or oblique to the predominant fault trend with frequent divergence and convergence of faults. This bifurcation of faults produced a wider fault "zone” than had previously been thought to exist. Arcuate faults along | the Baja shelf area and concave toward the Gulf trough I | axis were interpreted as growth faults. Areas of inferred 1 active sea floor spreading such as the Guaymas basin showed i j a central trough but uniform thicknesses of sediment across | ! the basin. This was interpreted as indicating a period of ! quiescence, sediment filling and subsequent intrusion of | crustal material and sea floor spreading over a wide area I j rather than along a discrete zone for the last 60,000 years. j Sharman (1976a) noted similar features in his detailed studies of the three Central Gulf basins. From | seismic profiles he noted asymmetric sediment thicknesses in the Farallon basin which he interpreted as evidence for I a jumping spreading center segment. The three discrete basins separated by basement highs in the Carmen trough were also interpreted as episodic, oblique rifting between the two transform faults thought to bound the trough. 1 Detailed analyses of the seismic sections by Sharman I ; revealed that the bathymetric expression of an inferred s fault scarp was not always the locus of present active | I faulting. Along the scarp between the Farallon and Carmen I ! _____________________________________ 30 basins the bathymetric expression trends 305° while the trace of active faulting reveals a trend of 327°» a trend confirmed by fault plane solutions of a recent seismic event in that basin (Reichle, 1975)* Sharman (1976b) i o ! further noted that the strike of faults increase from 290 j on the Rivera Fracture Zone south of Baja California to i o 1 320 in the Guaymas basin, i i I ' Magnetics Since their discovery (Vine and Matthews, 1963)9 1 magnetic anomalies, magnetic polarity reversals and magnetic reversal symmetry across mid-ocean ridge systems (Vine, 1966) have been a fundamental characteristic of sea 1 floor spreading* The symmetry of the anomalies is thought j j 1 1 to indicate that the new crust is being accreted to both ! j plates equally. Magnetic reversals and their coupling to I a time scale (Heirtzler et; al., 1968) allowed rates of i | spreading, spreading hiatuses and changes in plate motion i | direction to be deduced from the extent of the magnetic i signature left on the sea floor relative to the strike of the active spreading ridge. Distinct magnetic anomalies, indicating approxi mately h MY of sea floor spreading, are seen at the mouth i I of the Gulf of California (Larson, 1972). With approxi- I ! mately 2k0 km of separation between the tip of Baja Cali- ! ; fornia and its inferred original position along the continental slope off* Banderas Bay, a spreading rate of 6 cm/yr can be calculated. Along the inferred plate boundary from the Pescadero basin northward, however, no symmetrical anomaly patterns are seen. This fact, first ! documented by Larson, Mudie and Larson (197^) in the I Central Gulf and later by Klitgord et al, (197*0 in the I j Northern Gulf, did not lead to a dismissal of the mechanism i I of sea floor spreading in the Gulf of California because of the other geophysical data which did support the theory. Rather, they addressed the question of why the sea floor spreading process had not left a symmetrical magnetic im- ; print. An analogy was made to the magnetic "quiet” zones i ; of the Ocean basins (Heirtzler and Hays, 19&7) suggesting ! that during initial rifting large amounts of sediment were i ’ being deposited into the evolving ocean basins from nearby continental sources. Sediment injection, it was thought, I changed the normal extrusive process of pillow basalt formation into an intrusive process of sill and dike in jection and thus lowered the amount of thermal remnant magnetism initially acquired by the rock. Slow cooling and the growth of large phenocrysts may have retarded the magnetic properties of the basaltic rock. Moreover, it i * was suggested that hydrothermal metamorphism contributed ; to altering or partially destroying the thermal remnant i magnetization, l Xf the injection of sediment into inferred spread- 1 i _____________________________________________________________32_ ing centers is not the primary cause of diminished or destroyed thermal remnant magnetization, another possi bility may be that the evolution of this inferred plate j boundary involves multiple loci of crustal accretion per segment of sea floor spreading (Bischoff and Henyey, 197*0 • < Where accretion is presently occurring may not be the site i of initial rifting. Magnetic anomaly patterns of different t j loci of accretion may be overlapping and cancelling or i j enhancing each other to varying degrees. Xn either case a j characteristic set of magnetic anomalies indicative of a i I 4 MY to present spreading duration has been altered beyond j recognition. i Prom a detailed magnetic survey of the Guaymas j i ! Basin, Bischoff and Henyey (1974) were able to contour I i ' 1 I anomalies. They show discrete high anomalies (200+ gammas)' i over inferred loci of sea floor spreading with decreasing j ■ intensities toward the flanks of the basin. Also contoured j is a large 800+ gamma anomaly directly over the northeast I j escarpment of the Guaymas basin. This is in contrast to i I previous magnetic surveys by Hilde (1964) and Lohner (1969) i i who suggested a correlation of negative anomalies with 1 | inferred fault scarps. Thus, while magnetic lineations as | seen in the mouth of the Gulf (Larson, 1972) indicate sea floor spreading, the lack of symmetrical anomalies over , the other basins does not refute sea floor spreading j processes inside the Gulf in the opinion of Larson, Mudie i ___________ 33 and Larson (1972) and Klitgord e j t al, (197^0 • Symmetrical magnetic anomalies must, however, be precluded as criteria for recognizing tectonic elements in the Gulf* of Cali fornia. Seismicitv i i Fault plane solutions of earthquakes are yet another i I line of evidence to recognize strike slip motion. Fault plane solutions have been computed for earthquakes in the Gulf of California by Sykes (1968), Molnar (1973)9 Reichle 1 ! (1975) and Sharman (1976b). All first motion studies | reveal left lateral strike slip motion characteristic of 1 i transform faulting; however, as has been previously dis cussed Sharman (1976b) noted that the strike of the fault plane solutions change systematically from 290° at the j j mouth of the Gulf to 320 in the Guaymas basin. Mapping of epicenter data at the mouth of the Gulf (Larson, 1972 after Barazangi and Dorman, 1969) characterizes the region | of seismic activity as a narrow zone which follows the | Rivera fracture zone and the East Pacific Rise into the 1 1 1 Gulf. The present study presents a map of epicenter j locations from the Worldwide Standardized Seismograph net work (National Geophysical and Solar-Terrestrial Data ! Center, NOAA, Boulder, Colorado) for 1967-197^» I 34 Heat Flow Most of tlie heat flow measurements in the Gulf of California have been collected by L* Lawver (1973* 1975» ; 1976) in the Central basins (Guaymas, Carmen and Farallon)* Only a few stations exist to the south, all of which have I , been taken by von Herzen (1963) or Lewis jet al* (1976)* 1 ! Lawver found that along the Gulf trough axis heat flow is j extremely high compared to a world wide ocean basin ; average of 1-2 heat flow units (HFU)* Upon closer exami- | nation the measured heat flow values were found to be t higher on the flanks of the basins than in the troughs where active accretion of oceanic crust was thought to be 1 1 * occurring* The values also did not coincide with a i t j theoretical conductive heat flow model (Langseth, Le Pichon1 I and Ewing, 1969) for a spreading center* The heat flow probe only measures conductive heat flow* j One hypothesis to explain this discrepancy in the observed and theoretical heat flow over spreading centers ; invoked a convective cell with hydrothermal circulation as I j the driving mechanism (Lister, 1972)* This mechanism has | also been used to explain heat flow across the Galapagos ! Ridge (Williams at al* , 197^-) • The implications of hydro- i j thermal circulation at mid ocean ridges to the chemical ' mass balance of the oceans and the deposition of metallif- • erous sediments (Wolery and Sleep, 1976) extraordinary* 35 Prom tlie distribution and magnitude of* heat Plow values in the Carmen basin, Lawver (1976) argued strongly for hydrothermal circulation. The average heat Plow value | oP 4.0 HFU on the Planks and along the basin walls with a i | -0.2 HFU value in the central trough seems to substantiate j this interpretation. The Farallon basin shows a similar i | distribution (Lawver, 1973* Pig# 4) with a high oP 10 HFU t ; on the Planks and an average oP 3.0 HFU in the central trough. Evidence oP hydrothermal circulation in GulP Basin has important implications with regard to emplacement oP heavy metal deposits. Complicating the paucity oP available data and 1 hence the interpretation are the high sedimentation rates ! Pound in the GulP (van Andel, 1964) compared to open ocean i j environments. Rapid sedimentation deposits relatively cold i ! blanks oP sediment producing disequilibrium in the thermal i gradient which is subsequently measured as a low heat Plow i | value. Moreover, because the sediments in the GulP oP j CaliPornia are generally reducing and organic rich, the i ; probability oP sulPate reduction by bacteria and the j | Pormation oP pyrite with intermediate iron sulPides, an 1 i exothermic reaction, is great (Berner, 1964a; Goldhaber and Kaplan, 1974). A typical reaction might be: Fe^O^ + 4 H^S + 2 S 3 + ^ ^2^* ^ ' ^ le en't*lalpy °-^ Pormation Por this reaction is Hreaction = +97.00 kcal at 25°C and I |1 atm. Thus, a reaction is proceeding in the sediments i 36 that may have a small effect on the heat flow measurements (Kobayashi and Nomura, 1972) and could produce a 1 HFU in crease over the true heat flow value. Only one data point (4.2 HFU) taken by von Herzen (1963) exists in the Pescadero basin. The Mazatlan basin, jwhich has been surveyed by Lewis e_t al. (1976) and von Herzen (l9^3)» shows a similar pattern of high heat flow i :(7-11 HFU) on the flanks of the East Pacific Rise and low values (0.6-1.7 HFU) at the intersection of the Mazatlan basin with the Tamayo fracture zone. Low values of 2.3 HFU near the tip of Baja California and 0.8 HFU just west of the Southern Pescadero basin are probably due to rapid deposition of a cold blanket of sediment which serves as a ! 1 |temporary insulator. - j ! ! Origin of the Gulf of California 1 i Before the inception of plate tectonic theory, the Gulf of California was thought to have been formed by strike slip separation related to the San Andreas Fault system. !Wegener (1924, p. 198-199) was one of the first to suggest strike slip motion in Baja California. It appears, how- tever, that his sense of Baja*s relative motion was confused i inasmuch as he suggested that Baja was moving south rela tive to the Pacific Ocean to the west. Shepard (1950) conceptualized extentional rhomboid basins connected by strike slip faults in order to produce the irregular bathy- ; 37 metry observed in the Gulf* trough. Carey (1958) theorized that Baja California was drifting away from mainland Mexico as a raft of sialic material. Hamilton (1961, p. 1314) synthesized all previously collected geophysical and geological data into a theory that "Baja California may i have formed by the thinning, sundering and drifting apart of a part of a continental raft of sial, the heavier sub- i continental material having flowed in the gap behind the 1 moving plate to form the floor of the Gulf of California." The San Andreas Fault was an integral part of Hamilton's theory. "Up to IOO miles of cross-strike separation" was required as Baja rotated away from Mexico and moved north while the San Andreas remained a discrete strike slip fault with no separation. From geophysical data collected I on the Vermillion Sea Expedition, Rusnak and Fisher (1964) ,surmised that the Gulf was formed by upwarping and strike 1 !slip motion by gravity tectonics as the East Pacific Rise 1 !was overrun by the North American continent. In the past decade the theory of plate tectonics has i I been invoked to explain the origin of the Gulf of Cali- |fornia. Using magnetic anomaly patterns from the Pacific 1 jocean, Atwater (1970) described a possible evolution for 1 ;Cenozoic Western North America whereby the subduction of !the so-called Farallon plate allowed migration of a triple \ junction south to the tip of Baja California. At that time (4 MYBP), sea floor spreading separated what is now I Baja California from Sonoran Mexico producing the present Gulf# Moore (1973) and Karig and Jensky (1972) have dis cussed the formation of oceanic crust between two blocks of continental crust and the rifting of Baja to the north- 1 west. Prom structural associations on land and tectonic ! theory, Karig and Jensky (1972) speculated on the evolu- j tion of the present Gulf from a ’ ’protogulf1 1 epiric sea i prevalent from 10 to 4 MYBP. They suggest that during j this period Basin and Range-type north-south trending i normal faults and associated volcanism were intermixed with i strike slip faulting# At approximately 4-5 MYBP active rifting began inside the Gulf proper as short en echelon spreading centers and long transform faults which continues I | to the present. ! i 1 Discussion The surveys of Henyey and Bischoff (1973) in the i Northern Gulf province and Bischoff and Henyey (1974) and j j ] . Sharman (1976a) in the Central Gulf province suggest that i | the structure of the Gulf is indeed complex# As noted by : Bischoff and Henyey (1974), the juxtaposition and elevation ; contrast of continental and oceanic crust along with high ; rates of sedimentation complicate the delineation of structural trends# Therefore, in order to map the struc- i tural trends in the Southern Gulf of California, detailed geophysical surveys are necessary# The present objective is to delineate so-called tectonic elements, i.e., sea floor spreading centers and transform faults. The recognition of tectonic elements would lead to an interpretation of the Southern Gulf of California as part of the plate boundary between the North j American and Pacific plates. Xn the Gulf of California, j tectonic elements cannot be recognized solely from bathy- i i metric and seismic reflection profile surveys. Geo- I | morphologic characteristics of active faulting (Shepard, i 1 1950), however, can be recognized from seismic profiles I | and with other diagnostic characteristics, tectonic i 1 j elements can be defined regardless of the complexity of the structural and sedimentological province involved. Compilation of geophysical and geological measurements, i which may be influenced by or the result of sea floor . spreading and crustal accretion along an inferred tectonic ! boundary, is necessary. Magnetic anomalies and seismicity are two geo- j j physical parameters which have been used in the past (Lar- i son, 1972) to map the inferred plate boundary. High heat 1 j flow (Lawver, 1973$ 1975$ 1976) is also indicative of j recent extrusion of magma. These parameters will be ex- I 1 plored more fully in the Southern Gulf of California in the 1 i following sections of this study. 1 ! In the past, sediment distribution patterns and I sediment thickness have not been used as a diagnostic tool 40 to delineate tectonic elements. Rapid sedimentation in a tectonic environment of* slow sea floor spreading would most likely be a hindrance to recognizing tectonic elements. ^However, in an environment of fast sea floor spreading, i i.e., faster than the sedimentation rate, the sediment jthickness patterns in a tectonically active region will be I |indicative of plate motion or lack of it just as magnetic |anomalies are evidence of symmetrical sea floor spreading, j With detailed geophysical surveys and other geo- I physical data from the Gulf of California in the past i Jdecade, tectonic elements can be recognized and a more icomplete interpretation of the tectonics attempted. i i DATA COLLECTION i j Data for the present study was collected on three I ! cruises to the southern Gulf of California as follows: 1 March 27-April 11, 1974: R/V Velero IV. University of Southern California ■ March 28-May 2, 1975: R/V Velero IV January 20-February 18, 1976: R/V Samuel P. Lee. U. S. Geological Survey Ship tracks (plate 3) were run normal to inferred fracture zones (Henyey and Bischoff, 1973) to maximize control of their position and to document the true dip of slope on the escarpments. Detailed seismic and bathymetric surveys | were performed over the areas delineated as the Mazatlan and Pescadero basins by Rusnak, Fisher and Shepard (1964). I | I Navigation I i I OMEGA radio signal triangulation and radar were I used on the cruises of the Velero IV. Position fixes were taken every fifteen minutes and tracklines were linearly , adjusted between fixes. The error in positioning from I | radar is mostly from the error in the hydrographic charts | as previously discussed. The OMEGA system which was used 1 approximately 90 percent of the time on the 1975 Velero IV [ cruise because of unacceptable radar targets produced I j errors of less than 1 nautical mile. Satellite navigation | 42 \ and radar were employed aboard tlie Samuel P. Lee with fixes taken every 6 minutes. Track lines were computer j j generated taking into account changes in heading and speed I jbetween satellite fixes. U. S. Hydrographic Office charts ! 21017 and 21014 were used as base maps with the knowledge I that there is significant error in the positioning of the ( mainland Mexico coast. However, because of the low relief 1 j of the Mexican coastal plain, few radar targets are avail- 1 able and none were used for navigation or positioning of stations. ! | Bathymetry Continuous 3*5 kHz bathymetry records were obtained ! using either a Raytheon TJGR or Gifft precision depth I I recorder calibrated to an optimal sound velocity in sea- iwater of 1490 m per second. Depths were taken directly from the original analog records for every 15 minutes of 1 1 track. Correlations of depths at track line intersections 1 were surprisingly good (^10 m) considering the potential navigation errors discussed above. I 1 Magnetics I 1 1 Continuous total magnetic field profiles were i recorded on a Geometries proton magnetometer. Values of ,total magnetic field were taken from the original analog t i ■ records at 5 minute intervals along the track lines and I 43 digitized for computer analysis# A computer program j developed by T. L# Henyey and T. C. Lee at the University < i | of4 Southern California was used to calculate the magnetic I i anomalies. The International Geomagnetic reference field ] 1 of the year of data collection with modification for the ! latitude and longitude of the Gulf of California was sub- | tracted from the total measured field for each data point. ; No magnetic storms were detected during data collection. The resulting magnetic anomalies were computer plotted along the track lines. Seismic Reflection Profiles and Sediment Thickness i i : j Seismic reflection profiles were taken using a Bolt j ■ model 600B air gun with 10 and 20 in.^ chambers and a 50 element Teledyne hydrophone aboard the Velero XV. An i 80,000 joule sparker system and Teledyne hydrophones were S employed on the Samuel P. Lee for deep water (>1000 m) ; work, the majority of the survey. A Uniboom high resolu- 1 tion seismic system for shallow (0-600 m) depths and a medium resolution minisparker for depths of 600-1000 m I were used for seismic surveys in the La Paz Bay and La Paz 1 !basin. Hydrophones were towed approximately 100 m behind | I the ships. The air gun and sparkers were towed approximate-' Ily 10 and 20 meters behind the ships, respectively. The ! j analog records of the subsurface profiles were recorded on 44 a Raytheon UGR of* Gifft recorder at a four second sweep rate. Seismic information was not digitized or computer filtered in any way. All profiles illustrated in this study are photographs of the original records. I i Other Geophysical Data Presented I l ' Sediment thicknesses to acoustic basement taken off i | the seismic profiles are presented as an isopach map (plate i | 4) with contours in tenths of a second two-way travel time. With a nominal 2.0 km/sec sound velocity in the sediments (Phillips, 1964), .1 seconds two-way travel time equals t iapproximately 100 m of sediment. Less than 25 m of sedi- ! ment cannot be resolved on the seismic profiles, con- ; sequently the 3*5 kHz records were used to supplement the seismic records when necessary. All heat flow measurements |(Lawver, 1973* 1975* 1976; von Herzen, 1963; Lewis et al., 1976) presented in this study are in heat flow units (HFU). One HFU equals 10*"^ calories cm"^ sec’^ or 41.86 x 10*”^ -2 watt meters • Magnetic anomalies units are gammas. Gravity and piston cores as well as dredge hauls i have also been collected on these cruises and will be dis— 1 |cussed in detail in Part IX of this study. These geolog- I i ical data have been used to supplement the findings of the geophysical surveys. 45 DATA Herein, the results of the geophysical surveys Tor the three cruises to the Southern Gulf* of* California are ! I presented. The geophysical aspects of* the Carmen and i i i Farallon basins will be only briefly described for the sake of completeness. A recent study by George Sharman I (1976a) at S10 offers a detailed account of the bathymetry and seismicity of these basins. A contour map including all data taken on the aforementioned cruises is presented I j in plate 5* Bathymetry is in meters with a 200 m contour interval. Around the tip of Baja California, the bathy- j metry has been taken from Shepard (1964) and transposed j from fathoms into meters. Where bathymetric control is i I poor, particularly along the Mexican continental shelf, the ibathymetry of Rusnak, Fisher and Shepard (1964) has been 1 1 used to complete the map, again transposing to meters. j ! Bathymetry f Carmen and Farallon Basins Carmen basin (fig. 3) is an elongate, rectilinear basin approximately 85 km in length and 20 km wide trend ing northwest-southeast. The trough escarpment walls are j irregular in plan view with two ridges protruding into the 1 j basin normal to the northwest-southeast trend. The deepest Figure 3 Bathymetry of the Carmen and Farallon Basins* 47 00 Bahia Concepcion Loreto Isla Carm en Snnta Catalina f/% -^ql/U Isla San Jose ■iperitu Santc Bahia ae La Paz LA PAZ BASIN ' S O G Gviaymas CARMEN BASIN f A R A L LO N BASIN S C A LE ( km.) part of tlie basin is not in the center of the trough but offset slightly toward the southwest wall. A separate but smaller enclosed basin has been mapped in the northern end of the trough. The Farallon basin (fig. 3) is situated in close proximity to the Mexican continental shelf escarpment. A relatively narrow continental shelf area is observed in the area. The basin itself has the shape of an attenuated backward ’ ’S.” The basin is 35 km long and 15 km in width with a northeast-southwest trend. The escarpment to the northeast has a slope of approximately 45° (Sharman, 1976a, this study) and crosses the end of the basin, extending normal to the basin trend for approximately 65 km in each direction. This inferred fracture zone trend is only broken by a right angular reentrant into the continental shelf to the east of the Farallon trough and opposite the Fuerte River delta. Shepard (1964) shows this reentrant to be two submarine canyons, named the Fuerte and San Ig nacio canyons. Dredging on this escarpment by Shepard resulted in the recovery of highly sheared igneous and metamorphic rocks suggesting an element of faulting as well as submarine erosion for the origin of the canyons. The escarpment to the southwest of the Farallon trough is not as steep as its northeast counterpart and extends 55 km to the southeast with no equivalent bathymetric ex pression to the northwest. Pescadero Basin Complex The Pescadero Basin hereafter referred to as the Pescadero Basin Complex (fig, 4) consists of three deep, isolated basins connected by a more shallow elongate trough similar in shape to the Farallon basin, however consider ably more attenuated. The trough is approximately 163 km long and 20 km at its greatest width. The deep basins are approximately equally spaced along the trough trend. Two of the basins lie on the same northwest-southeast trend, the third on a parallel trend offset to the northeast ap proximately 25 km. An escarpment to the northeast shows considerable bathymetric expression adjacent to the indivi dual basins but is relatively less steep between the basins. The southwest scarp which borders only the central and southern Pescadero basins has a uniform 3° slope. The northern Pescadero basin sits in a 6 km wide depression with a 2000 m scarp to the northeast flattening to a plateau at about 900 m depth. The southwest scarp is ap proximately 600 m high and flattens abruptly to a 35 km wide gently inclined plateau which abuts Ceralbo bank (fig, 4). Ceralbo Island-Ceralbo Trough-Ceralbo Bank Ceralbo trough (fig, U) is a small, Y-shaped trough approximately 35 km long and 3 km wide which deepens from 30 Figure b Bathymetry of the Pescadero Basin Complex, Ceralbo trough, Mazatlan Basin, and Alarcon Rise region. 51 I s l a C e r a l b o A l a r g o n S e a m o u n t M A Z A T L A N B A S I N P E S C A D E R O ^ B A S I N / C O M P L E X M a z a t l a i J s l a s - T r e e northwest to southeast. Ceralbo Island rises 760 m above sea level to the west of* the trough and Ceralbo bank rises to within 100 m of* sea level to the east of the trough. Ceralbo bank is known to be a continental block of granitic material overlain with volcanic breccias and some metamorphosed sediments (Rusnak et al., 1964; this study). The walls of the trough are nearly symmetrical in cross- section and have about an 11° slope. The trough floor is flat suggesting sediment infilling. Seismic reflection profiles confirm .3 seconds of penetration to acoustic basement and well developed flat lying reflectors. Mazatlan basin-Tres Marias Islands Region The Mazatlan basin (fig. 4) is not a simple closed, U—shaped basin as mapped by Rusnak et al. (1964) but the intersection of the East Pacific Rise and a fault scarp first named the Tamayo fracture zone by Larson et al. (1968). There does appear to be a small closed trough which is deepest at the intersection and becomes progres sively more shallow to the southwest. Bathymetric profiles across this small depression show no sediment accumulation. These profiles, which are normal to the northeast-southwest trend of the trough, indicate the presence of two narrow ridges parallel to the trough trend and symmetrical about it. This symmetry is characteristic of extrusion zones on mid-ocean ridges such as the Mid Atlantic Ridge but not the East Pacific Rise (Rea, 1975)# Further to the southwest, the trough becomes a low relief rise of approximately the same width as the ridge—trough-ridge morphology seen in the Mazatlan basin. However, the symmetrical ridges decrease in relief from approximately 500 m in the Mazatlan basin to 100 m further to the southwest (Normark, 1976). The strong hyperbolic reflections on the bathymetric records suggest extremely rough terrain and may indicate recent volcanic extrusion along the axis of this trend. The flanks of the rise are characterized by shallow depressions filled with small thicknesses of sediment intermingled with, presumably, piles of volcanic debris. The area south of the Mazatlan basin is relatively smooth bathymetrically, not varying more than 500 m except for occasional seamounts. A considerable portion of the area is flat with what appears to be acoustic basement out crop providing the low relief. The discontinuous flat areas are at a common depth and appear from seismic pro files to be fine grained sediments (turbidites?) that have been ponded in the shallow depressions. There is usually no more than .1 second of penetration to acoustic basement in these depressions. A 75 km by 45 km plateau is observed at the base of the Mexican continental shelf escarpment to the northeast of the Mazatlan basin. At the southern end of the plateau the escarpment becomes more gently sloping, 54 Alarcon Seamount Region Xt appears that terrigenous sediments from Baja California have obscured tectonic features to the southeast and east. This is evidenced by a relatively flat, feature less bathymetric profile in contrast to other areas near continental shelves where inferred tectonically produced features are prevalent. Several large seamounts protrude up to 1200 m above the ocean floor. To the east of Baja California and equidistant be tween the Pescadero Basin Complex and the Mazatlan basin is an ”LM shaped bathymetric high hereafter referred to as the Alar9on Rise (fig. 4). The northwest-southeast trend ing segment of the "L" appears to be the bathymetric ex pression of the Tamayo fracture zone between the Mazatlan basin and the Alaryon Rise, bathymetrically expressed as the northeast-southwest segment of the "L.1 1 The bathymetry of this rise segment is quite different from that observed in the Mazatlan basin. There is no evidence of a central trough or symmetrical ridges about the Alar9on Rise nor is there any obvious block faulting (Lewis ejb al. , 1976; ¥. Snydsman, personal communication, 1976) from analyses of seismic profiles. Geomorphology appears to be similar to the East Pacific Rise (Rea, 1975) southwest of the Mazatlan basin. Little sediment is seen in bathymetric profiles and dredging along the crest of the Alar9on Rise returned fresh pillow basalts. 55 Seismic Reflection and Sediment Thicknesses Closely spaced seismic reflection profiles taken normal to the Gulf trough axis allow the traces of the inferred active faults (plate 6) as well as sediment dis tribution patterns and thicknesses (plate 4) to be de lineated in detail* In doing so a more complex structural pattern than had been previously inferred (Moore and Buffington, 1968; Larson et al* * 1968; Moore, 1973) is revealed* High sedimentation rates ranging from 6-100 cm/1000 yrs (van Andel, 1964; this study) from south to north appear to rapidly accumulate sediment thicknesses of up to 1 km* However, frequently narrow linear trends of little or no sediment thickness are observed* Selected seismic profiles show inferred structural and sedimen- tological inter-relationships* Locations of seismic profiles presented are mapped on plate 7* Seismic profiles A-A*-Af f show the fault bounded, graben like elongate channel of the Carmen basin* Profile A”-Al shows acoustic basement overlain with little sedi ment. The sediments are flat lying and may indicate turbidite deposition* As the Carmen basin trough is ap proached, acoustic basement deepens significantly, yet the bathymetric depth changes little* A large sediment wedge is seen in the profile (far right). The sediments are uniformly undeformed across the entire profile* At the 56 southern end of profile A*-A (far left), acoustic basement again approaches bathymetric depth, the sediment wedge thinning until the Carmen basin proper is entered* At the bases of the inferred faulted escarpments some sediment drapping is seen similar to that noted by Sharman (1976a). More extensive seismic profiling by Sharman (1976a) shows the ridges which protrude into the basin. The isopach map (plate ^) excludes the Carmen basin region because of lack of sediment thickness control. The southwest bounding escarpment of the Carmen basin becomes the northeast bounding escarpment of the Farallon basin. Seismic reflection profiles suggest a structurally active zone in this area. The attenuated backward ”S” shaped central trough has what appears to be faulted northeast-southwest trending walls and an excep tionally steep slope at the northeast end of the trough. Sharman*s seismic profiles show an active fault trend which differs from the trend of the bathymetric expression by more than 20°. Being in close proximity to a major river and delta (Fuerte River) on the Mexican coastal plain, the Farallon basin is very likely the locus of deposition for large quantities of terrigenous sediment. However, the central trough is relatively sediment free compared to the flanks. To the northwest of the central Farallon trough another small depression is seen (profile B-B*). Filled with undeformed sediment, Sharman (1976a) Profile A-A'-A", Carmen Basin and western flank. 58 A ' tt L-J a w Or VO Profile B—B 1 . Farallon Basin (far right) and northeast flank showing inferred location of abandoned spreading center (left center). 60 $ M has suggested that this trough was a spreading center abandoned approximately l/3 million years before present (MYBP). Seismic profiles presented by Sharman (1976a) reveal more detailed sedimentation discontinuities used to substantiate this interpretation. Profile B—B* also shows the relatively sediment free and inferred tectonically active Farallon basin at the far right. To the southeast of the Farallon trough, between the inward facing escarp ments, a dramatic thickening of the sediments is observed (plate 4). However, along the inferred active fracture zones less than .1 second of penetration is seen in most cases. The area to the south of the Farallon basin reveals several elongate pockets of sediment (plate 4), almost all of which appear to be flat lying suggesting sedimentation without subsequent deformation. Many of these pockets of sediment do not have bathymetric relief but are sediment wedges in depressions of the acoustic basement. One ex ample of a sediment filled basement depression in juxta position to an inferred tectonically active non sediment filled depression is seen in profile E-E'-E”, Except for the sediment filled depression seen on the far right of profile E-E1, the flanks of the Central Pescadero Basin are relatively sediment free. However, an unusually large ac cumulation of sediment is observed in the Central Pescadero basin proper. The sediment in the Central Pescadero Basin 62 proper. The sediment in the Central Pescadero Basin is also undeformed, Profile Ef-E" shows a cross-section of the Ceralbo bank and trough. As previously mentioned, the Ceralbo trough has little sediment filling especially when com pared to neighboring (profile C-C1) La Paz Bay. Conti- nentally derived sediments in La Paz Bay are dammed on a narrow continental shelf behind a basement high possibly a remanent of continental breakup along the Baja California side of the Gulf. More than 1.8 seconds of penetration is seen in the profile in La Paz Bay, however, depth of acoustic basement is unknown, thus the sediment thickness may be considerably greater. High resolution profiling in La Paz Bay reveals no recent fault traces in the surface sediments eliminating the possibility that the active trace of the La Paz fault, a major strike slip fault structure in southern Baja California (Normark and Curray, 1969)» extends offshore into La Paz Bay. It is possible that the fault trace is located just to the east of Isla Espiritu Santo along the base of the escarpment seen there. In the La Paz Basin (fig. 3) the sediments are probably largely of biological origin due to upwelling along the coast in this region. In the Pescadero Basin Complex, the northern (pro file D-D1) and southern (profile G-G1) Basins appear to be devoid of sediment. The central basin (profile E-E*), as 63 Central Pescadero Basin, inferred inactive fault trace filled with, sediment between the Pescadero Basin Complex and Ceralbo Bank; Ceralbo Bank and V-shaped trough between Ceralbo bank and Ceralbo Island. E E 65 Profile C-C?. La Paz Bay (far left) and Baja California continental shelf and slope break with basement darn hold ing large thickness (>1.8 seconds) of sediment in the bay. 66 c F 4 t r . . n, Profile D-DT. North. Pescadero Basin. 6 8 ON VO 10 KM — — D - ' E l . rr.- : ; • ' 3 J . • * ' . ' < • « W I } 1 ■ - - - i : . ■ • . rPzir* m — r^r^r : : ■ T ■ ' ’ Mir* ~jf- f |if:|ps S & illl -3900 METERS lias been mentioned, has as much as .4 second of penetration in the deepest part (plate 4). The northern Pescadero basin is the narrowest of all the basins in the study area. A steep and sediment free escarpment is observed on the Mexican continental slope (far right of profile) while on the Baja side (far left) sediment has accumulated and the escarpment has approximately half the vertical displacement of its counterpart. The sediment on the southwest flank appears to be somewhat deformed presumably because of tectonic activity in this area. The southern Pescadero basin (profile G-G*) shows a bathymetric disparity on its inward facing escarpments similar to the northern basin, the northeast flank reaching to a considerably shallower depth and being relatively sediment free. In the basin proper, little sediment is detected* The escarpments form angular connections with the basin floor indicating fault ing along the escarpment bases. The prominent offsetting of the northern Pescadero basin form the southern and central basins and does not appear from the seismic pro files to be the result of presently active north-south trending faulting. In the area between the Ceralbo trough and the Mexican continental shelf a series of subparallel structural trends can be mapped (plate 6). As has been mentioned some of these depressions are sediment filled, others are* not. Structural trends that have been filled 70 Profile G-GT. Southern Pescadero basin. 