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The Hall Canyon pluton: implications for pluton emplacement and for the Mesozoic history of the west-central Panamint Mountains
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The Hall Canyon pluton: implications for pluton emplacement and for the Mesozoic history of the west-central Panamint Mountains
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THE HALL CANYON PLUTON: IMPLICATIONS FOR PLUTON EMPLACEMENT AND FOR THE MESOZOIC HISTORY OF THE WEST-CENTRAL PANAMINT MOUNTAINS by Andy Crossland A Thesis Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE (Geology) August 1995 Copyright 1995 Andy Crossland UNIVERSITY OF SOUTHERN CALIFORNIA 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 thesis, written by under the direction of h..tS...Thesis Committee, and approved by all its members, has been pre sented to and accepted by the Dean of The Graduate School, in partial fulfillment of the requirements for the degree of d'rossI d MASTER OF SCIENCE Dean D ate..... THESIS COMMITTEE Chairm an DEDICATION: I wish to dedicate this thesis to my mom who has given up much for the sake of her children. ACKNOWLEDGMENTS: I would like to thank my advisor, Scott Paterson, for all of the help and ideas he put into producing this thesis, as well as Greg Davis and Gene Morrison for guidance and patience in my efforts to improve this document. Thanks also to Ken Fowler, whose insights are very much a part of this research, to Semele and Samantha for keeping me from giving up, to Marek for his Panamint expertise, and to Deb and Dad for their love and support. Lastly, I thank my brother Dave who, in a way, did more than anyone to see this thesis finished. TABLE OF CONTENTS Page DEDICATION.....................................................................................................ii ACKNOWLEDGMENTS......................................................................................iii LIST OF FIGURES ............................................................................................ v LIST OF TABLES............................................................................................. viii ABSTRACT....................................................................................................... ix PROLOGUE.........................................................................................................1 INTRODUCTION AND REGIONAL GEOLOGY................................................ 10 PREVIOUS WORK.............................................................................................16 Metamorphism............................................................ 16 Temperature and pressure constraints ...................................... 19 Petrology and geochemistry of the Hall Canyon pluton ........ 22 Age of the pluton............................................................................... 25 DATA................................................................................................................. 26 Country rocks......................................................................................27 Pre-Pluton Deformation ............................................. 27 D7............................................................................ 30 D2..................................................................................... 31 D3-D4..............................................................................31 Metamorphism.....................................................................................40 Mineralogy of Kingston Peak metamorphic rocks ........40 Porphyroblasts........................................................................49 The Hall Canyon pluton .....................................................................51 U-Pb dating...............................................................................51 Nature of the pluton contact ............................................... 55 D5 shear zone deformation ..............................................................58 Lineations................................................................................. 68 High-angle faults ................................................................................69 Hypabyssal dikes .................................................................................70 The Emigrant fault ............................................................................ 71 DISCUSSION.....................................................................................................71 Mesozoic History of the Central Panamints ............................. 71 Emplacement of the Hall Canyon pluton ..................................... 76 REFERENCES.....................................................................................................84 iv LIST OF FIGURES Rage Figure 1. Cartoon Illustrating the movement of a melt (shaded block) from the lower crust to the upper crust by horizontal material transfer. ....................................... 4 Figure 2. Flow around an ascending diapir as modeled by Cruden (19 88). Note flattening strains in the roof of the body................................................................................................. 7 Figure 3. Cartoon of extensional emplacement illustrating an extended or detached roof (from Paterson and Fowler, 19 9 3 b )....................................................................................8 Figure 4. Location map showing the Death Valley region. ..............9 Figure 5. Map of the west central Panamints including the Hall Canyon pluton (simplified from Labotka and others, 1 9 8 5 )...................................................................................... 11 Figure 6. Stratigraphy of the Death Valley region (from Miller, 1985). ....................................................................................... 13 Figure 7. Allochthons, extensional faults, and intrusives of the northern Panamints (simplified from Hodges and others, 19 8 9 )....................................................................................... 14 Figure 8. Map of the central Panamints showing Cretaceous Ar-Ar dates (Labotka and others, 1985) and the location of U-Pb sample. ................................................................................... 18 Figure 9. Map of the central Panamints showing metamorphic isograds (simplified from that of Labotka and others, 1985).,.................................................................................................... 20 Figure 10. Cross sectional view of pluton phases as mapped by Nibler (1991). Location of the cross section is similar to that of Figure 13. 23 Figure 11. Simplified geologic map of the Hall Canyon pluton and overlying country rocks (see Plate 1 for greater detail). ................................................................ 29 Figure 12. Photograph and outcrop sketch of refolded folds in the Kingston Peak Formation. Axial traces of D3 and D4 folding are indicated with dashed lines. View is looking south and shows west-vergent nature of D4 folding. Vergence of D3 folds is not illustrated in this Figure. ........................................................................................... 33 Figure 13. Cross sectional view of the northern portion of the Hall Canyon area. Form lines are drawn from the projection of actual beds in the natural cross section of Hall Canyon itself. Lines in the pluton indicate the presence of shear zone deformation. Location of section indicated on figure 11. 34 Figure 14. Cross sectional view of the southern portion of the Hall Canyon area. Form lines and attitudes of the pluton contact are schematic. Lines in the pluton indicate the presence of shear zone deformation. Location of section indicated on figure 11. 35 Figure 15. Map showing attitudes of D2 layering. .............................37 Figure 16. Kamb contour stereonet plots of country rock data. (A) poles to D2 layering, (B) poles to axial surfaces of D4 folds, (C) poles to foliation in outcrops of the Beck Spring Dolomite. ............................ 39 Figure 17. Kamb contour stereonet plot of all D3-D4 country rock lineations. .......................................................................... 41 Figure 18. Map of D3-D4 country rock lineation. ...............................43 Figure 19. Metamorphic facies series of Labotka (1981). Roman numerals in (a) and (b) represent the same facies, with IV being the highest. 49 Page Figure 20. Concordia plot of U-Pb zircon data from a sample of the biotite phase of the pluton (prepared by D. Walker)______________________________________________ 54 Figure 21. Photograph showing the irregular nature of the contact. View is looking southwest into Hall Canyon._____ 56 Figure 22. Map of C surface attitudes associated with the right-lateral shear zone (D 5)._________________________ 60 Figure 23. Kamb contour stereonet plots of shear zone data. (A) poles to C surfaces in the Hall Canyon Pluton, and (B) poles to C surfaces in country rocks._________________61 Figure 24. Map of shear zone (0 5 ) lineations.__________________64 Figure 25. Kamb contour stereonet plot of shear zone (D5) lineations. ______________________ 65 Figure 26. Timeline showing ages of important events. 72 Plate #1._______________________________________________map pocket Plate # 2 ._______________________________________________map pocket LIST OF TABLES lags. Table 1. Minerals present in schists of the Kingston Peak Formation............................................................................................. 