71 0 10 KM V • ' p f c . i f \ r~ ---- ? . — Z^ r “ 1 . ' • " • r -’ ^ ^ ■ £ ~ * . rllOO -1500 -1900 -2300 -2700 -3100 h 3500 r3900 M E TE R S are represented by long dashed lines on plate 6. South of Ceralbo bank an area of normal faulting (profile F-F*) is observed. The fault blocks appear to have been tilted as evidenced by the tilted sediments seen in some of the interfault basins. These faults may be similar to the growth faults delineated by Bischoff and Henyey (197^) in the Central Gulf province. The central (profile E-E*) and southern (profiles G-G* and H-H’) Pescadero basins appear to be situated at the coalescence of three convergent and divergent structural trends (plate 6). Similar fault trace patterns have been suggested for the Central Gulf province (Bis choff and Henyey, 197^) and the Southern California border land (Crowell, 197^? Howell ejt al., 197^). The escarpment between the southern Pescadero basin and the Alar9on Rise is prominent (profile H-H* , far left). A 2200 m vertical displacement is seen from the shelf break to the bottom of the basin. Another growth fault may be present on the Mexican continental slope from tilted sediment seen in this seismic profile. The Tamayo fracture zone connecting the Alarcon rise and the Mazatlan basin (Larson et al., 1968) is an extremely long structural trend. Its bathymetric ex pression appears to be dampened in areas by high sedi mentation. Near Baja California the structural trace is not readily discernible, being covered by sediments. Be— 73 Normal or growth faults along the Baja California continental shelf- slope area. 0 10 KM r 600 1000 1800 .‘ ~T~ 2200 2600 T1 'o t Profile -H*# Small basin in southern half of Southern Pescadero Basin: deepe basin (36OO m+) in the Gulf of California. 3800H tween Baja and the Mazatlan Basin the fracture zone mani fests itself as a southwestward facing escarpment. To the southeast of the Mazatlan basin, however, the Tamayo fracture zone is marked by a spectacular escarpment (profile J-Jf). Apparent uplift along the continental shelf break produced a structural dam for sand and silt size sediment similar to that ween in the La Paz Bay (profile C—C*). Two areas of extremely thick sediment cover have been documented from the seismic profiles taken on the continental shelf (plate 4). However, lack of track coverage over the entire shelf precludes the as sumption that the entire shelf has similar thicknesses of sediment. There are breaks in the continental shelf es carpment xdiich apparently allow sediment to be transported to the deep basins either by turbidite flows or pelagic sedimentation of clays transported beyond the shelf break. An example of this phenomenon may be seen just north of the Mazatlan basin. This plateau previously mentioned is an areally large depression of sediment with up to .4 second of penetration in the deepest part (fig. 4 and plate 5). In the Mazatlan basin, the seismic profiles (profile I—I ') detail a classic cross-section of a mid—ocean ridge. Confirming the bathymetric profiles, the seismic profiles show the trough with symmetrical ridges, little sediment cover and dense hyperbolic reflections indicative of 78 Profile J—J f. Mexican continental slielf (pro gulf?) and slope. Tamayo frac zone; inferred initial zone of continental rifting. 79 d - c+ 10 KM § El 1600 H £ V ;• 1200 “ — j - h * i r * 2000- 2400 - 3200 - 3600 - ...,,-,..., _ 00 o Profile I-I Mazatlan Basin with, rise axis and rift valley and crests and lack of sediment. Increased sediment thickness to the flanks. 81 ‘i i ilir [F tfrjB 'ii tfti'ijii-LiMiilwi. PROPOSED RISE AXIS 0 iO KM 1 ___________________________ I ;o Figure 5# Sediment thickness (units in tenths of a second two way travel time) be tween the inferred Alarcon Rise spreading center and the Mazatlan basin. 8.3 SEDIMENT THICKNESS (hundredths two way travel time) a second crystalline basement. To the flanks of the ridge crests, a profile gently sloping away from the trough exists with undeformed sediments filling small depressions. Both the Mazatlan basin and the Alarcon Rise show symmetric thicken ing of sediments away from the inferred ridge crest. Northwest of the East Pacific Rise trend sediment thick nesses increase slightly faster than to the southeast ap parently because of the influence of terrigenous sedi ments from Baja California. To the southeast sediment thickness is generally uniform (profile K—K !), however, occasional pockets of thicker sediment accumulations do exist as previously reported by Moore and Buffington (1968). All of these depressions appear to be filled with undis turbed, possibly ponded sediments as they are flat lying with well developed acoustic reflections and do not con form to the contours of the acoustic basement. At the base of the Tamayo fracture zone escarpment another thick ac cumulation of sediment is observed, possibly the result of sediment slumping. Frequently seamounts abruptly break through these uniformly thick sediments. A previously un named seamount (profile L-L?), hereafter called the Patrick seamount, is an example. Magnetics Magnetic profiles were taken simultaneously with seismic reflection profiles and hence are also normal to 85 Profile K-K** Ponded, flat lying- sequence of fine grain sediments soutli of the Mazatlan basin and west of the Tres Mar i a s Is1and s• 86 K K' nr : ^ - _ —: , >^w. ^ V*,v‘*? :v-"--r • A C - A - A A - — - r- T " - 4 " --- r. - ■ "r: ]'---------; : ^ - A . . . ~ ' - - J - : - ■ ' ! . • • --^:;"...•-., . . . _ r. . . ! - - - J . . .,. ..,v....4 A .L :C S ; ,-' ...........' • ...i... * ..,_ •. 1. y. i r t - . r 0 10 KM rllOO -1500 1900 1-2300 -2700 -3100 H H - 3 W > 3 0 0 Profile L-Lf, Inferred turbidite sedimentation around the Patrick seamount south of the Mazatla.n basin and west of the Tres Marias Islands, 88 " "F ' - ■ : j-v- 0 10 KM 1 _______________________________ I 00 VO M E T E R S inferred fracture zones (plate 8), Normally, magnetic surveys would be taken normal to inferred sea floor spread ing centers. However, as Has been discussed, previous workers (Larson, 1972; Larson ejb al. , 1972; Klitgord e_t al,« 1974) have adequately shown symmetric anomaly patterns not to exist inside the Gulf of California but only at the mouth of the Gulf, Profiles taken normal to fracture zone trends, a procedure adopted by Henyey and Bischoff (l973)> provide an opportunity to study magnetic varia tions not observed in surveys parallel to the inferred fault trends. Linear positive and negative magnetic anomaly trends are observed to be in association with bathymetric (structural?) trends (plate 8). Positive trends are generally associated with regions of little or no sediment accumulation (compare plates k and 8) which also appear to be zones of active faulting. This association is not without exception, however. Other inferred structural trends have decidedly negative anomaly trends. Anomalies over seamounts are highly positive suggesting recent volcanic activity. In the Carmen basin trough, negative magnetic anomalies of low amplitude were measured. Along the northeast escarpment, however, there is aLUeament of high positive anomalies, the highest being approximately 1000 gammas. A similar anomaly pattern was observed by Larson, 90 Mudie and Larson (1968) from profiles taken parallel to the trend of the Basin. This positive lineament does not coincide with the bathymetric expression of the escarpment but is slightly oblique to it. The extent of this linea ment is not dictated by the extent of the escarpment but only by the extent of the basin. On the flanks of the basin the anomalies become negative. The uniform 0-200 gamma negative anomalies over the basin extend along the linear feature corresponding to the inferred structural trend between the Carmen and Farallon basins. Only at the northwest end of the Carmen trough is there a 200 gamma positive anomaly over the basin proper, which increases to 400 gammas over the northeast escarpment. While the bathy metric expression of this scarp trends 305°> the strike of the positive anomaly lineament is 300°. Both the magnetic and bathymetric trends intersect at the northwest end of the basin. It is possible that this somewhat eroded es carpment (Sharman, 1976^0 is not at present the locus of active tectonism but is a remanent of previous activity. The northern half of the Farallon basin central trough, the flanks and the northeast escarpment are characterized by positive anomalies of 200-300 gammas. The southern half of the central trough and the southwest escarpment show a negative anomaly of 0—250 gammas. South west and parallel to the southwest escarpment is another 200 gamma lineament. This lineament is not associated 91 with, any mapped bathymetric or structural feature and its origin at this time is unknown. Sharman (1976a) and Larson, Mudie and Larson (1968) have identified lineated anomalies on the flanks of the central Farallon basin, however they were unable to identify any reversal sequence or a characteristic spreading rate because of the low amplitude ot the anomalies. Sharman further suggested that the high anomalies on the flanks may be due to fault ing or intrusion parallel to the central trough. The nega tive anomaly lineament over the southwest escarpment of the basin is similar to those in the Carmen Basin and may be of similar origin. The Pescadero Basin Complex and Ceralbo trough region is characterized by high positive anomalies parti cularly in the northern Pescadero basin and the Ceralbo trough. Low amplitude positive and negative anomalies (5:^100 gammas) persist over the rest of the Pescadero Basin Complex and its flanks. There are no discernible linea ments associated with or parallel to bathymetric ex pressions of inferred active structural features. The anomalies over the flanks of the northern Pescadero basin are approximately 250 gammas in contrast to the low nega tive values over the flanks of the central and southern Pescadero basins. The lack of anomaly trends in this region may suggest that recent intrusion has occurred along many inferred fault zones causing a confusion of anomalies. 92 Magnetic anomalies abruptly increase to high positive values to the south of the Pescadero Basin Complex. Specifically, the Alarcon seamount and Alarcon rise have anomalies as high as 840 gammas over them. Larson (1972) has also noted symmetrical highly positive anomalies over the Alarcon Rise. Anomalies decrease toward the Mexican continental shelf becoming slightly negative at the es carpment but increasing to low positive values on the shelf. Profile coverage on the shelf is, however, minimal making the delineation of trends difficult. Only a small number of profiles were taken over the Mazatlan basin because of the amount of data (Larson, 1972) that already exists. The profiles taken in this study confirm a high positive anomaly over the Mazatlan basin. There appears to be a low amplitude lineament which follows the trace of the Tamayo fracture zone across the mouth of the Gulf. The amplitude of the anomaly trend seems to be related to the degree of bathymetric expression and sediment thickness on the fracture zone. Near Baja California the anomalies are negative and of low amplitude, while bathymetric expression is low or nonexistent. Be tween Baja and the Mazatlan basin, the anomaly is highly positive in association with inferred recent tectonism as evidenced by lack of sediment along the inferred structural trend. At the Mazatlan basin the anomaly becomes highly negative possibly due to the sediment thickness contrast 93 between the sediment-free rise and the sediment filled depression to the north, of the Mazatlan basin. A high amplitude, positive anomaly of up to 350 gammas over the Mazatlan basin, probably delineates the main extrusive zone of the inferred spreading center. Seismicity Earthquake epicenters in the Gulf of California recorded by the Worldwide Standardized Seismograph Network (National Geophysical and Solar—Terrestrial Data Center, NOAA, Boulder, Colo,, written communication, 1976) for the years 1967-197^ were plotted and compared to bathymetry (plate 9)* Data from 1958 to 1966 were excluded due to the unacceptable error of epicenter location, 1967—197^ - events o were computer located with an —,1 error. All magnitudes are between 3*0 and 6,3 on the Richter scale. Several events have been located in the Carmen basin and along the inward facing escarpments. Southeast of the basin trough another cluster of epicenters have been located which also may be indicative of recent faulting, however, lack of seismic reflection profiles in this area does not allow the delineation of structural trends. More over, there may be less precision in the location of these events and hence they are located slightly offset from any readily discernible bathymetric expression. In the Farallon basin no recorded events are located 9k in the central trough, however, several are located on the southeast flank and along both the northeast and southwest escarpments* Again error in the location may have placed the epicenters onto the southeast flank rather than in the central trough, however, Sharman (1976a) has indicated from study of seismic sections in this area that the flanks of the Farallon basin may be areas of active faulting and intrusion* In the Pescadero Basin Complex a significant number of seismic events in the last ten years fall in the north and south basins, with no major earthquakes occurring in the central basin. The Ceralbo trough is the location of three major events at two different times with magnitudes between 4,5 and 5*6, South of the Pescadero Basin Complex recent major earthquakes are infrequent and do not correlate well with bathymetric trends. There are relatively few earthquakes on the East Pacific Rise at the mouth of the Gulf until just south of 21°N latitude (Larson, 1972, figure 3 data after Barazangi and Dorman, 1969), While it first appears that the paucity of seismici ty in the mouth of the Gulf is contradictory to the inter pretation of zones of inferred recent tectonism, it must be stressed that all events presented here are of magnitude 3,0 or greater. Those events less than 3*0 on the Richter scale are not included nor probably detected by the seismo- 95 graph, network. Recent studies using Ocean Bottom Seismo graphs (OBS) (Lewis and Lister, 1976; Prothero ejt al.. 1976) and sonobuoys (Reichle, 1975) have greatly increased the detectibility of microearthquakes and earthquake swarms of low magnitude. Many microearthquakes of approximately 1.0 magnitude were detected along the East Pacific Rise including the Mazatlan Basin in a recent survey by the University of Washington for a Deep Sea Drilling site in the Gulf of California (w. Snydsman, personal communication, 1976). Large earthquake swarms have been detected by Reichle (1975) in the Guaymas basin and by Thatcher and Brune (l97l) near the Colorado River delta. Therefore, it is possible that other inferred structural trends which appear to lack seismicity of greater than 3*0 magnitude may have significant microearthquake activity. Heat Flow Heat flow measurements presented in this study have been reported by the following workers: L. Lawver (1973* 1975, 1976), R. von Herzen (1963) and B. Lewis and others (1976). Data and the conclusions of these works have been discussed in the Previous Work section of this study. Discussion of Data Geophysical data collected for this study in the Southern Gulf of California appear to confirm the in- 96 ferences of previous workers (Moore and Buffington, 1968; Larson ejt al. , 1968; Larson, 1972 5 Moore, 1973) that the Gulf of California is an active tectonic zone and link be tween the East Pacific Rise and the San Andreas Fault system. However, detailed surveys reveal that the tectonics in the Southern Gulf are considerably more com plex than had been thought prior to the detailed surveys of Henyey and Bischoff (1973) in the Northern Gulf and Bischoff and Henyey (1974) and Sharman (1976a) in the Central Gulf. Interpretation of the complex pattern of fault traces mapped (plate 6) in the Southern Gulf can be sup ported to a large extent by the patterns of sediment dis tribution and sediment thickness (plate 10). These pat terns and thicknesses appear to be influenced by two but possibly three major mechanisms. The sediment patterns suggest that continuous plate motion over the last 4 MY has shifted sediments and/or not allowed large accumula tions of sediment to exist along the inferred active plate boundary. Terrigenous sediments possibly in the form of turbidite flows as evidenced from seismic profiles presented here and documented by Moore and Buffington (1968) and rapid biological sedimentation (van Andel, 1964 Calvert, 1966) dominate areas bordering the presently active tectonic zone (La Paz Bay and Basin, Mexican con tinental shelf; region south of the EPR trend). A third mechanism, which is probably of much lesser importance and has not adequately been substantiated, is bottom and tidal currents# Bischoff and Henyey (l97^) documented strong surface currents (8 km/hr) in the Sal Si Puedes channel between Baja California and Xsla Angel de la Guarda in the Northern Gulf province# They surmised that the lack of sediment on the channel floor was due to the scouring action of strong bottom currents# The Ceralbo trough may be an analogous environment for bottom scouring. The sedimentation patterns characteristic of an individual area appear to be the result of some combination of these three mechanisms. However, the combination is not a random mixture but rather the dominate mechanism usually discernible from the thicknesses and the change in thick nesses seen in the seismic profiles, the form of the sedi ments (flat-lying or distorted), the geographic location (proximity to the inferred active plate boundary or areas of high biological productivity) and the sediment type found (organic mud, pelagic clay, sand, etc.)# Hith high sedimentation rates (van Andel, 196^) and accepting a 6 cm/yr sea floor spreading rate along the inferred plate boundary (Larson, 1972), it can be inferred that in regions of continuous active tectonism sediments will not accumulate as quickly as in regions where tectonism is not occurring or occurs episodically. Thus, it can be surmised that unusual accumulations of sediment 98 in what appear geomorphically to be tectonic elements may be the result of tectonic activity or more precisely the lack of it. As seen in seismic profile E-E1-E", the Central Pescadero basin has an unusually large amount of sediment accumulation compared to the northern and southern basins. The basement low between the Central Pescadero basin and the Ceralbo bank has been filled. This sediment wedge appears as a linear feature on the isopach map (plate 4). The reason for these anomalous sediment ac cumulations is unclear as a sedimentological or tectonic explanation may be equally viable. One possibility is that the Central Pescadero basin is in the process of be ing tectonically deactivated, i.e., rifting at a slower rate compared to other inferred spreading centers, and consequently is being filled with sediment. The second possibility presumes that turbidites are being channeled preferentially into the Central Pescadero basin. Limited data on sedimentation rates along the trend of the Pescadero basin complex suggest a uniform rate of 50 cm/ 1000 yrs (van Andel, 1964; this study). Also, a bathy metric high exists directly to the northeast and in juxta position to the Central Pescadero basin which reasonably could represent a barrier to turbidite flows. The north and south Pescadero basins do not have such a sediment barrier and more likely would have sediment channeled to them. From seismic profiles D-D*, G-G* and H—H* this ap— 99 pears not to be the case. The sediment cores from the central basin show no signs of turbidite sands or silts but only homogenous olive gray mud. These lines of evidence lend credence to the hypothesis of tectonic de activation of the Central Pescadero basin and sufficient continuous spreading to negate any rapid sediment accumula tions in the southern and northern Pescadero basins. The nonexistence of symmetrical magnetic anomalies about inferred spreading centers neither confirm nor refute plate tectonic theory in the southern Gulf of Cali fornia. Where one line of evidence is inconclusive, others such as heat flow patterns (plate ll) and/or seismic event patterns (plate 12) with fault plane solutions indicative of strike slip motion (Sykes, 1968 and Molnar, 1973) provide more concrete evidence of recent tectonism. Of course, this pattern is not always the rule. Just the opposite is observed on the Alarcon Rise. This inferred spreading center is neither bathymetrically nor seismically prominent and only one heat flow measurement (5*7 HFU) exists (von Herzen, 1963)• However, symmetric magnetic anomalies measured over this area (Larson, 1972) strongly suggest that this low relief ridge is indeed an active rift zone. The magnetics presented show trends of high positive anomalies along inferred recent, sediment free fault zones. These anomalies may be proof of recent faulting and highly 100 magnetic rocks near the surface. As with other lines of* evidence presented, however, this is not a consistent relationship over the entire southern Gulf* region. Several trends of* positive anomalies are seen over areas of* thick sediment accumulations and inferred tectonic in activity (compare plates 13 and 10), Consequently, the magnetic anomaly patterns are difficult to interpret and may be the result of more than one process in this complex tectonic environment. 101 TECTONIC INTERPRETATION Discrete centers of sea floor spreading In tlie Mazatlan and Farallon basins and along the Alaryon Rise are observed in contrast to areally diffuse tectonic zones of oblique rifting and extension in the Carmen Basin and Pescadero Basin Complex (plate 14)• Sharman (1976a) has proposed several lines of evidence supporting the phenomena of jumping spreading centers and episodic rift ing in the Farallon (profile B-Bf) and Carmen (profile A-A,-A1 ') basins respectively. Other evidence of jumping spreading centers may be located with detailed surveys over other basins. Evidence for relict or no longer active structural trends especially in the Pescadero Basin Complex, here interpreted to be transform faults, is submitted (profile E-E*-Eu). I suspect that more seismic profiling on the flanks of the Carmen basin would reveal similar features. The Pescadero Basin Complex can be mapped as a series of these relict and active fault traces subparallel to the general trend of the major transform faults. Convergence and divergence of fault traces are mapped in the southern and central Pescadero basins. An analogy to this tectonic regime is seen in the Southern California Borderland where convergent and divergent strike slip faulting (Howell 102 et al. , 197^) niay have produced bathymetric highs seen as the offshore islands and banks and lows seen as the inter spersed basins, Crowell (197^) surmised that converging and diverging faults form where a weak or diffuse plate boundary zone exists between two rigid plates. The faults in the plate boundary zone are either parallel or sub parallel to the direction of predominate plate motion. Those that are subparallel need only be oblique by a few degrees. With continued plate motion the faults parallel to plate motion thrive and grow longer explaining the great length of some inferred transform faults in the Gulf. Those that are subparallel are rotated out of the predominate plate motion trend and transformed from pure strike slip motion to more oblique slip depending on the amount of rotation. In the Gulf of California rotation and oblique slip faulting may be occurring along with discrete jumping of spreading centers (Sharman (l97^^-)« The relative abruptness of the change in the locus of crustal accretion in spreading centers may also cause transform faults to be abandoned and subsequently attached to the more stable (i.e., less tectonically active) part of the plate as spreading rifts the deactivated transform fault away from the active plate boundary. As has been discussed, these abandoned transform faults do not necessarily have bathymetric expression; in the Gulf of California most of them do not because of the 103 high, sedimentation rates (van Andel, 1964) prevalent in the Gulf. Once the transform has been abandoned and is rifted away from the active plate boundary, rapid sedi mentation fills the fracture zones until an equilibrium profile is established (profile E-E'-E”). It is difficult to speculate as to how long the transforms have been abandoned for it is speculative to say that knowing the sedimentation rate in the area and the thickness of sedi ments in the abandoned fracture zone, an age could be calculated from the time the transform began to be filled. If turbidity flows fill the fractures, the variation in the amount of time it takes to fill any one fracture zone could be large. If it were possible to calculate the age of cessation of tectonic motion on a number of relict faults and jumped spreading centers, a paleotectonic history of spreading in the Gulf could be attempted. A more precise sedimentological history is needed for those areas where abandoned transform faults are delineated. The hypothesis of rotation of transform faults out of the active plate boundary zone and fixation to a more stable plate margin is supported by evidence from the change in strike of fault plane solutions on fracture zones along the Gulf trough (Sharman, 1976b). These data suggest clockwise rotation as well as northwest plate motion. A significant amount of rotation, realignment and deactivation of faults appears to be occurring in the 104 Pescadero Basin Complex. Active extension and rifting may be shifting to the east causing the Central Pescadero basin to be deactivated and in the process of being filled with sediment. The arguments previously presented for the over 400 m of sediment observed in the central Pescadero basin as opposed to the northern and southern basins support a tectonic rather than sedimentological explanation. Fur ther, geophysical evidence such as heat flow and seismicity studies in this area is lacking and until more data is collected this explanation must remain a working hypothesis. The proposed Alar9on Rise spreading center remains a geomorphologic enigma. Despite all the geophysical evidence supporting an active accretion center in this area, the bathymetric expression is a low relief ridge (Lewis e.t al. , 1976) > geomorphically distinct from the rest of the inferred centers of crustal accretion inside the Gulf. Why this spreading center is different from the rest is unknown. Its morphology is, however, similar to that of the East Pacific Rise further to the southwest. A possible explanation for the smooth profile may lie in the proximity of the Alarcon rise to Baja California and the terrigenous sediment derived from it. The rapid spreading rate (6 cm/yr), width of the locus of active accretion within the plate boundary zone and the downward block faulting of the axial block (Rea, 1975) may have combined to produce a low relief volcanic ridge segment 105 which is in turn bathymetrically smoothed by sediment deposition. A more classic Mid-Atlantic Ridge cross-section of* rift valley and symmetric ridge crests is seen in the Mazatlan basin but only where the East Pacific Rise and Tamayo fracture zones intersect. Further to the southwest the morphology of the ridge is similar to the Alarcon Rise. The depression at the intersection of the Tamayo and EPR which has come to be known as the Mazatlan basin is in fact a manifestation of the intersection of these two major tectonic elements. Xf the Gulf of California evolves in a similar fashion to other young ocean basins, undoubtedly with time the plate boundary will stabilize into longer spreading seg ments and fewer transform faults. Further consolidation of spreading segments may occur following a scheme pro posed by Sharman (1976a) where spreading centers are cap tured by one another forming larger spreading segments as they migrate over a distance described by a normal dis tribution curve. Xf overlap of the spreading centers occurs, capture may or may not ensue and the plate boundary proceeds toward a more stable configuration. 106 CONCLUSIONS The following conclusions can be made on the basis of the data presented: 1. The zone of inferred crustal accretion in the Southern Gulf of California is extremely complex compared to the Mid—Atlantic Ridge or the East Pacific Rise, sug gesting that the Gulf plate boundary is in the process of maturing into a more stable plate boundary. This evolu tion into a series of spreading segments and transform faults proceeds via jumping and capture of spreading seg ments and the abandonment of apparently unnecessary trans- form faults, 2, The plate boundary appears at present to be a discrete center of spreading in three places: the Mazatlan basin, the terminus of the East Pacific Rise; the Alarcon Rise, which has the morphology of a fast spreading ridge such as the EPR but is in close proximity to the con tinents and the Farallon basin, a classic pull apart rhombochasm where injection of sediment and simultaneous spreading cause the morphology of the spreading center to be a basin rather than a ridge (plate 14). The remainder of the plate boundary in the Southern Gulf is an unstable extension zone of leaky trans form faults where oblique tension and strike slip motion 107 occur more or less equally though not necessarily simul taneously. The result of this type of tectonism is deep elongate basins with steep fault scarps frequently with remanents of basement left as evidence of episodic spread ing or frequent changes in location of spreading with time • 4. Evidence exists for a component of clockwise rotation (Sharman, 1976a) of the plates which may be responsible in part for the rafting of transforms out of the active plate boundary and a fixture to the stable plate margin. Subsequent to deactivation of the transforms rapid sedimentation possibly in the form of turbidity flows or biological imput fills the fracture zones producing un usual patterns of sediment thicknesses. 5* To a large degree, the sediment patterns and thicknesses observed in the southern Gulf are evidence of active tectonism with bottom sediment scouring by currents secondary in the distribution of sediments already de posited. The source of the sediments is continental run off in the form of turbidity flows, slumping or pelagic sedimentation and biological sedimentation (van Andel, 1964; Calvert, 1966). 108 PART II GEOCHEMICAL EXPLORATION FOR HEAVY METAL DEPOSITS IN THE SOUTHERN GULF OF CALIFORNIA 109 INTRODUCTION Having complied a significant amount of geophysical data strongly suggesting the Gulf of California to be an active divergent plate boundary, exploration for heavy metal deposits similar to deposits found in the Red Sea and associated with the tectonic elements can proceed. However, the tectonic similarities to the Red Sea are not by themselves sufficient reason to search for heavy metal deposits in the Gulf of California. The proximity of a potential heavy metal source is not the reason heavy metal deposits exist along divergent plate boundaries. Other wise metalliferous sediments would be found along the en tire length of the mid—ocean ridge system, which is not the case. Geochemical and sedimentological environments are critical to the survival of heavy metal deposits with time. Is the Gulf of California a viable geochemical environment for the deposition of hydrothermal heavy metal deposits similar to those found in the Red Sea. If base metals are solubilized from the oceanic crust by hydro- thermally circulating, acidic, altered seawater and trans ported to the sea floor as a metal rich fluid as suggested from experimental work (Bischoff and Dickson, 1975; Sey- 110 fried and Bischoff, 1977), a suitable geochemical environ ment must exist for the precipitation of the metals from the fluid in order to form the heavy metal deposit* On the East Pacific Rise, south of the Gulf of California, metalliferous sediments have been found (Bostrom and Petterson, 1966, 1969) to exist as ferro manganese hydroxyoxides (Dymond ejt al, , 1973)* However, while Fe and Mn are approximately an order of magnitude higher in these sediments than in Pacific pelagic clays (Goldberg and Arrhenius, 1958), Cu, Ni and Zn are not ob served to be similarly enriched over concentrations found in Pacific pelagic clay* Xn the Red Sea, however, all base metals are enriched over pelagic clays especially Cu, Ni and Zn which appear to be precipitated mostly as metal sulfides (Bischoff, 1969)* The presence of metal sulfides in the Red Sea indicates the presence of organic matter, H^S and a reducing geochemical environment of deposition as opposed to an organic matter deficient, highly oxidizing environment on the East Pacific Rise. As will be seen in the following sections, the Gulf of California is also an environment of high organic matter content (van Andel, 1964; Calvert, 1966) and hydrographic conditions conducive to the formation of H^S rich, mildly reducing sediments (Berner, 1964b). Therefore, it is pos sible that a metal rich hydrothermal fluid exhaled along the active tectonic zone may have its solubilized metals 111 trapped and concentrated as base metal sulfides which would remain as a stable phase in the sediments under reducing conditions. Xt is further noted that Pliocene base metal sul fides at the Boleo Copper deposit (Wilson and Rocha, 1955)$ the Lucifer Manganese deposit (Wilson and Veytia, 19^9) and pyrolusite deposits on Punta Concepcion (Noble, 1950 ) along the east coast of Baja California are thought to have been formed by submarine hydrothermal processes. If a hydrothermal origin for these rich ores is correct, processes which formed these deposits at the suggested time of initial breakup of the continents to form the Gulf (Karig and Jensky, 1972) may still be occurring today along the presently active tectonic boundary. Part II of this study describes the search and techniques used to find heavy metal deposits associated with tectonic elements or any evidence of hydrothermal imput into the sediments and the results and implications of that exploration. 112 BACKGROUND History of* Mining and Ore Deposits in Baja California The descriptions of California written by the Jesuit missionaries (Aschmann, 1966) include references to ore deposits in Baja California including the silver mines at San Antonio near Ensenada and Santa Ana, south of La Paz, which were being commercially mined in 17^8. There are peaks and hills which give an indication of extensive ore deposits because some of their gravels yield silver when they are thrown on a fire. However, because of the extreme sterility and lack of firewood which becomes progressively scarser as one proceeds northward, up until now silver mines are only worked in the far south, the only fertile area. Copper is occasionally found free in the rocks and also may be recognized in rocks of bright green color. These were used by the Indians to paint their arrows. When rocks of this color are thrown in a fire even though they are soft they do not dis integrate, rather they give off little drops of copper. Harder rocks also give off copper when put in a fire. Pieces of virgin iron of various sizes and containing little foreign matter have been found, but in spite of considerable effort which has been expended it has not been possible to find the vein. There is native sulfur in great quantities which requires no more treatment than loading it and hauling it away. There was some blue vitriol or copper sulfate, but in the very place from which it was collected it cannot now be found, either because it was exhausted or because of lack of knowledge and recognition of it. * . . Although there are a number of hills that have craters at their summits or near them and which appear to be volcanoes, they have not been observed to erupt fire; but they do give off smoke from time to time. One of these craters has 113 tine peculiarity of having hot sand at its mouth . . . Fumerols or blowholes are found in two places; one is on a rocky slope and the other in an arroyo and out of both of them the wind blows continuously. It was not until the 1850*s, however, that ex ploitation of the mineral wealth of Baja California began in earnest. Journalists* reports (Leese, I865) state that the mines were not worked because of strong opposition from the missionaries. The miners were considered to be degenerate and would surely inflict their vices upon the settlers. E. Gould Buffum (Buffum, I850) was an army lieutenant stationed in La Paz during the 1846-1848 con flict between Mexico and the United States who wrote of the serenity of La Paz as well as the wealth buried in the mountains nearby. A residence of six months upon the Gulf of Cali fornia entirely changed the opinion I had previously entertained of the country (Mexico), which had been based upon reports of those who had merely sailed up or down its rugged coast. It has been described as the * tail end of an earthquake*— as possessing a soil upon which nothing could be grown, a hot and sickly climate and containing no internal resources of value. Buffum goes on to say: The resources of Lower California are its mines of silver, gold, copper and iron, the former metal being most abundant. The whole mountain range, which ex tends along the coast, is one immense silver mine equal in richness to those of Mexico or Peru. In making inquiries for a place to search for silver in Lower California, the old settlers in reply merely point their fingers to the mountain range and say *Por hay* (that way, anywhere there), and it is a fact that a shaft may be sunk in any part of the 114 mountain and silver ore is always extracted, varying in richness from 15 to 70° / o of* pure silver. The principal silver mines at present wrought are in San Antonio, half-way from La Paz to Cabo San Lucas, Mining companies began to spring up in the late 1850*s. The Mexican Company opened the first commercial mine in 1859 working silver deposits in San Pedro and San Nicholas, south of La Paz, The ore from a 2-10* thick vein brought about $150 a ton. The Triunfo, Peninsula, Santa Cruz and Marin Companies all worked mines at this time with others eager to start operations. Other economic deposits were to be had from the rugged terrain of Baja California, A journalist for the Alto Californian, stationed in La Paz, wrote (Leese, I865)s Our peninsula is rich in other minerals besides gold, silver and copper; we have abundances of iron ore of the finest quality convenient to the seaboard and paying as high as 7 5 ° / ° » Veins of black oxide of manganese, beds of alum, asphaltum, sulfur, gypsum and alabaster; pearls from the sea, fish in bound less shoals and whales visit our bays and harbors on both shores annually. While mining in Baja California was only in its infant stage in the 1850's, the 1849 gold rush to Sutter's mill in northern California was on. Four decades later when gold xvas discovered near IDnsenada in northwest Baja California, gold fever was still very much alive. The gold rush of I889 brought miners and fortune seekers to the Santa Clara valley to mine the placer deposits (Lingenfelter, 1967)# The placer as well as the quartz-gold vein deposits were quickly played out. Since I885, however, the 115 French owned Compagnie du Boleo had been organizing- the mining of what would become the most economic deposit in the history of mining in Baja California. The Boleo copper deposit was discovered at Santa Rosalia in 1868 but not mined until 1885 (Wilson and Rocha, 1955)* Ores of 4-5 percent copper were treated at a processing plant near the mine to produce blister copper. Total production from 1886 to 19^7 was 13*622,327 metric tons of ore and 5^0,3^2 metric tons of copper. Currently the mine has reserves of only low grade ore and mining operations are minimal. Pliocene Ore Deposits and Their Tectonic Implications Pliocene age ore deposits while important in rela tion to submarine hydrothermal processes in this study are by no means the bulk of mineralization in Baja California. The Mid-Cretaceous gold deposits of the Real del Castillo and Alamo districts in northwest Baja California and the early Tertiary Sierra de Victoria and El Triunfo silver complexes south of La Paz were also important (Wisser, 195^0. However, the geology of these deposits does not indicate a submarine hydrothermal origin but rather a mesothermal origin from fluids associated with the Southern California and La Paz batholiths. Consequently, the focus of this section will be on the geology and origin 116 of the Boleo copper deposit, Lucifer Manganese deposit and the pyrolusite vein deposit at Punta Concepcion (fig. 6). Boleo Copper Deposit The geology of the Boleo deposit has been described in detail by ¥ilson and Rocha (l955) and Touwaide (1930) and references therein from which the following summary is taken. The Boleo (formation) deposit is situated in early Pliocene interbedded tuff and tuffaceous conglomerate beds which unconformably overlie the Comondu volcanics of Middle Miocene age. The ore deposit is also underlain in places by a basal marine limestone and fossiliferous sandstones. The areal limit of the limestone is thought to indicate the extent of the early Pliocene seas and is regarded as the oldest known marine bed to be deposited in this area of the Gulf of California. The limestone is very impure and contains approximately 2 percent Fe^O^ and MnO. Thick sequences of gypsum which overlie the marine limestone are frequently seen to be interfingered with the ore beds. Touwaide (l930) suggested that the gypsum was formed by mixing of sulfate water from submarine hydrothermal springs with seawater. Alternatively, Wilson and Rocha (1955) surmised that evaporation in restricted bodies of seawater more likely formed the gypsum. 117 Figure 6 Location of major ore deposits in Baja California. 118 32 Rool del Castillo Alamo 116 112 10 * 28* 114 26 24< El Triunfo Sierra d < Victoria ORE DEPOSITS OF BAJA CALIFORNIA 119 The ore occurs in thin ore horizons of* soft, dark clayey tuff, each horizon associated with an underlying conglomerate or tuffaceous sandstone bed depending on the proximity to the Gulf of California. The average thick ness of the ore beds is about 80 cm although beds as thick as 5 ni were found in early mining. Unconformably overlying the Boleo formation is the Gloria formation, a marine sandstone and conglomerate facies. Structurally, the Comondu volcanics were faulted and tilted prior to the deposition of Pliocene formations. Most of the faulting is normal and westward dipping which produced eastward tilting blocks. Xn the Boleo district proper, some faults cut both the Comondu and the overlying Pliocene formations. It has been suggested that faulting originated in pre-Pliocene time with renewed activity after deposition of Pliocene beds. The deformation of the Comondu volcanics are economically important in that they may have been the conduits for submarine hydrothermal solutions as evidenced by the veinlets of Mn and Cu along the faults. Uplift and tilting deduced from uncon formities has occurred at least four times since the com mencement of Boleo formation deposition. Faults off setting the Pliocene beds are normal faults which have a regional strike of N 10—45° U and are parallel to the shoreline of the Gulf. The average dip on the faults is 65-70°. 120 After the first encroachment into this region in early Pliocene time of the then protogulf of California (Karig and. Jensky, 1972), local accumulations of detrital and marine limestones were laid down on the Comondu volcanics deposited earlier from offshore sources. Gypsum sequences were also being deposited after which a long period of subaerial erosion and volcanic eruptions deposited elastics and tuffaceous material to the region. Sediment sources changed from east to west and deltaic deposits were laid down, being interrupted at least five times by eruptions of volcanic ash and dust producing layers of tuff upon consolidation. At the end of the deposition of the Boleo formation solutions containing Cu and Mn are thought to have percolated through the clayey tuff beds depositing and concentrating the metals. The origin of the Boleo deposit is, however, controversial. Touwaide (1930) presented evidence that the copper was derived from sedimentary tuff deposits above the ore beds via extraction by percolation of con nate waters. Wilson and Rocha (1955) objected to the Touwaide theory on the following grounds: 1. It is improbable that the overlying tuff con tained enough Cu to serve as a source. 2, There is a lack of correlation between the thickness of the supposed source beds and the distribution of the ore. 121 3, A problem arises with, concentrating and trans porting the Cu in beds below the water table, h, The inability of the theory to explain the presence of vein deposits in the volcanics below the Boleo deposit, Wilson and Rocha (1955) subsequently submitted the hypothesis that the metals were transported via submarine hydrothermal solutions ascending along fractures and trapped in the clayey beds. Evidence for a submarine hydrothermal origin for the metal rich solutions includes: 1, The presence of veinlets of mineralization in the Comondu volcanics which are thought to be sub- aqueously emplaced, 2, Subaqueous mineralization along the contact be tween the Comondu volcanics and the Boleo formation in association with marine limestones, 3, Concentration of the ore at the bottom of the beds indicating a source of the metal rich solutions from below the ore beds. Considering the north-northwest trend of the ore associated structures in the deposit as well as the plate tectonic time framework, it appears that a submarine hydrothermal origin of the metals in conjunction with the formation of an active divergent plate boundary is reason able. 122 Lucifer and Punta Concepcion Mn Deposits The Lucifer Mn deposit is located just north of Santa Rosalia (fig. 6). The Mn deposits are intimately related to the Boleo Cu deposits as they are situated in the same formation and MnO^ minerals are commonly found in the Cu bearing horizons (Wilson and Veytia, 19^9)* Evidence of iron oxide, manganese oxide, copper minerals and jasper in veins in the Comondu volcanics, manganese oxide transgression from tuff ore horizons into adjacent conglomerates and the localization and structural control of manganese deposits lead Wilson and Veytia to propose a submarine hydrothermal origin for the Lucifer deposits. Noble (1950) reported on Lower Pliocene rocks of marine and nonmarine origin on Punta Concepcion (fig. 6) contain ing veins of almost pure pyrolusite. Most of the mineral ization is in basalts, conglomerates and some intrusive rocks. Noble invoked a similar hydrothermal origin to this deposit noting the structural and stratigraphic similarities with the Lucifer and Boleo deposits to the north. In summary, strong evidence has been presented by previous workers that the Boleo, Lucifer and Punta Concep cion deposits have been deposited under marine conditions in association with north-northwest structural trends. These trends appear to be similar to the predominate trends 123 seen along* the Inferred tectonic boundary today in the Gulf of California* The suggestion that these three deposits have been formed by the ascension of hydrothermal fluids and the association of these hydrothermal processes with divergent plate boundaries as seen in the Red Sea and on the East Pacific Rise indicates that metallogenesis in the Gulf of California may have been associated with the initial breakup of the continents to form the present Gulf of California, 124 SOURCES OF METALS IN GULF OF CALIFORNIA SEDIMENTS Metals in sediments can ultimately and independently be related to only one source, the igneous, metaraorphic or sedimentary rocks from which they are initially weathered or leached. The processes of releasing the metals from the source rocks as well as the states and phases in which the metals are presently found, however, are many and varied. Excluding the metals found in the source rocks, those found in all other states are in secondary or more likely tertiary stages of the geochemical cycle having proceeded along a distinct chemical pathway until they arrive at the most stable form for the chemical environ ment in which they reside. In the geochemically diverse environments of the Gulf of California metals are found in at least three phases: detrital, hydrogenous, and bio- genous. A fourth phase, hydrothermal, may be sub stantiated by evidence subsequently presented. Source Rocks and Detrital Phases Metals from continental source rocks are trans formed upon chemical and mechanical weathering into a detrital clay phase with Fe associated either as the major constituent heavy mineral (goetite), major constituent in the clay mineral (illite, nontronite), minor constituent 125 in the clay lattice (montmorillonite, kaolinite) or as an oxide coating or adsorbed species on the clay mineral surface (Carroll, 1958)* Mn can also be transported as MnO^ coatings on clay surfaces* Other metals such as Co, Cu, Ni, Zn and Cd may be transported under oxidizing condi tions as adsorbed species on clay surfaces, or on Mn and Fe hydroxides (Jenne, 1968). While these metals can also be in solution, all are reported in concentrations of less than 10 ppb in river water (Hem, 1970)• When the metals in solution or possibly as colloids in river water come in contact with seawater, adsorption processes and precipita tion of colloidal hydroxides of Fe and Mn proceed* The Fe and Mn oxides will remain as stable oxide phases unless or until they are subjected to conditions of +2 +2 Eh and pH where they are reduced to Fe and Mn at which time the Fe may be transformed to Fe monosulfides and eventually pyrite and the Mn will be left in the pore water* The energy of interaction of the clay surfaces for the ions in solution may result from chemical interactions (ion exchange), van der Waals forces or hydrogen bonding* The negative charge found on clay surfaces in aqueous media such as seawater with a pH of 8*4 can occur in three ways (Stumm and Morgan, 1970)* 1. Chemical reactions at the clay surface may produce the charge* Functional, ionizable groups such as 126 -OH, -COOH, and -OPO^H^ are found on clay surfaces. Re actions involving ions and functional groups are pH dependent; a low pH produces a positively charged surface and a high pH a negatively charged surface. Reactions can also occur where the solute is coordinatively bound to the surface, for example: Mn02.H20(s) + Zn+2 = MnOOHOZn* (surface) + H+ These phenomenon are referred to as adsorption. Experi ments involving pH dependent adsorption of metals on to MnO^ substrates in natural waters have been discussed by Murray (1975) and 0 * Connor and Kester (1975). 2. Surface charges can be produced by isomorphous replacement within a lattice or lattice imperfections at the surface. 3* Surface charge can be produced by ion adsorp tion due to van der Waals forces and hydrogen bonding. Typical examples are organic complexes (humic acids) ad sorbed on clay surfaces. The adsorption of metals out of solution and onto the surface of clays depletes the con centration of metals in seawater to between .1 and 20 ppb depending on the metal. The metals have passed from the primary state of the source rock into two secondary states, a soil phase with some metals adsorbed on the clay surfaces or residing as oxide coatings and a solution phase, a minor amount of the total metals. 127 Source Rocks and Hydrothermal Phases Ocean tholeiitic basalt can also be a source rock for metals in the marine sedimentary environment. Seawater-basalt interaction leaches metals from the rock and transports them at low pH as a hydrothermal fluid to open ocean, oxygenated bottom waters where they are precipitated as hydroxyoxides. Sediments formed in this way have been found on the East Pacific Rise (Bostrom and Petterson, 1966, 1969). If such fluids are discharged into reducing geochemical environments such as are found in the Gulf of California, sulfide precipitation might result. The Red Sea is a location where base metal sul fides are being deposited along with Fe-montmorillonite and amorphous goetite (Bischoff, 1969)* Bischoff has proposed a model for the concentration of metals whereby Red Sea water circulating through the basinal sediments exchanges seawater So^ for H^S via bacterial activity. Chloride salts from the great thicknesses of evaporites present are also added. The metals are originally derived from organic rich shales beds above the evaporite sequence. The metals bound in chloride complexes are driven by geo thermal heating at the spreading center to percolate up through fissures and be exhaled on the sea floor. Pre cipitation and subsequent deposition occurs in small isolated basins. The metal rich sediments are overlain by a hot brine. 100 Further exploration and discovery of East Pacific Rise type metalliferous sediments around Banu ¥ahu vol cano, Indonesia (Zelenov, 1964), Santorini, Aegean Sea (Smith and Cronan, 1975)* the Mid-Atlantic Ridge (Thompson et al,, 1975)* along the Clarion fracture zone (Bischoff and Rosenbauer, 1977) as well as evidence of hydrothermal ore mineralization in the Indian and Atlantic Oceans (Rozanova and Baturin, 1971; Bonatti et al«. 1976) sug gest that the Red Sea may be a unique example of metal liferous sedimentation at a plate boundary* The premise of hydrothermal solutions precipitating metalliferous sediments has evolved with time and the ad dition of both observational and experimental data. Ex planations for the presence of these metalliferous sedi ments varied considerable since first discovered. Turekian and Bertine (l97l) suggested a twist on the Red Sea concentration mechanism whereby sediments were deposited in restricted rift valleys under locally reduc ing conditions. Similar conditions may exist in the deep basins of the Gulf of California making them a prime target for the exploration of heavy metal deposits. Turekian and Imbrie (1966) in trying to explain high transition metal-aluminum ratios in Atlantic Ocean sedi ments suggested ponding of fine grained, continentally derived sediments. Bender ejb al (l97l) invoked authigenic precipitation of Fe and Mn from seawater and Bertine (1974) 129 proposed weathering of volcanic debris and winnowing of* sediments as a concentration mechanism. The presently accepted model for the origin of metalliferous sediments on active oceanic ridges involves the circulation of large amounts of seawater through fractures in the oceanic crust (Wolery and Sleep (1976)# The seawater is heated and under confining pressure of approximately 500 bars forms an acid, hydrothermal fluid capable of solubilizing metals from oceanic basalts. The fluid acts as a transporting medium for the metals being driven along fissures to the basalt-seawater interface and exhaling the metals into the oxygenated bottom waters with the subsequent precipitation of ferric hydroxides with transition metals and other phases. Evidence from geophysical as well as geochemical sources in the context of plate tectonics has aided in arriving at the above process. Heat flow studies across active spreading ridges (Lister, 1972; Williams ej; al.. 197M concluded that a major portion of the heat flow is convective rather than conductive and that a cellular system of hydrothermal circulation was apparently occurring. As has been mentioned, heat flow studies in the Gulf of California reveal similar patterns of relatively low heat flow over the basins (spreading centers ?) and higher values over the flanks (Lawver, 1975» 1973)* Lawver sup ports the concept of convective circulation in the Gulf 130 because of* this evidence. However, to date no hot bottom water or metalliferous sediment accumulations have been found with these hydrothermal convective systems. Geochemical evidence is in the form of rocks dredged from mid-ocean ridges. Xn studying the chemical differences in pillow and holocrystalline basalts, Corliss (1971) concluded that differential cooling of volcanic ex trusions on the sea floor depleted Mn, Fe, Co and REE1s from the interior portions of the rocks and subsequently concentrated the elements in residual fluids. Access ibility to seawater resulted in the dissolution of the metals and the formation of chloride complexes which were eventually incorporated into the sediments. Hart (1973) also found that greenstones were depleted in metals. Evidence from isotopic studies of metalliferous sediments Dasch et al,. , 1971 and Dymond ejt al. , 1973) for sulfur, uranium and oxygen isotopes indicated compositions attrib utable to formation from seawater at low temperatures. Strontium isotopes suggested equilibration with seawater and lead isotopes showed a composition similar to mid ocean thoeiites. Experimental modelling of seawater- basalt interaction from 25° to 350° and 1-500 bars (Bis choff and Dickson, 1975; Seyfried ejb al,. , 1975; Seyfried and Bischoff, 1977) has clearly shown that the fluid produced in high water-rock ratio experiments has the capability to leach heavy metals from basaltic glasses and 131 keep them in solution for transport to the basalt — seawat er interface. Moreover, the proportion of metals detected in the fluids are consistent with those found in metalliferous sediments. Seawater and Metals in Biogenous Phases The metals from the continental and oceanic crustal sources have passed to a secondary stage, being mechanical ly deposited (oxide coatings on clays), chemically pre cipitated (metalliferous sediments) on to the sea floor or in solution in seawater. The metals can now move to Tertiary stages which can take many forms depending on the geochemical environment in which the metals reside. First, the metals in seawater. There are two possible pathways to the Tertiary stage, both of which involve scavenging the metals out of solution and onto a solid phase. One process is organically mediated, the other inorganically mediated. The role of plankton, copepods and radiolarian in the transition metal geochemical cycle is significant. These plants and animals have the ability to enrich metals 7-8 orders of magnitude in their systems compared to con centrations in seawater (Table 1, cols* 1 and 2). The average concentration of metals in planktonic material is, however, similar to the concentrations in shales and sedi ments from high productivity areas in the equatorial 132 Table I. Average composition of Equatorial Pacific and plankton, the Gulf seawater, shale and sediment from the of California (percent log abundances) East Element 1 2 ..... 3 ......... 4 5 SiO 1.55 - 5.19 1.68 1.69 1.31 Al -0.62 - 8.00 0.90 0.81 0.19 Fe -0.36 - 8.00 O.67 0.33 0.21 Ti -1.36 - 9.00 -0.35 - -1.13 Mn -1.79 - 8.70 -1.08 -1.5b -0.31 Ba -1.09 - 7.52 -1.24 - -0.34 Zr -2.69 - -1.70 - -2.37 V -2.73 - 8.70 -1.89 - -2.31 Cr -2.32 -10.30 -2.00 - - Ni -1.99 - 8.70 -2,02 -1.68 -2.22 Zn -0.67 - 8.00 -2.10 -1.88 — Cu -1.48 - 8.32 -2.24 -2,06 1 • 00 0 Pb -2.19 -10.32 -2.70 — - B -1.42 - 5.3^ -2.00 — -2.5k 1. Average planktonic matter (Bostrom et_ al., 197^0 “ total dissolution of ashed samples. 2. Seawater (Horne, 1969). 3. Average shale (Krauskopf, 1967)* 4. Average organic rich (8 percent Corg#) Gulf of California sediment (this study). 3. Average Equatorial East Pacific sediment (high productivity area - 13°N-3°S, 120°-180°¥) Bostrom, 1975* as reported in Bostrom _et al., 1974). Pacific and the Gulf of California (Table 1, cols. 1, 3> b and 5)• Exactly why plankton enrich trace metals in their biomass is unknown. One possibility may be that while processing the major nutrients (nitrates, phosphates and silicates) in the photic layer of the oceans, the organisms inadvertently incorporate the metals Mn, Fe, Cu, Ni, and Co. etc. into their systems. Once within the bio mass the metals can be used in different ways. The metals may be utilized as limited nutrients (Boyle and Edmund, 1975) forming metallo-organic complexes (Smayda, 1971; Saxby, 1969)• These complexes may be extremely stable with the metals forming the strongest complexes (Goldberg, 1957)* Metals may be strongly bonded with enzymes (chela tion) or taken directly into the structure of the exo skeleton. Different species respond differently to enrichment of toxic metals, especially Pb and Cd. They naturally seek to rid themselves of these toxins and frequently moult off exoskeletons (Martin, 1970) and/or excrete metal rich fecal material. The settling exoskeletons and fecal material can also accumulate metals by adsorption from seawater long after leaving the animal. Because of the fact that animals such as copepodes are extremely abundant and moult fre quently during their lifetime, this process may contribute significantly to metals in sediments, particularly in the Gulf of California where primary productivity is 2-3 times 13^ greater than in the open ocean at the same latitude (Zeitz— schel, 1969)* Regardless of how the metals are taken into the biological systems of the plankton, they are eventually released either by excretion, moulting, death of the animal or plant, settling or dissolution. Some of the metals may be returned to seawater to be recycled with upwelling nutrients, however, a large percentage of the metals remain ing as insoluble phases have a generally short residence time in seawater and are deposited and buried (Broecker, 197M• The fact that metals can be concentrated in the sediments in association with large amounts of organic matter is seen in ancient as well as recent environments of deposition, Calvert and Price (1970) presented evidence of high metal content in sediments on the Southwest African shelf where organic carbon exceeded 20 percent of the total sediment, Upwelling and trace metal entrapment by living plankton in an area of the Permian Kupferscheifer Sea (Brongersma-Sanders, 1966, 1969) may have led to the development of an anoxic basin deposit and subsequently the vast Kupferscheifer stratabound Cu—Pb—Zn deposits. Upon burial some of the metals associated with organic matter and detrital clays undergo bacterial reduc tion and subsequent diagenesis to sulfide phases such as pyrite. A portion of the metals can be taken into solution by oxidation of the planktonic protoplasm that has been deposited, others are strongly complexed with organic 135 material and resist degradation. More than likely the metals become intimately related to humic substances (humic and fulvic acids) which are probably the end product of the planktonic degradation (Nissenbaum and Swaine, 1976) and comprise between 40-70 percent of the organic material in the marine sediment (Nissenbaum and Kaplan, 1972). Concentrations of metals in humates from the marine environment as determined by atomic emission spectrographic analysis of unashed, sediment extracted humates are 8-100 ppm Mn, 600—3000 ppm Fe, 600-4000 ppm Cu, 100—2000 ppm Ni and 350—4500 ppm Zn as well as other metals. A sizeable portion of the total Cu, Mo and Zn, lesser amounts of Ni, Co and Pb and very little Mn, Fe and V in the sediments are associated with humates (Nissen baum and Swaine, 1976). The transfer of Cu and Zn from the mineral phase to the humates may be dependent to a large degree on the dissolved organic matter (DOM) in pore waters. Elements concentrated in DOM are also concentrated on humic sub stances. The source of the metals in the humates is un doubtedly the mineral phases present as the amount of organic matter decomposition necessary to obtain the ob served metals is unrealistic (Nissenbaum and Swaine, 1976). Presley ejt al. (1972) have shown mobilization of Zn, Ni and Cu in Saanich Inlet sediments by humates. Nissenbaum et al. (1972) suggested that DOM is the precursor of 136 humates and plays an Important role in leaching: metals from the mineral phases to the humates where the metals exist as a stable complex* Seawater and Metals in Hydrogenous Phases The other possible mechanism for metal scavenging from seawater is the adsorption of Cu, Ni, Zn and Co onto hydrous mineral phases such as Mn oxides (nodules and crusts) and Fe oxides (Goldberg, 195^5 Krauskopf, 1956). Murray (1975) showed experimentally that the transition metals Cu, Co, Mn, Ni, and Zn had the greatest attraction compared to alkali and alkaline earth metals for hydrous MnO^ as well as the greatest amount of irreversible ad sorption* With increased pH from 2-8 adsorption of transition metals increased with Cu being greater than Co, Mn, Zn and Ni in resistance to desorption or what is termed adsorption selectivity (Murray, 1975; 01 Connor and ICester, 1975)* This implies that MnO^ crusts and nodules in the oceans are adsorbing significant amounts of transi tion metals from seawater onto their surfaces, and having them reside in that phase for relatively long periods of time. Amounts of metals adsorbed by MnO^ phases alone are difficult to estimate, however, O'Connor and Kester (1975) ran experiments adsorbing Cu and Co from seawater onto illites which showed 90 percent adsorption at pH 7-12. Experiments by Murray (1975) obtained similar results. In 137 the Gulf* of* California, the majority of* the clays in the sediments are illites (Grim et al,, 19^9)* suggesting that these clays might be a substantial sink for adsorbed metals. Scavenging residence times for Cu and Ni in sea- 1^4- water calculated from C data by Craig (l97^) are ap proximately 1400 and >3000 years, respectively. However, there appear to be other sources of Cu to the deep bottom waters in order to maintain the relatively high Cu con centrations measured in bottom waters (Craig, 197^0* Pos sible sources may be a flux of Cu from the seafloor sedi ments to the bottom water or a high concentration of Cu in the Antarctic Bottom Water flowing into the North Pacific. Xt is possible that Cu and other metals are being rapidly removed from seawater by adsorption processes onto MnO^ phases (nodules in the equatorial Pacific) as well as onto Fe-rich volcanogenic sediments along major rift zones, analogous to phosphorous removal in volcanogenic sediments (Berner, 1973) in order to maintain the equilibrium of Cu concentrations in deep ocean bottom water. Post depositional mobilization of metals, especially Mn, in nearshore reducing sediments leads to high concen trations at the sediment-seawater interface and hydrogenous coatings of MnO^ on exposed rock surfaces. In the Gulf of California it appears that most of the MnO^ crusts found in dredge hauls are of hydrogenous origin. Where ocean 138 circulation patterns and biological productivity produce upwelling and subsequently an minimum zone along the coast, Mn in the sediments which intersect with the 0^ +2 minimum water mass is in a Mn valence state# The Mn con centration in solid phases is low as evidenced by the con centrations of leachable Mn seen in the shelf sediments in the Gulf of California. Below the 0^ minimum zone, Mn is the stable valence state in the relatively oxygenated bottom waters and Mn precipitates out of solution as MnO^ crusts, coatings and high Mn concentrations in the surface sediments. Precipitation of Mn02 in the sediments is dependent, therefore, on the Eh, pH and whether or not 4-2 Mn is allowed to diffuse to the surface sediments. Xf sedimentation rate is faster than the diffusion of the pore water, no diffusion gradient is allowed to occur and con sequently mobilization does not exist. The Eh (millivolts) +2 / of the stability boundary between MnO^ and Mn (1—10 ppm in pore water) at a pH between 7-8 is the following: pH7______ pH8 1 ppm +2 Mn +680 +570 5 ppm ■ R T ' * ' 2 Mn +6^0 +560 10 ppm -, +2 Mn +625 +500 +2 Mn in equilibrium with other Mn minerals such as Mn^O^ +2 and MnCO^ have lower calculated Eh for the same Mn con centrations and pH; however, it is unknown whether or not these mineral phases exist in the Gulf of California sedi 139 ments. Eh. measurements of* the magnitude calculated for the precipitation of* MnO^ in the Gulf* of* California have been measured (Rozonov et al,, 1976)* Eh in the sediments and the probability of MnO^ precipitation is influenced in large part by the biological productivity in the water column and subsequently the amount of organic material in the sediments* The presence of MnO^ crusts and coatings is an indication of the redox potential in the environment of inferred pH and sedimentation rate (fig* 7A) * Xf the Eh boundary where MnOg precipitation occurs is in the sediment column (fig* 7A3), the top part of the sediment will be oxidizing and the bottom may be mildly reducing* This situation exists on the flanks of the East Pacific Rise* Figure 7® shows this phenomenon diagrammatically with the gradation from hemipelagic mildly reducing sediments to pelagic oxidizing sediments and the increase in thickness of the oxidizing layer with distance form the continents (Bonatti et al* * 197l)* Frequently more than one oxic zone exists in the sediment column caus ing the Mn concentration in the pore water not to increase steadily toward the seawater-sediment interface (fig* 8, II) but to have several maxima and minima (fig* 8, III, IV) (Enderfield, 1976)• With more and more anoxic conditions the Eh boundary of MnC^ precipitation rises in the sediment column to the sediment-seawater interface (fig* 7A2)* The Pescadero Basin Complex has high concentrations of MnO^ in 140 Figure 7* A. Effect of organic matter on Eh of sediments and resulting deposition of MnO^ in different geochemical environments (MnO^—Mn+^ boundary = arbitrarily chosen boundary of Eh where pH = 7-8 and a sedimentation rate exists such that diffusion of . O 5 ppm Mn in pore water is occurring). 1. Anoxic bottom water or minimum region with no deposition of MnO„ in sediments analogous to the La Paz Basin (Eh = —200 mv) at sediment-seawater interface. 2. Oxic bottom water with mildly reducing sediments; MnO^ deposit ed at sediment-seawater inter face possibly as Mn crusts analogous to the Pescadero Basin Complex. Eh of +200-+300 mv at sediment water interface. 3. Oxic bottom water and oxic sedi ments; MnO^ deposited throughout the oxic sediment analogous to EPR flanks south of Mazatlan basin. Eh = +500—+600 mv at sediment-seawater interface. Diagram modified from Bonatti ejb al. (1972). B. Increasing thickness of oxidizing sediment zone from nearshore to deep ocean. Diagram modified after Bonatti ejb al. (1971). i4i LA PAZ BASIN _______________ Mn0o- Mn bou ndary_____ _____ WATER *2. 2 Mn NO DEPOSITION OF M n02 SEDIMENT PESCADERO BASIN MrtOg MnOo- Mn ^ boundary_______ EA ST PACIFIC R IS E „ 3 Mn02 + ^y-Z7V7 'Mn02 "M n^ boundary B PELAGIC HEMIPELAGIC CONTINEN OXIdTzED] t D U C E D m iT n * / x Figure 8. Schematic profiles of dissolved Mn in an ocean section. X. Stratified water column where A-B boundary corresponds to the inter face between upper, oxic, sea water (a J and lower, anoxic sea water (b ) . XI. Anoxic sediment where A-B boundary at or near the seawater-sediment interface corresponds to the boundary between upper oxic sedi ment (A) and lower anoxic sediment (B). XXI. Mildly reducing sediment where Al—A2 boundary corresponds to the interface between oxic (Al) and anoxic sediment (A2-B) and the A-B boundary corresponds to the region of maximal Mn reraobilization (Li et al., 1969)• IV. Sediment with a thick oxic layer (Al) underlain by sediment contain ing discrete anoxic zones resulting in more than one maximum in the Mn profile. After Enderfield (1970). Ik3 I SEA WATER SEDIMENT ikk the surface sediments but little below the 2- cm interval, indicative of post depositional mobilization. The bottom waters are oxygen rich (3 ml/L, Roden, 1964). Xn an minimum area even the bottom water may be reducing and no deposition of MnO^ in the sediments is possible (fig. 7Al) because the position of the Eh boundary where MnO^ will precipitate may be situated in the water column. Extreme examples of this geochemical process are the Black Sea (Spencer and Brewer, 197l) and Saanich Inlet, British Columbia (Presley jet al., 1972)• The La Paz Basin in the Gulf of California is an example of this phenomenon al though the bottom waters do not contain H^S as do those of the Black Sea and Saanich Inlet. Eh, pH and organic matter in sediments may also be responsible for the formation of glauconite in which con siderable amounts of Fe may reside. Relatively sediment- free banks and shelf edges in association with some organic matter and a fluctuating redox environment, all of which are found in the Gulf, are characteristic of areas of glauconite formation (Berner, 197l)• Bacterial Sulfate Reduction and the Formation of Metal Sulfides Diagenesis in sediments with significant amounts of organic matter leads to biologically mediated seawater sulfate reduction to sulfides. The uptake of Fe from clays 145 and the abundance of S~ in the sediments leads to the formation of intermediate metastable phases of greigite and mackinawite which eventually become pyrite (Berner, 1964a, 1964b, 1969, 1970)# As long as the sediments are reducing pyrite is a stable phase. Berner (1964a) found as much as 1 percent sulfur as pyrite in the sediments of the Gulf of California with little evidence of the inter mediate, black PeS phases. The explanation for this was attributed to the abundance of oxidizing agent (organic matter) and reactive sulfur at the sediment surface causing a rapid transformation of FeS^. Figure 9 summarizes the sources, processes of deposition and forms in which metals may exist in the marine sediments, seawater, pore water and river water in the Gulf of California. The chemical pathways of the metals can be followed from source to final burial or most stable phase. It is likely that phases are mixed and certain types of sediments (i.e., hydrothermal metalliferous sediments) cannot be delineated because that component is overwhelmed or diluted by others which are more abundant. 146 Figure 9* Schematic drawing of sources, transport mechanisms, chemical enviromients and phases in which metals reside in the Gulf of California. Ib7 MECHANICAL WEATHERING CHEMICAL WEATHERING solution organic complexes (DOM) £ clays (Cu.Ni.Zn) i r colloids (Fe, Mn) SEAWATER: solution SUSPENDED CLAYS Q PLANKTON metal inrichment chelation adsorption \/ Fe,Mn oxide coatings^! TERRIGENOUS MnQg PPt. CLAYS P O S T - (crusts, sediments) DIAGENESIS pore water (Mn) AV H Y_DROT HER M A L Cl ORGANICS humates (Cu, N i,Zn) a i£ C U 1 A.IJ (Fe,Mn,Cu,Ni) ? me t a I i i f. sed ipien ts ? 7 M V \ I M E N H E M CRUST SEDIMENT DATA The purpose of this section is to describe the methods of sediment and rock sample collection, sediment lithologies and their distribution with regard to sedi mentation rates, distribution of biological components in the sediment and the distribution and type of bedrock col lected in dredge hauls. Four samples of anomalous lithology and color are also described. Geologic Sample Collection Two hundred forty gravity and dart cores, 16 dredge hauls and 20 piston cores were collected on the three cruises to the Southern Gulf of California. These samples were supplemented by 86 surface sediment samples from the Vermillion Sea Expedition of the Scripps Institution of Oceanography of 1959 (van Andel, 1964). Splits of the original samples were kindly provided by the Smithsonian Institution. Another 45 gravity cores were collected by the author in the Carmen and Farallon basins on the 1973 Gulf of California cruise of the R/V Oconostata (Scripps). The dredge hauls were augmented with dredges taken by F. P. Shepard on the Bacanyon Expedition of 1962 around the tip of Baja California as well as the Hypogene Expedi tion of 1972, both sponsored by Scripps. Core (solid 149 circles) and dredge haul (stars) locations are plotted in Plate 15, Exact locations of all samples are given in Appendix I* A variety of sampling devices were used to collect the sediment samples during the three cruises, however, for the most part gravity cores from 60-120 cm in length were obtained. Xn several instances the sediment was so unconsolidated that a cohesive sediment core could not be retained. Xn these cases a single plastic bag of sample was collected. On the shelves, the sediment was usually very sandy and the coring devices did not penetrate. At these locations Shipek grab samples were used to obtain the necessary quantity of sediment. The piston cores were taken with 6 m barrels although a 6 m sample was never obtained. The longest piston core collected was 420 cm. Core samples were sealed in their liners with tight fitting end caps, taped and placed in a refrigerator for preservation. Bulk samples were placed in plastic Ziploc bags with as much air as possible expelled and re frigerated. Dredge hauls were thoroughly examined and several representative samples of each rock type were bagged for later examination. Where basalts and/or granites were dredged, a suite of rocks showing increasing degree of alteration (weathering) were collected. Fre quently lithified sediments and manganese crusts were 150 dredged from the escarpments. The sedimentary rocks were examined for microfossils (foraminifera and diatoms) for age determination in a search for evidence of pre-Pliocene rifting of the Gulf (j. Hein, J. Barron, G. Calahan-Keller, oral communication, 1976). Nothing older than lower Pliocene age mudstones were recovered. Examination of the cores included extrusion and lengthwise splitting, description of all lithologies found, notation of unusual foreign objects (wood pieces, macrofossils, large pebbles, basaltic glass chips) and color. Each core was measured and a surface sample (0-5 cm), a sample half way down the core and one at the bottom of the core were taken. Approximately 10-15 grams of wet sediment were scrapped from the interior of the core with a plastic spatula. This procedure was used to prevent metal contamination during sampling as well as to avoid collecting any sediment which may have been in con tact with the plastic core liner. The piston cores were sampled in the same manner with a sample taken every 20 cm. Bagged samples were homogenized and considered to be the 0-5 cm section of the sediment. Samples were oven dried at 60°C and ground to 100 mesh size with an agate mortar and pestle to avoid contamination from metal implements. Samples of sand size were disaggregated to single grains. 