44 Table 2. U-Pb D a ta....................................................................................... 53 viii ABSTRACT An examination of the Cretaceous Hall Canyon pluton and the country rocks in the roof of the intrusion provides constraints on the mechanisms of pluton emplacement, and on the timing and nature of regional events in the west-central Panamint Mountains, California. The pluton is a two-mica granite that intruded strata of the Precambrian Pahrump Group. Roof rocks of the pluton have undergone four generations of deformation, the youngest of which is Jurassic in age. All of the Jurassic structures, including foliations, axial surfaces of west-vergent folds, and a sub horizontal lineation, are truncated by the pluton, as well as by related dikes. In the eastern portion of the area, these igneous rocks are undeformed indicating that country rock structures predate the intrusion. None of the deformation in the roof is associated with the intrusion. Cretaceous metamorphism which overprints earlier structures is best interpreted as resulting from heat supplied by the pluton, the proximity of the Cretaceous arc, and retrograde metamorphism during post-emplacement shearing. The roof contact is irregular with angular jogs that are suggestive of the stoping of individual blocks as large as TOO m in their longest dimension. Smaller, meter- and centimeter-scale blocks are found in the main body, especially near its upper contact. The pluton, and the westernmost exposures of roof rock, were deformed by a wide, right-lateral, mylonitic shear zone. In the pluton, shear zone deformation is characterized by ductile behavior of quartz and micas, whereas feldspars remain intact or deform brittlely. Exposures of country rock deformed by the shear zone show east-vergent folding and right-lateral shear that overprint Jurassic structure. No structures of an intermediate age that could be attributed to, or called upon to help make space for the pluton have been recognized. These structural and metamorphic characteristics place constraints on possible emplacement mechanisms. Folding occurred well before emplacement and is, therefore, unrelated. In situ expansion (ballooning) of the pluton may be ruled out as an important space making process because the roof of a ballooning pluton should exhibit syn-emplacement, margin parallel flattening strains that are not present in the area. Furthermore, pluton and roof rock structures indicate that fault motion did not make space for the intrusion. These results suggest that stoping was the major space-making process for the pluton at this structural level. PROLOGUE The study of mechanisms by which plutons ascend and are emplaced can make significant contributions to our understanding of a wide variety of crustal processes. For example, if a melt is added to the crust from the mantle, and crustal material is not simultaneously taken from the crust and added to the mantle, the volume of crust must increase (e.g., Paterson and Fowler, 1993a). This is thought to occur at spreading ridges, where plate growth is in the horizontal direction as a result of magma emplacement in an extensional setting. The problem of making space for the intrusion is, therefore, solved by allowing igneous material to fill space vacated by the lateral displacement of plates away from the spreading center. In a continental arc setting, the processes involved are not as well understood. It is possible that magma emplacement could result in horizontal crustal growth if the mechanisms involved provide a means of transporting material laterally away from the pluton. Such emplacement models have been suggested by a number of authors and involve various mechanisms of extension along strike-slip systems. For example, Hutton (1 9 8 2 ) suggests that pull-apart jogs along a fault can create space for intrusions. Tikoff and Teyssier (1 9 9 4 ) put forth a model in which P - shears along a major strike-slip fault provide extensional regimes into which plutons are emplaced. Several other variations of 1 extensional geometries have been presented by Hutton (1 9 8 8 , 1992) and Ben-Avraham and Zoback (1992). The alternative to lateral growth of the crust is the transport of material in the vertical direction, resulting in crustal thickening (e.g., Paterson and Fowler, 1993a). One mechanism which involves vertical transport is stoping. When this process is active, rock from above the rising body is transferred to lower levels as it sinks within the magma. Another process which could add to the thickness of the crust is upbowing of the roof of the pluton, as in the case of a laccolith. Although perhaps a bit more complicated, flow around an ascending diapir is also essentially a vertical transport mechanism as material from above the body flows around the sides and then fills the space vacated by the diapir. Other mechanisms of emplacement are less clear cut in terms of the direction of material transport. In situ expansion of a body, often referred to as "ballooning," produces shortening parallel to the direction of expansion. Along the margin of such a body, material could be transported horizontally or vertically depending on the attitude of the intrusive contact at which country rock is displaced. In the case of assimilation or zone melting, there need not be material transfer in any direction. The volume of melt simply increases as the volume of solid rock decreases and no movement of material is required except th a t involved in circulation within the melt. Lastly, it should be noted that although each space making process carries certain implications, individual plutons are likely emplaced by some combination of mechanisms (e.g., Buddington, 1959; Paterson and others, 1991) which further complicates the issues discussed here. For plutons which result from crustal anatexis, as in the present study, no new material is added to the crust, and pluton ascent and emplacement involves only the redistribution of material within a crust of constant volume. However, the issue remains the same in that individual redistribution processes require either horizontal or vertical material transport. Note that for the ascent and emplacement of a magma that resulted from crustal anatexis, lateral material transfer at the level of emplacement would result in the growth of the upper crust at the expense of the lower crust from which the melt was derived, as illustrated diagrammatically in Figure 1. In this simple cartoon, the shaded block is melted in the lower layer and is emplaced in the upper layer by horizontal material transfer. Vertical material transfer would result in a volumetric balance between different crustal levels as material from the upper crust would trade places with an ascending melt. In spite of an ever growing body of research, pluton emplacement remains poorly understood. A number of studies have pointed to the fact that the contribution of processes involved in a single intrusion will likely vary with such parameters as depth, tem perature difference between the magma and the rocks it intrudes, tectonic setting, stress regime, magma and wall rock composition, extent of previous intrusions along a given pathway, Figure 1. Cartoon illustrating the movement of a melt (shaded block) from the lower crust to the upper crust by horizontal material transfer. etc. (e.g., Buddington 1959; Marsh 1982; Paterson and Fowler, 1993a). Understanding pluton emplacement is thus a m atter of determining the importance of various mechanisms for a given set of such physical and chemical conditions and attem pting to constrain how the contribution of each process changes with each parameter. Determining the emplacement mechanisms for a single pluton is limited by incomplete knowledge of the three dimensional shape of a body, as well as our inability to document changes in conditions below exposed levels. Bouguer gravity anomaly studies, such as Brun and others (1 9 9 1 ), have modeled plutons in three dimensions to depths of several kilometers. Although the authors of such studies claim that they can determ ine the gross morphology of a large igneous body, the solutions are dependent on assumptions about the density structure of both the pluton and surrounding couqtry ,rock, which weakens their conclusions. In addition, geophysical models can not give any information about country rock deformation, stoping, assimilation, or other specific processes that may make space for a pluton. These can only be determined and quantified through the examination of field exposures. Although the argument has been made that emplacement issues may never be fully resolved (e.g., Krauskopf, 1968), there remain facets of the topic that have not been fully explored and may give us important insights. One example is the lack of extensive emplacement studies in pluton roofs. The majority of field based emplacement studies have been conducted on plutons with steeply dipping intrusive contacts. Deformation along these pluton walls has guided our thinking in constructing and evaluating emplacement models. Yet many of these models have specific, testable implications for structures that should be present in pluton roofs. For example, models which call for ballooning or flow around an ascending diapir require margin parallel flattening above the body as well as along its sides, as modeled in experimental studies by Cruden (1 9 8 8 ) and Schmeling and others (19 88), and as illustrated in Figure 2. Another example is emplacement in extensional settings. As noted by Paterson and Fowler (1993 b ), pull-apart emplacement models geometrically require either significant extension of the roof rocks, or that the roof contact itself is a fault (Fig. 3). Other models for em placem ent also have implications for roof structures. Laccoliths should have bowed roofs or, in the case of punch laccoliths, be ringed by reverse faults. Emplacement by stoping should result in an irregular contact that truncates pre existing fabrics, or, given enough post-emplacement heat flux, recrystallizes the roof rocks. Assimilation or batch melting of country rock should result in roof zone migmatites and appropriate chemical signatures. The present study tests these emplacement models in the roof of the Hall Canyon Pluton, located on the western flank of the Panamint Mountains, California (Fig. 4). It also provides an example of the relative importance of various space making Figure i (1988). Streamline Number "i r i i i i i l l ii i i i m i i n 11 h 11 i i ri i riTr i i .1. 