151 Sediment Lithologies Sediments collected from the Southern Gulf* of* Cali fornia (plate 16) are for the most part grayish-olive (5GY 3/2) to moderate olive brown (5Y 4/4) homogenous silty-clay corroborating the extensive sedimentological analyses by van Andel (1964). These sediments cover the central and deepest areas of the Gulf trough and are es sentially ubiquitous at the mouth of the Gulf. There are, however, other sediment types seen along both the Baja and Sonoran Mexico continental shelves. Parallel strips of sandy-silty-clay and clayey-sand adjacent and west of the sandy-silty-clay are delineated along the Mexican coastline. To the north three other sediment types are observed. Two small areas of sandy—shell hash, a poorly sorted sediment, can be seen along with an area of clayey- silt just off the Fuerte River delta and a small near shore region of sandy-clay to the north of the Fuerte River. Along the Baja coast the homogenous silty-clay is found very close to the coastline except in the Isla San Jose-Isla Carmen area where the sediment is a sandy-clay. It is of particular significance that several patches of glauconitic sediment have been found in the Pescadero Basin Complex region and south of the Mazatlan basin. Invariably the glauconite is associated with shallow banks or shelf edges (compare plate 16 with 152 plate 5) where the sediment has a significant proportion of sand or silt. The glauconitic sediments are also as sociated with areas of relatively low sediment thickness (compare plate 16 with plate 4). In addition the glauconite sediment appears to be situated just above or below the documented minimum zone (van Andel, 1964; Roden, 1964) and is marginally but not directly correla tive with regions of high organic carbon content in the sediments (compare plate 16 with plate 17)# Frequently the sediment cores do not have uniform lithology with depth. Often discrete layers of foraraini- fera, coarse sand and silt, diatomaceous ooze, volcanic glass chips, macrofossils, and pieces of wood are found. In a few cores (denoted by open stars on plate 16) alter nating dark and light laminae are visible. These laminae are presumably due to the presence of the minimum zone (<0,05 ml/L O^) and consequently the lack of bioturbation. The light layers are diatom rich while the dark are clay rich zones (Calvert, 1964). All these sediments are situated between 200 and 1300 m. Mottling is observed in large sections of some cores as well as thin streaks of black, presumably organic material. Cores collected across the East Pacific Rise in what van Andel (1964) has termed the "ocean facies" show two types of sediment. The top 20 cm are a moderate yellow brown (10YR 3/4) with a distinct color change below 20 cm to the moderate olive 133 brown or grayish olive color typical of the rest of the Gulf, As was previously discussed, relatively more oxidizing pelagic sediment overlies mildly reducing hemi- pelagic sediment as portrayed in figure 7B* All sediments collected are described in Appendix XX, Samples used in this study which were collected by van Andel in 1959 are described in van Andel (1964), For the most part the piston cores have uniform composition, texture and color with depth, that being a homogenous grayish olive brown silty-clay. Occasionally, single distinct layers of dark silty-sand 1-5 cm in thick ness are observed, Diatomaceous oozes are also seen as discrete layers though are distinguished by changes in texture rather than color. Core 21995» taken in the La Paz Basin, has a somewhat different appearance. Smelling of H^S throughout much of its length, the sediments are considerably darker in color, almost black, and have a relatively high water content. Sediment Distribution Patterns and Sedimentation Rates van Andel (1964) and Calvert (1966) have presented several sedimentation rates for the basins and slopes in the Gulf of California, It is evident from these data that sedimentation rates are high in the Central and Northern province basins but decrease approximately two 154 orders of magnitude in the Southern province as continental influences decrease. Rates vary from 273-^98 cm/lOOO years in the Guaymas basin, decreasing to 84-100 cm/lOOO years in the Farallon basin and slope area, to 46 cm/lOOO years in the South Pescadero basin and 6-12 cm/lOOO years in the Mazatlan basin and adjacent areas. Pour recent 14 / sedimentation rates from C age determinations (Krueger Enterprises, Geochron Labs, Cambridge, Ma.) corroborate the van Andel and Calvert results. The great range of rates in the Guaymas and Farallon basins reflects the influence that continental runoff as well as sea floor spreading motion have on the sediment distribution pat terns (plate 18). Xn the Farallon basin, for example, sedimentation along the base of the northwest escarpment of the central trough is about 100 cm/lOOO years, yet just to the east of the inferred fracture zone between the Farallon and North Pescadero basins the sedimentation rate is only 30 cm/lOOO years. In the South Pescadero basin and at the intersection of the Alarfon Rise and its northeast escarpment sedimentation rates are remarkably similar, indicating a much more uniform sedimentation rate over a larger region compared to the Farallon basin region where a three-fold range of sedimentation rates is observ ed. On the flanks of the East Pacific Rise relatively low rates of sedimentation (6—8 cm/lOOO years) are found. While these rates are low compared to the rest of the Gulf 155 of* California and the Southern California Borderland basins (sedimentation rates of 19—11^ cm/lOOO years have been reported by Emery and Bray (1962) for the Southern California Borderland), these rates are still an order of magnitude higher than generally accepted open ocean pelagic sedimentation rates of #1—1 cm (Lisitzin, 1972). Sedimentation rates in the southern part of the study area appear to be constant within a factor of 2 for the few determinations available# Active sea floor spreading appears to be producing a classic pattern of sediment thicknesses, the thicknesses increasing away from the inferred tectonic elements. Because of sea floor spread ing, sediment thicknesses in the deep basins are relative ly small compared to the substantial thicknesses seen on the tectonically inactive continental shelves. Xn the Farallon basin where sedimentation rates are far higher, greater thicknesses of sediment are observed in more intimate association with the inferred tectonic elements, however, the calculated sea floor spreading rate of 6 cm/year (Larson, 1972) more than compensates for the rate of sediment influx, thus creating the unusual sediment patterns and thicknesses seen. Distribution of Bedrock Outcrop ¥ith few exceptions, two types of crystalline rock are found in the Gulf of California (plate 19)* Fresh 156 pillow basalts with, glassy rinds and ocean thoeliites have been dredged from the trend of the East Pacific Rise at the mouth of the Gulf, along the crest of the Alarcon Rise and on the Alarcon Seamount# Granite, granodiorite or tonalite have been dredged from fault escarpments on the continental slope on cruises for this study and by Shepard (1964) around the tip of Baja California. Some granodiorite has also been recovered from the Ceralbo bank. Xn almost every dredge haul recovered, Mn crusts have been present. The crusts are usually present as thick coatings on other crystalline rock types. Xn the Carmen basin and Ceralbo trough volcanic breccias and vesicular basalts are present. Highly weathered basalts have been dredged from the Tamayo fracture zone and the Farallon and South Pescadero basins. These basalts frequently have thick (2-3 cm) weathering rinds and green, presumably zoolitic coatings. Occasional ly rosettes or cubes of pyrite are found along fractures in the rock. Other than pyrite no other mineralization is observed. One unusual rock type was dredged from a single location on the eastern flank of Ceralbo island. Rocks which appear to be schists and highly sheared quartzites were recovered. Shepard (1964) also noted highly sheared granitic and quartzitic rocks in dredges around the tip of Baja. Along with the crystalline rocks and Mn crusts, sedimentary rocks were also recovered. These are for the 157 most part semilithified mudstones and sandstones micro- paleontologically dated as Pliocene and Pleistocene in age. Anomalous Sediments Four samples quite different from the normal green-gray brown clays found in the Gulf were sampled (locations indicated by stars on plates 22—26). One sample (S-392) can be described as a semi-lithified pure manganese sediment which was collected on the flank of a seamount in the southernmost part of the study area (black star on plate l6). Another sample (S-38O) col lected in the same area was a manganese ooze with ex tremely high water content. A core of this sediment could not be retained because of the incohesiveness of the sedi ment. A third sample (S-330) collected along the trace of the Tamayo fracture zone contained a very coarse grained manganese sediment with little clay fraction. The fourth sample (DH-09) is perhaps the most interesting in terms of exploration for hydrothermal metallogenesis. This sample was dredged from the Mazatlan basin by the University of Washington (Lewis _et aJL. , 1976). Mostly light olive brown ( 5Y 5/6) with some dark yellowish orange (lOYR 6/6) flecks and thin layers of manganese intermixed, this semi-lithified sediment is probably not a metal liferous sediment precipitated from the exhalation of 158 hydrothermal fluids at the ridge crest of the hast Pacific Rise but may possibly be a hydrothermally altered sedi ment. Chemical analyses of these samples will be presented in a later section. 159 DISTRIBUTION OF BIOGENOUS COMPONENTS IN GULF OF CALIFORNIA SEDIMENTS Biogenic Component Analysis Total carbon and calcium carbonate carbon were determined Tor each sample using a LECO gasometric analyzer (Laboratory Equipment Co., St. Joseph, Mich.) and induction furnace Tor heating the sample to 2000°C to evolve CO^. Calcium carbonate was determined in two ways. First, by subjecting the sample to 3 ml oT 2M HC1 and evolving CO^ in a gas tight system which channeled the gas to the analyzer, or secondly, by leaching the sediment with 2M HC1 in a carbon Tree crucible and performing a total carbon analysis on the remaining residue. The value obtained from the second procedure is actually organic carbon content. Thus, the difference between the total carbon value and the organic carbon sample is the in organic carbon value which can then be evaluated as CaCO^ by calculation. The former procedure gave CaCO^ carbon directly and when subtracted from total carbon gave organic carbon. Both procedures produced similar results. Standard metal rings provided by LECO were used to cali brate the instrument and after every 30 samples to check calibration. This error is - .1 percent for both CaCO^ 160 and organic carbon at 1 standard deviation. Distribution of Organic Carbon Sediments of the Gulf of California contain one of the highest contents of organic carbon of any marine environment in the world (Table II). The highest percent ages of organic carbon are found along the eastern coast of Baja California from just north of Isla San Jose to Xsla Ceralbo and along the Mexican continental shelf—slope south of the South Pescadero Basin. Up to 9 percent organic carbon has been measured in these sediments (plate 20). In between these anomalously high organic carbon regions is a narrow low ( “ ^.2.0 percent) that falls directly over the South Pescadero Basin. Another low of similar magnitude exists over the southeast end of the Carmen basin. ¥ith distance from land, the percentage organic carbon content decreases gradually until open ocean values of less than 1 percent are detected at the farthest extent of the study area. ¥ith the addition of these additional data, the distribution of organic carbon has been refined from the original work done by van Andel (19^4). The general pat tern of high organic carbon along both coastlines further strengthens the argument of nutrient upwelling and high biological productivity being a mechanism for the high percentage of biogenic components in the sediments. 161 Table XI. Organic carbon content (°/o) of sediments in the G-ulf of California compared to other marine environments Gulf of California (this study) 6.50 (shelf-slope areas) 3.60 (basins) Baltic Sea (Lisitzin, 1972) .5-aU50 Black Sea (Lisitzin, 1972) 1.0-3.0 South West African Shelf (Calvert and Price, 1970) 7.^5 (Avg.) range of 5-20$ California Borderland basins (Emery, i960) 1.6 (slope) 3.9 (basins) Peru-Chile Trench (Trask, 1961) 2.3^ (upper slope) ,63 (lower slope and basins) Sea of Okhotsk (Lisitzin, 1972) .25-2.0 North Pacific (Lisitzin, 1972) .25- .5 H o \ K > Distribution of Calcium Carbonate The distribution of CaCO^ (plate 2l) in Gulf sedi ments is similar to that for organic carbon with two major exceptions. One small anomaly (^20 percent) exists off the Mayo River delta and may be the result of deposition of shell hash and coarse sand in the sediments nearshore. The other anomaly is of similar magnitude but greater extent and is found just south of the Fuerte River delta. This region may exist because of a lack of diluting terrigenous sediment being transported to this area. The sediments of the rest of the South Gulf are low (—5 percent) in CaCO^ content regardless of the depth of the sample. The other two large, anomalous areas correlate with high organic carbon content and can be ascribed to an origin involving the deposition and preservation of extreme amounts of calcareous planktonic tests because of high biological productivity in the water column. Results of the organic carbon and CaCO^ analyses for all samples in this study are reported in Appendix X. Distribution of Biogenous Components in Piston Cores Of the 20 piston cores taken in the Gulf during this study, the 12 longest were chosen as representative for discussion. Most of the cores were taken along the trough 163 axis from the Farallon to the South Pescadero basins (fig* 10). One core (21995)» taken in the La Paz basin, has been described previously as having high content of organic material in a region of minimum in the bottom waters. The distribution of biogenous components is presented in figures 11 and 12. Organic carbon and CaCO^ for all samples in the piston cores are reported in Ap pendix XXI. Organic carbon trends are uniform with depth in all cores except cores 21967* 20397* 21965 and 21984. Cores 21967 and 20397 show distinct maxima and minima with depth while cores 21965 and 21984 show gradual decrease in organic carbon content with depth. Core 21995 has the highest average organic carbon content of all piston cores at 6.20 percent. Core 20397 has the lowest average organic carbon content (l.90 percent). Calcium carbonate in the cores shows more varied trends and a larger range of absolute values than the organic carbon content. Cores 20398, 20397* 21985, 22009 and 22023 have uniform distributions ranging from 0-10 per cent CaCO^. Core 21972 increases in CaCO^ content from 10 percent at the surface to 25 percent at 320 cm. The other piston cores show sharp changes in CaCO^. 21967 has greater than 20 percent CaCO^ down to 60 cm depth, except at 10 cm, which then decreases to 0 percent at 60 cm, then increasing to 15 percent at 240 cm. 21970 shows a slight 164 Figiire 10, Location map of piston cores 16.5 1 0 8 1 1 1 * soI nora C H 27 — 2 7 TERRITORIO DC BAJA CALIFORNIA SUR Z o S < \ 8 , 2H t»r. $3 2 , 1 , 7 2 A *21115" . ZZoo<f ' ; > - 4 L a P a i DURANGO 24 2 4 {114' 111 1 0 6 166 Figure 11* Distribution of organic carbon in twelve piston cores. 167 • * - o Q O o o ( • v u?J « L d 3 Q 168 Figure 12 Distribution of calcium carbonate in twelve piston cores. 169 * Wr o C : •5 3 o i - ~ «- <r In f* 5* s | “ ’ - T>JV1 Cr- fl»-r v *>*o >3 « * - cr w j < > t- NiQt * * _ o - J " O-Ufi « n O o o o 1 <5 (no} WLdJQ 170 increase down to 220 cm, then a decrease and leveling off at approximately 7 percent from 240-380 cm. Three maxima are evident in core 21965 while 21977 has less than 10 per cent CaCO^ throughout the core except at 280 cm where over 26 percent CaCO^ was measured. 21995 has a high CaCO^ content at the surface, decreasing slightly to the 240 cm interval, followed by a broad maximum with as much as 31 percent CaCO^. 171 GEOCHEMICAL PROSPECTING AND TECHNIQUES Geochemical prospecting is the application of* geo chemical principles to exploration of economic mineral deposits (Levinson, 197^)• It is the hope of the geo chemical prospector to find a concentration of the elements or compounds for which he is searching that is greater than the levels normally found in the region being explored. Such a concentration is called an anomaly. One funda mental difference between a geological prospector and a geochemical prospector is that the former concentrates on outward and visible signs of mineralization (outcrops of veins, structures conducive to the emplacement of minerals, etc.) while the latter uses analytical instru mentation to detect indications of mineralization not readily visible on the surface. Consequently, geochemical prospecting is a direct method of exploration in that the element sought is the one being analyzed. Geophysical and geological methods of exploration are indirect in that physical properties of the elements or favorable sites of mineralization are measured but not the element itself. Geochemical surveys can be categorized into two basic types: reconnaissance and detailed. Their names imply their functions. Reconnaissance surveys are employed to evaluate 172 large areas such as the Gulf* of California where samples may be taken with a frequency of one per square mile or greater. Detailed surveys are restricted to small areas with the idea of locating a mineral deposit exactly. Samples may be taken every several feet. Within each type of geochemical survey, many materials may be used to analyze for the elements sought. Soils, rocks, sediments, water and vegetation have been used. Xn dealing with the Gulf of California, only two materials are viable for prospecting: sediments and rocks. It is evident, however, that in order to accomplish a reconnaisance survey over the entire South Gulf of Cali fornia, only the sediments are useful. Xn geochemical prospecting it is the dispersion of the elements from the ore body which one measures in the geologic materials surrounding the deposit (Levinson, 197*0 • Dispersion is caused by many geological and chemi cal agents (structural deformation, groundwater circula tion, oxidation-reduction, weathering and soil formation, etc.). Hawkes and Webb (1962) have related dispersion processes to two environments, the primary environment, processes intimately associated with the ore body at depth such as metamorphism and meteoric water circulation and the secondary environment which encompasses the surface processes of weathering and sedimentation. If heavy metal deposits are present in the Gulf of California in associa 173 tion with inferred tectonic elements, then a primary environment is represented, Xn actuality, the "ore" it self is being sampled rather than the dispersion of the elements from the ore body. A secondary environment is indicated, however, if metal anomalies are seen in the hemipelagic sediments. The dispersion of the metals from the ore body in the secondary environment are subject to many geochemical processes including pH and Eh, adsorption, the presence of organic matter, mobility of elements in the pore water and bacterial mediation. Thus exploration for heavy metal deposits in the Gulf of California involves sampling on and near inferred tectonic elements for rocks and sediments which may in themselves constitute ore bodies or the result of hydro- thermal processes which are manifest as metalliferous sedi ments, Geochemical prospecting for anomalously high con centrations of metals involves sampling and analyzing the hemipelagic sediments in the Gulf of California on a recon- naisance basis. Analytical Methods Because of the many possible sources of metals to the sediments in the Gulf besides hydrothermal processes, it is necessary in prospecting for evidence of hydrothermal metalliferous deposits to develop a technique which can partition the metals into fractions which might be indica- I ' j k tive of the possible sources of the metals. As a first approximation it is desirable to eliminate the metals bound in the silicate lattices of the clays as it is known that they are not of hydrothermal origin. Thus, a technique which could separate the metals residing in hydroxide, carbonate, organically bound, adsorbed and sulfide phases into one fraction and the silicate bound metals into another was needed. Also, the technique had to incorporate the traits of ease of procedure, inexpensiveness, ease of analysis and be able to detect large ranges of elements with accuracy and precision. Since a partitioning technique was needed, it pre cluded the use of X-ray fluorescence or emission spectro meter analysis of the bulk sediments through rapid methods because these give total analyses. ¥et chemical analyses such as colorimetric, gravimetric, electrochemical and volumetric procedures are possible, however, they are prohibitively time-consuming. Selective acid leaching is a rapid viable alternative technique which produces a solution which can be rapidly analyzed by atomic absorption spectrophotometry. This alternative was selected for this study because it best fit all the above criteria. The problem of the exact leaching technique to use, however, was still an unsolved problem as different sediment types (ferromanganoan sediments, red clays, hemipelagic muds, etc.) can be leached with different 175 combinations of* acids* Acid Leaching and Trace Element Partitioning; Previous Work Several workers have attempted to partition metals into lithogenous and non-lithogenous components via dif ferential leaching techniques. All previous work with one exception has been performed on deep, open ocean sediments where the principle components were either a siliceous or calcareous red clay (Horowitz, 197^5 Chester and Hughes, 1969; Chester and Messiha-Hanna, 1970) or a. ferromanganoan sediment associated with a divergent plate boundary (Sayles et al.. 1975; Sayles and Bischoff, 1973; Cronan, 1976). The one exception is the work by Nissenbaum (1972) on a single core from the Sea of Okhotsk. This region is quite similar in depth, sediment distribution and sediment type to the Gulf of California. Tectonic aspects are dif ferent, however, as the Sea of Okhotsk is a marginal basin with active subduetion occurring along the Kurile- Kamchatka arc trench to the east. All the trace element partitioning work on deep sea sediments (considering Nissenbaum (l97^) to be of nearshore affinity) again with one notable exception has utilized a leaching technique developed by Chester and Hughes (1967). This technique uses a combination acetic acid and hydro- xylamine hydrochloride reducing agent solution to dissolve 176 ferromanganese nodules, carbonate minerals and adsorbed trace elements from clay surfaces. The exception is the work by Heath and Dymond (1977) where an oxalic acid leach (Schwertmann, 1964) was used to remove amorphous ferric hydroxides and poorly crystalline ferromanganese oxyhy- droxides from the sediments in the EPR-Bauer Deep region of the East Pacific. They did not wish to attack the crystalline goetite or Fe-rich smectite phases. A compari son of the oxalic acid leach with the Chester and Hughes, dithionite—citrate—bicarbonate (Mehra and Jackson, 1969) and HC1 leaches (Heath and Dymond, 1977* fig. 2) revealed that only the oxalic acid leach did not release additional trace metals upon releaching the samples. Nissenbaum (1972) used a series of leaches to partition trace metals from the sediments of the Sea of Okhotsk. A time consuming process including a water leach, ^2^2 leac^1> acetic acid leach, HC1 leach and finally a Na^CO^ fusion was performed. While the Chester and Hughes leaching technique and others are sufficient for pelagic sediments with relatively high ferromanganese components, CaCO^ and little organic matter, they are somewhat inadequate for trace element studies in hemipelagic sediments. Nissenbaum (1972) took one approach to the problem with a series of leaches, how ever, it must be stressed that only one core was examined and treated. With the number of samples necessary to ac complish a statistically significant geochemical survey, it 177 goes without saying that performing five leaches per sample would be a monumental analytical task* It is the delineation of dramatic anomalies associated with hydro- thermal imput in the sediments, not the categorization of all metals leached, that is important in the present study* The other approach was to use a single acid leach which could take hydroxides, carbonates, adsorbed metals as well as oxidize organic matter which might also hold consider able metals and sulfides into solution and at the same time not leach metals bound in the clay lattices or dis solve detrital grains in the sand size fraction* Metal Analyses of Sediments in the Gulf of California A concentrated nitric acid leach was employed be cause of its ability to oxidize organic matter and sulfides and release the large amount of metals which were thought to reside in those phases, yet not attack the alumino- silicate minerals* One gram of sediment was boiled in 5 nil of concentrated HNO^ for one half hour or until all fumes had been evolved, whichever was longer (the complete analytical procedure appears in Appendix IV)* The HNO^ leachates were analyzed on a Perkin-Elmer 370 Atomic Absorption Spectrophotometer for Fe, Mn, Cu, Ni and Zn* Appropriate blanks and standards were made to duplicate the matrix of the leachate in order to avoid 178 errors due to interferences. Positive errors in Atomic Absorption Spectrophotometry due to the concentration of total cations and changes in efficiency of the atomization of solutions of geologic materials have been discussed by Govett and Whitehead (l973)* Minimizing the interferences requires dilution of the sample solution which in turn decreases sensitivity. Careful dilutions were made from the original leachates for each element analyzed in order to (l) bring the concentration of the element being analyzed within the standards for linearity prescribed by the manufacturer, and (2) decrease the interference effects of high concentration cations such as Fe. Instrument settings were those prescribed for optimum sensitivity by the manufacturer. Duplicates of each sample were analyzed and in several cases, separate aliquots of sediment were leached and analyzed to estimate analytical error. Precision for the analyses is estimated to be the following: Fe 4* 4- 10^ Mn 5 ° / o Zn 4* 15# Ni 4* k ° / o Cu 4* 6° / o Error estimates are 1 standard deviation based on 26 com plete replicate leaches and analyses. 179 Reliability of HNO^ Leaching Technique ¥ilde (1975), using the same HNO^ technique employed in this study, found that leaching the same aliquot of sediment twice liberated 7-85 percent more metals than were leached in the initial leach. Thus, though a strong acid leaching technique was employed to obtain the desired results, the amount of leaching time is most important in order to minimize the attack on the silicate minerals. Xn order to determine if, in fact, the leaching technique did attack any silicate phases (detrital clays or biogenous silica debris), analyses for Si and A1 were made on the bulk and HNO^ leached residue of typical olive-gray mildly reducing sediments from the Gulf of California. This ex periment revealed that an average of 8 percent of the total Alo0o was in solution and that there was a systematic 5 percent difference in the SiO^ analyses, the bulk samples always being higher than the HNO^ residues. To explain these results, a control experiment was performed with three samples of different chemical composition (red clay, diatomaceous ooze and USGS standard hemipelagic clay) along with two samples from the Gulf of California (a highly organic clay and a typical pelagic-hemipelagic mix ture from the mouth of the Gulf). These sediments were sub jected to the same HNO^ leaching procedure and analyzed for Si and A1 by flame AAS. The results are presented in 180 Table III* The silica found in the leachate represents less than *1 percent of the total silica present, however, the diatomaceous ooze has on the average three times more silica in solution than the other samples, possibly due to some dissolution of amorphous biogenic siliceous debris. Microscopic examination of bulk sediments and leached residues with high diatom contents was inconclusive as to the dissolution of the biogenous silica component. The systematic error in the total silica analyses is therefore considered to be analytical error. The aluminum error is substantiated by the leachate analyses. On the average 8 percent of the total Al^O^ is in solution, indicating that the alumino-silicate phase is attacked under low pH conditions and partially solubilized. The question now arises as to whether the same percentage of metals and Al^O^ are leached from the clay lattices. National Bureau of Standards standard plastic clay -$98A with analyses for SiO^, Al^O^, Fe^O^ and MnO was leached and the leachate analyzed as before. The results are presented in Table XV. The percentage of metals leached is in agreement with the percentage of Al^O^ leached and thus it appears that the percentage of Al^O^ leached is an indication of the amount of metals leached from the clay lattices. Therefore the reported leachable metals should be considered to be maximum concentrations. This appears to be an insignificant error considering the 181 Table III. Comparison of leached and total concentrations of elements in a mid-ocean ridge red clay diatomaceous ooze, standard U.S.G.S. hemipelagic mud and two sediments from the Gulf of California (bulk analyses, samples dried at 60°C) Sample Si Si < / > A1 A1 ° / o Fe Fe ° / o Mn Mn ° / o Leach Leach Leach Leach Mid-Atlantic Ridge Red Clay 58.91 0.02 0.1 16.35 1.37 8 3.84 2.82 73 .254 .239 94 19°30*n, 36°32*¥ Indian Ocean Diatomaceous Ooze 66.42 0.15 0.1 5.78 .75 13 1.83 .75 4l .053 .013 25 47°3l'S, 73°56'E Gulf of Maine Mag-1 49.74* 0.03 0.1 16.44* 1.50 9 1.18* - - .078* - 42°35*N, 69°331¥ Gulf of California Organic mud (S-269) 42.65 0.05 0.1 12.41 .18 1 3.15 2.24 71 .031 .016 50 24°48'N, 110°08'W Gulf of California Pelagic clay (s-365) 47.43 0.06 0.1 13.31 1.26 9 3.40 2.52 74 .113 .093 82 21°32'N, 109°26'¥ |— i 00 J \ ) Table III. Comparison of leached and total concentrations of elements in a mid-ocean ridge red clay diatomaceous ooze, standard U.S.G.S, hemipelagic mud and two sediments from the Gulf of California (bulk analyses, samples dried at 60°C) (continued) Cu Cu ° / o Ni Ni ° / o Zn Zn ° / o Sample (ppm) (ppm) Leach (ppm) (ppm) Leach (ppm) (ppm) Leach __________________________Li}_____ (L)_____________(T) (L)_____________(?) (L)________ Mid-Atlantic Ridge Red Clay 19°30’N, 36°32f¥ Indian Ocean Diatomaceous Ooze 47°31*S, 73°56iE Gulf of Maine Mag-1 42°35'N, 69°33'¥ Gulf of California Organic mud (S-269) 24°48'N, 110°081 ¥ Gulf of California Pelagic clay (S-365) H 00 124 90 73 46 20 43 49* 76 46 61 163 130 80 275 100 36 85 10 12 51 200 90 45 275 170 62 75 60 80 90 4o 44 l4o 85 61 305 265 87 * After Manheim e_t al# (1976). Ee, Mn, Cu, Ni and Zn not analyzed for leachable concentrations. Total analyses by emission spectrograph, (l) Leachable in concentrated HN0 . (t ) Total analysis by LiBOJ fusion and atomic absorption spectrophotometer. Table IV. Amount of SiO^, Al^O and MnO leached by HNO leaching technique from a National Bureau of Standards plastic clay #9°A from A. P. Green Fire Brick Company, Mexico, Missouri Total ( % ) Leachate (° /o ) ° / o Leached Si02 59.11 .02 0.1 A12°3 25.54 1.46 6 Pe2°3 2.05 .19 9 too .005 .ooo4 8 H 00 • P * geochemical prospecting nature of the study as well as the fact that the relative concentrations of the samples remain essentially the same. It is suspected that the alumino- silicates attacked may be authigenic phases as opposed to more crystalline phases. SiO^, on the other hand, seems to be limited to a few hundred ppm in solution in good agreement with the solubility of amorphous silica at low pH (Stumm and Morgan, 1970)• In summary, this HNO^ leaching technique is time dependent, yet appears to be acceptable as a means of partitioning the metals in hydroxide, sulfide, carbonate, adsorbed and organically bound phases into solution leaving the majority of the silicate lattice bound metals in the solid residue. The use of this simple and inexpensive technique and an Atomic Absorption Spectrophotometer allows a large number of samples to be analyzed in a short period of time, necessary criteria for reconnaissance geochemical prospecting. 185 DISTRIBUTION OF LEACHABLE METALS IN GULF OF CALIFORNIA SEDIMENTS The argument has been presented that in a nearshore environment such as the Gulf of California, the composition of the source rocks and climatic conditions under which those source rocks weather are independent variables upon which many other biological, geological and hydrographic processes depend* It is also true that the states in which the metals are found in the sediments (biogenous, hydro genous, detrital, hydrothermal) are related to the physical and chemical environments of deposition presently active in that locality and that each state will exist as a percentage of the total sediment mass. Thus, the distribution of elements, in this case metals, in marine sediments of the Gulf of California is dependent on the following: 1* Composition of source soils and rocks (continen tal or oceanic crust). 2. Climatic conditions under which continental weathering occurs. 3* Transport processes (continental runoff or hydrothermal exhalation of fluids). 186 4. Hydrographic conditions at the site of deposi tion. 5. Nature and activity of the biomass at the site of deposition and in the overlying water column. 6. Tectonic and/or volcanic events (pyroclastic deposition). 7. Diagenesis. It is the purpose of this section to describe the distribution of l®30*13* 3^ metals in the surface sedi ments and at depth in piston cores taken along the axis of the Gulf trough. Each metal (Cu, Ni, Zn, Mn, and Fe) for each surface sediment sample has been presented on a carbonate-free basis and contoured (plates 22-26). As only leachable metals are being reported, it is assumed that only metals associated with hydroxide, sulfide, carbonate, organically bound and adsorbed phases are taken into solu tion. A table of location, depth and metal and biogenic component analyses for all samples collected for this study is presented in Appendix X. All metal distribution maps have areas which are shaded. These anomalous areas will be discussed in more detail in the Discussion section of this study. 187 Distribution of* Leachable Metals in Surface Sediments Distribution of Leachable Copper The distribution of leachable copper in the sedi ments of the South Gulf of California is presented in plate 22. Concentrations range from less than 20 ppm in the silty-sand sediment on the Mexican continental shelf to greater than 160 ppm in the deep pelagic sediments along the EPR at the mouth of the Gulf. Several anomalously high concentrations of Cu persist along the Gulf trough axis, particularly over the Pescadero Basin Complex and Alarcon Rise. The Mazatlan basin is surrounded by a large anomaly greater than 100 ppm Cu which widens geographically and increases in concentration out of the Gulf. The extent of anomalies at the mouth of the Gulf south of the Mazatlan basin is somewhat vague, however, because of the lack of sampling control in this area. North of the Pescadero Basin Complex, the leachable Cu concentrations diminish and appear to have no correlation with depth. A few small regions of 40-50 ppm Cu are present; however, in general the concen trations are uniform, averaging 40 ppm Cu. One small area over the Carmen basin solicits attention because it has a Cu concentration of less than 20 ppm, yet is over a deep trough associated with inferred tectonic activity and is 188 very much, out of phase with sediments in the other basins to the south. Conversely, two areas of high metal content along the continental slope near Baja California are delineated. One, just east of Isla Espiritu Santo, is small compared to background levels of 30 ppm Cu in ad jacent sediments. The other, southeast of Xsla Ceralbo, is seen as an anomaly of 80 ppm Cu equal to some of the deeper basins. Distribution of Leachable Nickel There are several significant similarities and dif ferences between the distributions of leachable Ni (plate 23) and leachable Cu. The distribution of Ni is of low concentration on the Mexican continental shelf and in creases toward the deeper basins. An area of high Ni con centrations exists at the mouth of the Gulf, increasing in area and concentration toward the open Pacific. Two prominent Ni anomalies exist near Isla Espiritu Santo and Isla Ceralbo and an anomalous low anomaly is seen over the Carmen basin. The similarities end here as the distribu tion of Ni does not correlate with depth as well as the distribution of Cu. Small, isolated areas of high Ni con centrations do not exist over the deep basins and the con centrations are generally less than 100 ppm except south and west of the Mazatlan Basin where values begin to ap proach Pacific pelagic clay concentrations of 200—300 ppm. 189 Again, the anomalies delineated in this area are not exact due to the relatively small number of samples on which they are based compared to anomalies farther north. Another nearshore, slope associated area of high Ni content (>l4o ppm) is seen east of the Mazatlan basin and north of Xslas Tres Marias. Ni content increases rapidly with depth in this area, leveling out into a wide region of 100-1^0 ppm Ni to the west and then increasing to a 200—300 ppm Ni region further west. Distribution of Leachable Zinc Absolute values of leachable zinc in the Gulf sedi ments (plate 2k) are higher than Cu and Ni. Except on the Mexican continental shelf the concentrations are greater than 100 ppm and gradually increase toward the deep basins and the mouth of the Gulf. Three isolated anomalies exist inside the shadow of Baja California, each in close proximity to one of the three major basins in the study area. The northernmost anomaly, with greater than 170 ppm Zn concentrations, falls just west of the Carmen Basin with the 180 ppm peak falling directly over the central depres sion of the main channel. To the southeast, two 300 ppm Zn anomalies are delineated and fall over a 2000 m deep plateau on the northwest flank of the Farallon Basin. An increase in Zn concentration from 150 to 300 ppm over a small area is seen along the southeast edge of the anomaly. 190 The edge of* the anomaly falls directly on the slope break of the central trough of the Farallon basin. Southeast of the Farallon basin is still another anomaly which stretches north-south from Isla Ceralbo half way across the Gulf. This large 150 ppm area has two smaller anomalous regions of >170 and >200 ppm within it. In a similar fashion to that seen in the Farallon basin, the >170 ppm high falls at the edge of the slope break into the North Pescadero Basin and extends south—southwest toward the Ceralbo Bank. The >200 ppm high falls over the southern end of the Ceralbo trough. Outside the shadow of Baja California, the distribu tion of leachable Zn gradually increases to the south. A large area of >200 ppm and smaller regions of ^00-500 ppm Zn are observed. Just east of the tip of Baja an arm of 150 ppm Zn with a 200 ppm high area exists. This anomaly falls directly over the Alarcon Seamount. The 200 ppm contour encloses several smaller anomalies in and south of the Mazatlan basin. Directly over the Mazatlan Basin is an anomalous low of 150 ppm similar to low Cu and Ni anomalies seen in the Carmen Basin. This anomaly is restricted to the Mazatlan basin only and is enclosed on three sides by Zn concentrations at least double that seen in the basin. A southeast trending band of 300 ppm Zn roughly corresponds to the trend of the EPR although sampling control is less than adequate in this area. East-northeast of the low Zn 191 anomaly in the Mazatlan Basin, a small 300 ppm high and to the south a narrow 300 ppm region which widens to the south is found. The latter anomaly has a 500 ppm peak in close proximity to the Mazatlan Basin and two larger kOO ppm highs further to the south. Distribution of Leachable Manganese Leachable manganese (plate 25) presented as ppm/lO plots a distribution quite different from the other metals analyzed. In the northern part of the study area, Mn is less than 400 ppm in the shelf sediments shallower than 1000 m. Below 1000 m, where the depth increases rapidly, Mn concentrations follow suit. Hence, the pattern produced is one of relatively high Mn anomalies coincident with the Carmen ($5000 ppm) and Farallon (.$3000 ppm) basins. Small, isolated anomalies also exist in each of the basins of the Pescadero Basin Complex. The South Pescadero Basin has the highest concentration with > 6000 ppm Mn. Outside the shadow of Baja California, the distribution of leachable Mn is uniformly high over large areas and gradually increases from 400 to 4000 ppm with distance from the continents. Distribution of Leachable Iron As presented in plate 26, the distribution of leach able iron does not follow the increasing metal concentra 192 tion with, increasing depth pattern common to the other metals analyzed. In the Carmen and Farallon basins just the opposite is evident. Four nearshore anomalies stand out, two on each side of the Gulf and roughly opposite each other. A large (>2.0 percent) Fe anomaly with a >3*0 per cent high peak north of Isla Carmen extends east toward the Gulf trough axis just north of the Carmen Basin* Directly opposite is a small >2.0 percent Fe anomaly situated just offshore from the Mayo River and delta. The Mayo River annually transports 7»5 million metric tons of sediment to the Gulf (Byrne, 1957)* thought to be the source of this anomaly. Over the Carmen basin a >1.0 per cent Fe anomaly exists similar to that for Cu and Ni in the same location. The rest of this area has a uniform 1.0- 1.5 percent Fe content. The other pair of Fe anomalies are situated in the Farallon Basin and just east of Isla San Jose. The former anomaly of> 2.0 percent falls over and exactly parallel to the trend of the Farallon basin, extending to the center of the Gulf trough. This anomaly is associated with the Fuerte River and delta which transports approximately 42.4 million metric tons of sediment annually to the Gulf. The latter anomaly is in the shape of a north-south trending "J" of> 2.0 percent Fe with a >3*0 percent high peak in the hook of the MJ.” The 2.0 percent Fe contour which runs from Isla 193 Espiritu Santo east across to the Fuerte River area, then south along the Mexican continental shelf* break, turns east near the South Pescadero basin again intersecting the Mexican mainland, can be considered a dividing line south of* which the Fe concentrations increase to > 3*0 percent in the mouth of* the Gulf*, Several anomalies, however, exist in this region. A small area of* >3.0 percent Fe is seen just north of* Mazatlan where the San Lorenzo, Elota and Piaxtla Rivers enter the Gulf*. The San Lorenzo river alone provides 42.7 million metric tons of* sediment to the Gulf* annually. Small ,>3*0 percent Fe anomalies are present just east of* Isla Ceralbo and over the North Pescadero Basin. A larger 3*0 percent Fe anomaly with a >4.0 percent Fe peak Falls over the South Pescadero Basin-Alar9on Rise region. Two "L" shaped anomalies are also present, one over the northwest end of the Tamayo fracture zone near the tip of Baja California, the other over the Mazatlan Basin. Both anomalies have concentrations >3*0 percent Fe. Although several anomalies can be delineated in the South Gulf of California, the anomalies are areally small and emphasize that the distribution of leachable Fe is generally uniform, not varying more than 1 percent, from the Pescadero Basin Complex south. 194 Distribution of Metals with Depth in Piston Cores The distribution of leachable metals (figs. 13-17) in the 12 longest piston cores recovered from the Gulf of California (fig. 10) is presented. Concentrations of metals as well as location, depth, and biogenic components for all piston cores recovered are reported in Appendix III. Distribution of Leachable Copper The distribution of leachable Cu (fig. 13) in the piston cores is either uniform (cores 20398, 20397* 21970, 21977, 21972, 21985, 21995, 22009), increases or decreases with depth (cores 21967, 21965, 21984, 22023). Except for 22023, the cores show little abrupt change in concentration over short intervals. Core 21967 shows an initial high concentration at 10 cm with a subsequent decrease at 20-100 cm, then a steadily increasing concentration of Cu to the bottom of the core. The cores in close proximity to 21967 (20398, 20397, 21970) show no such minimum at the same depth, suggesting that environmental variations at local sites of deposition are important in regard to the distribution of metals. 195 Figure 13. Distribution of Copper in twelve piston cores* 196 Q & o o Q o o c o u _ 197 Figure l4# Distribution of Nickel in twelve piston cores. 19S ‘ -n >y o l- O S - — • • tJr O t\r l / s * < » * ? O * • ^ * - t H • C-" h*<* «* ^% i cr r o & o o Q 6 0 Cm 199 Figure 15* Distribution of Zinc in twelve piston core s. 200 | £2* «•] r j * • 01- ■>? 0H- <r£ o on-, **5 *': o t - ~ 3*3 < n t " h*.?; “. Wo ri ou- V - + ' * * 13Vo- m - 3 < m - t*o ^ oy- cr ^ ^ -s| a”: •11- < s ~ > 0 o t r t T - OU- oU- w o ^3 < rtt- ®0 Vj r * *w- CO t4W» o • • v > tni J o o o o 201 Distribution of Leachable Nickel Ni (fig. 14) follows Cu almost exactly in distribu tion but is slightly higher in absolute values. The trends down the cores are more pronounced, as for example in cores 21967 and 20397# Distribution of Leachable Zinc Zn (fig. 15) also follows Ni and Cu in its distribu tion, however, the absolute values are again higher. The cores which show very uniform concentrations of Cu and Ni show some subtle variations and a wider range of Zn con centrations. Core 20397 shows three distinct Zn maxima, while Cu and Ni showed only one definite maximum. Core 21970 shows a distinct maximum at the top of the core which quickly decreases to approximately a 120 ppm uniform level. Xn 21995 the ratio of Zn to Cu and Ni is low compared to all other cores. Distribution of Leachable Manganese Several different trends stand out in the distribu tion of Mn (fig. 16, log scale). In the northernmost cores (21967, 20398, 20397) intervals of maximum and minimum Mn concentration are evident. A high concentration of Mn at the surface of core 21967 decreases to a minimum at the 20-100 cm interval similar to that seen in the Cu 202 Figure 16, Distribution of Manganese in twelve piston cores. 203 ,« x - » • * * - C £ ) u. $ G o (uup; Hi-d3Q a —i — e £ A & 20^1 and N± distributions. At 120 cm the concentration abruptly increases. Core 20398 shows just the opposite distribu tion; a maximum at the surface, a small minimum at 30 cm, a broad maximum between 30 and 120 cm and then another minimum. Core 20397 has a maximum at the surface also, decreasing to approximately 300 ppm, followed by three sharp minima between 14-0 and 260 cm. Cores further to the south (2197°, 21965, 21977) show maxima at the surface and generally uniform distribu tions at depth. A very uniform 200 ppm Mn concentration is found in core 21972. Cores 21984, 21985 and 21995 show Mn minima at the surface which increase to maxima at 80, 120 and 160 cm, respectively. Core 21995 shows another maximum at the I8O-360 interval, although absolute concen trations are less than 500 ppm. The cores farthest to the south (22009, 22023) show uniform distributions with maxima at the sediment surface. These two cores show high absolute Mn concentrations. Core 22023 has at least 1000 ppm Mn throughout the core with 3300 ppm Mn measured at the sediment surface. Distribution of Leachable Iron The trends of Fe in the cores (fig. 17) are similar to the Mn distributions with three exceptions. Cores 21967 and 21995 show minima where Mn maxima exist, and core 21965 shows three very high maxima which are not at all reflected 205 Figure 17. Distribution of Iron in twelve piston core s* 206 rJ -r o 5 S* ” * • • • « - 2 ® v , r ? ^oViCS «rt- S ^ O ool- o © o (W?) f!i-d3Q u j 00 u . .VJ 207 in the Mn or other metal distributions of* that core* The Fe concentrations in this core are nearly doublt the con centration of the average sediment in the other cores on a bulk sediment basis. Core 21972 shows two Fe minima, one at 60 cm, the other at 180 cm* Neither minimum is seen in the Mn distribution, however, the 60 cm minimum is reflected in the Cu, Ni and Zn distributions. Anomalous Metal Accumulations in Individual Samples As previously mentioned, four samples collected in the Southern Gulf of California (stars on plates 22-26) have anomalously high metal contents relative to the sedi ments in close proximity. Table V presents the transition metal concentrations of these samples along with two manganese crusts and two manganese nodules dredged from widely spaced locations in the Gulf. These metal concen trations of Gulf samples are compared to average Pacific pelagic clays, EPR metalliferous sediments, a central equatorial Pacific Mn nodule, and inferred hydrothermal and hydrogenous Mn crusts from the Mid—Atlantic Ridge. Comparison of the chemical compositions of these samples from radically different tectonic and non-tectonic, deep and shallow water environments is difficult. There appears to be no comprehensive chemical patterns from which to delineate hydrothermal from hydrogenous or diagenetic 208 Table V. Comparison of concentrations of metals, Si, Al, C , CaCO in Mn crusts, nodules, sediments of inferred hydrogenous, hydro?Ef(rmal and diagenetic origin Fe Mn Cu Ni Zn Co Si Al C CaC0o oi\ (cL\ ( ( oL\ (oL\ (oL\3 Sample . M _ ...(so (ppm) (ppm) (ppm) (ppm) «) w w (fop S-392* 19.4 8,60 510 1280 390 200 7.0 0.5 0.3 0.08 S-38O* 2.76 29.8 260 700 300+ 150 5.0 0.5 0.3 0.00 S-330* 4.62 24.2 270 1500 680 80 - - 1.0 2.75 DH-09* 11.7 10.4 140 550 200 50 7.0 0.5 - 44-mn* 14.3 13.0 210 2210 350 200 5.0 0.5 - - 155-MN* 5.09 17.1 510 6450 870 150 7.0 0.7 - - Farallon Nodule* 2.10 53.5 55 255 - 1350 7.8 0.7 - — Delfin Nodule* 1.50 52.0 120 46o — 1100 11.0 2.0 — — Central Pacific Nodule* 5.0 27.2 10350 11280 1370 500 2.0 0.3 Hess Metallif erous sediment* 26.5 15.6 800 1560 510 100 1.5 0.2 MAR "hydro-(a) thermal1 1 crust 0.6 39.0 42 352 19 MAR "hydro-(a) genous" crust 18.1 9.8 880 1280 2720 Pacific Pelagic clay* (b, f) 5.15 1.8 560 210 85 150 26 8.3 _ 3.0 Pacific Pelagic clay* (c) 6.5 1.2 740 320 160 23 9.2 m m m m ro o vo Table V. Comparison of concentrations of metals, Si, Al, C. > CaCO^ in Mn crusts, nodules, sediments of inferred hydrogenous, hydrothermal and diagenetic origin (continued) Sample Fe W Mn W) Cu (ppm) Ni (ppm) Zn (ppm) Co (ppm) Si w Al (96) O ' O 'cRh * O ^ O LO East Pacific Rise High Heat flow Sediment** (d) 18.0 6,0 730 430 380 105 6,1 0.5 80 EPR province "a"** (e) 9.5 2.4 990 690 285 213 13 b.l 58 (a) Scott et al. (1974). fb) Landergren (1964)• fc) Goldberg and Arrehenius (1958). fd) Bostrom and Petterson (1969) - average. fe) Bostrom and Petterson (1969) - average. (f) Landergren and Manheim (1963) as reported in Sayles and Bischoff (1973). * All dried at 110°C, ground to 100 mesh size and washed to remove all salts; Fe, Mn, Cu, Ni and Zn analyzed by HF-HNO^ dissolution and Atomic absorption spectrophoto meter; reported on carbonate-free basis; Co, Si and Al analyzed by emission spectrograph. ** Carbonate-free basis. Fe-Mn deposits. Even supposed hydrothermal Fe-Mn deposits classified by their association with known active tectonic environments and mineralogy, when plotted on a ternary diagram (fig. 18) of Fe, Mn and Cu+Ni+Co (xio) (Bonatti et al., 1972), fall in fields also occupied by shallow water Mn rich sediments of probable diagenetic origin. The question that must be asked is whether or not any Fe-Mn deposit can be classified as hydrothermal, diagenetic or hydrogenous on chemistry rather than location or mineralogy. The answer at this time appears to be no. Using Bonatti*s (1972) classifications, the Mn crusts and sediments from the Gulf of California appear to be formed by a combination of processes. S-392 falls nearest the hydrothermal field and close to the position of the Hess depression metalliferous sediment. It is pos sible that this Fe-Mn sediment sampled from the side of a seamount is of hydrothermal origin formed by the exhalation of hydrothermal fluids (altered seawater). ^4-Mn and DH-09, both dredged from active plate boundary zones, fall between the hydrothermal and diagenet ic fields and may have been formed by the combined pro cesses. The other samples, S-330, S-380 and the Delfin and Farallon basin Mn nodules are very much of diagenetic origin according to Bonatti*s criteria, falling close to the Mn end member. 155-Mn is another composite sample presumably formed by hydrogenous and diagenetic processes 211 Figure 18. Plot of Mn sediments, crusts and nodules from the Gulf of California and. other metalliferous sediments and hydro- thermal crusts from tectonic environ ments (after Bonatti et a_l. , 1978). 212 HYDROGENOUS Pec. Nod MAR-B S-392. S-33Q HESS FE HYDROTHERMAL MN DIAGENETIC and falls near the central Pacific Mn nodule. This whole scheme is disrupted by the positions of the two crusts from the Mid-Atlantic Ridge (Scott jet al., 1974). MAR-A is believed to be a hydrothermal crust, yet falls solidly in the diagenetic field. MAR-B is purported to be of hydro genous origin, yet falls between the hydrothermal and hydrogenous fields. Calculations of Si/Al and Fe/Mn ratios (Table VX) show a further dichotomy between crusts, nodules and sedi ments of inferred hydrothermal, hydrogenous and diagenetic origin. The two samples (S—392 and DH-09) with the great est chance, however small, of being hydrothermally produced or altered have the highest Si/Al ratios in good agreement with low Al content sediments from high heat flow areas of the EPR (Bostrom and Petterson, 1969) anc* sediments col lected from the Bauer Deep in the East Pacific by Sayles and Bischoff (1973)* Inferred hydrothermal crusts from neither the Mid-Atlantic Ridge (Scott ejt al., 1974) nor the Galapagos Rise (Moore and Vogt, 1976)* another area of hydrothermal activity, unfortunately do not have complete analyses for comparison. Samples S-38O, 44-MN, and 155-MN have similar Si/Al ratios which are slightly lower than the aforementioned samples. These samples are inferred to be formed by diagenetic processes. All Mn nodules analyzed have similar Si/Al ratios which are about a factor of 2 greater than the Pacific pelagic clays. The nodules are 214 Table VI. Comparison of Si/Al and Fe/Mn ratios in manganese sediments, crusts and nodules of inferred hydrothermal, hydrogenous and diagenetic origin (see Table V for original analyses) Sample Si/Al Fe /Mn S-392 14 2.3 S-380 10 .09 S-330 - .19 DH-09 14 1.1 44-MN 10 1.1 115-MN 10 .3 FaralIon Nodule 3.7 .04 Delfin Nodule 5# 5 .03 Central Pacific Nodule 6.7 .18 Hess Depression Metalliferous Sediment 7 1.7 MAH "Hydrothermal” Manganese Crust - .02 MAR "Hydrogenous” Manganese Crust - 1.8 Pacific Pelagic clay (Landergren, 1964) 3.1 2.9 Pacific Pelagic clay (Goldberg and Arrehenius, 1958) 2.5 5A EPR high heat flow sediment 12 3.0 EPR province ”a" sediment 2.8 4.0 JO H V j i probably of hydrogenous origin. The Fe/Mn ratios, on the other hand, show little correlation with the Si/Al ratios. The inferred hydro- thermal and hydrogenous crusts (Scott et al., 197^) from the Mid-Atlantic Ridge have ratios of .02 and 1.8, re spectively. If we assume their inferred origins to be correct, a comparison with other deposits suggests opposite relationships to those reasonably expected. For example, the Fe/Mn ratio of the Farallon basin and Delfin basin nodules are .04 and .03, respectively, indicating a hydro— thermal(?) origin. Conversely, the Hess Depression metal liferous sediment and the East Pacific Rise high heat flow sediment (Bostrom and Petterson, 1969) have Fe/Mn ratios of 1.7 and 3*0, respectively, suggesting hydrogenous origins. Moreover, Bauer Deep metalliferous sediment (Sayles and Bischoff, 1973) which have average absolute concentrations of Fe and Mn of 13*5 and 3»7> respectively, have Fe/Mn ratios very similar to average Pacific pelagic clays whose absolute concentrations are a factor of 3 lower. This suggests that the Fe/Mn ratio is not a definitive method of comparing heavy metal sediments, nodules and crusts for the purpose of determining the origin of the anomalous metal accumulation. 216 Metal Accumulation Rates and Sedimentation Rates Using the expression for metal accumulation rates (Dymond and Veeh, 1975)> A=C«S* />(l.00—W), where A = Accumulation rate C = Concentration of element S = Sedimentation rate (cm/1000 yrs) P - Bulk density of sediment (g/cc) ¥ = Water content (percent as a decimal), accumulation rates for sediments with known sedimentation rates can be calculated. Water content was approximated from data by van Andel (1964) and bulk density was assumed to be 1 g/cc (Byrne, 1957). These data along with metal accumulation rates of EPR metalliferous sediments and Pacific pelagic clays are presented in Table VIX. Metal accumulation rates for Fe in EPR metal liferous sediments are similar to those calculated for the sediments in the Farallon and Pescadero basins, yet there is between 20-60 times greater sedimentation rates in the Gulf basins. Accumulation rate ratios of Fe/Al (Table VIII) for the Gulf basins and the EPR further support the hypothesis that the Fe in the Central basins of the Gulf is associated with detrital phases and is, relatively speaking, not accumulating nearly as fast as the hydro- thermal sediments of the EPR. Except for Fe all the metals accumulating in the Gulf are being overwhelmed by 217 Table VII* Metal accumulating rates and sedimentation rates for sediments of the Gulf of California compared to metal accumulation rates on the East Pacific Rise and the North Pacific Sed. Area Depth ..Lm)_. Rate (cm/ 1000 yr) Bulk P (&/ cc) Water Con tent Accumulation Fe Mn Rates Cu (mg cm" Ni ■2 -3\ XT . . Zn Farallon Basin R-82 East Slope-Fuerte River 3165 100 1.0 5 3 66*0 8.60 .056 .033 .68 R-85 Farallon basin AHF 219^6 732 84 1.0 63 76.0 .85 . 068 .090 .33 30- 40 190-197 cm cm 2306 30 1.0 51E 35.0 35.5 1.2 3127 .06 .06 .075 .09 .20 .23 Pescadero Basin R-47 South Pescadero Basin AHF 22023 2822 k6 1.0 63 hi .5 1.17 .14 .12 .36 20- 30 120-127 cm cm 3495 k7 1.0 55E 50.0 60,0 4.3 3.3 • 16 .16 .123 .13 .30 .34 West slope R-79 East slope, Mazatlan 1619 60 1.0 69 35.0 .463 .039 .059 .20 R-l6 Mazatlan Basin flank S-403 1372 12 1.0 65E 7.0 .07 .015 .016 .038 0- 7 112-119 cm cm 2930 6 1.0 63E 6.0 5.0 .13 .11 .019 .018 .017 .0125 .036 .028 w H 00 Table VII* Metal accumulating rates and sedimentation rates for sediments of the Gulf of California compared to metal accumulation rates on the East Pacific Pise and the North Pacific (continued) Area Depth . (m). Sed* Rate (cm/ 1000 yrl Bulk P (s ( cc) Water Con tent W Accumulation Fe Mn Rates Cu ( “2 -3\ Ni Zn East Pacific Rise blank S-4l6 0- 7 cm 100-108 cm East Pacific Rise V19-54, 2838 8 1.0 6oe 9.0 8.0 .24 .135 .03 .025 .039 .09 .024 .053 17°S, ll4°¥ (Bender et_ ajL. , 197l) DSDP site 319-1 2830 1.5 1.3^ 61 82 28 .16 13°S, 101.5°¥ - 0-8 m (Dymond ej; al* , 1976) North Pacific uncon 4290 .11 1.16 79 2.9 . 86 .022 solidated sediment (Bostrora e r f c al* , 1973) .1-.5 2.5- 8.7 .25- .99 .012- .054 *011- - .038 ro h» K O Table VIII* Accumulation rates of Si and Al and metal/Si and metal/Al ratios for samples in Table VII Sample Accumulation Rate (mg cm"^ yr~3) Accumulation Rate Ratios Si (est*) Al .(est*) Fe/ Si Fe/ Al Mn/ Si Mn/ Al Cu/ Si Cu/ Al Ni/ Si Ni/ Al Zn/ Si Zn/ Al R-82 1150 320 . 06 .21 .01 .03 .01 .01 .01 .01 .01 .01 R-85 760 210 .10 .36 .01 .01 .01 .01 .01 .01 .01 .01 AHF 21966 370 105 .09 .33 .01 .01 .01 .01 .01 .01 .01 .01 R-47 365 115 .11 .36 .01 .01 .01 .01 .01 .01 .01 .01 AHF 22023, 20- 30 cm 490 130 .10 .38 .01 .03 .01 .01 .01 .01 .01 .01 120-127 cm 485 140 .12 .43 .01 .02 .01 .01 .01 .01 .01 .01 R-79 415 93 *08 .38 .01 .01 .01 .01 .01 .01 .01 .01 R-l6 79 30 .09 .23 .01 .01 .01 .01 .01 .01 .01 .01 S-405, 0- 7 cm 42 15 .14 .40 .01 .01 .01 .01 .01 .01 .01 .01 112-119 cm 44 11 .11 .45 .01 .01 .01 .01 .01 .01 .01 .01 S-4l6, 0- 7 cm 65 20 .14 .45 .01 .01 .01 .01 .01 .01 .01 .01 100-108 cm 75 20 .11 .4o .01 .01 .01 .01 .01 .01 .01 .01 V19-54 - .61 - 134 - 46 - - - .26 - - DSDP 319-1 3.1 * 64 .93 4.5 .28 1.3 - - .01 .03 - - North Pacific sedi ment (avg. of 73 locations) 4.1-18 “* •48-.61 m m .06 .01 .01 ro ro o combination detrital sediment influx and biogenous components influx. Away from continental influences, accumulation rates of Fe and sedimentation rates decrease an order of magni tude, However, compared to sedimentation and accumulation rates of Pacific pelagic clays, the sedimentation rates are different by an order of magnitude while the Fe and all other metal accumulation rates are of similar magnitude. This suggests a dilutant in the Gulf which contributes to the sediment mass but not appreciably to the metal content. Possibly the large biogenic component in the Gulf (Calvert, 1966) (foraminifera, diatoms, radiolaria, sponge spicules) is of low enough metal content to be that dilutant. Sub- aqueously transported sands and silts of low metal content (turbidite flows and slumping) are another possibility. Mn, Cu and Ni show similar trends to Fe, with ac cumulation rates of the same order of magnitude as the open ocean sediments but with sedimentation rates as much as two orders of magnitude higher. Accumulation rate ratios of metal/Si and metal/Al for Mn, Cu, Ni and Zn are extremely low, indicating that Si and Al bearing materials are being deposited orders of magnitude more rapidly than the metals. In contrast, on the EPR (Dymond and Veeh, 1975) Fe and Mn are accumulating 1-2 orders of magnitude faster than Al, and Al is accumulating only four times faster than nickel as indicated by the chemical data available for this core 221 (Bender et; al. , 197l) • Accumulation rate ratios of metal/ Si in Gulf sediments compared to DSDP site 319 surface sediment indicate an order of magnitude faster accumulation of Fe over Si and at least 2 orders of magnitude faster accumulation of Mn. Xt must be said that comparisons of metal accumula tion rates from the Gulf of California and the deep North Pacific and EPR areas are not strictly relatable. Compari sons should be made between the Gulf of California and other hemipelagic areas which do not have tectonic associa tions in order to see if the association of tectonic elements effects the metal accumulation rates appreciably. The literature suggests that no such work has been done. However, from these data it appears that detrital and biogenic sediments, as evidenced by the accumulation rates of Si and Al, overwhelm the accumulation of metals in the sediments of the Gulf. The degree of dilution of the metals may be important due to rapid sedimentation by turbidity flows and imput of large amounts of low metal content biogenic siliceous debris. 222 DISCUSSION: GEOCHEMICAL DATA With, only four samples having anomalously high transition metals content and being widely spaced across the South Gulf, it appears, to the extent of this study, that there are no extensive heavy metal deposits in the Gulf of California such as are found in the Red Sea* How ever, by employing the geochemical prospecting techniques mentioned, several regions of high metal content in the sediments have been delineated. Moreover, if other environmental parameters are known, it is possible that a qualitative approach to the question of whether or not hydrothermal imput into the sediments is proceeding, can be taken. As has been shown, much information on sedi- mentology, hydrography, climate and biological components is available for the Gulf of California (van Andel and Shor, 1964). This study has added to that wealth of data by filling in some of the information gaps* A simple process can be employed whereby positive correlations of environmental factors (organic carbon, CaCO^, proximity to river influx, clay mineralogy, presence of an minimum, etc.) with metal anomalies mapped eliminate those anomalies from consideration as possible evidence of hydrothermal metallogenesis. If the assumption 223 that the leaching technique used in this study does not appreciably attack metals bound in silicate detrital phases is correct, the detrital fraction of the sediments is automatically eliminated. Furthermore, the association of any anomalies not eliminated by correlation with environ mental factors which correlate with inferred tectonic elements further refines the areas of possible hydrothermal imput to the sediments. ¥ith the aid of multivariate statistical analysis, further definition of the states in which the metals reside may be possible and will be em ployed. Correlation of Metal Distributions with Environmental Factors Metals and Biogenic Components Knowing that organic material and organic sub stances such as humic acids in sediments are powerful ac cumulators of metals and that plankton!c forms also en rich metals from seawater to their protoplasm, it is as sumed that any anomalous metal concentrations which correlate with anomalously high organic carbon content can be considered to be derived from a biogenic source and eliminated as a possible hydrothermal deposit. Compari sons of plate 20 with plates 2 2 - 2 6 show the correlation of metals with organic carbon; the shaded areas are anomalous 22k metal concentrations which do not coincide areally with organic carbon anomalies. The Cu-organic carbon compari son shows the above relationship well. Where there are high organic carbon contents (up to 5 percent), there are also high Cu concentrations (up to approximately 80 ppm), However, sediments with Cu contents greater than 80 ppm, as in the Mazatlan Basin area, have organic carbon contents less than 5 percent. Another way of presenting the data is in graphic form. Figure 19 shows the plot of leachable Cu (ppm, carbonate-free basis) against organic carbon (per cent) , In area I all samples with organic carbon greater than 5 percent were plotted regardless of their Cu content. In areas II and III, all samples with Cu content greater than 80 ppm are plotted. Necessarily all these samples have organic carbon (Corg ) contents less than 5 percent. All samples with Cu less than 80 ppm and C less than org. 5 percent have not been plotted but would fall in the lower left corner of the plot. Coincidentally, the samples were also separated into depth regimes. Area I samples are all collected from depth less than 1500 m while other samples are in depths greater than 2300 m. The samples with Cu greater than 80 ppm can be divided into two groups. Area II (crosses) comprises all samples that did not fall in the shaded anomalies of plate 22. Area III (solid triangles) is all samples that do fall in the shaded anomalies and which are associated with inferred 225 Figure 19* Organic carbon versus leachable Copper, • = all samples with. C >5 percent org, ^ + = all samples with Cu >80 ppm A = all samples associated with inferred tectonic elements 226 ORGANIC CARBONW o LEACHABLE COPPER (ppm) 03 o cn O O ■ 1 - 1 » — i - » » « __ 3 _ _ _ — A _____i l ------ J _ _ _ ------------L — -----U ----- ro o o (zzzzzzf ro- 0 4 - C T3 OV co- C£>- \ \ \ • I ■/ o + 242 tectonic elements* A good separation of the population occurs with Area XIX samples having somewhat higher Cu contents but similar C to Area II samples* Very little org. overlap of the two populations is seen* This evidence suggests that three separate sources of metals (at least for Cu) can be delineated* Area I could be interpreted as samples whose Cu content is controlled by organic carbon content or of a biogenous origin. It is interesting to note, however, that no matter how high the C , the con- 9 9 * = > org* 9 centration of Cu does not exceed 80 ppm. As shown by Cal vert and Price (1970)> the higher the organic carbon, the higher the metal content in the sediments. This relation ship does not appear to hold strongly in the Gulf of Cali fornia sediments. This suggests that an external factor such as inorganic detritus is acting as somewhat of a dilutant. Area II samples might be characterized as hav ing Cu which resides in the sediments mostly as adsorbed species on fine clay particles at depths greater than 2300 m. As shown experimentally (Murray, 1975; O ’Connor and Kester, 1975)y Slatt (197^0 found similar increases in trace metal concentrations with decreasing grain size and increasing depth in Conception Bay, southeast Newfoundland, a possible small scale equivalent to the Gulf of Cali fornia. The association of tectonic elements with samples grouped as Area III may suggest hydrothermal imput in ad dition to adsorbed Cu on clays. Any further quantitative 228 separation of the groups is speculative. The Ni and organic carbon comparison shows a similar correlation with the Cu and C distributions* org. However, the absolute values of Ni concentrations are ap proximately 20 ppm higher than Cu for the same ^org • Again the Mazatlan basin is characterized by high Ni and low C , org. Zn and C in contrast to Cu and Ni have only one org. J anomaly correlation, east of Isla Ceralbo, where a 200 ppm anomaly coincides xo-th a 9 percent C region. High Zn org. anomalies in the northern part of the study area do not correlate with high ^org. contrary to what might be ex pected considering the high biological productivity in this area. Graphic representation of C and leachable Zn * • t ' org. (fig. 2 0 ) again show a distinct separation of two popula tions. Only three samples with C greater than 5 per- or g. cent have Zn concentrations greater than 180 ppm. However, the separation of samples associated with inferred tectonic elements from all samples having greater than 180 ppm Zn is impossible. Several high Zn concentrations associated with tectonic elements have low C , however, the scatter and org.