3 5 7 9 11 13 15 17 19 n 33 35 37 39 31 33 J5 37 I I I I I I I | || I 111 I I I I I I I I I H I " ' ' <>'"•' i+ in m u u u (CRUDEN, 1988) -• Flow around an ascending diapir as modeled b} Note flattening strains in the roof of the body. Cruden 7 Figure 3. Cartoon of extensional emplacement illustrating extended or detached roof (from Paterson and Fowler, 1 993b). Tucki Mtn Km 20 -O Stud/ Area Manly Peak pluton Figure 4. Location map showing the Death Valley region. 9 processes for the set of physical and chemical parameters exhibited in the Panamints. INTRODUCTION AND REGIONAL GEOLOGY The Panamint Mountains are located in southeastern California and bound Death Valley on its western side. They represent a structural block of the southern Basin and Range province and lie within the Cordilleran foreland fold and thrust belt. Evidence for east-vergent Mesozoic thrusting is preserved in the northern Panamints in the area of Tucki Mountain (Wernicke, 1988), as well as to the west and east of the study area. The Panamints also contain Mesozoic intrusive rocks, including the Jurassic Manly Peak pluton (Armstrong and Suppe, 1973) and the Cretaceous Hall Canyon pluton, which are considered to be easternmost expressions of the Mesozoic Sierran arc that lie to the west of the range (e.g., Labotka and others, 1985). The large-scale structure in the Panamint block is dominated by an asymmetric anticline with an eastern limb th at dips shallowly eastward and a steep western limb (Labotka and Albee, 1980). Basement rocks in the core of the fold are the oldest rocks seen in the range and are exposed just to the east of the field area (Fig. 5). Lower Proterozoic basement gneisses and schists of World Beater Dome (the anticline core as expressed to the south of the study area) have 207pb/206pb ages of 1,720-1,760 Ma (Silver, 1961) and U-Pb zircon ages of approximately 1,790 Ma (Lamphere and 10 Jail Canyon Hall CanyonV, m Basement ^ Eocambrian Rocks O Crystal Spring Formation [7] Hall Canyon Pluton ( 2 Beck Spring Dolomite □ Quaternary Sediment □ Kingston Peak Formation Q]) Cenozoic Breccia Figure 5. Map of the west central Panamint Mountains including the Hall Canyon pluton (simplified from Labotka and others, 1 985). 11 others, 19 64). The latter study also analyzed a quartz monzonite exposed in the basement that yielded a U-Pb zircon age of 1,350 Ma. The basement is unconformably overlain by the late Proterozoic Pahrump Group, which is in turn unconformably overlain by Eocambrian and younger rocks associated with the initiation of the passive margin sequence (e.g., Labotka and Albee, 1980; Miller, 1985; Fig. 6). The west-central portion of the Panamint Range has been complexly deformed and affected by at least two episodes of Mesozoic metamorphism — one in the Jurassic and a second in the Late Cretaceous (Labotka and others, 1985). Intrusion of the Hall Canyon pluton occurred between these two events, although it may overlap with the earlier portions of the Cretaceous event. The Mesozoic history of the region is discussed in detail below, but the age of the major anticline that cores the range is Mesozoic and related to folding in the study area, as one limb is intruded out by the Hall Canyon Pluton. The Cenozoic history of the Panamint Range is dominated by low-angle normal faulting that has cut through the Panamints creating a series of large-scale blocks, or allochthons within the range (Hodges and others, 1990; Fig. 7). The time at which extension began is not well constrained. The Harrisburg fault is thought to be the oldest of the system and has a minimum age of 10.6 Ma -- the age of the Little Chief Stock, which truncates the fault (Hodges and others, 1990). A maximum age of ~ 1 0 0 Ma is given by an Rb-Sr errorchron for the Skidoo Pluton, an apophysis 12 o c a 2 < O 77- Z < a a 2 < O U J a c & ZABRISKIC OUARTZITC J s S d P j P W i ? ' WOOD CANYON FORMATION 8TMLINQ OUARTZIT8 1 • • . t . JOHNN4C FORMATION NOONDAY OOtOMITE P A H R U M P GROUP KINGSTON PSAK FORMATION m+ ^ . ^ W “ • • 1 s « * B E C K 8 P R I W ® © © L O W f ® CRYSTAL SFRMO FORMATION 1 4 * * K tf % V •QNCOUS AftS O MSTAMORRHie ROCKS > 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 - 0 0 0 0 0 0 0 f 0 0 0 0 0 0 0 >5000 : >4000 •3000 2000 1 0 0 0 0 m Figure 6. Stratigraphy of the Death Valley region (from Miller, 1985). 13 Km ■A ' ////////; y h b rn s tx irg A 4 F a il y . <&/ / / / / / % Hall Canyon; Pluton f>^ J L ittle Chief) y / s Stock y/////////// ^ Upper Allochthon Middle Allochthon H j Lower Allochthon Parautochthon Figure 7. Allochthons, extensional faults, and intrusives of the northern and central Panamints (simplified from Hodges and others, 1989). of which is locally cut by the fault, although evidence from the Death Valley area as a whole suggests that extension did not begin until the Miocene (Hodges and others, 1990). The Hall Canyon Pluton and the present study area lie in a structural block between the Harrisburg and Emigrant Fault systems as illustrated in Figure 7. Separation of the Panamint block from neighboring ranges by Basin and Range-style extension represents the most recent deformation in the region. One facet of the Cenozoic history of the area that is relevant to the present study of Mesozoic events is the amount of tilting associated with normal faulting of the range. As the intrusive contact is currently at a very shallow dip, large Cenozoic rotations would make it a wall contact instead of a pluton roof and thus effect the interpretation of structures and relationships along the contact, (see cross sections presented as Figs. 13 and 14). A number of attempts have been made to quantify the amount of tilting in the Panamint Mountains (e.g., Labotka and Albee, 1990; McKenna and Hodges, 1990). Although these studies sometimes attem pt to extrapolate tilting estimates to the whole range, the restoration of attitudes of Mesozoic structures may differ in the various allochthons that make up the range. Furthermore, if extensional faulting produced a rolling, antiformal hinge in the lower plate (e.g., Wernicke, 1990), the amount and direction of tilt would vary in the range depending on the position of the hinge. In the block containing the Hall Canyon pluton, Labotka and Albee (1 9 9 0 ) used a lack of pressure variation in metamorphic 15 mineral assemblages across the central Panamints to infer that eastward tilting could not have been greater than 15°. Nibler (1 9 9 1 ) suggests that this part of the range may have been tilted up to 35 or 40° to the east based on the orientation of east dipping, compositional sheeting at the contact between the two main phases of the Hall Canyon Pluton. A further constraint on tilting comes from the attitude of the right-lateral shear zone discussed below. This feature currently dips an average of 50° to the west. If it restores to vertical, an eastward tilt of 40° is implied, although this is very conjectural. Several studies have attem pted to constrain tilt in other allochthons within the Panamint Mountains. For example, McKenna and Hodges (1 9 9 0 ) estimated eastward tilts of 5-25° based on the attitudes of late Tertiary volcanics on the eastern flank of the range. Although estim ates such as this one contain less uncertainty than those discussed above, they do not pertain directly to the block in question. None of these estimates give a firm or reliable value for tilting within the block that contains the Hall Canyon Pluton. Consequently, it should be emphasized that the roof of the pluton may not be in its original orientation. The roof contact currently dips an average of 4° to the east; using the values given above, the restoration of Tertiary tilting gives the contact a maximum westward dip of roughly 30-35°. In spite of the uncertainty, this maximum dip allows that the country rocks in the area are the roof rocks of the pluton, as a dip of 35° would still represent an area 16 that is largely above the pluton. Supporting evidence for this conclusion include features along the contact and geochemical trends in the pluton, both of which are discussed below. PREVIOUS WORK Metamorphism Labotka and others (1 9 8 5 ) used Ar-Ar dating of micas and hornblendes to conclude that two distinct metamorphic events effected the Pahrump Group and overlying eocambrian rocks in the Mesozoic period. Cooling from the first event occurred in the Jurassic from 170 to 150 Ma, and cooling during a second, retrograde metamorphism has been assigned to the late Cretaceous with ages ranging from roughly 80 to 55 Ma. There is no spatial trend in cooling ages for the Jurassic event. The Cretaceous data may be interpreted as having younger ages to the west and older ones to the east, but this is based on only four samples along a transect that runs roughly north-south, as shown in Figure 8. In addition, the 25 My age range includes rocks that have been effected by a large, right-lateral shear zone (discussed later) and thus include multiple events. Nonetheless, a westward progression of cooling is consistent with the thermometry discussed below. The Jurassic event metamorphosed the rocks to lower amphibolite facies, and, although the Cretaceous event locally reached similar tem peratures, it is expressed in retrograde textures and 6 6 + 3 B • 6 6 ± 3 M 5 5 ± 2 B 61 ±3 M i in Jail Canyon Location of U-Pb Sample Hall Canyon 80±1 B 66 ± 2 M Surprise Canyon World Beater( . Dome . 