* * intermixing of the two populations is evident, making an interpretation of hydrothermal imput tenuous. Pe and C show positive correlations in three org. ^ locations, two areas near the Baja coast and another over the Carmen basin. The rest of the study area shows a 229 Figure 20, Organic carbon versus leachable Zinc, , = all samples with C >5 percent org, + = all samples witb Zn >180 ppm A = all samples associated with inferred tectonic elements 230 o o O _JL_ LEACHABLE Z I NC ( ppm) GO O <T> O _l _ _ 1X5 O O ro- o ZX) GD It> 01- -jx~ O O cn« CD O 05- / / s N \ \ \ co co ' o 240 - ro 05 O CM rv5 o * CM o> o 4X O O _2 o> C7I definite negative correlation, especially in the South Pescadero Basin-Alarcon Rise region where a ^.0 percent Fe anomaly is correlated with a 2.0 percent corg region. Mn and C also show a distinct negative cor- org. relation. Low Mn concentrations are found almost exclu sively along the shelf-slope regions which are areas of high ^org • Very high Mn anomalies persist in the deepest basins where C is low. org. Pairing of metals with CaCO^ content produced no discernible positive or negative correlations in spite of the fact that the metals are reported on a carbonate free basis. As can be seen from the pairing of Zn and CaCO^ (plates 2h and 2l), the highest Zn anomalies are over the low CaCO^ areas. The relative concentrations of Zn over the study area are not appreciably effected by the CaCO^ content. The explanation for a negative correlation with all metals in the Gulf of California sediments is unknown, especially in light of the fact that Turekian and Imbrie (1966) found positive correlations between Cu and CaCO^ in the Atlantic Ocean. It is possible, however, that the cor relation of Cu and CaCO^ on the Mid-Atlantic Ridge may be misleading and only mathematically significant. It can be argued that the metals come from a source independent of the biogenic component and are coincidentally correlative. The Mid-Atlantic Ridge is shallow enough to allow large amounts of CaCO^ to be incorporated into the sediment as 232 well as being the locus of high Cu concentrations possibly from volcanic emanations or adsorption onto hydroxide phases which may also be present in anomalously high amounts along the extent of the ridge system. C and org, CaCO^ (plates 20 and 2l) show some correlations along the shelf areas as would be expected considering the high biological upwelling along the coasts. Metals and Other Environmental Factors Because of the negative correlation between C org. and Mn and the obvious correlation of Mn with depth, it was first thought that, indeed, the Mn distribution could be correlated with the inferred tectonic elements (plate 3l) and thus possibly the high Mn concentrations were of hydrothermal origin. However, the abundance of Mn crusts dredged from slopes below 1500 m and the 0^ content of 3 ml/L in bottom waters below the 0^ minimum suggested that the Mn-depth-fault traces-Hydrothermal origin correla tion was misleading. Xf we compare the leachable Mn dis tribution with the extent of the 0o minimum zone and C 2 org. seen in plan view (plates 27 and 17)* there is a strong suggestion that diagenetic processes and the geochemical behavior of Mn under reducing and oxidizing conditions are very much in control of the distribution of leachable Mn in the South Gulf of California. The comparison of the distribution of leachable Fe 233 (plate 26) with, other environmental factors produces several interesting associations. Besides being the most abundant metal studied, Fe also resides in many different sediment phases depending on the geochemical environment into which the Fe has been deposited. Statistically, Fe and C do not show a strong correlation. Xn samples org. with greater than 5 percent C # the Fe—C correla- 0 * org.9 org. tion coefficient (hereafter denoted by "r") = .01 (Ap pendix V, Table 3)# Even though the leaching process probably solubilizes the organically bound Fe, it is probably only a small percentage of the total Fe in the sediment. Martin and Knauer (1973) report Fe in plank- tonic material in the nearshore environment to have con centrations between 92—315 ppm, approximately 1 percent of the average leachable Fe found in Gulf of California sedi ments. Nissenbaum and Swaine (1976) found that Fe is mostly bound in the sulfide phases in reducing environ ments with only .5 percent of the total Fe being tied up in humate substances. In the mildly reducing sediments on the shelf-slope areas of the Gulf, the transformation of Fe oxides to pyrite is rapid (Berner, 1964a). Since the leaching technique probably oxidizes pyrite and any Fe mono- sulfides present metastably as well as any oxides, parti tioning of the two phases is impossible. However, since the total leachable Fe in the sediments does not change with the transformation of Fe oxide coatings on clays to 234 pyrite, the distribution of Fe remains constant. This further supports the observed general uniformity of Fe distribution over the study area. As has been discussed, anomalies of leachable Fe fall close to major rivers along the Mexican mainland. This suggests that a major component of the total leachable Fe is from Fe oxide coatings on clay minerals transported to the Gulf as suspended sediment load. All anomalies not correlated with high C or river sediment discharge org. regions are shaded (plate 26). Xf a major portion of the leachable Fe in the South Gulf sediments is from hydroxide coatings on clay minerals, might not there be a correlation between percentage of clay and Fe content? While percentage of clay for all samples was not measured, some data exist for samples col lected by van Andel (1964). These data were compared to the leachable Fe content producing a correlation coef ficient of .03 or scatter plot of the data. A correlation of clay percent/silt percent ratios to Fe content produced a similar result with 4 = .08. While it is not known why the Fe—Clay percent correlations are so low, these findings do not preclude the possibility of hydrothermal imput of Fe into the sediments in the South Gulf. Mineralogy of the sediments also was not determined for these sediments, however, some data does exist (Grim et al., 19^9)* The sediments contain illite, montmoril- 235 Ionite and kaolinite with illite the most abundant and kaolinite the least. Recognition of what appears to be glauconite in several cores during sampling for this study was confirmed by X-ray diffraction analyses. The loca tions of glauconite are plotted in plate l6. Comparison of the distribution of Fe (plate 26) with sediment dis tribution (plate 16) reveals that several of the anomalies, some associated with high C and some not, are cor— org. * related with the presence of glauconite in the sediments. The occurrence of glauconite also appears to be coinciden tal with the fringes of the minimum zone (plates 26 and 17) and suggests residence in environments of fluctuating redox potential. Both Fe anomalies thought to be ex plained by their correlation with Corg are exactly co incident with the occurrence of glauconite. Two shaded anomalies with greater than 4.0 percent Fe are also coincident with glauconitic sediments, however, the presence of glauconite does not appear to explain the entire anomaly in both cases. The Fe anomalies over the Mazatlan and North Pescadero Basins as well as the majority of the anomaly in the South Pescadero basin remain un effected. Cobalt, which has not been included in this study, was measured in the leachates of 54 samples. The uniformly low concentrations in the Gulf sediments (12 ppm average) compared to other marine environments can be explained by 236 the tendency of Co to form soluble, complex ions in near shore sediments (Carvajal and Landergren, 1969)* More over, Co may be preferentially adsorbed to MnO^ phases (Murray, 1975)• MnO^ crusts from the Gulf analyzed for Co reveal concentrations of approximately 100-200 ppm. In summary, it is possible to qualitatively eliminate metal anomalies in sediments which are as sociated with known environmental factors. If the remain ing anomalies correlate exclusively with inferred tectonic elements, the possibility remains that hydrothermal imput into the sediments is presently occurring. Inter—element Correlations with Depth in Piston Cores Six of the twelve piston cores (21967 (fig. 2l), 20397 (fig* 22), 21965 (fig. 23), 21984 (fig. 24), 21995 (fig. 23), 22023 (fig. 26) were selected to show variations in metal content and biogenous components with depth within each core. In general the distribution of metals is quite uniform with no sediments showing evidence of extraordinary metal emplacement indicative of hydrothermal metallogenesis• However, many subtle variations in metal content are ob served. Except for Fe, the three cores located in the Farallon basin show good inter-core metal-metal correla tions which appear to be related to organic carbon content 237 gure 21, Inter-metal and biogenous component trends in piston core 21967* 238 0 9 o l o t - o l o o o e ' * o * % cr £ ? Vi > £ ( m ? ) U .L d 3 Q £ o~ _s r f i c - 4 239 Figure 2 2 Inter—metal and biogenous component trends in piston core 20397. 2 ho Itf6 S f i £ 3 ? Q O o TH (c*0 n n « N> a O • -D - * - -a £ e g t - ? . » » £ ^ -s -» # S - -no Figure 2 3 Inter-metal and biogenous component trends in piston core 2196.5* 2 k 2 o Q % o o Q O Q C ^ > O r — - j V j 1 —9 l / \ o o rj— f " 4 *0 Oo _- • « O , i n o - w W ^ 4 o s r - S > (no; fijLd^Q 2^1- 3 Xnter—metal and biogenous coraponen' trends in piston core 2198k, « ! • O t t ol «"5 ‘ . i t o o < a o o o o O O cr " t o S 3 fii-d3Q & C N i 2k5 Figure 2 5. Inter-metal and biogenous component trends in piston core 21995. 2 h6 L \ ] Z • 8 $ £ DEPTH (cm. ) § e s § $ oa -J O 5 * o o *. o _ o ~q S' -X ) *s*-. e~ C . * - r* ■ 1 D ( w^ w («<W) ( * * V ; * z w w i ( ^ 3J i glare :6, Inter-metal and biogenons component trends in piston core 22023# VJ 1 t t j r -mr\ o Q O o o o cA cJ O C"l >7 $ . * £ ! « ? t o ( w ? } H J L d 3 Q 2k9 with depth* Pe in cores 21967 and 21965 appears to be independent of other elements with only a moderate cor relation coefficient of approximately . 40 with CaCO^. This may indicate that a considerable amount of the Fe is as sociated with hydroxide coatings on clay minerals. Mn in 21967 shows two maxima and a minimum down the core which may correspond to oxic and anoxic layers, respectively. Li et al. (1969)* measuring Mn concentrations in pore waters in the Arctic basin sediments, also found maxima and minima related to anoxic and oxic layers. One might expect that an oxic layer would have low organic carbon, possibly sand—silt grain size and high leachable Mn; anoxic sections would have high organic carbon and low leachable Mn. However, in 21967 the opposite is observed. Organic carbon and leachable Mn correlate with a coef ficient of .89* This might suggest that a considerable amount of the Mn is tied up in organic complexes or huraic substances associated with clay minerals. While pore water studies on these cores would be a better way of judging the extent of Mn mobilization at depth, the occurrence of Mn crusts and coatings in great abundance on the sea floor below the minimum and high concentrations of leachable Mn in the surface sediments of the cores indicates that post-depositional mobilization of Mn is occurring in the sediments. The extent of Mn mobilization from one geo graphical area to another can be qualitatively judged from 250 solid, leachable Mn phases present as well as sedimentation rates and presence or absence of the minimum zone. The absolute concentrations of metals in the three cores in the Farallon basin area reflect differences in depositional environments and accumulation rates. As previously mentioned, sedimentation rates vary from 30—100 cm/lOOO yrs over a small area indicating rapid and ir regular deposition of terrigenous sediments. Several minima in all the metal and biogenous component concentra tions in core 20397 may reflect turbidite layers with relatively more low metal and organic carbon content sand and silt. The unusually high Fe in core 21965 ^s> however, an enigma. The moderate correlation of Fe with CaCO^ can be explained by the fact that Fe is reported on a carbonate free basis. However, the bulk Fe content is still two times higher than in any other core collected. The periodicity of the high Fe content with depth may reflect episodic influxes of clays with Fe oxide coatings which have not been diluted with other low metal sediments. However, the proximity of this core to an inferred active fracture zone and the associated high Fe content may be evidence of hydrothermal metallogenesis similar to that found by Bischoff and Rosenbauer (l977)» Butuzova et al, (1976) and Aoki e_t al, (1975) near the Clarion fracture zone • 251 Core 21984 shows higher metals in the surface sedi ments with decreasing concentrations with depth. A good correlation of .87 between organic carbon and Zn, Cu and Ni may reflect a totally biological source for the metals along with increasing dilution from terrigenous clays of low Zn, Ni and Cu contents with depth in the core. Core 21995 is located in the most extreme chemical environment of the South Gulf of California. The sedi ments are reducing and almost sapropelic in nature with the smell of H^S and high measured organic carbon (^*7^) • The absolute Zn, Cu and Ni concentrations are high compared to other cores reflecting their association with organic components in the sediments. Low concentrations of Mn, however, suggest that this element is predominately +2 in a Mn valence state and resides in the pore water. Fe and Mn show opposite trends, the reason for which is unknown. From 180-340 cm in the core a relatively more oxidizing environment must exist for more leachable Mn to be present. However, the fact that the leaching technique probably solubilizes all pyrite and Fe oxides indicates that the total leachable Fe content of the sediments has decreased rather than been transformed into an acid in soluble phase. The abruptness of the changes in Fe and Mn concentrations at 160-180 cm and the negative correla tion of the trends suggests that the imput of terrigenous dilutant of a relatively oxic nature is the explanation 252 for these trends rather than some post depositional geo chemical process of4 Fe-Mn segregation* Core 22023 is generally low in organic carbon and has essentially no CaCO^ component* Fe and Mn have similar trends with evidence of Mn mobilization in the surface sediment. Cu, Ni and Zn show particularly erratic trends decreasing from the surface sediment to a minimum of 60 cm, increasing, then sharply decreasing at 140 cm* The sediment in the 1^0 cm interval can be characterized as a diatomaceous ooze which is evidently low in metals because of dilution with low metal(?) siliceous debris. Xn summary, the distribution of metals with depth in the South Gulf of California is generally uniform with no order of magnitude changes in metal content. The metals correlate well with organic carbon and show dependence on the geochemical environments in which they reside. Post depositional mobilization is apparent from high concentrations of Mn in the top 20 cm of many cores. Frequently the metal contents are observed to be abruptly lower for a single interval of a core indicating changes in lithology. Turbidite layers of sand and silt and diatomaceous oozes may be examples of sediment lithologies responsible for these abruptly changing trends. The Fe content of core 21965 is noticeable higher on a carbonate free and bulk basis than other cores reaching 6.0 percent leachable Fe on a carbonate free basis. Preferential lack 253 of* low metal dilutants in specific sections of this core caused by episodic sedimentation may be an explanation, however, the location of the core in an inferred active fracture zone demands that a hydrothermal component in this sediment not be precluded* Correlation of Metal Distributions with Tectonic Elements Comparison of the Cu distribution and inferred tectonic elements in the South Gulf of California shows that all but one of the anomalies not eliminated by as sociation with organic carbon (shaded) are correlative with tectonic elements. As can be seen in plate 28 speci fically and as graphically presented in figure 19> the largest of the remaining, uneliminated anomalies falls over the Mazatlan basin and the extension of the EPR. The other shaded anomalies are quite small, yet each falls directly over an inferred tectonic element. For Ni (plate 29) just the opposite is true. The shaded anomalies do not correlate directly with inferred tectonic elements but are instead situated on the flanks of the Mazatlan basin and the EPR. The Zn distribution also shows a negative correlation with tectonics (plate JO). Anomalies in the northern part of the study area are in close proximity to the Carmen and Farallon basins but do not fall directly over them. Over the Mazatlan basin a distinct Zn 254 minimum is delineated with larger anomalies on the flanks of the EPR similar to anomalies for Cu and Ni* As pre viously stated, Mn correlates well with tectonic elements (plate 31) in the Carmen-Farallon-Pescadero basin regions* However, over the Mazatlan basin and the EPR no anomalous concentrations exist* Fe, on the other hand, correlates well with the tectonics in the Pescadero and Mazatlan basins (plate 32). A large Fe anomaly falls over the con vergent and divergent fault traces which form the South and Central Pescadero basins. A smaller anomaly falls over the North Pescadero basin. The two ’ ’ L” shaped anomalies previously described fall over the northwest end of the Tamayo fracture zone near the Alar9on Rise and the Mazatlan Basin. Thus, it appears that some definitive tectonic— metal correlations exist which cannot be totally explained by environmental factors and must not be precluded as be ing of hydrothermal origin. Both Cu and Fe show very dis tinct and exact correlations of metal anomalies and inferr ed tectonic elements. However, as evidenced by the Mn- tectonic-O^ minimum correlation, results can be inter preted in more than one way and be equally viable. Con sidering the sedimentological, hydrographic, and biological processes at work in the Gulf of California, it is dif ficult to invoke a hydrothermal origin for all metal anomalies that correlate with tectonic elements but not 253 with, environmental factors. The evidence for hydrothermal metallogenesis especially in the Mazatlan basin region is permissive. The low sedimentation rate and organic carbon content provide an environment where metalliferous sedi ments in small isolated area may survive dilution by terrigenous sediments. The sedimentological and geo chemical complexities of the South Gulf of California make it difficult to define exactly in which phases (biological, hydrogenous, hydrothermal, detrital) the metals reside. However, in order to better evaluate the phases in which the metals might reside, a series of multivariate statisti cal analyses (factor analysis) were computed. Statistical Analyses (Factor Analysis) Theory Factor analysis is a statistical technique which reduces a large set of observations among many variables into simpler relationships among a smaller number of variables or factors. Geological variables, in this case concentrations of metals and biogenic components in the sediments and depth, can be grouped depending on their geochemical and geological similarities or dissimilarities. The distribution and nature of these groups is effected by basic geological factors such as chemical environments of deposition and transport, rates of sedimentation, chemistry 256 of source rocks, etc. (Spencer, 1966). Factor analysis locates the pertinent groups of* variables and measures the influence of the groups in a particular locality, in this case the South Gulf of California. From this knowledge and the information from the composition of the groups one can attempt an interpretation as to which basic, geological factors are influencing the variables measured. Two possible statistical analyses exist. The R-mode analysis (factor analysis) deals with the relationships among the variables and Q-mode analysis (vector analysis) expresses the relationships among the cases or samples. The classical factor analysis consists of a correlation coefficient matrix, initial factor matrix, rotated factor matrix and the cumulative percentage of variance accounted for by the number of factors that have been rotated. The number of factors rotated is determined by the user and generally the least number of factors to explain a majority of the variance is desirable. Harmon (1967) has written on the mathematical aspects of factor analysis and Imbrie (1963) has applied factor analysis to geological problems if the reader wishes further elucidation. Data and Discussion Both R and Q mode factor analyses were computed on the variables and samples, respectively. The Q-mode analysis was a distinct failure in that its purpose was to 257 cluster the samples into geographic areas which might relate to biogenous, hydrogenous and hydrothermal and detrital (adsorbed) fractions in the sediment* In fact, the Q-mode analysis assigned 91 percent of the total variance to the first factor, indicating that the metals in the sediments are from many, well mixed sources and cannot be separated on a geographic basis* The R-mode (variables versus variables) analyses produced more definitive results. However, the variables also did not cluster into groups that could easily be labeled bio genous, hydrothermal, hydrogenous, and detrital (adsorbed). The eight variables and 370 samples were analyzed to produce four factors which accounted for 78.5 percent of the total variance (Appendix V, Tables 1 and 2). Factor 1 (37 .8 percent of total variance (percent TV)) gave high factor loadings for Cu, Ni and Fe with a lower loading for depth. Immediately it can be seen that Cu, Ni and Fe are highly correlated in any environment or depth no matter what the major source of the metals, suggesting that these metals are distributed among many phases. Factor 2 (15*5 percent TV) has a high depth loading and a high negative CaCO^ loading indicative of a biogenous component of the sediment which is highest in shallow water depths due to upwelling along the shelf-slope regions in the Gulf. Factor 3 (13*0 percent TV) is high in organic carbon with a small negative loading (-.33) for Mn and a small 258 positive loading (.32) for Zn* This factor might be considered the diagenetic factor which shows that in +2 organic rich sediment Mn is generally as Mn while Zn may be partially related to organic carbon as a metallo-organic complex, at least more so than Cu or Ni. Factor h (l2.2 percent TV) has high loadings in Mn, Cu, Ni and Zn with Mn being the highest. This factor reflects the hydrogenous processes occurring in association with Mn crusts and sediments precipitated at the sediment-seawater interface* The strong adsorption of Cu, Ni and Zn on MnO^ surfaces in seawater has been documented experimentally by Murray (1975). The source of some of the Zn may be detritus from the weathering of granodiorite and volcanic terrains prevalent around the Southern Gulf. These rocks are generally higher in Zn ('•'■TOO ppm) than other rock types. A factor analysis using all the samples which incorporate many geochemical environments, extremes in depth and sediment types does not describe the geochemical distributions of metals as well as the graphic correla tions of the tectonic, biogenous component and metal dis tribution maps. In order to alleviate this scatter and better explain the more than 50 percent of the variance factor 1 accounted for in the first four factors, factor analyses for specific groups of data were computed. The groupings were selected with only depth and organic carbon chosen as dependent variables* The great range of organic 259 carbon and obvious correlations with some of the metals from the distribution maps gives organic carbon the poten tial to be a master variable in the Gulf sediments# All samples with organic carbon greater than 5 per cent and depth less than 1500 m were analyzed with four factors to be defined (Appendix V, Tables 3 and 4)# 83*8 percent TV was accounted for with 73 percent of the 83.8 percent accounted for in the first two factors# Factor 1 (37*5 percent TV) has high Cu, Fe and Zn loadings with lower but significant depth and Ni loadings. Mn, CaCO^ and organic carbon loadings are insignificant# The high Fe, Cu and Zn loadings with lower Ni may represent Fe and Mn oxide coatings on clays (detrital) and hydrogenous phases in depths greater than 1500 m because of the lack of inclusion of a high organic carbon loading and a secondary depth loading. This factor suggests that Cu, Fe and Zn are related more to detrital and hydrogenous phases in deep water where organic carbon is less than 5 percent. Factor 2 (23.3 percent TV) is highly loaded in organic carbon and Ni with a lower loading in Cu. This is the biogenous factor with its most highly associated metals. Ni, as was seen in the distribution map, is very much associated with organic carbon, more so than with Cu. The moderately high loading for Cu (.44) reflects the fact that Cu is found in many phases in nearshore sediments. Factor 3 (12.2 percent TV) is highly loaded in CaCO^ and 260 not associate with, any other variable. The complete dis sociation of CaCO^ with the metals and depth is here cor roborated from similar evidence seen in the distribution maps. Factor 4 (l0.8 percent TV) is strongly loaded in Mn and depth, relating to the strong influence that the minimum zone has on the diagenesis of sediments and mobilization and precipitation of Mn below the minimum. To corroborate the above findings, the converse factor analysis of all samples in greater than 1 5 0 0 m water (Appendix V, Tables 5 and 6 ) was computed with the total variance accounted for in four factors equal to 8 5 . 3 per cent* Factor 1 (44.5 percent TV) shows a strong indica tion that below 1500 m a large percentage of the Cu, Ni and Zn is being incorporated on to hydrogenous Mn oxides by adsorption. Factor 2 (17.0 percent TV) is representa tive of the biogenous component (high negative loading for CaCO^) negatively correlated to depth indicating that most of the biogenous component resides in depths less than 1500 m. Factor 3 (12.4 percent TV) is the detrital clays and adsorption factor showing high loadings in Fe, Cu, Ni and Zn. Loadings for Cu and Ni are higher than Zn, sug gesting a relatively greater affinity for these two metals to be adsorbed species than Zn. Enrichment factors in sediments over seawater concentrations (Turekian and ¥edepohl, 1 9 6 1) and nodules (Arrehenius, 1 9 6 3) indicate that Cu and Ni are enriched an order of magnitude over Zn 261 in sediments and two orders of magnitude in nodules. Factor 4 ( l l . 4 percent TV) is attributed to organic carbon alone, suggesting that below 1500 m depth the metals in the sediments are not associated with biogenous phases but have a preference for detrital (adsorbed coatings) and hydrogenous (and hydrothermal?) phases. 262 DISCUSSION: COMPARISON OF THE GULF OF CALIFORNIA AND THE RED SEA At the outset of* this thesis, one of* the primary assumptions made was that the Gulf* of* California was a tectonic and geochemical environment similar to the Red Sea. Now that the inferred tectonics of the Gulf of Cali fornia have been completely mapped (Henyey and Bischoff, 1973? Bischoff and Henyey, 197^5 this study) and the deep basins explored for heavy metals, none of which were found, it is prudent to compare the known geologic facts about the Red Sea and the Gulf. From this comparison it should be possible to answer the last remaining question originally proposed: Why do we not find any heavy metal deposits or conclusive evidence of metallogenesis in the Gulf of California? Tectonic Comparison of the Gulf of California and the Red Sea Geophysical data collected in the Red Sea has been corroborated from cores collected by the Glomar Challenger on Leg 23 (Whitemarsh et al., 1972) of the Deep Sea Drill ing Project. It is hoped that a similar endeavor will be carried out in the Gulf of California in the near future. Briefly, the evidence for the Gulf of California and 263 the Red Sea being areas of oceanic crustal accretion can be summarized from work by Girdler and Styles (1974), van Andel and Shor (1964) and data presented in Part I of this study* 1. The Red Sea is an elongate, rectilinear basin that narrows at its southern end to a sill that has pre sumably been tectonically opened and closed with time. The Gulf of California has no sill feature but instead widens and deepens continuously toward its mouth and the Pacific Ocean. 2. The Red Sea has symmetrical magnetic anomalies parallel to axial trough. Except at the mouth of the Gulf of California, magnetic anomalies are obscure and non- symmetric. 3. The Red Sea was formed from what appears to be a single, straight line segment of crustal accretion with few offsetting transform faults. The Gulf of California plate boundary is mostly long transform faults with short, en echelon sea floor spreading segments between the trans forms. The loci of active spreading are manifest as basins rather than ridge segments seen in open ocean environ ments. 4. The Red Sea (Erickson and Simmons, 1969) and the Gulf of California (Lawver, 1975» 1976; von Herzen, 1963) are regions of high heat flow. Both appear to be underlain by oceanic crust, however, in the Northern Gulf 264 of California, there is a possibility that some sort of intermediate crust underlies the sediments (Phillips, 196*0 • 5, A two stage spreading history has been invoked for the Red Sea, Initial spreading occurred from *fl-3*^ MYBP, followed by a hiatus in spreading, at which time approximately 5 km of evaporites were deposited. This is followed by reactivation of spreading at 5 MYBP which continues at present with a spreading rate of 1 cm/yr. The Gulf of California has been continuously active for the last 4 MY, having started as a shallow epiric sea (Karig and Jensky, 1972), A 6 cm/yr spreading rate is apparent from magnetic anomalies at the mouth of the Gulf (Larson, 1972). I contend with this brief comparison that, in fact, the Red Sea and the Gulf of California are significantly different in their tectonic characteristics aside from the fact that they appear to be active tectonic plate boundaries. I also submit that the Gulf of Aden is a much better analogy to the Gulf of California, physi- ographically, sedimentologically and tectonically (fig. 27). Laughton, ¥hitemarsh and Jones (1970) state that the Gulf of Aden was formed approximately 10 MYBP and has been spreading via a series of short, en echelon spreading centers and transform faults (fig. 28) at a rate of 2 cm/yr. The Gulf of Aden has high heat flow (von Herzen, 1963) 263 Figure 27* Diagr amnia tic b a t liyme try and. features of tlie Gulf of Aden (after Laughton, et al,, 1970)« 2 66 Mountainous Topography ^ Valleys Continental Slope Submarine Canyons Swale Topography Abyssal Plains i L t U t.U<& r m n , Figure 28. Position of transform faults, spread ing centers and magnetic anomaly linea tions in the Gulf of Aden (after Laughton, et al., 1970). 268 S2 f fc/W 269 6 0 E over the central rift valley as well as active seismicity. Seismic reflection profiles show turbidite deposition on the flanks of the trough. Symmetric magnetic anomalies along its length (fig. 28) is the only tectonic difference between the Gulf of Aden and California. However, even this discrepancy can be explained by the differences in the amount of sediment and sedimentation rates in the two localities if theories proposed by Larson et; a_L. (1972) and Klitgord ejt al. (l97^) are correct. It becomes apparent, however, that the Gulf of California is even more complex tectonically than the Gulf of Aden. The Gulf of Aden appears to be a relatively stable plate boundary of discrete alternating spreading centers and transform faults; the inferred Gulf of Cali fornia plate boundary is a collection of spreading centers, fracture zones, zones of oblique extension as well as con vergent and divergent transform faults with no apparent spreading centers separating them. The tectonics in the Gulf of California may be unique as an example of con tinental breakup in its earliest stages. Nowhere else is a presently active divergent plate boundary less than 5 MY old. If we consider the Gulf of California to be a Stage I plate boundary, then it is possible that the Gulf of Aden is a Stage XX boundary, one that has evolved into a more stable accreting sequence of tectonic elements via a process of consolidation and abandonment of transform 270 faults and spreading centers* The Red Sea may be a Stage XIX boundary consisting mostly of a single spreading center with, few transform faults* Whether or not subsequent separation of continental blocks will allow the plate boundaries in the Gulfs of California and Aden to evolve into so-called "stable plate boundaries" such as the DPR or the Mid Atlantic Ridge is difficult to determine. Sharman (1976a) has suggested that a "stable plate boundary" consists of approximately 5 transform fault off sets per rhumb line segment, whereas in the Gulf of Cali fornia approximately 8 offsets per rhumb line segment are seen. This suggests that the Gulf of California is under going continual readjustment via migrating accretion zones across the plate boundary zone as a river would meander across a floodplain. The fact that the Gulf of California is the transition zone between a major mid ocean ridge divergent plate boundary on the East Pacific Rise and a true strike slip transform fault plate boundary on the San Andreas fault complicates the picture further. Environmental Comparison of the Red Sea and the Gulf of California The latitude, shape and strike of the trough of the Gulf of California cause climatic and oceanographic pertur bations to which the sediment types and consequently the sedimentary metal contents are intimately related. Climate 271 is an independent variable which controls biological, geological and hydrographic processes. Roden (1964) has written an extensive summary of the oceanographic and climatic aspects of the Gulf of California from which the following summary is taken. The Gulf is essentially a large evaporation basin with an open and deep connection to the Pacific Ocean. Air temperatures range from approximately 1 7 ° 0 in the winter to 30°C in summer with rainfall restricted mostly to July- September. Torrential rains are the rule rather than the exception. Baja California has an arid climate with no permanent rivers emptying into the Gulf or the Pacific Ocean but instead arroyos carry the torrential rains to the Gulf with approximately 3 percent of the total annual sediment load (Byrne, 1957)* The Mexican mainland has several annual rivers, particularly south of the Fuerte Delta. Byrne has estimated the average sediment load of the major rivers along the South Gulf province only to be 140 million metric tons annually. The climate on the Mexican coastal plain, considering the vegetation present, is semiarid to semi-tropical. High winds and typhoons (locally called Chubascos) are prevalent from August- October. ¥ind direction is variable depending on the season. Winds from the northwest prevail in the winter, pushing surface waters south and out of the Gulf, allowing bottom water to be upwelled along the Mexican continental 272 shelf* and slope. In the summer the opposite occurs, the wind blowing from the southeast causing upwelling along the Baja coast, Upwelling estimated by Roden to be 3 meters/ day brings nutrients to the surface photic zone producing high biological productivity (Zeitzschel, 1969)• Fre quently the sea is so full of planktonic material that its color is red, the source of one of the Gulf's nicknames, Vermillion Sea. Summer temperatures and salinity distribution measurements show surface water to be 3 0°C and 3 5°/°o and <2.0°C and jh.7°/oo at 3000 m depth. There is a salinity minimum of 34.54°/oo at approximately 6 0 0 m which is co incident with the 0^ minimum (^.05 ml/L) from 200 to 1000 m. No evidence of locally high bottom water tempera tures or salinity associated with the deep basins and the inferred plate boundary has been reported. The 0^ concen tration increases below 1000 m to 2.5 ml/L at 3000 m. In plan view the 0^ minimum has a horseshoe shape with the closed end impinging on the bottom sediments just south of Tiburon Island and the ends of the horseshoe hugging the shelf-slope areas leaving the deep basins below the 0^ minimum zone. The 0^ minimum is biologically mediated. 0^ is consumed by oxidation of organic material that settles below the high productivity zone (Calvert, 1964). The position of the 0^ minimum is determined by circulation patterns in that it occurs where there is minimum advection 273 of from below and little horizontal movement of water masses (¥yrtki, 1 9 6 2). As previously discussed, the Red Sea and the Gulf of California have significantly different shapes and bathymetry* The Red Sea narrows at its southern end with a sill that comes within 1 5 0 m of the surface at the present time* Along with the desert climate and evapora tion greatly exceeding runoff + precipitation, this tectonic sill produces a large salinity and temperature difference between the Red Sea water and Gulf of Aden (Indian Ocean) water* Hydrographic profiles (Seidler, I9 6 9) indicate that the flow of Indian Ocean water across the sill produces a 200 m deep layer of 24—30°C water be low which a single mass of 22°C water resides * Salinity shows the opposite trend* A less saline surface layer (38-40°/oo) is underlain by a uniform 40-4l°/oo layer* The absolute values of salinity are considerably greater than open ocean water or the Gulf of California* It has been known for some time that high salinity and temperature brines exist in the deep, isolated basins. Precipitation is minimal in the Red Sea region and consequently continental runoff is also small. This is borne out by sedimentation rates in the Red Sea (ivu jet al. , 1 9^9 )* Their study indicates that total sedimentation rates in the Red Sea basin are vetween 5-60 cm/1000 yrs which could be broken down into a brine derived material, 274 carbonate and detrital silicates. The brine derived material was calculated to be accumulating at a rate of* 40 cm/1000 yrs and two lutite cores produced rates of* 10 cm/1000 yrs (with 80 percent carbonate content), giving carbonate and detrital accumulation rates of* 8 and 2 cm/lOOO yrs, respectively. Compared to the rates of* 6-500 cm/lOOO yrs measured in the Gulf* of* California, 10 cm/lOOO yrs biological + detrital contribution to the sediment is small. The combination of* a tectonically active sill at the southern end of* the Red Sea and the excess evaporation over precipitation led to the deposition of* great thick nesses of* evaporites on the shelf* regions. This is documented from seismic profiles and deep cores (Whitemarsh et al., 1974)• At this time there is no evidence to sug gest that a similar environment existed in the Gulf of California in the last 4 MY. The only known association of metal deposits and evaporites is that seen in the Boleo and Lucifer deposits. Thus, it becomes increasingly clear that as the Red Sea and the Gulf of California are on opposite sides of the earth, they are also significantly different in climatic and hydrographic characteristics. This in turn produces differences in the sediments in each locality and con sequently differences in the relative concentrations of metals in the sediments. 275 CONCLUSIONS The following conclusions can be made from the data presented: 1. From detailed geophysical surveys made in this study and a compilation of previously reported geophysical data, it appears that the Gulf of California is a segment of the divergent plate boundary between the Pacific and North American plates. 2. In the Southern Gulf province the inferred plate boundary is a complex combination of short spreading centers (Alarcon Rise, Farallon Basin), oblique extension and rifting (Carmen Basin) as well as convergent and divergent transform faulting (Pescadero Basin Complex). 3. The sea floor spreading process in the Southern Gulf in conjunction with rapid imput of biogenous and terrigenous sediment (van Andel, 196^-; Calvert, 1 9 6 6 ; this study) is evidenced by rapid and variable sedimentation rates which produce unique sediment distribution patterns and thicknesses. The apparent periodic readjustment of the plate boundary over the past k MY has deactivated fracture zones no longer an integral part of the active diverging boundary. Sediment rapidly fills these abandoned tectonic elements producing distinct wedges of sediment on 276 both, sides of the inferred active tectonic zone, 4, Exploration for heavy metal deposits associated with the divergent plate boundary similar to those found in the Red Sea revealed no such deposits to exist in the Gulf, Reconnaissance geochemical prospecting techniques were employed to delineate several heavy metal anomalies in the sediments, A compilation of environmental data from this study and previous workers (biogenous components, sediment types and grain size, depth, redox potentials in different environments, extent of an minimum zone (<0,05 ml/L) and areas of high river sediment discharge) was compared to the metal anomalies in order to eliminate those anomalies which were correlative*. The anomalies which were solely correlative with inferred tectonic elements remain as permissive evidence of hydrothermal im- put to the sediments, 6, For the most part, the metals in the sediments can be assigned to three fractions: (a) a detrital phase with large amounts of Fe oxide coatings on clay surfaces with Cu, Ni and Zn adsorbed to the coatings, (b) a hydro- genous-diagenetic phase with Mn mobilized in increasingly reducing sediments and precipitated at the sediment- seawater interface below the 0^ minimum zone and Fe trans formed from oxide coatings to Fe monosulfides and pyrite, (3) a biogenous phase of planktonic material which en riches metals from seawater and is deposited mostly on the 277 shelf and slope areas where metals may reside as stable metallo-organic substances (humates), 7. Although permissive evidence of a hydrothermal phase in the sediments in the Mazatlan Basin—East Pacific Rise region exists, for the most part metalliferous sedi ments similar to those found in the Red Sea either are not being deposited because of the plate boundary con figuration and apparent readjustment occurring or are be ing deposited and rapidly diluted by the influx of ter rigenous and biogenous sediments* 8. The Gulf of California is a young and rapidly evolving ocean basin tectonically, hydrographically and sedimentologically similar not to the Red Sea but to the Gulf of Aden as it appears today or the Atlantic Ocean as it appeared 110-120 MYBP at the initial breakup of Africa and South America (Thiede and van Andel, 1977)* The lack of metalliferous sediments in new ocean basins may be the rule rather than the exception. 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K,, 1964, Iron and Manganese in exhalations of the submarine Banu Wuhu volcano, Indonesia: Doklady Akademii Nauk USSR (in English), v, 155* P# 94—96, 296 APPENDICES APPENDIX I 298 cn C M r- m 00 ON C M O H o H VO vo m C M 00 C M o r- ON o - 3 * O C M m 00 C M - 3 * cn - 3 - cn cn C M o m • • • • • • • • • • • • • • • • • • • 0'— - 3 * m m m C M cn o O 00 cn pH r- VO ON o O vo 00 O H H H pH pH pH - 3 - m cn 00 VO r- 00 VO in r- in ON ON H C M m ON vo -3- o cn o cn H 00 H m 00 C M -3- VO H VO m r - cn in 00 O w • • • • • • • • • • • • • • • • • • • o cn cn -3- cn -3- cn -^ t -3- -3- cn cn cn -3- m -3- -3 - -d- r t f t ft C M ON 00 in cn ON H C M o 00 C M o i> cn pH pH N ft 00 00 - 3 " ON H r - n- H O ON - 3 " 00 cn cn r - C M pH t> W H H H H H H H pH pH pH S • H P cn NO -^ t 00 O n H v o C M 00 o vo cn H -3 - m v o cn 5 5 P C M C M -^ t cn C M -^ t -3 - m -d * C M C M cn cn cn -^ t cn -3" cn s f t ft o f t m 00 00 vo C M cn cn ON • cn C M m 00 pH m O C M m r - pH H cn cn C M cn cn -3- cn pH pH C M C M C M cn C M C M C M 00 ON ON cn cn o o ON vo vo cn pH o r - t" - C M pH C M ON ON -3- pH -3* vo r - o 00 00 cn -3- C M C M m cn C M -3- ON H cn m pH pH pH pH H pH pH H pH pH pH pH pH pH r - -3" C M pH C M C O ON 00 C M m cn VO r - cn r - vo r - r - J - H rH vo -3- m cn cn ON pH O 00 ON pH o C M r - 00 o cn • • • • • • • • • • • • • • • • * • • H pH pH pH pH rH rH pH C M pH H pH pH pH pH pH •ft rH ON m C M C M C M C M H ON r - o -cf VO -3" m ON 0 0 C M vo ■ P ^ -> i > O v o ON -3- pH -3 - 0 0 ON i > -3 - p H p H m c n t > r - p H c n f t E p H in m 0 0 0 0 C M C M vo 0 0 H C M C M ON 0 0 m c n O '—p Q p H pH pH pH pH H rH p H p H p H 0 rr^ 52 52 52 52 52 52 52 52 5* 52 52 52 52 52 52 52 52 52 vj ft O VO o O r - 0 0 O 0 0 - 3 " O m m c n o -2 t o + 5 • • • • • • • • • • • • • • pH • • • * •rl C M O n ON J " C M 0 0 r - p H o o p H ON v o c n ON -3- m & -3- c n -^ t -3- o H m c n c n C M p H p H p H C M -3 - -3 - m -3 - c n ft O o O 0 o O o o o o o O 0 o o O o O o o o O o o pH H o o o o O o o O o o o o o h P pH pH H pH pH H rH o p H pH pH pH p H p H pH I — 1 o H H H pH pH pH rH pH rH pH pH pH pH p H p H p H p H pH pH rH rH 0 r r i 55 !5 !5 55 55 55 55 55 55 55 55 55 55 55 55 15 55 55 55 W f t VO -3 * c n C M VO -3 * O m m O n- m O O c n c n -P • • • • • • • • • • • • • • • • • • • •H pH c n m -3- H c n -3* o o -3 - c n m VO ON c n VO v o •p pH o m -3 - C M H pH c n -3- m m -3- c n C M o m m -3" m 0 0 0 o 0 O O o 0 o o o 0 o 0 o o o O o J r - r - vo VO VO VO vo vo vo v o vo v o vo v o v o m m m m C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M 0 rH -3 - m vo r - 00 ON rH -3- m vo 00 ON o pH C M cn -3" m ft rH pH pH pH pH pH C M C M C M C M C M C M C M cn cn cn cn cn cn E C M cm C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M 0 1 i 1 1 1 1 1 1 1 1 1 1 I i 1 1 1 I I C O c o C O C O C O C O C O C O C O C O C O C O C O C O C O C O C O C O C O C O Depth Fe Mn C u Ni Z n Corx r # CaCO Sample Latitude Longitude (m) ( ° / o ) (ppm) (ppm) (ppm) (ppm) (%)_____ (° / o ) in c m rH CM 00 in m ON cn VO ON vo ON r- C M rH CM 1 >- vo c m CM O O m C M vo *> o rH m 00 vo VO 1 >- CM • • • • • • • • • • • • • • • • • • • on - s t cn m 12 CM m vo 00 ON o H C M ON cn m -S t CM cn ON H m t- vo C M ON o m Jt- -S t -S t C M 0 0 m -S t m 0 0 vo VO 0 0 o 0 0 H cn m 0 0 00 Jt- 0 0 VO ON r- m C M 0 0 -S t • cn • -S t • cn • H • • cn • -st • -S t « -S t • -S t ♦ -st • • -S t • cn • C M • cn • r H • rH • cn vo m -St m 00 o m cn cn m cn v o cn VO in CM ON CM -St 00 oo v o rH m m m CM cn m rH vo vo cn vo o m rH rH H rH H rH rH rH rH H 00 c n H H rH H rH C M C M C N cn H l> n 00 I> V O t - O N O 00 O cn O N vo cn n n oj c m H rH cn cn cn cn cn H cn cn cn c m w e n i n v O V O t ' - O N C M V O O O C M t ' - - S t C M - S t O N O C M H m cm cm h H c M c n c n c n c M H c n c M - s t c M r H c M t ' - -S t vo ON iH cn o ON VO CM cn - S t i - v o On v o H CM 0 0 -st CM - S t ON o 0 0 - S t 0 0 VO cn CM ON -s t t- H CM 0 0 CM cn rH rH H CM rH rH CM H H rH rH - S t - S t H H -st CM rH VO ON H H ON ON O cn CM CM rH ON 00 ON CM rH cn rH ON -st O O -S t -st cn -S t cn H cn CM 1 > - ON o rH • • • • • • « * • • • • • • • • • • • rH H CM H H rH H H H rH H rH rH rH rH 00 rH o cn o C M o ON C M H m H H C M r - cn 00 00 00 -s t C M C M o cn 00 00 C M t - vo cn C M vo -St t - 00 C M C M m C M VO -st t - -s t C M o H ON ON ON 00 vo cn C M C M H rH H rH H H H H H H H H rH C M Sa h s - la > |a t* Sa Sa Sa S a la Sa la la la la 1 > - cn Jt- m cn 00 o O O O m cn C M O o H m o O • • • • • • • • • • • • • • • • • • • -st cn rH -s t 00 £— ON cn ON VO C M 00 O -s t cn O n - m H C M H o m -s t m o C M C M cn cn C M C M rH rH C M rH C M cn O o o o o o o o O o o O o O O O O o o O o o ON ON ON o o o o o O o o o o o o o H H H o O o H H rH o o H H H H H H H H rH rH H H H H H H H H H H H H rH H H rH H 53 53 53 a 53 53 53 53 53 53 53 53 53 53 53 53 53 53 S3 O cn m O o -st o cn m cn O 1 > - cn O O m O VO in • • • • • • • « • • • • • • • • • • • t - 00 o 00 ON 00 vo o vo m VO o ON VO m 00 vo t - o H cn cn C M H o m H cn C M cn cn -s t m m o H rH o o o o O O o o O o O o o o o o o O O v o vo vo vo VO vo vo m VO m m m m m m m vo VO vo C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M vo ON O H C M cn -st m vo 00 ON o H C M cn -st m VO cn cn cn -St -S t -st -s t -st -st -s t -St -St m in m m m m m C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M 1 i 1 1 1 1 1 1 1 1 1 1 i 1 i 1 1 i 1 to to to to to to to to to to to to to to to to to to to c n o. o 0' o bo— O'— ■ o s •H P. 55 P s p p O p . S P P cn CM 00 CM 00 - i t C M 00 iH o C M t - m C M c n o o c n cn v o 00 CM H e- f - e- iH - it cn C N H C M - i t C M - it f - m o - i t • • • • • • • • • • • • • • • • • • • m C M H - i t m iH cn H H - i t H cn H C M H r H CM C M m m - i t cn iH C M C M O N - i t C M H 00 00 C M rH c n V O C M C M o C M c n o o V O H C M 00 00 00 C M O O 00 o cn V O C M vo - i t C M O N H m • cn • - it • C M • - i t • cn • C M • H • C M • - i t • m • H • f - • m • C M • iH • • • C M • H o V O m - i t m - i t m m m 00 O O o C M O !> - C M O N C N O N H m H C M iH CM - i t C M C N 00 H H C M H m iH O H cn H v o H - it H o o in e- 00 o o iH - i t O O t'- m rH C M cn l>* H C M m m C M 00 O m m - i t m H H H C M - i f C M f - - i t C M H H H H C M C M O vo C M cn - i t - i t f - f - cn m 00 f - C M H - i t f - f - C N O N cn - it cn cn m H H iH cn cn H cn cn C M H rH H H 00 iH - i t V O O N O - i t - i t C N o o - i t v o v o C M - it C M 00 - it m M O C M - i t iH !> - C N V O V O o o C M v o n- 00 r H iH vo e ' C N 00 cn H C m cn iH cn cn C M C M H H iH m cn C M H en C N 0* VO C M O m o cn C M f - ON cn H n - - i t C M cn f - CN vo VO C M vo CN ON H - i t - i t - i t - i t m C M - i t - i t cn cn H m cn ON • • • • • • • • • • • • • • • • • • • H C M - i t C M H C M iH H H C M iH H H H iH C M iH H £ -p. P S <Dv Q 0 P -p •H & P O J 0 T3 P +3 *H -P 0 P) 0 rH P s 0 C O O ON VO - i t e *- H cn o o - i t . i t H vo - i t H cn - i t m e- m ON m H CN m m ON vo vo - i t m iH cn m J N - C M m o C M m r*- cn vo iH H - i t - i t vo m C M o m - i t C M C M H H C M C M H H H H C M C M H C M cn Is 53 5s I* 5s Is 5s ts is is Is Is IS Is Is Is is Is Is n- m cn in 0 0 m O cn - i t iH O 0 0 CN O m vo C M vo O • • • • • • • • • • • • • • • • • • • C M -it v o -it 0 0 C M cn e ' -it C M ON e- vo e ' O N C M e- e- ON - i t cn m cn o - i t cn e n in O o o in e n C M C M - i t m - i t 0 0 o 0 0 0 o 0 0 O 0 0 o o 0 0 o o o o o o o o CN CN CN CN O o o CN ON CN ON CN ON ON H iH iH H H o o o o H H iH o O o O o o O H H H H iH H H H H H H H H iH H H H H iH 55 55 55 55 5 55 55 55 55 5 5 5 5 5 55 5 55 5 5 O O 00 m m H O e- H H O vo vo 00 O O ON m • • • • • • • • • • • • • • • • • • • m vo iH vo e- C M O vo H - 3 * 00 00 vo - i t H 00 - i t m ON H C M C M o H - i t - i t C M H O m - i t m iH C M C M cn cn C M o 0 0 o O O 0 O O 0 o o o 0 0 O o 0 0 v o VO VO m m m m m m m - i t - i t - i t m m m m in m C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M e- 00 CN o C M cn - i t m VO e- 00 CN O C M cn - i t vo e- o o m m m vo vo vo VO vo VO vo vo vo e- e- e- e- e- e- e- C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M i 1 1 1 1 i 1 1 1 1 1 1 1 1 1 1 1 1 1 c o c o c o C O C O c o C O C O C O C O C O C O C O C O C O C O C O C O C O 301 Depth Sample Latitude____Longitude (m) s-279 25°23.5 N 0 • - 3 - 1 T \ O 0\ O H ¥ 3093 S-280 25°l6.5 N 109°46.l ¥ 2379 S-281 25°17.5 N vo • 00 ir\ O O N O H ¥ 2105 S-282 25012.3 N C T \ • O O O H H ¥ 2 k 7 9 S-283 25°03.0 N ir\ * cn H O O O H ¥ 1372 S-285 25°24.0 N 110°l6.0 ¥ 2004 S-286 25°35.1 N 109°57.0 ¥ 2196 S-287 25°45.2 N 109°31.2 ¥ 267 S-288 25°37.0 N 109°36.5 ¥ 613 S-289 25°27.5 N 109°52.2 ¥ 3093 S-290 25°12.3 N 100°17.0 ¥ 1967 S-291 25°05.0 N 110°12.0 ¥ 1876 S-292 25°34.0 N H O vo O K ) K ) • -V ! ¥ 33 S-293 25°24.5 N 109°21.6 ¥ 123 S-294 24°55.6 N 110°08.3 ¥ 1473 S0295 24°55.5 N 109°52.6 ¥ 1546 S-296 25°20.4 N 109°12.0 ¥ 101 S-297 25°10.9 N M O • ov 0 0 ov 0 H ¥ 1299 S-298 25°05.5 N ov • 00 H 0 ov 0 H ¥ 1720 Fe ( f o ) Mn (ppm) Cu (ppm) Ni (ppm) Zn (ppm) c m- CaC0o M 3 1.16 318 27 30 136 3.46 2.42 1.50 665 19 18 102 2.42 1.67 1.11 482 27 37 l4l 3.37 3.66 1.39 185 27 80 109 4.18 2.96 1.47 1214 43 57 196 4.29 11.61 2.07 807 46 52 113 4.65 5.75 2.34 2403 46 56 154 4* 68 2.17 1.87 294 18 12 142 1.09 1.25 2.19 265 20 20 93 2.97 1.83 2.67 2371 35 32 132 2.90 .92 1.69 487 56 57 142 4.92 1.50 1.92 691 52 62 136 4.30 3.08 1.94 303 15 16 81 cn 00 * .92 2.68 312 18 14 87 1.39 19.91 5.58 268 39 45 124 2.81 29.07 2.19 551 59 61 161 5.98 16.58 1.93 298 29 19 95 1.76 5.91 2.31 323 20 25 106 2.60 7.08 2.74 306 26 32 111 3.13 8.58 Cn rH CN NO ON NO 00 cn -3" C M in NO C - t - H -3- t - ON NO 0 — -3" 00 rH rH O 00 C M cn t - NO t - O -d" t - O -3- NO 0 ^ • • • • • • • • • • • • • • • • • • cdw 0 C - t - rH 0 0 rH rH CN O rH C M rH ON C M t - C M cn NO rH cn t - C M C M C M C M C M in C M m rH NO • 00 CM O m C M O NO NO m -3- NO 0 O O n- m C M ON C t O —■ 0 0 - 3 - m n- 00 CN c- NO rH cn O m m ON C - 00 ON ON O - • m • NO • • VO • - 3- • -3 * • cn • NO • rH • • rH • rH • VO • - 3 * • NO • in • m • m O ft p ON NO r- O m ON m NO 0 0 0 H c- c- cn m in NO NO N 1 P m rH 0 0 « H t - ON NO rH rH rH C M rH m rH t - NO t - NO NO rH cn rH - 3 " rH 0 cn « H rH cn rH 'a •H P 0 0 CN -3- NO H -3- NO ON O C NO VO NO 0 O O a P t - CM 0 0 NO -3" t - rH rH rH C M t - VO 00 in NO ft P O P C M rH NO 0 0 rH 0 0 0 0 C M C M NO m 0 C M cn cn O -3- -3* NO rH - 3 - NO cn cn NO H rH C M NO in t - 00 m in 'b ON O ON - 3- IN - m cn NO 0 0 00 NO C - 0 0 cn NO r- 00 - 3 " S P 0 0 00 H 0 m ON cn H 0 0 0 cn 0 0 -S f C M - 3 * -d - 0 0 rH r— f C M C M C M NO C M cn cn C M C M cn rH in cn C M cn cn C M O' ft ^ A -Px— ft 6 Q o T ) ft •H f t o J < D H ft CO rH 00 NO H 0 c- cn c- cn 0 in c- CM - d - - d - CM r- 00 m CM - d - cn CM CM t- - 3- in J- vo rH in m CM in 0 vo • • • • • • • • • • • • • • • • • • CM CM CM CM CM CM CM CM CM rH rH CM CM CM CM CM CM rH cn CM rH rH ON - 3 - 00 in t ^ - ON in CM t- - 3 " NO O O cn 00 t- cn - 3 - rH H ON cn rH ON ON NO cn cn ON CM - 3 " NO NO H vo O H NO in VO cn 0 0 H CM H CM H CM rH H H rH rH rH rH Is |S |S |S Is |S Is Is IS is is IS IS |S is Is is is m in O cn cn 00 cn cn - a - in O 0 cn O in m O NO ON ON ON ON 0 rH rH cn rH cn - d - C- - d - CM CM - 3 - 00 cn - 3- CM m 0 cn rH cn - 3 " m cn - 3 - m - 3 - - 3 - CM cn CM rH 0 O 0 0 0 O O 0 O 0 O 0 0 O O 0 O O ON ON ON 0 ON ON ON ON 00 0 0 00 0 0 ON ON ON ON ON ON O O O rH O O O O 0 0 0 O O O O O O O rH rH rH rH H rH rH rH rH rH H rH rH rH rH rH rH rH 5 2 5 5 2 5 5 2 5 5 2 5 1 2 ; 5 2 5 | 2 5 12 | 2 5 | 2 5 | 2 5 | 2 5 i z ; | 2 5 | 2 5 i z ; I z ; i z ; O 00 ON VO in 00 in O in in O rH 0 m VO NO O O • • • • • • • • • • • • • • • • • • cn VO CM rH ON 0 cn - 3 " O rH in t- 0 0 CM O cn cn in CM CM CM cn - 3 - 0 cn 0 O m rH rH rH 0 O O 0 O O O O 0 0 0 0 O 0 O O O O 0 0 0 m - 3 - - 3 - - 3 - m - 3 - m in - 3- - 3 - - 3 - - 3 * - 3- - d - - 3- CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM ON O rH CM cn - 3- m NO t> 00 ON O rH CM cn - 3 - in NO ON O O O 0 O 0 O O O O rH H rH rH rH rH rH CM cn cn cn cn cn cn cn cn cn cn cn cn cn cn cn cn cn 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO J -317 24°l8.4'N 108°53.0' ¥ 2223 1.90 468 63 37 122 3.82 3.75 ffOC Sample Latitude Longitude Depth (m) S-318 24° 25.3 N 108° 42.0 ¥ 1629 s-319 24° 32.9 N 108° 27.3 ¥ 1153 s-320 24°27.0 N 108°13.5 ¥ 723 s-321 24°l6.o N 108°30.0 ¥ 1354 s-322 23°53.8 N 109°02.1 ¥ 2342 s-323 23°37.5 N 109°18.7 ¥ 1812 s-324 23°32.5 N 109°10.9 ¥ 1903 s-325 23°4l.8 N • 0 00 O H ¥ 2371 s-326 23°59.8 N 108°30.6 ¥ 3660 s-327 24o03.8 N 108°38.5 ¥ 1629 s-328 25°o4.5 N 108°23.0 ¥ 933 s-329 23°38.6 N m • cn -3- 0 00 0 H ¥ 2123 s-330 23o26.0 N 109°00.0 ¥ 2306 s-331 23°l4.7 N 109°02.5 ¥ 2672 s-332 23°18.2 N H 0 00 O -P- 00 • 0 ¥ 2608 S-333 23°26.7 N 108°35.5 ¥ 2498 S-334 23°36.1 N 108°2^.7 ¥ 2489 S-335 23o45.0 N • 00 C M O 00 0 H ¥ 2727 S-336 23°40.8 N 108°13.1 ¥ 1336 Fe do) Mn Cu (ppm) (ppm) Ni (ppm) Zn (ppm) CW ‘ CaC0o M 3 1.91 260 37 38 122 4.11 3.92 1.92 249 26 28 103 3.37 3.67 1.66 273 22 22 111 3.18 1.00 1.78 260 39 44 92 5.22 3.92 1.85 537 82 68 188 4.88 1.33 1.64 248 21 20 112 1.58 3.25 3.27 122 13 18 73 1.07 1.33 1.96 439 87 59 200 3.91 2.08 2.41 10486 io4 60 158 3.77 1.17 2.13 354 52 52 130 4.90 6.25 2.06 266 36 42 132 4.87 9.66 2.33 348 75 51 140 3.91 3.00 2.05 - 3 - !> !> 00 242 230 761 .92 2.75 l.4o 581 48 34 112 1.42 2.25 2.35 425 87 54 184 2.78 2.58 2.23 423 94 61 181 3.79 1.67 2.47 426 104 60 227 3.78 1.92 1.97 474 73 47 126 3.12 2.58 2.64 373 87 107 229 2.89 39.15 cn O o ft' o O' o A + » ^ - ft S 0 w Q < 3 > -o ft -p •H f e d a o J cn C \ H 00 IV 00 00 m O ON rH m 0 C n m C M m O cn -c f -3* O H in m I V m CN CN C M m CN C M -cf I V O m • 0 rH • 00 rH • 00 • rH • rH * cn • • -c f • • cn rH • 00 • m • cn • CN rH • rH • H • H • O • cn CN I V 0 I V I V cn rH CN CN m -= f I V C M NO cn 0 0 -c f C M C M m 0 m -c f CN cn m -c f cn I V rH 00 m NO NO I V C M 0 • • • • • • • • • • • • • • • • • • • NO I V NO -c f cn cn C M C M cn m 00 cn 0 0 ON cn m C M cn cn y ^ ~ - ' - a f t ft m m O rH C M NO CN 0 V O IV NO -cf -C f cn -d - 00 0 -c f N f t -3 " - 3 - 00 cn H -c f V I V m m C M 00 NO m m O NO H -c f rH iH H C M C M C M H rH rH rH rH rH rH rH cn C M cn cn " 5 •H f t rH NO O rH CN cn O -= f 00 rH rH 00 I V C M IV cn m C M cn f t m V 00 NO NO V CN NO NO CN CN -3 - 0 -3- IV 0 H rH C M > f t ft O f t 0 0 00 cn H NO IV -3- O NO IV C M NO rH O rH rH NO H m rH m H CN rH CN v— ' -V m NO CN CN CN 00 CN O m m C M IV NO CN 0 0 cn cn m r k £ 2 00 NO 0 -3- rH cn cn rH 00 cn IV I V rH C M 00 IV rH NO rH O rH 00 s ft rH 0 - c h C M NO m 0 0 0 0 m C M 00 rH CN cn in cn -3 - NO O > — * C M C M C M m -C f m I V -c f cn C M rH C M rH rH -c f cn NO -= f m 00 C M IV 0 0 IV H cn IV m IV O C M m cn cn V iH rH O rH 0 IV O CN rH C M NO -c f NO NO m -d - C M NO rH NO C M O 00 rH • • • • • • • • • • • • • • • • • • • rH C M H C M C M C M cn C M C M C M rH C M rH H C M C M cn C M cn C M c n CN 0 CN C M I V 00 00 m m NO C M O I V NO 0 c n CN m m - 3 - 00 00 m CN 0 m rH 0 m 00 NO O m - 3 - rH CN H - 3 - - 3 - -c f c n I V 00 CN 0 0 rH cn m 00 c n ON CN ON H H C M C M C M C M C M C M rH rH C M C M C M C M c n h m o c o n o o i v o -3 - m m c n m -3 - h c n m cm oo oo m - c f - o iv o rH o Iv o rH H O O 00 o H - 3 - rH O C \ f o C\i o H o m cm c n c n o o 00 00 00 00 00 00 o o o o o o H <H iH rH rH iH cn m cm -3- cn cm o o I V o H - 3 - o IV vo o o rH rH c n c n oo O H o o IV IV o o rH rH m cm c n m o o IV IV o o H rH rH rH o - 3 - o o 00 00 O O C M C M O 00 o rH 0 f p t & ! z ;5 z ;2 ;5 z ;S 55 z ; J z ;5 z ;J z ;5 z ;5 z ;! z ;5 z ;5 z ;5 z ;5 z ;J z ;& f t O in 0 0 0 -c f m C M NO 0 in m m NO -c f CN m m C M -p • • • • • • • • • • • • • • • • • • • •H C M cn - 3 - in 0 0 0 NO cn 0 0 0 0 0 0 0 0 m cn rH 0 0 m CN C M -P m -3 - cn C M rH rH m 0 0 cn C M O 0 0 O m m C M -c f f t 0 0 0 O O O 0 0 0 0 O 0 0 0 O 0 0 O O i - J cn cn cn cn cn cn C M cn cn cn cn cn cn cn cn cn C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M 0 rH I V 0 0 CN 0 rH C M cn m NO I V 00 CN 0 rH C M cn -c f m f t cn cn cn -c f -c f -cf -c f -3- -c f -cf -^t -cf m m m m in m e cn cn cn cn cn cn cn cn cn cn cn cn cn cn cn cn cn cn cn f t 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 co co CO C O C O C O C O C O C O C O C O C O C O C O C O C O C O C O C O C O 305 cn 00 en 00 0 E- O xn xn cn C M O 00 vo O 0 ^- xn 00 0 xn 1 —1 O C M O 0 C M cn O O O 0 0 O O O'cR • • • * • • • • • • • • • • • • • • • C f l W H xn H O - 3- rH VO O O H 0 00 nE O tH xn • O ON xn ON C M C M xn xn H i * C M ON C M ON rH ON ON H f c t O ^ ON vo pH 0 0 xn 00 ON vo 0 0 xn VO O H H i * hE O C M xn H j - J “ T c ^ - • • • • • • • • • • • • • • * • • • • O'—• C M C M cn C M cn C M cn cn rH H H rH rH C M C M E- H vo cn O E2 £ ft cn XA ON xn rH xn vo C M xn C M H O C M ON xn ON xn C M N f t 0 C M xn 0 pH rH vo C M E- xn cn O O VO iH cn - 3 - 0 "~- cn cn C M C M cn C M H C M C M cn cn H C M xn cn rH vo H rH S •H f t -3- ON 0 O cn xn O 0 0 xn C M xn cn O E' 00 ON vo cn C M IS f t VO H C M O H rH ON ON E - E- E - 00 O en xn VO VO e- • J t tH H t H H rH H pH H rH H C M H ' s £ f t 0 f t NO 0 0 0 0 0 0 0 C M - 3 - VO xn rH H J - H H i * O H i * cn vo 0 0 xn cn xn O C M C M H rH cn cn cn t- O vo C M xn - 3 * C M H H t H rH rH rH H H H rH H rH H H , ^ - S E £ £ e- E' 0 C M C M ON C M C M ON C M cn ON O E - ON 00 0 0 VO xn S f t VO en 0 0 0 C M H xn vo vo cn xn C M 0 0 rH f " - n t - 0 0 pH > « —p E ' vo vo - S ' - d " vo cn xn ON e- 00 00 - 3 - rH 0 0 rH tH H C M vo C M H f C M 0p t£ -P — ft B © w Q 0 £ j * > •rH £ o J 0 H ft C / 3 O n -d- O ON ON rH ON xn cn vo nE H xn O n VO 00 ON C M vo C M O xn cn h E C M C M vo 0 rH t - ON O xn 00 nE O xn • • • • • • • • • • • • • • • • • • • cn cn cn C M C M C M C M C M C M cn cn rH C M cn C M H rH C M H C M E - cn xn C M H O cn O xn xn 0 O C M ON vo xn VO cn 00 H 00 cn 00 ON 00 e— C M h e C M ON vo ON HE VO rH O 00 e- E - ON vo 00 e- nE 00 O 00 e- 00 xn ON O cn C M O cn C M C M C M C M C M C M C M C M cn C M C M C M C M C M cn tH H |S > Is 5s Is Is Is is Is Is Is IS Is Is is Is IS h — IS C M cn O rH 00 vo xn 00 O O O vo 00 ON 00 H f H VO cn • • • • • • • • • • • • • • • • • • • C M ON C M xn xn 00 00 0 vo 00 ON ON E ' H C M O HE E' C M H H H O xn nE cn Hi* C M H O HE en C M xn cn en en nE 0 O O 0 0 O 0 0 0 O O O 0 O 0 0 0 0 O 00 00 00 00 00 t - t - t - ON ON ON 00 00 00 e- vo vo vo vo 0 0 0 0 0 O 0 O O O O 0 0 0 0 0 O 0 O rH H rH H H rH rH rH rH tH tH rH H tH H rH tH H tH 55 55 55 55 15 15 55 15 55 15 15 15 15 15 55 15 15 15 5 0 rH ON xn xn VO 0 C M cn O -3 - HE cn C M C M VO C M xn xn • • • • • • ♦ • • • • • • • • • • • • 00 H 00 cn H vo t - 00 C M rH O ON 0 C M E— 00 O O C M pH C M cn xn nE HE cn cn C M pH O C M cn xn nE cn H xn D O 0 0 0 O 0 0 0 O O O O 0 0 O 0 O 0 C M C M C M C M C M C M C M C M H C M pH O H tH rH C M C M C M H C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M C M VO t - 00 ON rH C M cn -3 * xn vo t - 00 ON O H C M cn HE xn xn xn xn xn vo VO vo vo vo vo vo VO vo t - t - t - t - t - E' cn cn cn cn cn cn cn cn cn cn cn cn cn en en en cn cn en 1 1 1 1 1 1 1 1 1 1 1 1 1 l l l 1 1 1 C /3 C / 3 C / 3 C / 3 C / 3 C /3 C / 3 C / 3 C /3 C / 3 C /3 C /3 C / 3 C / 3 C / 3 C / 3 C /3 C / 3 C / 3 306 307 Depth Sample______Latitude____Longitude (m) S-37 6 21° 42 9*N 106° 55.0 ¥ 2840 S-377 21°37 5»N 107°03.9 ¥ 1961 S-378 21°28 0 *N 107°18.5 ¥ 2900 S-379 21°22 4»n 107°26#3 ¥ 2480 S-38O 21°13 5»N 107°39.7 ¥ 2516 S-38I 21°07 4'N 107°59.9 ¥ 3065 S-382 21°23 6* N 107°49.8 ¥ 3050 S-383 21°34 5'N 107o33.9 ¥ 2734 S-384 21°46 5'N 107°l6#1 ¥ 2852 S-385 21°56 7'N 107°02.2 ¥ 2790 S-386 22°10 0 *N 106°50#8 ¥ 1298 S-387 22°22 4'N 1o6°52#3 ¥ 1536 S-388 21°12 4'N 107°08# 0 ¥ 2229 S-389 22°02 6* N 107°2l# 5 ¥ 2635 S-390 21°48 5»N 107°39.6 ¥ 2758 S-391 21°36 3*N 107o56.7 ¥ 3085 S-392 21°42 95 *N 108°03#5 ¥ 2380 S-393 22°10 7»N 107°37.l ¥ 2995 S-394 22°22 6'N 107°22.85*W 2545 Fe Mn (ppm Cu ) (ppm) Ni Xppm) Zn (ppm) CaC0_ (%)3 2.26 597 67 57 154 2.63 .25 3 • 48 178 21 28 93 1.12 1.17 2.22 568 92 96 250 2.57 .25 3.07 941 71 127 179 .93 .25 1.16 56676 128 326 291 .31 0.0 2.98 8322 166 219 464 1.95 1.83 2.99 2320 168 258 537 2.19 1.17 2.36 380 82 96 246 2.42 0.0 2.35 566 74 75 200 3.01 .75 2.19 1322 62 61 144 2.95 .58 3.61 146 23 39 75 2.85 4.00 1.96 239 42 33 138 4.60 6.91 2.36 251 50 47 122 2.58 .25 2.48 770 83 111 318 2.60 1.83 2.79 830 101 158 107 2.55 7.91 2.93 1309 138 189 4l0 2.4l 5.33 15.5 23200 425 865 4 56 .29 .08 2.85 1300 116 164 422 2.62 7.66 2.54 374 90 81 227 3.26 7.50 308 Sample Latitude Longitude Depth (m) S-395 22O44.0*N 107°19.55’W 1570 S-396 22°29.15'N H O O ■ P " VO • K w 2904 S-397 22°l8.0 *N 107°59.0 ¥ 2858 S-398 22°04.9'N 108°11,1 ¥ 2895 S-399 2l°59#5!N 108°25.5 ¥ 2749 S-400 22°13.1,N 108°22,6 ¥ 2936 S-401 22°24.55!N 108°12.7 ¥ 2814 S-402 22°4i.5!n 107°32.5 ¥ 2868 s-403 22°43.5,N 108°00.6 ¥ 2939 s-4o4 22°42*2*N 108°03.4 ¥ 2941 s-405 22°48.6»N 107o58.4 ¥ 2930 s-4o6 22°55.6'N 108°10.7 ¥ 2908 S-407 22°58.55 *N 108°10.7 ¥ 2976 S-408 22°51.3»N 108°17.1 ¥ 2799 S-409 22°39.0*N -3- 00 0 0 00 O H ¥ 2732 s-4io 22°34.4'N 108°01.4 ¥ 2869 S-4ll 22°38.1»N 107°53.9 ¥ 2891 S-412 23°04.1*N 107°4l.8 ¥ 2207 s-413 23°07.05!N 108°00,0 ¥ 2532 Fe Mn Cu Ni ($) (ppm) (ppm) (ppm 2.21 352 88 130 2.41 742 106 103 2.28 653 97 117 2.65 794 117 136 2.62 722 100 117 2.42 590 126 99 2.77 753 34 132 2.31 547 109 9k 2.33 502 111 104 2.63 462 117 93 2.49 454 117 93 2.52 600 84 78 3.08 916 104 93 2.03 295 53 47 1.80 299 67 63 2.5^ 589 102 105 2.20 4o6 85 92 2.11 283 64 59 2.45 343 93 81 Zn Ippm) c nr CaCO M3 221 6.80 29.49 247 3.18 7.16 279 2.94 2.17 301 2.85 .33 224 2.15 2.33 228 2.71 0.0 291 2.92 .42 215 2.86 ^.33 232 3.31 2.83 224 3.kk 0.0 226 3.66 0.0 164 • 00 ro 12.16 218 2.98 1.75 124 2.18 .42 135 1.83 4.17 263 2.81 3.67 515 3.06 .92 162 3.08 5.66 284 4,06 .50 309 Sample Latitude Longitude Depth (») S-4l4 22°40, 51N 108°l8.7f¥ 2780 S-415 22°15.10*N 108°39.7*¥ 2812 S-4l6 22°21,1*N 108°48.8 f¥ 2838 S-417 22°39.6*N 108°52.85f¥ 2893 S-418 22°53.9*N 108°38.05'¥ 29^0 S-419 22°05.1*N 108°29. 9 * ¥ 2810 S-420 22°17* 31N 108°l4. 85 *¥ 2395 S-421 23°24.5fN 108°03.5f 1 W 2423 S-422 22°33.7*N 107°30.1f¥ 1626 S-423 23°43.5*N 108°02,1f¥ 1250 S-424 23°37•9 *N 108°12 * 351 ¥ 1300 S-425 23°08.4*N 108°52 * 4 f¥ 2830 S-426 23°l8.4'N 108°57* 7f¥ 2694 S-427 23°27.45*N 108°56,41 ¥ 2641 S-428 23°25.2'N 108°59* 5'¥ 2691 S-429 22°26.9*N 109°02 * 01 ¥ 2447 S-430 22°28#9*N 109°04.3f¥ 2168 S-432 23°21.2*N 108°52.45 f¥ 2679 S-433 23°25.6*N 108°47.85 *¥ 2598 Fe (*) Mn Cu (ppm) (ppm) Ni (ppm) Zn (ppm) cw CaC0_ ( ° / c )3 3.08 46l 118 92 266 2.98 1.50 3.32 597 126 126 316 1.91 7.33 2.72 760 101 122 274 2.12 5.00 Z.k3 555 101 98 216 1.64 H .25 2.52 362 104 75 214 2.88 0.0 2.56 643 85 81 176 2.44 11.33 2.47 313 73 67 269 3.4-2 1.75 2.27 321 75 71 204 4.45 0.0 2.22 260 56 77 183 5.33 10.50 2.17 219 49 74 158 7.20 5.83 3.40 364 21 21 161 1.35 .25 2.32 474 91 77 163 2.45 17.99 2.83 4lo 83 70 171 3.45 9.50 2.71 378 93 75 210 3.68 8.00 3.79 435 74 63 170 3.28 9.50 3.90 624 89 80 209 3.74 10.50 6.51 526 81 130 173 .27 1.33 3.39 4o6 79 63 169 2.90 7.16 3.20 369 88 73 179 3.66 1.75 Sample Latitude Longitude Depth (m) S—43^ 22°37.6fN 108°31.1!W 2630 S-435 23°47.51!N 108°28.81¥ 1930 S-436 23°58# 65 fN 108°27.6!¥ 920 S-437 23°55.6'N 108°34.3f¥ 1540 S-438 23°49.4fN 108°42.6‘¥ 3312 S-439 23°44.96‘N 108o47.05'¥ 2650 S~44o 23°51.5fN 108°44.81W 3610 S-441 23°59.8fN 108°40.4‘¥ 2360 S-442 24°06.0fN 108°37*251¥ 1555 S-443 23°56.3'N 108O48.3'¥ 3280 S-444 23°50.7fN 108°55.0!¥ 2470 S-445 23°57.6!N 108°52 * 21¥ 3480 S-446 24°02, 01N 108°50.51¥ 3685 S-447 24°09.85!N 108°46.3'¥ 1626 S-448 24°04.0fN 108°56,03'¥ 3018 S-449 23°56.2»N 109°02,3'¥ 2140 S-450 23°35.4 fN 109°13.0f¥ 2250 S-451 23°55.851N 109°20.4»¥ 2000 S-452 24°05.2‘N 109°04.7'¥ 2220 Fe M Mn (ppm) Cu (ppm) Ni (ppm) Zn (ppm) CW ' CaC0o M 3 2.76 539 73 62 163 3.77 .33 3.39 279 52 55 114 2.90 1.67 2.37 181 21 26 75 2.31 8.25 4.17 115 13 20 59 1.62 3.17 2.36 4l4 42 35 92 1.96 4.91 3.62 772 78 71 199 3.90 10.00 3.76 2081 86 66 258 3.95 11.50 3.48 330 55 55 144 3.69 5.91 2.73 224 37 49 112 4.87 6.25 3.44 294 22 21 81 1.60 3.oo 3.24 506 77 75 196 4.38 1.33 2.97 2054 67 51 144 2.31 8.00 3.17 6859 82 59 157 4.05 1.33 2.90 396 33 38 94 1.59 17.74 3.26 509 32 33 103 3.02 3.33 2.91 376 57 68 156 3.70 7.08 2.82 300 51 54 130 4.02 2.75 3.44 269 31 35 110 2.66 3.42 2.76 395 56 62 156 4.58 2.25 Depth Sample Latitude Longitude (m) S-453 24° 10 35 fN S-454 2 4° 2 8 4fN S-455 24°24 2’N S-456 24°18 5'N S-457 24°15 15!n S-458 24°26 3fN S-459 24°32 6'N S-460 24°38 45fN S-461 24°4l 91N S-462 24°47 4fN S-463 24°51 4fN S-464 24°47 7fN R- 1 21°20 01N R- 3 21°34 6 fN R- 4 21°39 2 1N R- 5 21°45 2»N R- 6 21°32 0 !N R- 7 21°59 01N 00 « 311 22O03 9fN 108°59.1 w 3098 108°51.3 w 1540 109°03.4 ¥ 2400 109°20.0 ¥ 1739 109°28.5 ¥ 892 109°39.2 ¥ 875 109°28.4 ¥ 1598 109°18.8 ¥ 2500 109°11.9 ¥ 2571 109°05.6 ¥ 1176 109°08.8 ¥ 1175 I09°l6.6 ¥ 3110 109°0.0»¥ 2965 108°43.3 ¥ 2708 108°33.1 ¥ 2824 108°25.7 ¥ 2877 108°l6.8 ¥ 2800 108°6.11 ¥ 2805 108°00.0 1 ¥ 2891 Fe (i) Mn Cu (ppm) (ppm) Ni (ppm) Zn (ppm) c ?r 0 - 0 2.95 440 17 22 72 1.59 4.66 3.23 236 34 47 109 3.87 8.91 2.64 326 44 44 120 3.66 1.00 3.31 284 53 74 150 5.42 6.66 2.70 169 62 107 114 9.31 3.25 4.07 61 24 31 44 00 H . H 30.07 2.65 165 28 36 65 1.84 16.41 2.36 522 51 53 122 3.92 1.58 1.74 376 54 42 81 2.56 4.67 2.98 217 26 29 74 2.59 2.83 3.32 281 39 65 102 3.72 3.58 2.67 629 34 32 90 2.67 1.92 4.03 777 170 181 221 1.14 6.00 3.85 556 163 100 218 1.55 8.34 3.72 1447 128 160 226 2.00 6.10 4.08 1643 132 174 224 2.04 2.60 3.64 843 103 137 251 2.13 5.10 3.75 1180 104 114 195 2.61 3.55 3.33 954 105 117 218 1.96 5.70 Depth Sample Latitude____Longitude (m) R-9 22°09* 6 N 107°5^.l ¥ 3051 R-ll 22°21.7 N 107°4o.6 ¥ 2895 R-12 22°28.7 N 107o33.1 ¥ 2769 R-l4 22°38.4 N 107o07.7 ¥ 2029 R-15 22°k3.5 N 106°59.5 ¥ 1537 R-16 22°5k.2 N 106°52.5 ¥ 1373 R-17 23°00.0 N 106°44.0 ¥ 622 R-18 23°o6.5 N 106°35.7 ¥ 92 R-20 23°12.0 N i07°oo#7 ¥ 461 R-21 23°23.5 N io6°k5.k ¥ 59 R-22 23°22.0 N 107°03.k ¥ 322 R-24 22°25.5 N 109°17.7 ¥ 3047 R-25 22°25.5 N 109°08.0 ¥ 3029 R-26 22°31.9 N 108°58.0 ¥ 3034 R-27 22°38.4 N 108°51.5 ¥ 2891 R-28 22°43.8 N 108°43.0 ¥ 2886 R-29 22°k9.2 N 108o3^.5 ¥ 2962 R-30 22°55.0 N 108°25# 8 ¥ 2696 R-31 23°00.8 N 108°l6.7 ¥ 2946 LO Fe M Mn Cu Nx Zn CaC0_ (ppm) (ppm) (ppm) (ppm) {%) ' ( ° / o ) 1.87 555 32 3.86 727 113 2.62 405 75 2.53 259 69 2.11 145 4l 1.68 181 38 2.74 265 23 • 0 0 255 15 1.62 199 4l 2.87 314 15 2.19 242 26 3.03 945 115 3.31 440 43 2.32 776 103 2.58 744 100 2.31 616 95 2.25 63 100 3.04 721 113 2.42 573 83 85 2.77 6.31 239 3.53 2.25 137 3.06 3.80 140 4.25 7.40 85 3.28 17.20 94 7.^4 6.00 89 5.02 17.20 74 1.78 5.90 93 5.65 9.50 71 1.30 4.4o 88 5.21 .84 244 1.39 4.80 159 2.36 2.16 136 .95 7.20 249 2.40 4.60 194 « 00 00 7.53 263 2.20 10.61 249 2.94 2.90 204 1.01 10.82 39 123 66 64 39 4l 21 18 80 Ik k7 115 kl 95 105 95 83 96 75 Depth Sample Latitude Longitude (m) R-32 23°o6 0 N 108°08.0 ¥ 2800 R-33 23°i4 5 N 107°59.8 ¥ 2480 R-34 23°i6 0 N 107°53.5 ¥ 2370 R-36 23°31 5 N 107°34.7 ¥ 1354 R-37 23°38 2 N 107°25.0 ¥ 641 R-38 23°45 0 N 107°17.1 ¥ 97 R-39 23°50 0 N 107°09.5 ¥ 38 R-42 23°17 0 N 109°15.8 ¥ 1940 R-43 23°24 0 N 109°03.8 ¥ 2260 R-44 23°29 5 N 108°55.0 ¥ 2480 R-46 23°39 0 N 108°37.8 ¥ 2452 R-47 23°45 3 N 108°28*0 ¥ 2822 R-48 O 23 53 3 N 108°23.5 ¥ 1162 R-49 23°59 1 N 108°15.1 ¥ 714 R-50 24°o6 1 N 108°06.5 ¥ 430 R-51 24°13 0 N 107°57.5 ¥ 97 R-56 0 23 57 5 N 109°31.5 ¥ 1739 R-57 24°03 4 N 109°23.8 ¥ 1235 R-58 U) i - j 24°08 3 N 109°15.1 ¥ 1373 Fe M Mn Cu Ni (ppm) (ppm)(ppm) Zn (ppm) Corg. (il CaCO M 3 2.36 501 84 68 192 2.20 6.20 2 # 4o 479 67 71 162 3.1^ 6.06 1.59 302 45 37 121 3.77 3.90 1.00 237 14 20 52 5.9^ 15.70 1.16 72 23 24 92 h.9h 11.20 2.09 285 15 19 70 1.70 8.80 6.03 927 38 35 202 .93 13.65 .74 142 27 21 102 2.9k 7.10 .65 161 26 20 80 z.9h 7.10 .69 144 37 27 188 2.19 1.18 1.37 247 42 4l 116 2.95 6.70 2.44 687 84 69 212 ^.05 4.00 1.73 238 46 59 140 4.91 3.50 1.78 237 34 54 123 5.23 7.20 1.20 212 17 22 62 3.08 10.00 1.40 138 14 4 56 1.82 8.50 1.20 120 37 40 123 5.^0 15.70 1.16 98 33 30 i4o 5.13 17.20 1.42 92 21 4o 80 5.7*1 10.30 Depth Sample______Latitude____Longitude (m) R-59 24°15.1 N 109°05.2 W 2910 R-60 24°20.5 N 108°58.0 ¥ 2708 R-61 24°24.0 N 108°46.2 ¥ 1921 R-62 24°25.0 N 108°37.9 ¥ 1501 R-63 24°38.8 N 108°32.0 ¥ 1116 R-64 24°45.4 N 108°23.2 ¥ 714 R-66 ro - p- 0 O • 00 N 109°38.3 ¥ 1700 R-68 24°24.3 N 110°i4.4 ¥ 653 R-69 24°30.5 N 110°06.0 ¥ 723 R-70 24°36.1 N 109°57.1 ¥ 906 R-71 24°42.5 N • 00 - 3 - O On O H ¥ 1263 R-72 24o50.0 N 109°38.0 ¥ 1905 R-74 24o03.9 N 109°17.4 ¥ 1693 R-75 25°10.9 N 109°07.2 ¥ 1025 R-79 25°07.7 N 110°25.1 ¥ 1620 R-80 25°13.5 N 110°15.9 ¥ 2013 R-81 25°19.0 N 110°06.5 ¥ 2470 R-82 25°26.6 N 109°58.5 ¥ 3166 R-83 25°15.7 N 109°49.5 ¥ 2827 h* ■ p - Pe ( f o ) Mn ( p p m ) Cu (ppm) Ni (ppm) Zn (ppm) cx w 1.06 458 44 25 197 4.44 .63 197 40 15 94 3.72 .99 10 21 15 68 2.00 1.74 184 22 28 91 2.58 1.26 123 18 16 65 3.12 • 00 -a 153 9 3 60 .81 1.32 128 37 36 130 4.32 .86 13 36 27 73 3.79 .86 12 39 42 96 6.03 .93 71 28 30 103 5.70 1.34 114 4l 39 125 5.95 1.48 89 17 20 62 .39 1.13 88 20 52 65 2.89 .75 228 11 4 68 2.02 1.87 249 21 32 107 6.55 1.69 590 40 38 180 2.87 1.16 1450 30 34 138 3.44 1.4l 1844 12 7 146 2.10 .91 577 34 30 132 3.60 CaCO 1.20 5.00 4.80 11.00 4.90 3.60 13.40 23.10 18.60 14.26 11.90 2.80 7.20 3.50 11.60 17.10 12.60 2.65 9.00 cn o o a o o G t S 3 •H ft o > . £ ■p^ ft S < D w- P C D H P i S C /3 0 0 0 0 NO NO O O 0 0 O O O -3* -d- O O O NO On t— 00 CM cn CM cn -3- NO ON cn t— rH CM NO ON NO -3- • • • % • • • • • • • • • • • • • • • H m iH ON rH 00 r- ON cn NO 0 0 cn -St O cn CM NO H m CM H rH cn rH pH On cn CM -Cf 00 r —1 -3- NO O t— 0 00 t— -d- O ON CM NO ON 00 cn VO CM rH rH rH -S’ ON NO CM 0 0 NO 0 0 CM rH NO • • • • • • • • • • • • • • • • • • • CM iH CM CM -d- m rH CM cn cn CM CM rH O cn CM 0 0 c- m 00 CM O -=t rH 00 ON 0 - C j - m 0 CM m O 00 0 rH ON ON ON O cn 00 ON 0 0 in ON 00 00 i> NO m iH rH pH rH rH rH <H ON r- iH -3- rH 00 O NO cn CM NO 0 cn ON CM CM !> CM CM iH H CM cn cn cn rH CM CM CM rH m cn CM CM pH H CM ON iH 00 ON - 3- 00 ON O 00 CM 0 0 0 0 00 pH pH C N i CM pH CM CM CM CM CM pH CM CM pH CM -3* CM -3- cn cn CM NO m 00 NO -ct 00 cn NO rH cn O CM O CN ON O CM t— 0 0 0 00 NO CM NO pH cn CM pH rH NO NO O 0 ON CM H CM -d- cn CM CM CM cn CM CM cn -d- 00 cn pH cn ON m m ON O -3- rH O rH cn NO CM !> O rH ON ON in cn 1 A -cf cn H 0 0 ON ON m 0 -d- rH -d- CM NO ON NO m • • • • • • • • • • • • • • • • • • • cn CM CM CM H rH H H pH rH pH rH H cn CM pH rH pH NO CM m cn rH cn rH 00 NO m m O 00 pH 0 0 ON cn O pH O cn m H CM ON O H ON 0 0 -3" m cn rH 00 00 H CM rH cn NO NO 00 in cn cn NO m cn 0 CM rH rH pH pH pH rH pH pH ft ft ft ft ft ft ► s - t —» ft ft ft ft h * . ( —* ft ft ft ft O 0 in in O in NO -3- CM m 0 00 -st 0 NO 0 O O % • • • • • • • • • • • • • • • ♦ • • O H CM 00 ON O ON cn cn CM 0 in cn NO NO 00 ON ON in J- cn CM m -d- CM CM rH O m -d- pH m -S’ cn CM rH 0 O 0 O 0 O 0 O 0 O O 0 O 0 0 O 0 O O ON ON ON ON 0 O O O 0 O O ON ON pH 0 O 0 O O O O 0 O 0 rH H rH rH rH pH 0 O pH rH rH rH rH O H iH iH iH H rH rH H pH rH rH rH rH rH pH rH rH pH rH 5 2; ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft 0 0 m O m in O -=t cn m 00 00 O O O 00 cn -3- O -d- 0 NO O ON m rH 00 CM NO rH VO NO O cn ON NO CM ON cn j- -3- m cn -3* m m 0 0 rH rH CM CM cn cn - 3- m m 0 0 0 0 0 0 0 0 0 0 O O O O 0 0 0 0 0 m in m m m in in m NO NO NO NO NO NO NO NO NO NO NO CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM cn m NO 00 ON -3- m NO j>- 0 rH CM cn m NO 00 ON 0 0 0 O 0 O 00 0 0 00 0 0 ON ON ON ON ON ON ON ON ON pH rH rH rH H rH 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft 315 cn O. o C t J - o f c l i J —■ o S s a tsi a • H P J ft P S P P J o P S Pi 0/ — £ -p < —> a a ©>— Q 0 T3 P -P • r i fad P o 0 rH Pi B a to o o P t o cn 00 o in- cn O 00 in- m cn ON t - C M cn cn C \ C M C M C M vo o r - C M 00 M O rH H m VO I N — VO C M C M • • • • • • • • • « • • • « • « • « « in- ON cn rH 10 m cn p t C M IN - cn rH rH rH rH rH rH m C M O N i n - 00 O N J N- Pt O o o t- 00 o o cn o C M o p t O N c d cn O N O 0 0 C M C M 00 O N IN- O N CM VO 00 O N • • • • • • • • • • • • • • • • • ♦ • C M c n C M p t c n cn p t rH c n rH cn C M C M C M cn CM rH rH m 00 00 00 rH oo m 1^ IN- IN- ON ON o CM ON cn ON CM cn oo vo cn VO rH ON vo VO CM m CM ON ON IN- rH 00 IN- e ' CM rH rH CM cn CM rH H CM ON cn Pt O cn m ON e ' rH m CM CM vo ON vo CM m en H rH CM Pt cn CM cn en m cn CM CM CM rH CM CM i —! rH cn Pt cn CM CM cn 00 ON cn IN- o O e- IN- r- O VO O rH H rH CM CM CM rH CM CM Pt CM CM rH «H CM rH rH rH IN- VO m O IN- oo o rH cn Pt 00 VO 00 rH e- e ' Pt rH o CM ON CM CM 00 IN- 00 ON pt CM ON Pt 00 o vo en in O CM -S’ CM CM Pt ON m rH cn pt 00 ON rH 00 m pt IN- ON in- IN- cn 00 CM rH CM rH rH 00 rH Pt ON 00 pt CM o rH VO Pt Pt CM Pt 00 CM m cd m CM 00 Pt 00 ON CM ON VO cn CM vo ON VO VO vo O vo vo m • • • • « • « • « • • • • • • • « • • t-H rH rH rH CM rH rH iH rH rH rH rH rH rH 00 cn I n— o cn Pt m cn rH VO vo 00 ON o cn m cn rH Pt IN- o m 00 00 m rH vo cn IN- ON Pt in vo cn rH cn Pt rH CM ON VO vo pt Pt CM O ON rH rH o CM 00 cn CM rH CM CM rH rH rH CM CM CM CM rH CM cn CM CM rH CM CM CM CM iS iS is Is is is is is is is is is is is is is is is is O Pt O O Pt in m cn o CM O rH O vo pt o O CM VO • « • • • • • • • • « • • • • • • • • n- ON IN- IN- VO CM ON CM VO e- cn rH m ON cn m o 00 ON cn rH CM m m Pt cn m o m m m Pt cn CM pt Pt cn cn o O O o o O o o o o 0 o o o o o o o 0 o o ON o o o o ON o ON ON ON ON ON ON ON ON ON ON rH rH O rH rH rH rH O rH o o o 0 o o o o o o rH rH rH rH rH rH H rH rH rH rH rH rH rH rH rH rH rH rH ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft ft O cn O in m o cn m CM -Pt rH Pt m o CM rH in o rH • • • • • • • • © • • • • • • • • • • VO CM 00 Pt ON rH CM o CM o m ON rH m rH m 00 cn m rH rH rH m Pt CM rH pt cn cn cn CM CM rH CM rH rH CM CM O O o o O o O o o o o O O O O O O o o VO VO VO vo vo vo vo m m m m m m m m m m m m CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM rH CM Pt m O rH CM pt m vo IN- 00 ON o rH cn pt m vo CM CM CM CM rH rH rH rH rH rH rH rH rH CM CM CM CM CM CM rH rH rH rH 1 1 1 1 1 1 1 1 1 1 1 i 1 1 1 1 1 1 1 O O O o o o O o o o o o O o O ft ft ft ft 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 316 Depth. Sample Latitude____Longitude (m) GC-27 25°21.3 N 109°50.8 ¥ 2397 GC-28 25°23.2 N 109°56.0 w 3093 GC-29 25°29.2 N 109o52.6 w 3065 GC-30 25°37.5 N 109o46.9 w 3083 GC-31 25°26.6 N 110°02.2 ¥ 2147 GC-32 25°37.5 N 110°01.8 ¥ 2342 GC-33 25°34.0 N 110°l6.2 ¥ 2059 GC-32 25°37.5 N 110°01.8 ¥ 2342 GC-33 25°34.0 N 110°l6.2 ¥ 2059 GC-35 26o08.4 N 110°30.1 ¥ 2306 AHF-20379 25°26.2 N 109°50.4 ¥ 2562 AHF-20397 25°22.4 N 109°4o.7 ¥ 2315 AHF-20398 25°25.5 N 109o52.3 ¥ 2818 AHF-21965 25°12.6 N 109°59.5 ¥ 2369 AHF-21966 25°18.0 N 109°50.0 ¥ 2306 AHF-21967 25°25.6 N 109°38.3 ¥ 2086 AHF-21970 25°17.5 N 109°32.8 ¥ 2l4l AHF-21971 25°10.0 N 109°43.9 ¥ 2397 AHF-21972 25°o4.l N 109o54.2 ¥ i486 Fe Mn Cu (#) (ppm) (ppm) 1.26 1248 17 1.32 1895 17 1.78 2188 25 1.79 3156 29 1.99 834 48 1.41 1853 22 1.30 1251 26 1.4l 1853 22 1.30 1251 26 1.26 3566 25 1.60 2315 25 1.30 667 13 1.15 1109 21 2.37 6l4 53 2.15 764 34 2.09 687 33 1.85 931 39 2.30 627 37 2.27 222 49 22 85 2.78 20 89 2.71 22 87 1.79 29 77 2.49 55 137 3.67 31 164 3.88 64 316 3.84 31 164 3.88 64 316 3.84 31 100 4.96 34 412 2.34 19 112 1.85 32 125 2.20 51 145 4.00 39 117 3.20 35 136 2.34 4l 224 3.67 42 114 3.55 58 144 5.20 CaCO„ J .62 1.30 1.25 .46 1.69 1.36 5.81 1.36 5.81 6.42 I.27 1.11 .83 5.58 1.75 18.49 9.75 3.83 9.91 Depth Sample______ Latitude____Longitude (m) AHF-21976 25 Ob. 5 N 109 38.0 ¥ 2479 AHF-21977 25 11.3 N 109 26.9 ¥ 1976 AHF-21981 25 31.2 N 109 ^5.3 ¥ 2736 AHF-21984 24 50.6 N 109 23.3 ¥ 2379 AHF-21985 2b 40.8 N 109 22.7 ¥ 2287 AHF-21986 2b bb.2 N 109 15.6 ¥ 2599 AHF-21987 2b 39.3 N 109 09.9 ¥ 3001 AHF-21995 2b 26# 6 N 110 09.2 ¥ 705 AHF-22009 2b 27.0 N 109 16.0 ¥ 2882 AHF-22011 2b 16,2 N 109 10.1 ¥ 3138 AHF-22016 2b 11.8 N 109 00.6 ¥ 3120 AHF-22022 2b 07.6 N 108 ^3.0 ¥ 1382 AHF-22023 2b 02.7 N 108 51.0 ¥ 3^95 H 00 Fe Mn Cu Ni Zn Cprg ^ CaC0_ (i) (ppm) (ppm) (ppm) (ppm) HI' {° / > ) J 130 3.97 3.50 1.81 435 36 51 1.89 738 32 3 6 2.55 735 23 13 2.63 480 67 59 2.22 541 63 67 3.04 2777 48 b3 2.62 1341 75 60 1.75 172 39 64 2.13 536 64 57 2.49 1386 b5 48 2.10 1598 51 43 2.90 7 5b 53 37 2.84 3270 83 65 130 3.b6 3.75 75 I.07 8.75 191 4.13 11.91 173 5.13 3.83 153 2.44 3.50 147 4.48 .75 101 6.80 18.66 161 4.25 2.92 123 4.03 .75 128 3.43 3.25 108 2.55 1.75 158 4.19 2.00 APPENDIX SEDIMENT DESCRIPTIONS KEY Color Texture 0 = olive green B s s brown G- s s gray B1 = black R = red Y = yellow ¥ = white Si-C = silty clay C-Si s s clayey silt S-C s s sandy clay Si-S-C = silt-sand clay Sh = shell hash Structure Miscellaneous Constituent H = homogenous G1 sr glauconite M ss mottled F sr To ramini Te ra L = laminated MN ss manganese sediment PS = poorly sorted, OM ss organic matter clastic debris V ss volcanic glass T sand-clay inter layered 320 Miscel- Sample Coloi? Texture Structure laneous S-2l4 OG Si-C H — S-213 OG Si-C H - S-216 OG Si-C H — S-217 OG Si-C H - S-218 OG Si-C H - S-219 OB S-C H S—221 OB Si-C H — S-22^ OG Si-C H S-225 OG Si-C H - S-226 OG Si-C H — S-227 W-B S-Sh PS GL-F S—228 OG Si-C H - S-229 OG Si-C H — S-230 OB Si-C H - S-231 OB Si-C H - S-232 OB Si-C H - S-233 OG Si-C H — S-234 OG Si-C H — S-233 OG Si-C H — S-236 B-G Si-C H - S-237 OB Si-C H - S-239 OB Si-C H — S-240 W-G C-S-Sh PS F S-2^1 B-G S-C H — S-2^2 OB Si-C H — S-2^3 OB Si-C H — S-24^ OG Si-C H — S-245 OG Si-C H — S-2^6 OG Si-C H — S-248 OG Si-C H — s-249 OG Si-C H — S-250 OG Si-C H — S-251 OB Si-C H — S-252 OB Si-C H — S-253 OB Si-C H — S-254 OB Si-C H — S-255 OB Si-C H — S-256 OB Si-C H — S-257 OB Si-C H _ S-258 OB Si-C H — S-259 GB Si-C H — S-260 OB Si-C H — S-262 OB Si-C H _ S-263 OG-B C-Si H — S-264 G-B C-Si H — S-265 G-B Si-C H — 321 Miscel- triple Color Texture Structure laneous s-266 OG Si-C H - s-267 OG Si-C H - s-268 OG C-Si H GL s-269 G-B C-Si H GL s-270 OB Si-C H - s-272 OB Si-C H - s-273 OG C-Si H - s-274 G SH PS P s-276 OG Si-C H - s-277 OB Si-C H - s-278 OB Si-C H - s-279 OB Si-C H - S—280 OB Si-C H — S—281 OB Si-C H — S—282 OB Si-C H — S-283 OG Si-C H - s—283 OB Si-C H - S-286 OB Si-C H — S-287 OG-B C-Si H — S-288 OG-B C-Si H — S-289 OB Si-C H - S-290 OB Si-C H - S-291 OB Si-C H - S-292 OB C-Si H - S-293 OB C-Si H — S-29^ OB C-Si H GL S-295 OB Si-C H — S-296 OB C-Si H - S-297 OB Si-C H — S-298 OB Si-C H — S-299 OB Si-C H - S-300 BL-B S-C H — S-301 BL-B S-C H GL S-302 OB Si-C L — S-303 OB Si-C H — S-30k OB Si-C H — S-303 OB Si-C H — S-306 OB Si-C H — S-307 OB Si-C-SH PS F S-308 OB Si-C-S H GL S-309 OB Si-C-S H — S-310 OG Si-C H — S-311 OG Si-C H — S-312 OG Si-C H — S-313 OG Si-C H — S-314 OG Si-C H — s-315 OG Si-C H — 322 Sample Color Texture Structure S-316 OG Si-C H S-317 OG Si-C H S-318 OG Si-C H S-319 OG Si-C H S-320 OG C-Si H S-321 OG Si-C H S-322 OG Si-C II S-323 OG Si-C H S-32k OG S-Si-C H S-325 OG Si-C H S-326 OG Si-C H S-327 OG-B Si-C H s—328 OG-B Si-C H S-329 OG-B Si-C H S-330 OG-B Si-C H S-331 OG-B Si-C H S-332 OG-B Si-C H S-333 OG-B Si-C H S-332 * OG-B Si-C H S-335 OG-B Si-C H S-336 OG-B Si-C H S-337 OG-B Si-C H S-338 OG-B Si-C H S-339 OG-B Si-C H S-3^0 OG-B Si-C H S-3^1 OG-B Si-C H S-3^2 OG-B Si-C H S-3^3 OG-B Si-C H S-344 OG-B Si-C H S-345 OG-B Si-C H S-346 OG-B Si-C H S-347 OG-B Si-C H S-348 OG-B C-Si H S-3^9 OG-B Si-C H S-350 OG-B Si-C II S-351 OG-B Si-C H S-352 OG-B Si-C H S-353 OG-B Si-C H S-35^ OG-B Si-C H S-355 OG-B Si-C H S-356 OG-B Si-C H S-357 OG-B Si-C H S-358 OG-B Si-C H S-359 OG-B Si-C H S-360 OG-B Si-C H S-361 OG-B Si-C H S-362 OG-B Si-C H Miscel laneous GL-F F F F F F 323 Miscel- Sample Color Texture Structure laneous S-363 OG-B Si-C H S-364 OG—B Si-C H — S-363 G-B-Y Si-C H F S-366 OB Si-C H F S-367 OG-B Si-C H F S-368 OG-B-Y Si-C H F-V S-369 OG-B-Y Si-C H F-V S-370 OB-G Si-C H — S-371 OB Si-C M — S-372 OG-B C-Si H OM S-373 OG S-SH H F S-374 OB Si-C M OM S-373 OB Si-C M F-OM S-376 OB Si-C H — S-377 OB S-C H GL S-378 OB Si-C H — S-379 B-Y S-C H — S-38O G-B S-C H — S-381 B Si-C M OM S-382 OG-B Si-C H — S-383 OG-B Si-C H _ S-384 OB Si-C H — S-385 OB Si-C H _ S-386 OB S-C M GL S-387 OB S-C H GL-F S-388 OB S-C H GL S-389 OB Si-C H S-390 OB Si-C H _ S-391 OG-B Si-C H — S-392 BL-R Si-S L MN S-393 OB Si-C H _ S-39^ OB Si-C H MN-V S-395 OB Si-C H _ S-396 OB-Y Si-C H _ S-397 OB Si-C H _ S-398 OB Si-C H _ S-399 OB Si-C M OM S-400 OB Si-C H _ S-401 OB S-C H _ S-402 OB Si-C H S-403 OB Si-C H _ S-404 OB Si-C H S-403 OB-R Si-C H S-4o6 OB-R Si-C M _ S-407 OB Si-C H S-408 OB Si-C T 32h Miscel- Sample Color Texture Structure laneous S-409 OB-Y Si-C H M S-410 OB Si-C H F S-411 OB Si-C H — S-412 OB Si-C M F-V S-413 OB-R Si-C M — S-4l4 OB Si-C Ii - S-415 OB-R Si-C H-M — S-416 OB Si-C H F S-417 OB Si-C H — S-418 OB Si-C H — S-419 OB Si-C H — s-419 OB Si-C H — S-420 OB Si-C H — S—421 OB-R Si-C H — S—422 OB Si-C H — S-423 OB-G Si-C H — S-424 OB-G Si-C H — S-425 OB-G Si-C H — S-426 OB-G Si-C H — S-427 OB-G Si-C H — S—428 OB-G Si-C H — S-429 OB-G Si-C H — S-430 OB Si-S-C H GL-MN S-432 OB Si-C H — S-433 OB Si-C H — S-434 OB Si-C H — S-435 OB Si-C H — S-436 OB Si-C H F S-437 OB-BL S-C H GL S-438 OB Si-C H — S-439 OB Si-C H — S-440 OB-R-BL Si-C L OM S-441 OB Si-C H _ s-442 R-B-0 Si-C H _ S-443 OB Si-C H _ s-444 OB Si-C H OM S-445 OB Si-C H _ S-446 OB Si-C H _ S-447 OB Si-C H _ S-448 OB Si-C H _ S-449 OB Si-C H _ S-450 OB Si-C H _ S-451 OB S-C H _ S-452 OB Si-C H _ S-453 OB Si-C H — S-454 OB Si-C H _ S-455 OB-R Si-C H _ 325 Sample Color Texture Miscel- Structure laneous s-456 OB-R Si-C H S-457 G S-C H S-458 BL-Y Si-S-C PS S-459 OB-BL Si-S-C PS S-460 OB-R Si-C H S-461 OB-R Si-C H S—462 OG Si-C H S-463 OB Si-C H S-464 OB Si-C H GC-10 OG Si-C H GC-11 OG Si-C H GC-12 OG Si-C H GC-14 OG Si-C H GC-15 OG Si—C H GC-16 OG Si-C H GC-17 OG Si-C H GC-18 OG Si-C H GC-19 OG Si-C H GC—20 OG Si-C H GC-21 OG Si-C H GC-23 OG Si-C H GC-24 OG Si-C H GC-25 OG Si-C H GC-2 6 OG Si-C H GC-27 OG Si-C H GC—28 OG Si-C H GC-29 OG Si-C H GC-30 OG Si-C H GC-31 OG Si-C H GC-32 OG Si-C H GC-33 OG Si-C H GC-35 OG Si-C H OM F—GL GL 326 APPENDIX III 327 Interval(cm) _ FeW) Mn(ppm) Cu(ppm) Ni(ppm) CaCO^W) Organic C( ° / o ) ._________ Zn(ppm) 0- 10 2.15 764 34 39 1.75 3.20 117 10- 20 2.27 862 4l 47 2.45 3.49 144 20- 30 2.39 826 43 51 3.08 3.61 140 40 2.41 704 34 4o 2.00 2.69 114 60 2.59 87 6 43 51 3.00 3.43 182 80 2.33 1517 4o 48 4.42 3.12 134 100 2.42 1656 46 57 4.00 3.71 155 120 2.45 2145 42 64 6.25 3.43 147 140 1.76 1781 4o 61 4.00 3.14 178 160 1.96 1508 45 67 4.50 3.85 160 180 2.31 1712 44 70 7.66 3.07 158 200 2.43 2227 4l 62 6.58 3.27 150 220 2.19 3835 45 68 6.91 ..... 