0 Basement f2 £3 Crystal Spring Formation Q ca Beck Spring Dolomite [~] 1 I Kingston Peak Formation [Tf| 66±2M Ar-Ar Age i n Muscovite 6 6 ± 3 B Eocambrian Rocks Hall Canyon Pluton Quaternary Sediment Cenozoic Breccia Ar-Ar Age in B iotite Figure 8. Map of the central Panamints showing Cretaceous Ar-Ar dates (Labotka and others, 1985) and the location of U-Pb sample. 18 assemblages, or simply the preservation of Jurassic mineralogy (Labotka, 1981; 1987). Temperature and pressure constraints Mineral assemblages associated with the Jurassic event indicate increasing temperatures to the west (Labotka, 1981; Labotka and Albee, 1988). Isograds for this prograde event, taken from Labotka (1 9 8 1 ), are plotted in Figure 9. The intersection of sillimanite and diopside isograds is attributed to variable percentages of water in metamorphic fluids. Garnet-biotite thermometry indicates maximum temperatures of ~650°C near the Hall Canyon pluton with temperatures decreasing to the east in a thermal gradient of greater than 50°C/km (Labotka, 1981). Note that this gradient is unrelated to the pluton, which was not emplaced until the Cretaceous. Presumably, the Jurassic gradient is a result of the Jurassic arc that was active to the west at this time. The Manly Peak pluton of the southern Panamints, which has yielded a Jurassic K-Ar age, may be an expression of this arc (Armstrong and Suppe, 1973). Cretaceous, retrograde metamorphism shows similar trends. Retrograde textures are most intense in the core of the anticline with tem peratures increasing rapidly to the west and locally exceeding that of the Jurassic event (Labotka 1981; Labotka and Albee, 1990). These studies attribute the Cretaceous gradient to 19 Jail Canyon NSSS: ^ \ S S l W \ \ \ Hall Canyon / - ■ . • • f y - ■ \ \ \ \ V . ■ • / y s . • * Surprise Canyon \ L World Beater Dome m Basement □ Eocambrian Rocks E3 Crystal Spring Formation □ Hall Canyon Pluton 0 Beck Spring Dolomite □ Quaternary Sediment □ Kingston Peak Formation cn Cenozoic Breccia Sillimanite Isograd s * % t Diopside Isograd Figure 9. Map of the central Panamints showing metamorphic isograds (simplified from that of Labotka and others, 1985). 20 contact metamorphism associated with the intrusion of the Hall Canyon pluton and the Cretaceous arc. Constraints on pressures during metamorphism are not robust, but are important in estimating the depth at which the Hall Canyon pluton was emplaced, as well as characterizing the metamorphic conditions. Attempts at barometry for both Jurassic and Cretaceous events have suffered from a lack of appropriate assemblages and poorly constrained equilibrium constants (Labotka, 1981; Labotka and Albee, 1 9 8 8 ). Stratigraphic reconstructions offer the best estim ate and indicate that approximately 10 km of section would have overlain the area in the Jurassic; mineral assemblages associated with the Jurassic metamorphism are consistent with a depth of 10 km (Labotka and others, 1980; Labotka, 1981; Labotka and Albee, 1981; 1990). However, this value gives only a rough constraint as the overburden could have been thickened during Jurassic thrusting (e.g., Dunne, 1986; Saleeby and others, 1992) Cretaceous pressures are less constrained. Jurassic estimates may not apply as the amount of thickening from thrusting and thinning from erosion is not known. Mineral assemblages associated with the Cretaceous, retrograde event are permissive of a 10 km depth, but do not provide any quantitative constraints (Labotka, 1981; 1 9 8 7 ). Another possible way to constrain Cretaceous pressures (and depth of pluton emplacement) is the presence of muscovite in the pluton. Although this normally implies a minimum pressure of roughly 3 kb (e.g., Zen, 1988), the 21 abundance of ferric iron in the muscovites allows for a lower minimum pressure (Labotka and Albee, 1990 ). For example, if ferric iron content shifts the stability curve of muscovite by 50°C, the minimum pressure would be 2 kb (Zen, 1988). Ductile textures in the latest Cretaceous mylonitic shear zone, discussed below, indicate that the rocks were not near the surface, but, again, do not give a well constrained depth. Subsequently, although previous studies have assumed that emplacement occurred at a depth of 10 km (e.g., Labotka and Albee, 19 90), this estimate should be considered to have an error of at least ±3 to 5 km. Petrology and geochemistry of the Hall Canyon pluton The Hall Canyon pluton is a composite body. It consists of a lower, biotite-muscovite phase and an upper phase containing only muscovite (Nibler, 1991; Fig. 10). The contact between the upper and lower phases is characterized by a narrow zone of interlayering in sheet-like bodies, although some areas where the contact is more sinuous were noted in the present study. The gradational nature of some sheet contacts led Nibler (1 9 9 1 ) to conclude that both phases were molten at the same time. The geochemistry of rocks along the boundary between the main phases is consistent with mixing of the two phases (Mahood and others, in press). Near the pluton-country rock contact, the upper phase contains magmatic garnets and is sometimes pegm atitic. Pegmatitic and aplitic dikes are also common along the contact and 22 -1400 UZ -IOOO L Z Figure 10. Cross sectional view of pluton phases as mapped by Nibler (1991). Location of the cross section is similar to that of Figure 13. 23 in adjacent country rocks. Detailed study of compositional variations between and within different phases was conducted by Nibler (1 9 9 1 ) and Mahood and others (in press). These studies showed that the lower phase was fairly homogeneous in major and trace element composition; the upper phase is zoned, with an enrichment in S1 O2 and Rb and depletion of Mg, Fe, Ti, Ba, Zr and Sr as the roof of the intrusion is approached. These trends imply fractionation of the upper phase with more evolved melts closer to the roof of the intrusion. Fractionation of plagioclase from the upper phase is also implied by rare earth element trends which show a negative europium anomaly (Griffis, 1987). The lower phase exhibits a positive europium anomaly leading to the inference that the two phases may have originated from different source rocks (Griffis, 1987). This conclusion is supported by the occurrence of higher initial 87S r /86Sr and lower £Nd values in the lower, more mafic phase relative to the upper phase (Nibler, 1991). Evidence of a crustal source for the Hall Canyon pluton is found in several studies of its geochemistry. REE concentrations for the body are consistent with a crustal source (Griffis, 1987), as are initial 87S r/86Sr values, which are as high as 0.736, and eNd values, which are as low as -19.0. (Nibler, 1991; Mahood and others, in press). The heterogeneity of trace elem ent compositions for this suite of rocks is also in line with crustal sources for the two mica granites of the region (Griffis, 1986). Mahood and others (in press) conclude that there is no evidence for 24 a mantle component and that possible sources include partial m elting of m etapsam m ites and dehydration m elting of intermediate composition rocks, such as biotite-hornblende gneiss or tonalite. Studies of similar muscovite-bearing plutons to the north in the hinterland of the fold and thrust belt have suggested that this suite of Cretaceous intrusives was derived from crustal melting at depths as shallow as 20 to 25 km (e.g., Miller and Bradfish, 1980; Snoke and Miller, 1988). These studies are based on the presence of migmatites in rocks from these depths (Snoke and Miller, 1988) as well as thermal modeling of the region as a whole (Barton, 1990). Miller and Gans (1 9 8 9 ) suggest that wet granite melting conditions may have been reached at depths as shallow as 15 km in central Nevada. Age of the pluton Labotka and others (1 9 8 5 ) dated two samples of the Hall Canyon pluton using the Ar-Ar method. Muscovite in a sample from exposures in Surprise Canyon (Fig. 8 ) yielded a flat spectrum corresponding to an age of 66 ± 2 Ma. The second sample was from Jail Canyon and gave a muscovite age of 61 ± 3 Ma and a biotite age of 55 ± 2 Ma. As these values were treated as cooling temperatures at an assumed depth of 10 km, the authors concluded that the pluton crystallized between 70 to 80 Ma. 25 However, this line of reasoning is somewhat suspect. A large shear zone, discussed in a later section, cuts through the area. Exposures in Jail Canyon show intense, ductile deformation which would have effected Ar-Ar systematics. Ar-Ar values from this area should, therefore, be viewed as relevant only to the age of the shear zone, not to the age of the pluton. Surprise Canyon exposures show only minimal deformation, but, based on the trend of the shear zone, were likely proximal to this feature. The Surprise Canyon sample could also have been effected thermally by the Cretaceous metamorphism that is present in the area and at least partially post-dates emplacement. Nonetheless, Mahood and others (in press) recently calculated Rb/Sr and Sm/Nd isochron ages for the upper phase of the pluton, attaining values of 7 2 .8±0.8 and 7 2 .3 ± 1 2 .8 Ma, respectively, which makes a Late Cretaceous age likely. DATA The present study focused on structural aspects the area. Mapping was conducted at a scale of 1:8,000 and was concentrated in the country rocks. Several transects into the pluton were also made, but it was not as extensively mapped due to steep topography. Over ninety thin sections were made and examined, predominantly from samples of the Kingston Peak Formation. In addition, the zircons from the pluton were dated using U-Pb techniques. 