3.59 172 Sample No.: AHF 21967 Depth: 2086 m Latitude: 2 5°2 5.6,N Longitude: 109°38.3'¥ Interval(cm) Fe«) Cu(ppm) Ni(ppm) _Ca_co ($) Organic C{%) Zn(ppm) 0 0- 10 20 4o 6o 74 80 100 120 i4o 160 180 200 220 V jO ro oo 2.69 1.72 2.06 1.47 1.91 1.91 2.48 2.21 1.51 1.60 1.82 2.18 1.96 2.04 687 3703 664 415 520 518 547 601 3018 2322 2633 2531 1814 1482 33 49 25 20 21 23 20 25 46 50 43 58 50 54 35 61 30 22 22 24 28 32 62 68 60 79 83 75 18.49 4.42 23.24 3.58 .00 5.42 6.83 6.83 11.16 11.74 10.33 12.66 12.91 12.33 2.34 4.23 2.04 1.86 1.97 2.24 2.27 2.21 4.07 4.02 3.40 4.08 4.37 3.74 136 151 103 73 84 99 116 97 162 165 154 211 220 185 Sample No«: AHF 21966 Depth: 2306 m Latitude: 25°l8.0lN Longitude: 109O50.0tW Interval(cm) Fe(#) Mn(ppra) Cu(ppm) Ni(ppm) CaC03W) Organic c($) Zn(ppm) 240 2.2 2279 62 78 13,99 3.9! 235 Sample No.: AHF 21970 Depth; 2141 m Latitude; 2 5°17.5'N Longitude; 109°32.8fW Interval(cm) Fe_«) Mn(ppm) Cu(ppm) Ni(ppm) CaCO W) Organic 0 ( ° / o ) Zn(ppm) 0 1.85 931 39 4l 9.75 3.67 224 20 2.56 506 34 42 9.16 3.65 150 40 2.53 557 29 38 9.83 2.87 115 60 1.90 756 38 46 10.33 3.^2 126 80 2.52 559 33 42 8.06 3.^2 116 100 2.31 630 33 40 9.91 3.20 108 120 2.33 504 30 37 10.83 2.86 108 l4o 1.96 721 32 42 12.58 2.94 124 160 1.91 837 4l 51 13.99 3.^1 143 180 2.67 707 36 44 12.16 3.28 129 200 2.06 861 47 54 16.41 3 .hk 154 220 2.93 2858 57 72 21.07 3.86 I83 240 2.00 1208 36 48 5.58 3.^2 123 260 1.88 973 38 49 5.41 3.61 134 280 1.86 772 36 46 6.66 3.51 133 300 1.75 859 35 48 8.08 3.37 122 320 1.98 881 37 48 9.16 3.^7 133 340 2.00 1808 40 52 7.08 3.5^ 138 36O 2.01 86l 36 47 5.91 3.37 134 380 2.46 1272 32 38 8.4l 2.32 108 400 2.17 1359 4o 11.00 2.74 156 420 2.04 1736 33 38 11.25 2.61 117 ro vp Sample No.: AHF 21971 Depth; 2397 m Latitude: 25Q10.0!N Longitude: 109°43.9fW Interval (cm) FeW) Mn(ppm) _ Cu(ppm) Ni(ppm) CaC03W) . Organic C ( ° / o ) _1 : __ Zn(ppm) 0 2.30 627 37 42 3.83 3.55 114 20 2.24 532 43 48 1.08 4.41 128 40 1.47 658 30 37 2.67 2.52 108 50 2*17 569 31 37 2.25 2.95 105 6o 1.90 1011 49 56 4.08 4.06 199 80 2.34 1026 46 53 9.41 3.39 143 90 1.31 626 25 33 5.66 1.97 92 100 1.74 1291 47 59 6.33 3.69 144 112 1.54 712 21 26 11.49 2.02 98 120 2*28 1448 ^3 52 7.83 3.84 l4l i4o 1.91 2200 53 68 4.08 4.79 184 160 2.22 1565 54 68 6.66 4.o4 182 180 2*25 2653 51 72 8.75 4.26 142 200 2.20 2793 54 73 8.66 4.38 180 220 2.64 1703 4i 53 8.08 3.57 142 zko 2.30 2076 42 54 9.16 2.95 138 260 2.36 2379 47 63 11.25 2.91 157 280 2.49 1589 4o 48 10.08 2.48 l4l Sample No*: AHF 21972 Depth: i486 m Latitude: 2 5°04.1»N Longitude: 109°54.2t¥ Interval(cm) FeW) Mn(ppm) - Ou(ppm) .Ni(j2Pm).. . CaCOJll Organic C(%) Zn(ppm) 0 2.27 222 49 58 9.91 5.20 144 20 2.18 255 50 61 9.91 5.22 l4o 40 2.43 275 54 65 12.75 5.36 149 60 1.46 187 35 44 9.16 4.00 108 80 2.47 300 48 60 13.33 4.86 158 100 2.32 267 51 64 17.58 4.81 154 120 2.78 295 55 65 15.24 4.98 143 140 3.22 306 53 65 15.08 5.02 181 160 2.95 317 54 68 18.08 4.85 160 o Sample No.: AHF 21972 Depth: i486 m Latitude: 2 5°04.1*N Longitude: 109°54.2*¥ Interval(cm) Fe ( °/o ) Mn(ppm) Cu(ppm) Ni(ppm) CaCO^ ( °/o ) Organic C (° /o ) Zn(ppm) 180 1.62 266 54 71 17.16 5.09 145 200 2.54 319 53 70 18.41 5.34 153 220 2.26 281 57 68 14.66 5.76 157 240 2.50 300 58 69 20.91 4.94 160 260 2.37 310 53 69 19.33 4.88 161 280 2.33 316 56 68 20.91 4.57 169 300 2.13 328 52 64 20.66 4.33 144 320 2.16 323 54 66 25.82 3.74 152 340 2.35 296 50 59 22.16 3.98 125 360 1.98 278 45 50 20.82 3.53 135 380 2.15 307 44 53 18.74 3,5Q 108 Sample No.: AHF 21976 Depth: 2479 m Latitude: 2 5°04.51N Longitude: 109°38.0*¥ Interval(cm) Fe(°/0 Mn(ppm) Cu(ppra) Ni(ppm) CaCO^M) Organic C(%) Zn(ppm) 0 1.81 435 46 51 3.50 3.97 130 20 1.93 417 37 43 1.58 3.30 122 40 1.90 562 48 56 4.00 3.94 156 60 2.11 570 26 30 3.58 2.52 118 80 1.88 730 49 58 4.16 4.31 148 100 1.83 682 22 27 7.58 1.60 93 120 1.94 992 54 69 7.25 4.14 174 140 2.20 846 39 56 7.75 3.98 130 160 1.83 lo4i ....... 60 7.75 4.25 164 Sample No.: AHF 21977 Depth; 1976 m Latitude: 2‘ 5°11.3fN Longitude; 109°26.9f¥ Interval (cm) Fe(/£) Mn(ppm)_____Cu (ppm) Ni (ppm)____ CaCO^(^) Organic C (°/o ) Zn(ppm) 0 1.89 738 32 36 J 3.75 3.46 130 20 2.13 410 28 36 2.75 3.49 116 4o 1.74 430 32 38 4.75 3.02 114 H Sample No.: AHF 21977 Depth: 1976 m Latitude: 2 5°11.31N Longitude: 109 °26.9fW Interval(cm) Fe ( °/o ) Mn(ppm) Cu(ppm) Ni(ppm) CaCO^W) Organic C ( ° /o ) Zn(ppm) 60 2.36 4l4 27 34 4.50 2.92 102 80 2.24 393 28 35 2.33 3.36 99 100 2.29 367 29 36 3.33 3.27 108 120 2.27 383 27 35 5.00 3.09 96 i4o 2.05 517 32 38 7.08 3.19 116 160 2.59 516 33 4l 7.00 3.22 118 180 2.19 531 33 40 5.75 3.41 128 200 2.19 564 37 45 7.83 3.51 132 220 2.55 543 31 42 6.16 2.95 114 240 2.22 574 29 39 7.55 2.97 109 260 2.09 524 38 48 . 66 3.68 133 280 2.86 709 48 63 26.66 3.19 162 300 2.39 530 31 4l 7.25 3.86 108 320 2.08 897 34 45 7.50 3.18 115 340 2.69 754 37 47 14.49 2.33 127 360 2.07 397 40 49 11.83 2.66 150 280 2.09 473 39 45 11.16 2.62 158 Sample No.: AHF 21984 Depth: 2379 m Latitude: 24°50.6'N Longitude: 109 °23.3f¥ Interval(cm) Fe(Cb) ... Mn(ppm) Cu(ppm) Ni(ppm) CaC0„(?/ ») Organic C (°/o ) Zn(ppm) 0 2.63 580 67 59 J 11.91 4.13 191 20 2.48 871 64 64 11.58 4.04 176 40 2.93 1002 55 49 21.16 2.40 136 60 3.25 1199 48 33 9.91 2.97 120 80 3.19 1299 4o 35 15.33 2.03 103 100 2.99 598 38 35 11.58 2.22 95 120 2.86 583 29 27 10.66 1.82 85 140 2.19 503 27 24 8.83 1.52 74 160 2.84 574 42 36 8.91 2.76 101 180 2.41 476 44 38 1.67 3.31 98 Sample No.: AHF 21984 Depth: 2379 m Latitude: 24Q50«6fN Longitude: 109°23.3fW Interval(cm) Fe(tf) Mn(ppm) . . Cu(ppm) Ni(ppm) CaC0„M) Organic C ( ° / o ) Zn(ppm) 200 2.46 387 31 20 J 4.08 2.09 83 220 2.59 405 25 25 4.83 1.70 .. 77 Sample No.: AHF 21985 Depth: 2287 m Latitude: 24°4o.8*n Longitude: H [S °22.7f¥ Interval(cm) _ FeW) _ _ Mn(ppm) Cu(ppm) Ni(ppm) .. CaCO W Organic C(%) Zn(ppm) 0 2.22 541 63 67 J 3.83 5.13 173 20 2.31 924 65 63 2.58 5.05 172 4o 2.09 1362 67 63 3.75 4.92 174 60 2.13 1569 68 63 2.50 4.91 170 80 2.33 2128 72 67 6.00 4.31 178 100 2.37 3072 71 67 5.58 4.60 181 120 2.44 3213 68 62 6.00 it.63 172 140 2.42 2184 72 65 6.58 it.63 182 160 2.52 2694 70 65 7.16 it. 50 157 180 2.30 828 68 62 5.83 4.75 181 200 7.54 1203 73 67 7.66 5.03 186 220 2.47 2376 73 73 7.00 4.74 189 240 2.31 1795 73 70 4.25 4.58 201 260 2.56 2769 77 80 9.00 4.18 212 280 2.35 2226 73 71 8.75 4.59 193 300 2.38 l64l 74 70 9.16 4.44 204 320 2.39 2026 79 75 7.66 4.39 206 340 2.26 1914 68 64 4.92 4.42 185 360 2.49 1962 ______ J 8 ..Z7„ ____ 2 . 7 5 , . 4.20 - 215 Sample No,: AHF 21987 Depth: 3001m Latitude: 24°39.3'N Longitude: 109°09.9t¥ Interval(cm) Fe.W.) . . . . . Mn(ppm) Cu(ppm) Ni(ppm) CaC0„(°i) Organic Cl ? o ) _Zn(ppm) 0 2.62 1341 75 60 J .75 4.48 147 20 2.64 1405 77 6l 2.50 4.27 152 40 2.62 632 28 30 2.00 2.8 6 101 60 2.45 666 23 21 4.58 1.93 88 80 2.50 1246 39 33 6.91 2.66 115 90 2.67 1326 68 57 5.00 3.62 157 100 _ 2.53 828 40 _33__ 3.41 2.88 119 Sample No.s AHF 21995 Depth: 705 m Latitude: 24°26.6fN Longitude: 110°09.21¥ Interval(cm) FeW) Mn(ppm) . . . Cu(ppm) . Ni.(2PE) CaCO (fo) Organic C ( ° / o ) Zn(ppm) 0 1.75 172 39 64 18.66 6.80 101 20 1.59 182 4l 68 17.83 6.24 100 40 1.60 181 43 72 11.75 7.31 107 60 1.67 185 45 72 13.66 7.16 111 80 1.85 I83 44 77 17.91 6.70 106 100 2.03 196 44 76 13.33 6.80 110 120 2.15 202 4o 69 IO.83 6.55 108 140 2.20 214 h3 70 11.41 6.70 109 160 1.92 202 43 76 10.75 6.78 97 180 1.02 413 46 73 12.83 6.65 105 200 1.00 386 hi 73 11.99 6.73 100 220 1.06 425 47 73 8.33 6.87 106 240 1.07 431 47 77 7.25 7.08 102 260 1.10 438 50 lh 13.33 6.15 113 280 1.16 504 47 65 20.57 5.20 115 300 .90 332 50 74 21.83 5.21 102 320 1.01 466 54 83 27.99 5.21 89 340 .99 435 54 82 31.^9 4.69 118 360 uj ■ p - 1.92 162 43 70 27.66 4.86 102 Sample No#; AHF 21995 Depth; 705 m Latitude: 24°26.6fN Longitude: 110°09.2'W Interval(cm) F e ( ° / o ) Mn(ppm) Cu(ppm) Ni(ppm) CaCO^W) Organic C(^) Zn(ppm) 380 1.77 170 42 70 14.83 5.31 87 400 _ 1.-54 _ 132 ____36 _ 56 7.50 5.72 82 Sample No*: AHF 22009 Depth: 2882 m Latitude: 24°27.0'N Longitude: 109°l6*01W Interval(cm) Fe(°i) Mn(ppm) Cu(ppm) Ni(ppm) CaCO^(^) Organic C ( ° / o ) Zn(ppm) 0 2.13 536 64 57 2.92 4.25 161 20 2*07 44o 52 47 2.58 3.74 128 40 2.10 542 59 55 3.92 3.92 152 60 2.26 587 70 63 3.08 4.07 169 80 2.29 477 56 53 3.08 3.74 138 100 2.19 470 39 42 2.83 3.71 113 120 2.34 492 62 61 1.67 4.28 142 140 2.27 520 52 47 2.67 3.99 134 160 2.39 576 71 67 4.25 4.17 173 180 2.00 499 55 48 3.67 3.14 128 200 2.59 739 77 74 6.25 3.97 183 220 2.32 71k 74 73 __ 6.25 3.85 178 Sample No*: AHF 22011 Depth; 3138 m Latitude: 24°l6.2»N Longitude: 109°10.1 *W Interval(cm) Fe (c / o ) Mn(ppm) Cu(ppm) Ni(ppm) CaCO^(^) Organic C ( ° / o ) Zn(ppm) 0 2.49 1386 45 48 .75 4.03 123 20 2.24 355 19 21 3.92 2.68 86 40 2.51 409 31 30 4.17 2.54 97 60 2.59 .......... 18 30 4.17 2.60 86 Sample No.; AHF 22016 Depth; 3120 m Latitude: 24°11.8>N Longitude; 109°00.6IW Interval(cm) FeW) Mn(ppm) Cu(ppm) Ni(ppm) CaCO.W) Organic C(^) Zn(ppm) 0 2.10 1598 51 43 J ’ " ' J ' 3.25 3.43 128 20 2.14 778 45 38 3.75 3.55 116 40 2.24 565 23 29 3.75 3.45 84 60 2,39 667 44 39 2.92 3.24 115 Sample No.: AHF 22022 Depth: 1382 m Latitude: 24°07.61N Longitude: 108°43.0'W Interval(cm) Feifo). . . . . Mn(ppm) Cu(ppm) Ni(ppm) CaC0„ ( ° / o ) Organic C( ° / o ) Zn(ppm) 0 2.90 754 53 37 j 1.75 2.55 108 20 2.4l 322 32 28 3.25 2.29 82 40 2.70 444 33 61 7.25 1.58 92 60 2.34 376 37 27 4.50 2.07 81 80 1.68 527 24 19 3.33 . 1.27 75 Sample No.: AHF 22023 Depth: 3495 m Latitude: 24°02.7!N Longitude: 108' °51.0,¥ Interval(cm) F e ( ° / o ) Mn(ppra). Cu(ppm) Ni(ppm) CaCO (° / o ) Organic C(%) Zn(ppm) 0 2.84 3270 83 65 J 2.00 4.19 158 20 2.43 2054 77 60 1.42 4.19 143 40 2.27 1875 70 52 1.58 3.73 133 60 2.69 1341 58 48 2.25 3.19 125 80 2.42 2360 77 60 1.50 3.35 142 100 2.45 1706 76 60 1.83 3.39 147 120 2.73 1548 79 62 1.50 4.05 161 140 1.91 1013 25 30 .83 3.10 86 160 2.19 2709 52 49 3.08 3.06 118 180 2.83 2266 - ............. 82, _ . . . * 1 ............... ........ 4.26 166 U) O N Sample No,: AHF 20379 Depth: 2562 m Latitude: 25°26.2fN Longitude: 109°59.4IW Interval(cm) __F e M XJ v \ J WAX • Mn(ppm) _ J \ J £ » A i l AJCA Cu(ppm) __ Ni(ppm) A * CaCOjf*) AJUAIPS J - W UUU • XV 7 Organic C(^) Zn(ppm) 0- 20 1.60 2315 25 34 1.27 2.34 412 20- 4o 1.05 603 15 22 1.43 2.29 93 ho- 6o 1.21 575 22 32 1.4l 2.80 124 60- 80 1.22 560 21 29 1.00 2.39 109 80-100 1.28 540 20 29 1.18 1.46 112 100-120 1.31 622 21 32 1.42 2.44 118 120-140 1.30 571 20 33 1.75 2.40 111 140-160 1.36 591 23 36 1.06 2.69 120 160-170 1.37 1161 27 4l 7.38 2.59 149 170 1.45 1125 22 36 .-7.23 2.49 122 Sample No,: AHF 20397 Depth: 2315 m Latitude: 2 5°22.41N Longitude: 109' IS * O ^t O Interval(cm) FeW) Mn(ppm) Cu(ppm) Ni(ppm) CaCO ($) Organic Cd o ) Zn(ppm) 0- 20 1.30 667 13 19 1.11 1.85 112 20- 40 1.22 344 12 19 .00 2.24 68 4o- 60 1.22 301 12 19 1.29 1.71 78 60- 80 1.20 274 13 19 1.22 2.53 85 80-100 1.20 283 13 21 .83 2.19 106 100-120 1.27 312 13 21 .92 2.06 118 120-140 1.39 337 11 19 2.25 2.10 81 140-145 1.35 340 11 21 3.58 2.22 75 145 1.23 280 9 17 2.99 1.58 105 160-180 1.26 514 15 25 .92 2.28 190 180-195 1# 42 422 12 20 3.^6 1.30 73 195 .90 212 6 10 .00 .84 47 200-220 1.27 521 14 23 .58 2.37 76 220-235 1.24 348 13 22 ,00 2.15 77 235-240 .61 109 2 5 .50 .24 57 240-250 1.37 487 13 22 1.37 2.13 90 250 1.76 ^99 13 22 1.75 2.17 78 LO LO Sample No,: AHF 20398 Depth; 2818 m Latitude: 25°25.5IN Longitude: 109°52.3IW 0- 20 1.15 1109 21 32 .83 2.20 125 20- 27 1.10 797 21 33 .83 3.36 118 27 .81 478 16 26 1.75 3.35 71 4o- 60 1.22 999 21 30 .58 2.43 106 60- 80 .9^ 1650 23 38 .58 3.07 113 80-100 1.33 1895 26 37 .00 2.92 122 100-120 1.20 1454 25 4l .00 3.07 122 120-140 1.24 1931 29 44 .00 2.99 150 l4o-l6o 1.22 526 16 26 .00 2.36 91 160-180 1.33 780 22 30 .00 2.92 96 180-200 1.35 971 20 3.1 .00 2.95 118 Sample No.; AHF 21965 Depth; 2369 m Latitude; 2 5°12.6'N Longitude: 109°59.5,¥ Interval(cm) Fe($) Mn(ppm) . . . Cti(ppm) Ni(ppm) _CaC0 1$),- Organic C(°/0) _Zn(ppm) 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 o o 00 2.37 2.02 1.97 3.00 1.66 3.26 4.50 3.36 3.03 4.54 6.01 5.14 2.97 4.58 4.64 615 567 543 677 622 835 703 516 480 688 1304 606 359 623 544 53 57 66 49 51 56 49 39 28 37 26 27 24 29 34 51 48 54 45 51 58 43 50 31 42 38 30 30 39 37 5.58 IO.38 8.08 8.41 6.66 5.41 1.83 7.91 18.16 11.4l 25.57 7.58 5.66 13.33 11.75 4.00 3.H 4.12 3.01 3.41 3.09 2.01 2.38 1.34 1.41 1.20 1.37 1.56 1.55 1.80 145 124 l4l 126 129 163 134 121 103 117 118 115 83 97 159 APPENDIX IV 339 NITRIC ACID LEACHING TECHNIQUE AND PROCEDURE I. REAGENTS AND EQUIPMENT A. Reagent grade HNO^ (concentrated) B. Deionized water c. Culture tubes, 16 x 130 mm, calibrated at volume 10 ml D. Teflon boiling chips E. Hot plate fitted with an aluminum heating drilled to hold culture tubes block F. Centrifuge G. Spectrophotometer, atomic absorption H. Metal standards II. PROCEDURE A. Place 1.00 grams of finely ground sample in calibrated culture tube B. Add a few teflon boiling chips and 3 ml concentrated HNO C. Place tube in one hole of the heating block on the hot plate D. Heat to boiling for 30 minutes or until all brown NO^ fumes have been evolved, whichever is longer E. Remove tube from heating block and cool to room temperature F. Add 5 ml deionized water and mix solution and sediment G. Heat to boiling H. Cool and make up to 10 ml volume with concen trated HNO I. Mix contents of culture tube thoroughly J. Centrifuge for 20 minutes at medium speed K. Pour off supernatant for analysis III. DILUTION FACTORS FOR CU, NI, MN, ZN AND FE A. Cu - original solution (lOX dilution} analyzed B. Ni - original solution (10X dilution) analyzed C. Mn - original solution X 20 = 200X dilution analyzed D. Zn - original solution X 20 = 200X dilution analyzed E. Fe - original solution X 20 X 30 = 10000X dilution analyzed 340 IV. STANDARD CONDITIONS FOR ATOMIC ABSORPTION (Perkin Elmer 370) Wave- Working Element length, (nm) Slit (nm) Gain range (ppm) Cu 324.7 0.7 6 1-3 Ni 232.0 0.2 6 1-3 Mn 279.5 0.2 6 .5-2 Zn 213.9 0.7 6 H 1 m • Fe 248.3 CM • O 6 1-3 341 APPENDIX Table 1# Correlation coefficient matrix of all samples Number of samples = 370 Number of variables = 8 3; +3 Correiation Coefficients CaCO^ C org Cu Ni CaCO^ 1.00000 0.11841 -0.18151 -0.11346 C or g 0.11841 1.00000 -0.06210 -0.04105 Cu -0.18151 -0.06210 1.00000 0.87771 Ni -0.11346 -0.04105 0.87771 1.00000 Mn -0.09756 -0.15675 0.36456 0.42054 Fe -0.05578 -0.21911 0.58780 0.57610 Depth -0.45639 -0.16090 0.53686 0.33434 Zn -0.02546 0.01443 0.29263 0.25334 Eigenvalues 3.02106 1.24293 1.04027 0.97636 Cumulative proportion of total variance 0.37763 0.53300 0.66303 0.78508 L0 . £ r - P - Mn Fe Depth Zn -0.09756 -0.05578 -0.45639 -0.02546 -0.15675 -0.21911 -0.16090 0.01443 0.36456 0.58780 0.53686 0.29263 0.42054 0.57610 0.33434 0.25334 1.00000 0.07842 0.12057 0.16836 0.07842 1.00000 0.28386 0.09961 0.12057 0.28386 1T00000 0.18648 0.16836 0.09961 0.18648 1.00000 0.82754 0.48180 0.31960 0.09040 0.88852 0.94874 0.98869 0.99999 Table 2 Rotated factor matrix for four factors for all samples 3**5 Rotated Factor Matrix Factor 1 2 3 4 CaCO^ 0.04735 -0*88348 0.09920 -0.03792 C org -0*08182 -0.11784 0*90786 -0*02734 Cu 0*84831 0.25800 0*05292 0.33448 Ni 0.84114 0.08331 0*02633 0*38034 Mn 0*13650 -0*01335 -0*32958 0.81779 Fe 0*86815 0.02730 -0.17852 -0.14533 Depth 0.37145 0.77596 -0*01642 0*07683 Zn 0*13033 0*12412 0*31869 0*62963 Table 3 Correlation coefficient matrix for all samples with organic carbon content greater than 5*0 percent Number of samples = 157 Number of variables = 8 3^7 Correlation Coefficients CaCO C Cu Ni 2 _________________________ CaCO^ 1.00000 0.11869 0.23655 0.17^15 Corg 0.11869^^00000 0.34662 0.64473 Cu 0.23655 0.34662^jr:00000 0.81116 Ni 0.17415 0.64473 0.81116^1; 00000 Mn -0.10485 -0.19890 -0.06441 -0.12007 Fe 0.11396 0.01185 0.50148 0.38481 Depth -0.09964 -0.33077 O.31388 -0.04175 Zn 0.11930 0.03361 O.76723 0.51525 Eigenvalues 2.99694 1.87040 0.97326 0.86582 Cumulative proportion of total variance 0.37462 0.60842 0.73008 0.83830 - p - 00 Mn Fe Depth Zn 0.10485 0.11396 -0.09964 0.11930 •O.19890 0.01185 -0.33077 0.03361 0.06441 0.50148 0.31388 0.76723 0.12007 0.38481 -0.04175 0.51525 1.00000 -0.02255 0.44645 -0.02025 > 0.02255 1.00000 0.17941 0.35981 0.44645 0.17941 1.00000 0.42596 • 0.02025 0.35981 0.42596 1.00000 0.69812 0.33690 0.18147 0.07705 0.92557 0.96768 0.99036 1.00000 Table h Rotated factor matrix for four factors for all samples with organic carbon content greater than 5*0 percent 3**9 Rotated Factor Matrix Factor 1 2 3 4 CaCO^ 0.10266 0.06505 0.98900 -0.06005 C org -0.02877 0.93260 0.04124 -0.15719 Cu 0.83822 0.44319 0.13232 0.09482 Ni 0.56151 0.77141 0.06840 -0.04879 Mn -0.13168 -0.02916 -0.01553 0.92076 Fe 0.72698 -0.05368 0.05291 -0.11928 Depth 0.46862 -0.30372 -0.11174 0.69209 Zn 0.84605 0.10904 0.03056 0.15279 Table 5» Correlation coefficient matrix of all samples with depth greater than 1500 m Number of samples = 203 Number of variables = 8 351 Correlation Coefficients CaCO C Cu Ni 3_______ org______________________ CaCO^ 1.00000 0.25294 -0.16494 -0.16471 c 0.25294^ ^ 1; 00000 -0.20053 -0.25997 org Cu -0.16494 -0.20053 1.00000 0.93144 Ni -0.16471 -0.25997 0.93144^^1; 00000 Mn -0.14595 -0.23796 0.49900 0.46291 Fe -0.04701 -O.25013 0.62015 0.62847 Depth -0.45148 -0.13974 0.32459 O.20636 Zn -0.16125 -0.16605 0.75772 0.66593 Eigenvalues 3.56300 1.35963 0.98710 0.91731 Cumulative proportion of total variance 0.44538 0.61533 0.73872 0.85338 LO ut ro Mn Fe Depth Zn 0.04701 -0.45148 -0.16125 0.14595 -0.13974 -0.16605 0.23796 0.25013 0.62015 0.32459 0.49900 0.75772 0.46291 0.62847 0.20636 0.66593 0.54662 O.O8783 0.08850 1.00000 0.08612 0.08783 O.3188O 1.00000 0.08612 0.08850 1.00000 0.25921 0.54662 0.31880 0.25921 1.00000 0.52505 0.35571 0.24651 0.04566 0.91901 0.96348 0.99429 1.00000 Table 6 Rotated factor matrix for four factors for all samples with depth greater than 1500 m 353 Rotated Factor Matrix Factor 1 2 3 4 CaC03 -0.08441 -0.80486 0.03361 0.28482 C org -0.11370 -0.12252 -0.15690 0.93635 Cu 0.35300 0.19592 0.77830 0.02130 Ni 0.49788 0.11325 0.78859 -0.08005 Mn 0.90888 O.OO885 0.02161 -0.19592 Fe -0.07022 -0.02333 0.91604 -O.I8567 Depth O.O6560 0.87129 0.15215 0.08841 Zn 0.73935 0.18302 0.44494 0.06727 / , o n y i i 4 u i O e * t e d s ' J J * i L t r A * * * f f o m i u My S r y - .f y Aqua CuLtnfP ^ . - ' • ^ v > Vt t » J < £ / ■ % i^tSk' \ '■ • r * v \ - \ 4 / . .... ^ L A P A Z ■flood to fat fa* tfaTU\*c° Jlfr«t» lU fitio P 5 / /$ i > ) ? 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CD CO o o o CP o R/V Velero 197A R/V Velero 1975 R/V Lee 1976 rrl P L A T E 3. Trackline Coverage of the Southern Gulf of California CD O O Z O CO O o IOOKM PLATE A. Sediment Distribution and Thicknesses (tenths of a second two-way travel time) Mazatlan Bathymetry (contour in t e r v a l =200 meters) tela Esperitu Santo S C A L E < k m . ) D e p t h i n m e t e r s AI a rf Seamount * H L 7?. P«XAfi. ( c > PU\TF 6 . Fault Map of the Southern Gulf of California A S f a u l t t r a c e s f e 2 0 0 0 m I O O O — 2 0 0 0 n S O O — l O O O m S 5 0 0 m R E L I C T T R A C E I M P L I E D T R A C E isla ---- Santa Catalina Cera Iba Bank Mazatlan MAGNETIC ANOMALIES (POSITIVE ANOMALIES SHADED) SCALE 1 —300 + gamma — gamma PLATE 8. ‘' h SL'ds > 77 y V ^ V / flaXn. % ^ 5 3P c 2 A ^1 Guaymas Bahia Cancepeian A R M E N BASIN Santa Catalina //,^s^ o / / U FA R A L L O N BASIN Esperitu Santa Bahia do S C A L E ( k m . ) D e p t h i n m e t e C A D E R O Isla Ceraibo Ceralba Bank m a z a t l a n BASIN PLATE 9. Seismic Events of Richter I'Tacnitude 3.0 to 6.5 ! 0 0 0 - 20 0 0 m PLATE 10. Fault Traces and Sediment Distribution and Thicknesses A/ CO • 3.0 b & 100 KM CO o z o FAU L T T R A C E S W I D T H O F T R A C E D E N O T E S A P P A R E N T V E R T I C A L D I S P L A C E M E N T > 2 0 0 0 m IOOO—2000m 5 0 0 — I O O O m 5 0 0 m R E L I C T T R A C E I M P L I E D T R A C E "T-TL 1 ? . TV l » 7 / A A? PLATE 11. Fault Traces and Heat Flow Measurements (heat flow units) CO o IOO KM ~n o =o PLATE 12 SEISMICITY • ^ EVENTS OF MAGNITUDE W 3.0- 6.5 (1967- 1974) ★O EVENTS WITH FAULT PLANE SOLUTIONS o zo FAU L T T R A C E S W I D T H O F T R A C E D E N O T E S A P P A R E N T V E R T I C A L D I S P L A C E M E N T 2 2000 m 1000-20001 5 0 0 — l O O O m S 5 0 0 m R E L I C T T R A C E I M P L I E D T R A C E MAGNETIC ANOMALIES (POSITIVE ANOMALIES SHADED) — 300 + gamma _ - - O — gamma _ ^300 A SCALE C u x A/L>1 I plots, B /<. T 2 '71 AS & 7 / p/cCtSUV -2 PLATE 1A. Schematic Representation of Plate Tectonic Boundary in the Southern Gulf of California " a ' 7? /<£ 7 / ' A Af Se d im e n t Sample D redge H a u l BAJA CALIFORNIA >a < , + *♦ *’** Vi t + l CD O O =o CO o o CO t o 100 KM ,ro\ 5 i5r -Z /4 AT PLATE 17. Association of Organic Carbon (%) and the 0o Minimum Zone PLATE 18. Sedimentation Rates (cm/1000 y r s.) and Sediment Thicknesses (tenths of a second two-way travel time) Volcanic Breccia, Vesicular Basalt Weathered Basalt Fresh Pillow Basalt Granitic Rocks Ketamorphics A' £ 7 / I ' PLATE 20. 71 istribut ion OF Organic Carbon (%) ^ £-£.2 A A /7 I p(aXa£l PLATE 21. Distribution of Calucium Carbonate (%) CD O o . O =o CO o o 50 o o 40 vO 50 lOO KM _ 50 _ 60 ^80 O, O \oo o :o fcP‘ o o I3( _o o o /v<£ ? I PLATE 22. D istribution of Leachable Copper (ppm) C O o o ' \T> o o o o o o C V J o ro O Co o o' o < o o o o o O ■ S T O O So /Oo -p O' R I BUT I ON OF L e a CHABLE 99999999999999299999999999999999999999999999997 CD O O o o CO o CO o o o o o o o CO IOOK M o o 8 I CM 250 I O o o i 300 o PLATE 24. Distribution of Leachable Z inc (ppm) CD O o GO Q / o « o o cvi ro CO o >p "p o KfeS? o ! | 0 0 o OO KM " O ' o o o o o v- • E - O A'l P L A T E 25. Distribution of Leachable Manganese (ppm/10) i CD O o o o CO O \5 i n o 2.0 O O ' A 5 2-0 IOOKM O ' H i 6- * * ! O ' o <o <v PLATE 26. Distribution of Leachable Iron (%) CD O 3 Q O =o CO o o o OJ »QO o IOO KM C L e x . o o o PLATE 27. Association of Leachable Manganese (pm/10) and the O2 Minimum Zone IOOKM \i,.U ( ^ v J i , ' 11 / v i OiaXo a 2/4 r > i x <3 3 U L T T R A C E S DTH OF TRACE DENOTES ENT VERTICAL DISPLACEMEN » 2000 m l000- 2000r 500-1 OOO m -L 500 n r. CT TRACE IMPLIED TRACE PLATE 28. Correlation of Leachable Copper (ppm) and Inferred Tectonic Elements 07 O o O IO O K M o o o o r O CO o o' O o F A U L T R A C E S A P P A R E N T V E R T I C A L D I S P L A C E M E N T I 000-2000m i L» ro O o O IMPLIED TRACE 80 /Oo o t o "O o *3^ Af & 7 / PLATE 29. Correlation o f 1_eachable Nickel ( p p m ) a n d Inferred Tectonic Elements 5 JH PLATE 30. Correlation of Leachable Zinc and Inferred Tectonic Flehents FAU LT TR ACES W I D T H O F T R A C E D E N O T E S A P P A R E N T V E R T I C A L D I S P L A C E M E N T PLATE 31. Correlation of Leachable Manganese ( p p m /1 0 ) and Inferred Tectonic Elements CD O O =o o IOO KM o o CO o 1 .5 2.0 O FAU LT T R A C E S W I D T H O F T R A C E D E N O T E S A P P A R E N T V E R T I C A L D I S P L A C E M E N T O ' I M P L I E D T R A C E R E L I C T T R A C E \ 2- 5 o PLATE 32. 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C a r o l d e & P * ' \ L a 'J ■ r n , ^ f S J j l / S a r v - j i c A i J p " f t > 4 -5 STATScr SONORA le a v in g the h a rb o r o f Oaa/mas f r o m O u a r m t u to H e r i t m d f l o - P ro m H e rir.ii,l U, I t [/r e s F r o m P e r n tr s illo to J a t i l a C ru z f r o n t i e r o f th e n o r th R o a d t e E l Tucson & u p p e r L a li f c r n ia F r o m S a n ta C ru z tu E r o n te ra s - R o a d /o B P c n s o a d N o rte Foosn F r m itr ra s to E lP a s s o d d N o r te i f th e C a n o n d e G u a d a l u p e F r o m G res to A l t a r F r o 111 N r rs to A t a p t - 0 / th e soa p o f th e R iv e r o f S o n o r a f r o n t d r u p e to F r o n t e r a s F r a u s U re s to M o n t e z u m a F r o m U r n to S a /u iu r r o a F r o m U re s i a th e N . E . to La. T r in i d a d [n in e w a y t o r C h ih u a h u a . F r o m t h e T n n id iu lt o th e to w n e t C f i i h u a h i u i F rom N rrs to A lam os b r a n t A la m c s t o E l F u t r t t f r o n t i e r e f th e S ta te A Sue a le a- f r o m ( m a y m a s t c E l P a ss o d r ! - P o r te , on {he l i n e o f th e p r o je c t e d R a i l w a y S T A T E o . C H t H U A H N A P r o m t f i e t o w n o f f / t i / t , t a J i u a . t & E l P a * o f f o r b r fr o m C fu h tta k u u C o .ilu i/ m t$ to U o f'S o n v ru S T A T f ** S IN A L O A Fwtri the F u r r t r ta t h t t o w n o f * * t R o f o u F r a u d c t o + * < S S i * a l > * t o F u l f a c a a Frwm Ciduxpa* to Ct'.fata- f/v a t fuUaouu C o th r h a r t o r o f 4 a tu h a tt IMFR C A L I F O R N I A F r o m M o :c ;e f h a r f o r j t o £ a /> i r i + j j . r o u j t o U p p e r (atifor/U A fro m J U o le ji to L o Fax Froyt Ly F a t to 7Vdat iVi From L e e Fa* t o S um Jbtt ? ( jr Q o o d V h f o t t r o t t d FFauqtunA \ M u l t T r a il J s ^ d f S nB e n tv \ ' - Q | > ^ \ j " ~ V , E S*Aug tit- \ r s a d c ln A a /m d a d e t c ua M ' a y a n X . i l l M i t i e Trad » S r> IVeursLttaef exkrrds ' 7 l A'hi I p W L i " SJ A runt i. P ortion of N ew M a p of Sonora by Col. E. de F le u ry, published by A . Gensoul, San Francisco, 1864. Reproduced fo r the Baja C a lifo rn ia Travels Series, 1965. \ i 100 KM 'H.v. Q xJL ' ? ? 7x1*11 ^/flJtL.10 a $ 3 - 1 A A/ FAULT TRACES WIDTH OF TRACE DENOTES APPARENT VERTICAL DISPLACEMENT > 2 0 0 0 m l0 0 0 -2 0 0 0 m 5 0 0 -1 0 0 0 m < 500m RELICT TRACE IMPLIED TRACE PLATE 10. Fault Traces and Sediment Distribution and Thicknesses 4.0, 4.3 r* •4 .2 • 3.3 FAULT TRACES WIDTH OF TRACE DENOTES APPARENT VERTICAL DISPLACEMENT > 2000 m l000-2000m 5 0 0 -l0 0 0 m S 5 0 0 m RELICT TRACE IMPLIED TRACE • as\ • 2.3 \ 6.2 5.4 • 6.3 • 1.7 • 5.5 PLATE 11. Fault Traces and Heat Flow Measurements (heat flow units) 100 KM PLATE 12. SEISMICITY • j . EVENTS OF MAGNITUDE 3.0-6.5(1967-1974) ★O EVENTS WITH FAULT PLANE SOLUTIONS ^1. fault traces / Rr, r, WIDTH 0F tr a c e d e n o t e s . a p p a r e n t v e r t ic a l d is p l a c e m e n t > 2000 m I 000~2000m 5 0 0 -l0 0 0 m S 500m RELICT TRACE IMPLIED TRACE PLATE 1 3 , MAGNETIC ANOMALIFR (POSITIVE ANOMALIES SHADED) SCALE p300 + gamma I --0 — gamma I ^300 /V b i t 2 5 1 ’2 (\ ' R . ' V . '11 /V&H fldXLtl J s- j- jzA /M PLATE 1H, ^ C \ O - t \ -A - 3 5 V ' 5 '.^ I b o <* t* o Schematic Representation of Plate Tectonic Boundary in the Southern Gulf of California c c c o p a s m WGQ.D£U&^% CALIFORNIA 7 i . 4 rr* A X - & - £ cA Ui y r 0 * iD % * > * v- !☆ ☆ + ♦* *X*+ + * + 1*#* *1* * + + + + ^ + * . *+ + + + ' + * - V * * l> + + ****** -+ > r t; to © oo r ; V - - V * * n V.y/*v« fe -r Z> % (0 £ CO *-* C=* & * CO o o 30 > 1 0 0 m _____ i PLATE . 1 . 8 , Sedimentation Rates (cm/1000 yrs.) and Sediment Thicknesses (tenths of a second two-way travel time) Guaymas Bahia Concepcion Loreto I — 1 s la Carmen CARMEN BASIN Isla Santa Catalina Isla San Jose FARALLON BASIN Isla E sperltu Santo Bahia de La Paz LA PAZ BASIN D e p th in m e te r s La Paz PESCADERO BASIN COMPLEX Isla Ceralbo C eralbo Bank £3 A la rco n Seamount M A ZA TLA N BASIN Mazatlan Is as Tres Marias Volcanic Br ec c ia, Vesicular Basalt W eathered B asalt Fresh Pillow B asalt G r a n it ic R ocks !• Netamorphics ‘P i i . v . 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C . i v a i/a J / i e ~ > . . 7. jn ■ ■ • 7* Vmfifsn y- ■ ' . j f f / o l c i lijfc rv'4;,^ Dt (o T n n c A n , H\0 ^ttbtcaciott^c f t s Siouos . ^ ) C q p r t a lr r c / r E s la d o g i d d r iA r s /r r to .v © C i t id m /r s O COerifoer P d r r . c t e / ia r r ln f u p n • d/irnc hose \ A d u n c h r r ia s < f r / r t d t a s , . rti" (TiAre . 4 * X k /<A .. crfr fw a /rn a o ff j. m r CoTujP/afh- » * B f J 3laceresr d r fh rp ' Cam e n o r ■ jJ j d e r r fr s i s~j7 ('/iio *£r.'sra/cros ■ n i s r ' C y -W/w A c C illrrro rd o \Cbsftiudid .Sir '/ '( ( f l- tX v a j ' ■ . Candor o n . f£otales P R ll.m ilO n K M A /.A 'kr.A l C i PLATE 2. by A . tie n fo u l lip the C lerks M ure o£ the Zhstrvcl Court j / t £ flc rth e rn D is tric t o f the State o f C itfrrn ia BriHonef Co, Lith., S,k ~7& r s c s * sc?' ///' w " ' ' /o s * ' C o r t y i/ n d f / s r jt t e d a f / m e n w t r h P o rtio n of N ew M ap of Sonora b y Col. E. de F le u ry , published by A . Gensoul, San Francisco, 1864. Reproduced fo r the Bufa C a lifo rn ia T ravels Series, 1968 /o r IOOKIVi PLATE 20. D is trib u tio n o f Organic Carbon (%) A1 c / 100 KM j __________i plaXb 5 I D is trib u tio n o f Calucium Carbonate (%) 2 ^ 4 & 3 1 purl;? 3 2*5-5 2 A A/ 100 KM i ----- 1 I I . PLATE 22. D is trib u tio n o f Leachable Copper (ppm) G / / Y ^ PLATE 23. D is trib u tio n o f Leachable N ic k e l CpptO 1 0 0 KM J ---------- 1 IOOKM 250 250 200. >5Q| PLATE 24, D is trib u tio n o f Leachable Zinc (ppm) A f PLATF 25. Dis t r ib u t io n of Leachable M anganese ( ppm/1 0 ) IOOKM v . ’V . N& 7 ^ o \ ■ ■ g ^ A PLATE 26, D is trib u tio n o f Leachable Iron ( % ) ( : 6 \ L V jl 100 KM & i / PLATE 27. Association o f Leachable Manganese (ppm/10) and the O2 Minimum Zone )T IOOKM C/> o z o : u > FAULT TRACES WIDTH OF TRACE DENOTES APPARENT VERTICAL DISPLACEMENT ; > 2000 m !000-2000m 500-1000 m < 500m RELICT TRACE IMPLIED TRACE 0 L_ IOOKM j--------- - C O o o 20 y > FAULT TRACES WIDTH OF TRACE DENOTES APPARENT VERTICAL DISPLACEMENT m m m > 2 0 0 0 m ■I ■ ■ ■ 1000 - 2000m — 500-1000 m <500m RELICT TRACE IMPLIED TRACE E nlarged area LOCATION rr-- r — .— ..— f\ 5 0 100 -J n.v. cfu ’ f t p ( a f e 3 ^5^-2 A 7 1 1 PL ATE 3, Trackline Coverage of the Southern Gulf of California \ SCALE (km.) - - - - - - - - - - - - - - - - R/V Velero 1 9 7 ^ 4 - - - - - - - - - - - - - - - - R/V Velero 1975 R/V Lee 1976 IOOKM C /) o 2 O 2 3 > FAULT TRACES WIDTH OF TRACE DENOTES APPARENT VERTICAL DISPLACEMENT > 2000 m I 0 0 0 - 2 0 0 0 m 5 0 0 —1000m < 500m RELICT TRACE IMPLIED TRACE 10 0 KM $ \ FAULT TRACES > 2 0 0 0 m l0 0 0 -2 0 0 0 m 5 0 0 -l0 0 0 m < 500m k RELICT TRACE IMPLIED TRACE WIDTH OF TRACE DENOTES APPARENT VERTICAL DISPLACEMENT <3-ie '7? p l a i t - 3 1 > s 5 x A ■ p i PLATE 31, Correlation o f Leachable Manganese (ppm/10) and Inferred Tectonic Elements / ■ 100 KM 'R .v FAULT TRACES WIDTH OF TRACE DENOTES APPARENT VERTICAL DISPLACEMENT \ 2 0 0 0 n I0 0 0 -2 0 0 0 m 5 0 0 -l0 0 0 m < 500m RELICT TRACE IMPLIED TRACE PLATE 32. C orrelation o f Leachable Iron ( % ) and In ferred Tectonic Elements 2S3T-2 A i*l PLATE A, Sediment Distribution and Thicknesses (tenths of a second two- way travel time) Guaym as Bahia Loreto Carm en CARM EN BASIN Isla Santa C atalina F t* c f> San Jose F A R A L L O N B A S IN ~ ~ - A E s p eritu B ahia <te La Paz LA PAZ BA SIN SCALE ( km.) Depth in meters P E S C A D E R O B A S IN C O M P L E X Is la C eralbo C e ra lb o Bank A la r$ o n Seam ount M A Z A T L A N BA SIN C2t M azatlan Islas M arias ' f k . ' V plates t r s - * A » 1 PLATE 5. Bathymetry (contour interval=200 meters) Suaytnas Bahia Concepcion Lareto Isla Carmen CARMEN BASIN isla Santa Catalina Isla San Jase 1 FARALLON BASIN / V isla E speritu Santo Bonia de La Paz LA PAZ BASIN ■ ' .Depth in meters La Pa PESCADERO BASIN COMPLEX Isla Ceralbo Ceralbo Bank Alarcon Seamount M AZA TLAN BASIN Mazatlan Islas Tres Marias A'6?/ PLATE 6. Fault Map of the Southern Gulf of California A FAULT TRACES WIDTH OF TRACE DENOTES APPARENT VERTICAL DISPLACEMENT > 2 0 0 0 m l0 0 0 - 2 0 0 0 m 5 0 0 — 1OOO m & 500m RELICT TRACE IMPLIED TRACE Guaymas Bahia Concepcion V | Lareto Isla Carmen CARMEN BASIN Isla Santa Catalina i F A R A L L O N B A S IN Is la E s p e ritu Santa B a h ia de La Paz LA PAZ BA SIN Depth in meters PE S C A D E R O B A S IN C O M P L E X Isla C eralba C e ra lb o Bank . A la rp o n Seamount M A Z A T L A N B A SIN M azatlan Islas T res M arias T > platan A A | PLATE 7 . L o c a tio n Map o f S e ism ic R e fle c tio n P r o f ile s MAGNETIC ANOMALIES (POSITIVE ANOMALIES SHADED) SCALE i- 3 0 0 *■ + gamma ” — 0 — gamma Z 3 0 0 PLATE 8, ) ^ /V&11 s»ST<2 A f < \ Guaymas Bahia Cancepcion Lareto p — Isla Carmen * q ARMEN BASIN Santa Catalina Isla San Jose FARALLON Isla , Esperitu Santa Bahia de La PazN \ . ' \ v LA PAZ j BASIN Depth in meters CADERO IN PLEX . La Paz Isla Ceralbo Ceralba Bank . A larcon t • Seamount M AZA TLAN BASIN G Mazatlan Istas Manas o Bahia Lora to Jr let Isla . -------- Carm en "*7 O =o k < § > ' Isla Santa C atalina A CA RM EN BA SIN \ « p p_ Isla San Jose’ Is la E s p e ritu S anta B a h ia de L a Pa: F A R A L L O N , B A S IN © B A S IN L a Paz .Depth in meters P E S C A D E R O B A S IN C O M P L E X Is la C eralbo / C e ra lb o B ank A la rc o n Seamount M A Z A T L A N B A S IN M azatlan M arias ^ T > Q w L v 7 7 I pUxi 7 - 2 . J2. /4 A) PLATE 9. Seismic Events o f Richter Magnitude 3.0 t o 6.5

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Creator Niemitz, Jeffrey William (author)

Core Title Tectonics and geochemical exploration for heavy metal deposits in the Southern Gulf of California

Degree Doctor of Philosophy

Degree Program Geological Sciences

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

Tag Marine Geology,OAI-PMH Harvest,Plate Tectonics

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c29-344300

Unique identifier UC11218852

Identifier DP28546.pdf (filename),usctheses-c29-344300 (legacy record id)

Legacy Identifier DP28546.pdf

Dmrecord 344300

Document Type Dissertation

Rights Niemitz, Jeffrey William

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