26 Country rocks Country rocks in the study area include the Late Proterozoic Kingston Peak Formation, its basal conglomerate, and a few exposures of the underlying Beck Spring Dolomite (Fig. 11). The Kingston Peak Formation varies in thickness and composition throughout the Panamint Range (see Miller, 1985 for a more complete discussion). In the vicinity of the Hall Canyon pluton, it is composed of calc-silicate and pelitic schists with rare beds of quartzite and marble. Amphibolites (metabasalts) are also present in the Kingston Peak Formation and appear to have been involved in all episodes of deformation. The present study focuses on the calc-silicate and pelitic schists. Pre-Pluton Deformation Field mapping and thin section analyses have revealed a minimum of four generations of deformation/metamorphism which clearly predate intrusion of the pluton. These episodes are expressed as follows: 1) m icrostructural evidence for a metamorphic fabric that predates the compositional banding (D1), 2) formation of compositional layering which is the most visible fabric in the area (D2), 3) tight to isoclinal folding of D2 on all scales into west-vergent, recumbent folds and resulting in the dominant mineral alignments (D3), and 4) west-vergent folding of 27 Figure 11. Simplified geologic map of the Hall Canyon pluton and overlying country rocks (see Plate 1 for greater detail). 28 Beck Spring Dolomite | 1 | Kingston Peak Conglomerate | | Kingston Peak Schist Hall Canyon Pluton [A 1 Cenozoic Breccia I | -Quaternary Sediment a \ ure13 W ure 14 V o s \ N \ N K \ \ S / / / / /! A / / \ \ \ \ VA v \ ' / / / / / / / i' / / / / / / / \ N X S N N N \ ' / / / / / / / SX X\ \ N\ S ' / / / / / N S t \ \ \ ' / / > ^ J s s s D3 axial surfaces on at least the meter scale and larger (D4). It is probable D3 and D4 represent a continuous event. Older deformations (D1 and D2) may also be continuous with this event, but are considered separately as evidence to evaluate their continuity has not been found. D1 Microfabrics visible in thin sections from the area show that the compositional bands in the Kingston Peak Formation formed axial planar to crenulations of an earlier foliation. Crystals within microlithons that are parallel to D2 layers occasionally exhibit weak preferred orientations that are at an angle to the layers themselves. The orientation of oblique fabrics will shift within an individual thin section and may represent limbs of a pre-existing crenulation. This fabric is defined primarily by actinolite, but is also expressed by biotite and muscovite. In a few cases, candidates for fold noses in muscovite-rich layers are preserved. Further evidence for D1 can occasionally be seen in the strain shadows of porphyroblasts where oblique mica alignments may define a fabric that predates the banding. In most instances, D1 structures have been obliterated by D2 and subsequent episodes of deformation. 30 D2 This event resulted in a well defined, compositional layering in the Kingston Peak Formation. Centimeter- to millimeter-scale bands rich in biotite and actinolite are common in calc-silicate beds. In more pelitic units, amphibole-rich layers are absent and muscovite-rich bands are common. Layers are also defined by differences in the amount of quartz, plagioclase, and potassium feldspar. Mineral foliations, which are related to D3-D4, commonly crosscut D2 banding. However, in cases where D2 is isoclinally folded, banding and mineral lineation can be subparallel. In these cases it is not possible to determine the age of the mineral alignment as it may be related to D2, D3-D4, or possibly both. The orientation of D2 banding is discussed below, as it has been effected by subsequent folding. D3-D4 D3 and D4 represent folding and refolding of D2 compositional bands. The two are considered together as they appear to have formed during a single progressive, non-coaxial deformation. D3 folds are generally tight to isoclinal, west- vergent, and recumbent in orientation; D4 folds are open, west- vergent and have axial planes that dip to the east. The distinction between the two is in some cases artificial in that D3 structures which did not reach recumbent attitudes will have east-dipping 31 axial surfaces and are generally more open. In such cases, it is assumed that deformation was not as intense as in cases where clear refolding occurs. Conversely, D4 structures are only recognizable where they openly refold D3; intense D4 folding would be difficult to distinguish from D3 deformation as it could approach recumbent attitudes. Nonetheless, the division into separate events is useful in cases such as illustrated in Figure 12, where axial surfaces of D3 folds are refolded by D4. D3 folding is disharmonic and, at least on the large-scale, clearly non-cylindrical. Folds are superimposed on all scales. Wavelengths of centimeters to hundreds of meters are visible in the field, and mapping indicates the presence of at least one large anticline that folds the rocks on the kilometer scale (Fig. 13 - locations of cross sections are indicated on Figure 11). In the schists exposed in this northern portion of the area, smaller folds with wavelengths on the scale of meters to tens of meters dominate. To the south of Hall Canyon, several anticline-syncline pairs are visible as the dominant wavelength shifts to a scale of one hundred to several hundreds of meters (Fig. 14; Plate 1). Typical attitudes of D2 banding in the area are illustrated in Figure 15. A complete map including all D2 data is included as Plate 1. Note that these attitudes do not always represent mineral foliations, which are sometimes oblique to the D2 compositional bands. As the obliquity of the mineral foliation is often slight, it is generally only visible in thin section or in the noses of small scale folds. 32 4 Figure 12. Photograph and outcrop sketch of refolded folds in the Kingston Peak Formation. Axial traces of D3 and D4 folding are indicated with dashed lines. View is looking south and shows west-vergent nature of D4 folding. Vergence of D3 folds is not illustrated in this Figure. 33 K/j Beck Spring Dolomite lM KingstonPeak Conglomerate □ KingstonPeak S c hist HaliCanyon Plutcr. □ Quaternary Sediment s * s / v ✓/>• > / / 7— r s s / v ^ / / / ✓ x / i s s s ✓ ' / \ / \ y \ \ V , \ \ \ \ \ s \ \ \ s s \ \ N ^— ■ / - r - X \ \ \ n \ A ><> / / > — 7 - > \ \ S \ ' \ S s A v \ N > 1 s, \ \ \ > V / • > * X// / S / S V / / / / / / > ' / / / / / / / ' / / / / si s s / s s / s s / s r N Y y > . A \ ,v v \ \ / . ,' w N ' s V N s r \ s \ \ ' r > . \ \ . s \ \ \ \ s \ N . \ \ \ N ' >■ / /A* / ✓ ✓ // //✓ / / !*' s s f / J / z s / . J / s s / s / s / s s / s s / s / s s s / x \ \ /\\y\.\j. \ A\ \ x y \ \ \ \ 7 \ s \ \ A \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ - / j /Is y / s / f M / i / t / s j /is s / s l s / s s / s s s s s s s s / s s s s s s s s s s s v / 1 ? ' / s, ' / *. s , //s s /s js s 7/ / f s s s s ; s s s s s s s s s s / s s / s s s s s / // / / / / •' jr \ V \ / \ \ A ,< *S.'N \ \ / / ” / < v s s i s / / s s , / 4 s s s s s i s / l / s s s s s s s s / s s / s s s / s s / s / / s s l f f * t / j * f j / / f / / / f / l / / t f / F J / / / l / S S S S S / S S / S p / / S / S S S S S S ' \ s \ A X \ A \ / \ \ / \ y y \ \ > . N A s s / \ \ \ \ s s \ \ \ s s ' . s \ v \ \ n \ \ \ \ \ \ \ * • s//. s t / s / s// s // s/s/s s si s r sis s /,/ s /s s s/ s /s / /. * / / / / / / / / / / n v \/\ x > \ s \ A \ X \ \ \ \ \/\ s \ A \ \ A \ \ \ \ \ \ n \ \ \ \ \ v \ n \ \ \ \ \ \ \ // S S S & S S S S S / S S S S S F S S S S S / S S / S S S S S / S S S ' S S * / / / < ■> «>______________________________ KM . /2 Figure 13. Cross sectional view of the northern portion of the Hall Canyon area. Form lines are drawn from the projection of actual beds in the natural cross section of Hall Canyon itself. Lines in the pluton indicate the presence of shear zone deformation. Location of section indicated on figure 11. w E . / : V H Kingston Peak Conglomerate 7 j ,—1 Q Kingston Peak Schist ^ N ' x ^ v Q Hall Canyon Pluton 1 ^ ^ N % ' ~ " } t < v ^ - - - - 0 Km 1 /2 ~ ~ \ \ L » *............. s f A A A A A » XV ✓ > * \ f / X \ \ \ » S S \ \ S \ \ \ '• » . > r ^ \ ^ S \ \ \ s, 1 , J. . f X a a a Ia a a a a s a a a a a a a a a , / / / / / / ^ ✓ / / ? t ^ . _ \ \ \ \ V \ N \ \ N \ \ \ \ \ \ \ \ \ \ \ S \ \ \ \ \ >T\ t V \ \ \ \| _ , ■ / , / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /* ■ ! -*• / / / / / \ / r^> / / _ - N \ J » \ \ N \ V S \ \ S \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ S \ \ \ S \ \ \ \ \ \ \ \ \ A V \ \ \ \ \ >7 a a a a a a a a a a a a a a a a a a a / a a a a a a a a a a a / a a a / a a a a a a a a a a a a X s / \ \ K \ \ \ k \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ s \ \ \ \ \ \ s s \ \ \ \ \ s \ \ \ \ \ \ \ \ ^ A ' A A/ AAA a[ A A A A A A A A A A A A A / A A A A A A A A A / A A / / A A A A A A A A A A A A A A ^ _ —TV A l A A f A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A > T AA* A! A A A a[ a > A, A l A A f A A A A A A A A A A A A A A A A / A A A A A A A A A A A A A A A A A A A A A A A A A / A , -^7 A A JA A A A\A V A A A f A A A ' A A A A A A A A A A / A A / A A A / A A A A A A A A A A A A A A A a A A A A A A A A A A A A A A A A A A A A A lA l A t A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A / A l A A J A l A A A A i A A l A A V A A A A 4 A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A ^ r \ / \ S y V \ S S / \ A s S / \ N S \ . S S N N \ \ \ S \ \ V . \ N S \ \ \ S \ S S S N S \ S \ \ \ \ N \ N \ S S \ \ \ \ \ S \ N N \ \ \ \ /=) / /• / / / / i / / / / , / 4 A AjA A, A A\ A Y A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A . A / A JA A aF A A A A a a[ a a a AlA / A A A *A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A / A Figure 14. Cross sectional view of the southern portion of the Hall Canyon area. Form lines and attitudes of the pluton contact are schematic. Lines in the pluton indicate the presence of shear zone deformation. Location of section indicated on figure 11. Figure 15. Map showing attitudes of D2 layering. T y Beck Spring Dolomite U Kingston Peak Conglomerate | | Kingston Peak Schist |y { Hall Canyon Pluton P H Cenozoic Breccia [~~] Quaternary Sediment /a Country Rock Foliation N A S N. V \ V A \ \ S ' t ss s ss /s s s I V \ S V . \ S S N \ W \ / s s s s s s s s f , . \ i /'V ''V 'V 'V 'V 'V 'V N /T ' 7 0 S \ S S \ \ \ S J *• * S S Av/ s S S / s \ t \ s \ * s s VJ s s s * 37 Stereonets that describe the folding are presented in Figure 16. Figure 16A is a plot of poles to D2 banding in the schists and basal conglomerate of the Kingston Peak Formation for the entire field area. It illustrates consistent folding about a subhorizontal, north-trending axis. Because of the continuum between D3 and D4 structure, this plot represents both deformations. Figure 16B includes only poles to clear D4 axial surfaces in the Kingston Peak Formation and shows the consistent, eastward dip of these surfaces. Foliations within the Beck Spring Dolomite, which underlies the Kingston Peak Formation, are also consistently east- dipping as depicted in Figure 16C. The similarity between Figures 16B and 16C suggests that fabrics in the Beck Spring Dolomite are the result of D4. In thin section, D3 and D4 fabrics are manifested in a variety of ways. These include any or several of the following: 1) growth of biotite along axial surfaces of folds and oblique to D2 layering, 2) penetrative alignment of quartz and feldspars parallel to axial surfaces, 3) crenulation of D2 banding and 4) limited west-vergent S-C fabrics resulting from slip between layers or bands. Although crystals do show preferred orientations, they rarely exhibit any internal strain, such as undulose extinction or subgrain formation. It is therefore likely that metamorphism associated with this episode outlasted deformation, allowing the crystals to anneal. The character of grain boundaries is also consistent with annealing The Kingston Peak Formation in this area was also strongly lineated during D3-D4 folding. In pelitic and calc-silicate units, 38 A) Equal Area ........ I l t f i i J t li ' ■ 1 * [ s & i i i l i M W S U .i. •'•••jih jiji'ijij!*'** ij'fijiii F 1 " * ' .... / N * 373 C) Equal Area B) Equal Area C.l.» 2.0 sigma i p i i j i i i i * , t !iii!i!iii!*‘ im l * S * 1 * 1 * 1 liliiiiililj! li-llP iir - E S iilllilf l " iV * Mif r . 'iiijljllill! • W l f r & l l j ! « ! ■ ' ! M i l life* i J jjj 1 J M jj i j ' i W i ’ i j ! i L i . - ' i t i f P u ! - . . ! - i‘ i« : i n j t , Iji'i'iji l i j l i i i i ! f III 4 1 1 1 1 1 : 1 j j i g j i ' l l ' : l ft l:i N * 16 C.l. = 2.0 sigma N = 12 C.l. = 2.0 sigma Figure 16. Kamb contour stereonet plots of country rock data. (A) poles to D2 layering, (B) poles to axial surfaces of D4 folds, (C) poles to foliation in outcrops of the Beck Spring Dolomite. 39 the lineation is defined by elongation of micas, quartz, and to a lesser extent, feldspars; in the basal conglomerate, pebbles and cobbles are also elongate. A stereonet of D3-D4 country rock lineations in the area (Fig. 17 ) illustrates the consistent, subhorizontal, north-south trending attitude of the lineation, which is parallel to the axis of D3-D4 folding. The distribution of lineations are indicated in Figure 18, with a complete map of lineation data included as Plate 2. Metamorphism Mineralogy of the Kingston Peak metamorphic rocks A summary of minerals present in schists of the Kingston Peak Formation, based on thin section analyses, is presented in Table 1. Quartz and biotite are uniformly present, with muscovite and feldspars also common. Distinguishing between plagioclase and potassium feldspar is often difficult given the small crystal sizes, but both are clearly present in a significant number of samples. The presence of potassium feldspar was confirmed on -1 0 of the samples by staining rocks with sodium cobaltinitrite. Actinolite is prevalent in most calc-silicate samples, often occurring in millimeter- to centimeter-scale bands. Clinozoisite is also common in calcium-rich rocks, primarily as a fine grained matrix mineral, but also rimming epidotes which grew as 40 EqualArea C.l. = 2.0 sigma Figure 1 7. Kamb contour stereonet plot of all D3-D4 country rock lineations. 41 Figure 18. Map of D3-D4 country rock lineation. 5 H □ 0 0 □ M t Beck Spring Dolomite Kingston Peak Conglomerate Kingston Peak Schist Hall Canyon Pluton Cenozoic Breccia Quaternary Sediment Wall Rock Lineation \ \ \ S X X s s s A \ s s . X X X X X X ' ^ s / s X X X > X X X ' s s S O y / s X X X X X X X V V S // \ \ x x x x x x x x X * Table 1. Minerals Present in Schists of the Kingston Peak Formation Sample ID quartz biotite muscovite chlorite K-spar plagioclase actinolite hornblende 38 A X X X X X X 39A X X X X ± 39B X X X X ± 40A X X X X 43D X X X X 51 X X X 69 X X X X 72wr X X X 85 X X X X + 90 X X X X + 120 X X X X X 151 X X X X + X 162 X X + X X 163 X X X + X 164 X X X + X 1 65 X X ± X X 1 66 X X + X X 167 X X + X 168 X X X ± X 169 X X + X X 203b X X X X X 213A X X X X 273 X X 275 X X X di X 275B X X X X 279 X X X 280A X X 299 X X X X 300 X X X + + 305 X X X i + 403 X X X X 404 X X X X 405 X X X X 406 X X ± X 407 X X X 408 X X X X + + 409 X X X X X X 410 X X X X X 412 X X X X X 431 X X X X 432 X X X X Table 1 (cont.). Minerals Present in Schists of the Kingston Peak Formation relict Sample ID clinozoisite epidote graphite garnet cordierite calcite sphene sillimanite 38 A X X X X X 39A X X 39B X 40A X X X X 43D X X X 51 X 69 X X X 72wr X 85 X X 90 X 120 X 151 X X X X 1 62 X X X 1 63 X 1 64 X X X 1 65 X X X X X 166 X X X X 167 X X X 1 68 X X X 1 69 X X X 203b X 213A X 273 X 275 X 275B X 279 X 280A X X X 299 X 300 X X 305 403 X X X 404 X 405 X 406 X X 407 X 408 X 409 X 410 X X 412 X 431 X 432 X X porphyroblasts. The dominant opaque in nearly all of the schists is graphite. All of these minerals, with the possible exception of clinozoisite rims on epidote, are characteristic of the prograde, Jurassic event as discussed by Labotka (1 9 8 1 ). As illustrated in Figure 9, rocks in the study area were heated above the sillimanite and diopside isograds as defined by Labotka (1 9 8 1 ). He further divided prograde assemblages into a series of four facies, as presented in Figure 19. Although metamorphic assemblage data were not collected in the present study, samples generally fall in the highest grade of these facies (facies IV), which is consistent with Labotka's interpretations of increasing grade to the west. Prograde minerals appear to have grown synchronously with folding of the rocks (D 3-D 4). Biotite, muscovite, quartz, feldspars, graphite, and matrix clinozoisite can all be found aligned parallel to the axial surfaces of these folds. Evidence of the retrograde event, is more limited. This is attributable to the fact that temperatures in the study area were similar for Jurassic and Cretaceous events (Labotka, 1981), the Cretaceous "retrograde" event simply preserving previous mineralogy. Nonetheless, there are some indications of retrogression. The clearest of these is tied to the occurrence of chlorite. The transition to facies IV is marked by the disappearance of chlorite (Labotka, 1981; Fig. 19). Thin section analyses in the present study have shown that where chlorite occurs in the area, it is often replacing biotite and is thus 46 m ic r o d in e 1 1 o FeO MgO chlorite Ilia m i c r o c / i n e g a m e / a n o r t h i t e 1 1 & m u s c o v i t e b i o t i t e a m p h i b o / e MgO m ic r o d in e a m p h i b o / e \M gO f h t o r it e a n o r t h i t e I Va m i c r o d i n e g a r n e t . Illb b i o t i t e p i o p s i d e p m p h i b o t e MgO a n o r t h i t e g a r n e t i F eO / c h l o r i t e \MgO b i o t i t e a m p h i b o / e IVb m u s c o v i t e m u s c o v i t e g a r n e t \ FeO MgO ' b i o t i t e g a r n e t FeO / b i o t i t e VMgO a m p h i b o t d i o p s i d e Figure 19. Metamorphic facies series of Labotka (1981). Roman numerals in (a) and (b) represent the same facies, with IV being the highest. 47 attributable to the retrograde event. Evidence for fluid flow can also be seen in the distribution of chlorite. The alteration of biotite to chlorite is often preferentially expressed adjacent to veins or to fracture surfaces, indicating the importance of fluid flow to retrograde reaction. Indications of fluid flow through the schists are common. Veins containing potassium feldspar, clinozoisite, calcite and occasionally sphene pervade the pelitic and calc-silicate rocks. Other evidence for the retrogression of minerals can been seen in garnet and sillimanite porphyroblasts. Garnets often appear as irregular relicts in small pods that do not contain the fabrics seen in the matrix of a sample. The simplest explanation of these textures is the retrogradation of the garnets. In fact, Labotka (1 9 8 7 ) illustrates that garnet and chlorite do not coexist under equilibrium conditions; the two minerals are found in a number of samples as shown in Table 1. Usually the garnets in these samples are only relicts of once larger porphyroblasts suggesting that garnet was reacting to form chlorite. Sillimanite is rare and consistently replaced by white mica, which according to Labotka (1 9 8 7 ) is yet another expression of the Cretaceous retrograde event. A more detailed discussion of porphyroblasts and their timing is given below. A few small portions of the intrusive contact in the Hall Canyon area preserve narrow zones of hornfelsic texture. Where present, this aureole is usually only several centimeters thick, although occasionally it can be found as thick as several meters. 48 In thin section, hornfelsic rocks are characterized by abundant actinolite and chlorite that have replaced biotite and grown in random orientations. Porphyroblasts Schists of th e Kingston Peak Form ation contain porphyroblasts of epidote, garnet, cordierite, sillim anite psuedomorphs and hornblende. All of these minerals exhibit relationships indicating that the minerals grew prior to D3-D4 folding of the rocks. Biotite, muscovite and quartz crystals aligned parallel to D3 foliations wrap around each of the porphyroblasts. This places porphyroblast growth before D3-D4 deformation, or at least towards the beginning of that event. Garnets, which are by far the most common porphyroblast, often contain inclusion trails that are oblique to mineral alignment associated with D3-D4 deformation. Cordierite can also be found with aligned inclusion trails at an angle to these fabrics. In some cases, these internal fabrics are parallel to compositional banding (D 2) and in others the fabrics are oblique to this texture as well. In general, included fabrics are not curved, implying a straight overgrowth onto a previous foliation without syn-deformational growth of the garnet or cordierite. In rare cases, a slight curvature of inclusions trails could be argued for at the margin of a garnet. It is unclear whether included fabrics are related to D l, 49 D2 or perhaps both. The timing of garnet and cordierite growth is therefore constrained only as post-DI and pre-D3. Some garnets may have had two phases of growth. In a few samples scattered throughout the field area, garnets can be seen with inclusions in their cores and rims that are inclusion free. The rims could have grown in continuum with the cores and be the result in a change in the growth kinematics of the garnet. Such changes could include an increase in rates of diffusion of material peripheral to the garnet, changes in the composition of the fluid phase, or a slowing of porphyroblast growth rate (e.g., Kerrick and others, 1 9 9 1 ). Alternatively, they could be the result of a subsequent growth episode, related to Cretaceous heating. No clear means of distinguishing the two possibilities is available without detailed geochemistry. Although matrix minerals do wrap around garnets with rims, the rims are generally not thick enough to determine whether the rims truncate minerals that wrap around (thus post-dating fabric development), or if the entire garnet was present when the matrix was bent around the porphyroblast. Although garnet and cordierite are found throughout the area, hornblendes and psuedomorphed sillimanites are less common. Samples containing these porphyroblasts were generally from areas proximal to the pluton contact, but the limited occurrence of the minerals does not allow for a clear correlation. As the porphyroblasts predate folding, they can not be pluton related; but it is possible that they were more widespread prior to retrograde metamorphism in the Cretaceous. As noted above, Labotka (19 81 ) 50 showed rapidly increasing tem peratures to the west in the Cretaceous, which allows for the preferential preservation of higher grade minerals closer to the pluton. Although the Cretaceous metamorphism is too long lasting to be solely from the pluton, the intrusion could have helped preserve pre-existing assemblages near the contact. However, with the exception of minerals in local hornfelsic rocks, and possibly inclusion free garnet rims, no porphyroblasts appear to have grown in the Kingston Peak schists as a result of the pluton. The Hall Canyon pluton Figure 11 shows the distribution of felsic intrusives exposed in the area. This study focuses on plutonic rocks in Hall and Jail Canyons; the main exposures of the Hall Canyon pluton. The two areas are separated by a region of younger breccia and alluvium. Intrusive contacts are truncated or obscured to the north, south, and west by Late Cenozoic normal faulting (Figs. 5 and 11). Smaller, felsic intrusives in Surprise Canyon to the south and scattered exposures to the north are considered to be related or part of the same body by Albee and others (1 9 8 1 ) and Labotka and others (1 9 8 0 ). Griffis (1 9 8 7 ) suggested th at these smaller exposures may represent different intrusions based on the heterogeneity of trace element chemistry. Farther to the north, the Skidoo Pluton has a bulk composition and probable age that is similar to that of the Hall Canyon piuton (Griffis, 1987; Walker, unpublished data) implying that felsic intrusives in the range may be more widespread than suggested by current exposure. U-Pb dating An attempt was made to date the pluton using U-Pb ratios in zircons. The sample for this analysis was collected from undeformed biotite-muscovite granite in the upper plate of the fault that cuts the pluton in Jail Canyon (Fig. 8). This area contains schists of the Kingston Peak formation and both phases of the Hall Canyon pluton. The rocks are brittlely deformed, but maintain enough coherence to be certain of their origin and that they were proximal to the roof of the pluton. This is the only accessible area where the lower, "less evolved" phase of the pluton was not mylonitized by the shear zone discussed in a later section. Three zircon fractions from the sample were analyzed by Doug Walker at the University of Kansas. Resulting U-Pb values are included in Table 2. Figure 20 shows the discordant nature of the results, with a lower intercept of 69 ± 58 Ma and an upper intercept of 1713 ± 230 Ma. In spite of the large uncertainties in these results, they add two facets to the discussion. Firstly, the age of the pluton is bracketed with a minimum given by the Ar data discussed above and a maximum age in the Early Cretaceous. A Late Cretaceous age is the most likely if the pluton is interpreted to be a heat source for some portion of Late Cretaceous metamorphism. This is also in 52 Fractions U (ppm) Table 2 U-Pb Data Pb (ppm) 206Pb/238U 207Pb/235U 1 357.6 8.1 0.020883 0.21451 2 922.6 68.1 0.072685 0.98391 3 409.5 9.1 0.020751 0.22200 0.089 HCP-Biotite 500 0.079 0.069 400 0.059 0.049 300 Intercepts at: 1713 ±230 Ma and 69 ± 58 Ma M SW D=I49.I0 0.039 200 0.029 0.019 poo 0.009 0.05 0.25 0.45 0.65 0.85 1.05 ^ Figure 20. Concordia plot of U-Pb zircon data from a sample of the biotite phase of the pluton (prepared by D. Walker). agreement with previous studies (Labotka and others, 1985, Mahood and others, in press). Secondly, the upper intercept matches the age of the basement rocks exposed in the range (Lamphere and others, 1964), albeit with large error bars. This is consistent with the pluton having been derived from local basement. It also shows that the pluton contains a significant amount of inherited zircons, strengthening the evidence for a crustal source for the melt. Nature of the pluton contact The character of the intrusive contact is best illustrated by exposures in Hall Canyon proper. In this area, the irregular nature of the contact is striking, with sharp changes in orientation that occur on the scale of tens to hundreds of meters (Figs. 13 and 21). These irregularities are best explained by stoping as no evidence for faulting can be found along the contacts or along projections of individual segments of the contact into the pluton or the country rock. Stoped blocks of meter to centimeter scale are common along the contact and occasionally farther into the pluton. The majority of the blocks are recognizable as belonging to schists of the Kingston Peak Formation, although rare small blocks of the underlying Beck Spring Dolomite can be found. Occurrences of Beck Spring blocks were only found in Jail Canyon exposures of the pluton. In this area the Beck Spring Dolomite lies to the east of the pluton and its contact with the overlying conglomerate is steeply dipping (Fig. 1 1 ). Therefore, the stoped blocks Figure 21. Photograph showing the irregular nature of the contact. View is looking southwest into Hall Canyon. 56 from this unit had to be transported laterally, or more likely upwards to their present positions. This could result from either internal circulation in the pluton, floating of the blocks, or passive ascent of blocks with the pluton. Larger stoped blocks are present in the pluton where it is exposed in the upper plate of the Emigrant fault in the western portions of Jail Canyon. This area was not mapped in detail, but a brief examination of the area has shown that although the upper plate is brittlely deformed, stoped blocks that are tens to hundreds of meters across are preserved with clear igneous contacts. Because of the irregular, non-planar nature of the contact, areas can be found where all structures associated with pre-pluton deformation are truncated by the intrusion. This includes D2 banding, axial surfaces of D3-D4 folds, and the subhorizontal lineation. Pegmatitic and aplitic dikes are commonly found intruding the country rock and also truncate all structures except those related to the shear zone (D5 - discussed below). Another common feature found along the intrusive contact is the assimilation of small stoped chips and minor amounts of melting along the contact itself. The disaggregation and melting of Kingston Peak schists is visible on the centimeter scale. Large, unaligned biotite crystals within the pluton are common in centimeter-scale bands along the contact and around stoped blocks. These sometimes grade into unmelted or hornfelsic schists. The highly evolved nature of adjacent plutonic rocks that contain only muscovite (± garnet) implies that biotite is present along such 57 contacts as a result of contamination from the schists. This leads to the conclusion that at least a minor amount of assimilation of country rock at the contact and of stoped blocks was active during the late phases of pluton emplacement. The contact between the Hall Canyon Pluton and the Kingston Peak Formation in exposures around Jail Canyon is not intrusive, but rather a fault related to the mylonitic shear discussed below. The fault dips west at -6 0 ° and shows kinematic evidence for right lateral slip. Blocks of Kingston Peak schists and conglomerates which are surrounded by pluton are common along the contact and range in size from meters to roughly a hundred meters. The majority of these blocks are the result of stoping. However, the contacts between blocks and pluton often act as a focus of ductile shear and it is possible that some of the blocks are stringers along the fault that came to their present position well after the pluton was emplaced and solidified. D5 shear zone deformation A major, right-lateral, strike-slip shear zone (D 5) has deformed a significant portion of the field area. Kinematics of the shear are evident from pervasive, solid-state, S-C structures in the pluton and, less commonly, in western exposures of the Kingston Peak Formation (Figs. 13 and 22; Plate 1). In both units, C surfaces dip moderately to steeply to the west (Figs. 23A and 23B). A subhorizontal, north-south trending lineation is also well 58 Figure 22. Map of C surface attitudes associated with the right- lateral shear zone (D5). 59 O Beck Spring Dolomite 111 Kingston Peak Conglomerate □ Kingston Peak Schist fv ] Hall Canyon Pluton f^~| Cenozoic Breccia | | Quaternary Sediment j Shear Zone C Surface Unfoliated Pluton A N A ;V' \ \ < \ \ \ \ f S S S S / s v. ^ s \ \ s f / t f s s t \ V. \ \ \ \ s ‘ 6 2 'J s X \< ’ \ 7 * 6 - / / / / < / / ^ 'VV^6&.V i* s / s s / 84HN S \ N \ ' s s s / * * ^70^ v - N > ^ ^ > > N \ N s s * f /0 6JU / s / ' .* .* s . '77 As • i > 6 8 3 v Km A) EqualArea ...M .t.M W iity n n frii N= 93 C.l. = 2.0 sigma B) EqualArea ,*» ! < ! ’ ! M § R M M M C.l. = 2.0 sigma Figure 23. Kamb contour stereonet plots of D5 shear zone data. (A) poles to C surfaces in the Hall Canyon Pluton, and (B) poles to C surfaces in country rocks. 61 developed in sheared plutonic rocks, as shown on the geologic map (Fig. 24, Plate 2) and in a stereonet plot of the data (Fig. 25). This lineation is parallel to the presumed direction of motion on the shear zone. All of the pluton has been mylonitized in the shearing, with the exception of the easternmost exposures in Hall Canyon (Figs. 11, 12, and 22, Plate 1). In this area, the pluton shows no recognizable fabric, although q uartz is still partially recrystallized into new, polygonal grains. Moving from west to east within the pluton, there is a change from penetratively deformed rock, to a transitional zone where discrete shear bands separate pods of less deformed rock, and finally into rocks that show no evidence of D5 deformation. The western edge of the transitional zone roughly corresponds to the north-south trending contact between pluton and country rock and an area of steep topography. Minor splays of the shear zone can be found to the eastern limit of the field area. The decreasing intensity of D5 deformation to the east is also expressed in thin section. Within the pluton, D5 deformation is accommodated by quartz ribboning and ductile deformation of micas which align the minerals parallel to the fabric. In addition, the igneous micas have been replaced by finer grained, metamorphic mica that has also deformed. As the intensity of fabrics in the pluton decreases to the east, the quartz and micas show less deformation and metamorphic micas are no longer 62 Figure 24. Map of shear zone (D5) lineations. 2 m □ s □ □ \ Beck Spring Dolomite Kingston Peak Conglomerate Kingston Peak Schist Hall Canyon Pluton Cenozoic Breccia Quaternary Sediment Shear Zone Lineation s \ K s s n \ \ \ *„ \ \ \ \ \ \ N ^ S N \\ N N * s V * A . ' S S \ V \ S V. \ S * 'I' s / S S A S i \ \ \ \Y\ \\ s / / y .1 / . s \ s s \ \ / / ,\ / / / s S \ f r \ \ \ ✓ ✓ Si ' s s s S S S S . / S S / * _ n \ s>' s N^Q / / / s y s s s s \ \ D \ s \ \ \ / / . o s / s / / \ \ \ \ S N • / / / w V / \ S S \ X - A . \ \ i ✓ »*■» N V O s S S N | ✓ ✓ /-W ^ * / S / N \ \’T S s » N • * * N ✓ ✓ V-XJ ✓ S / NSSfSSSN V \ V \ V . 'i \ s s s s /I s \ S \ \ S X \ C.l. = 2.0 sigma Figure 25. Kamb contour stereonet plot of shear zone (D 5) lineations. 65 present. Feldspars remain largely undeformed or are occasionally fractured. In the country rocks, fault-related ductile fabrics are less widespread. Thin sections from the Kingston Peak Formation show a narrow (usually no more than 10's of meters), western zone where quartz crystals have more elongate textures and exhibit extensive internal deform ation. Micas in this zone are characterized by smaller grain size and realignment. These textures are associated with east-vergent folds that have an axial planar cleavage oriented parallel to shear zone C surfaces, suggesting th a t the shear zone may have been locally transpressive. Although the cleavage and folding disappear within a short distance from the pluton contact, biotite growth parallel to D5 axial planes and C surfaces was observed in thin section at least several hundred meters farther to the east. In addition, shear zone fabrics at some intrusive contacts can be seen refracting to shallower attitudes in the schists, which may allow for deformation to occur subparallel to the preexisting foliation, thus making it harder to recognize in the field. Data from the southern Panamints indicates the presence of right-lateral shear in the South Park Canyon pluton that is likely a southward continuation of the right-slip shear zone (Cichanski and Crossland, 1 994). Shear in this area has similar characteristics to those described here. Based on the behavior of quartz and feldspar, rough estimates may be made of the temperature at which shear zone deformation 66 occurred. The temperatures at which these minerals begin to deform ductilely have been the subject of extensive experiments by a number of authors (e.g., Christie and others, 1964; Hobbs and others, 1972; Tullis, 1983; Tullis and Yund, 1977, 1 9 8 7 ). Experiments are conducted at strain rates that are much higher than found in nature, and the results are then extrapolated to give the figures sited here. In addition, the temperature at which creep occurs if effected by factors such as water activity and pressure (e.g., Tullis and Yund 1980; Tullis, 1 9 9 0 ). As a result of extrapolation and these other variables, creep can only be used to give a general temperature range. In rocks effected by the shear zone, quartz was ductilely deformed while feldspars were unaffected or deformed brittlely. Studies of quartz deformation indicate that creep begins at 250±50°C (e.g. Christie and others, 1964; Hobbs and others, 1972) which is thus the minimum tem perature in the shear zone. Feldspars become ductile at a temperature of 450±50°C (e.g., Tullis, 1983; Tullis and Yund, 1977, 1987). As feldspars were not ductilely deformed, temperatures during shearing must have been at some intermediate value -- between 200° and 500°C. The upper portion of this range is consistent with limited garnet-biotite thermometry in the west-central Panamints that has indicated tem peratures of 4 0 0 -5 0 0 °C for the retrograde, Cretaceous metamorphism (Labotka, 1981). However, as crystals effected by D5 shearing show intense internal deformation, movement in the 67 shear zone at least partially postdates heating, and the lower end of this temperature range is, therefore, also viable. Lineations Country rock lineations associated with pre-emplacement deformation (D 3-D 4) have the same attitude as those in the D5 shear zone (compare Figs. 17 and 25), but the available evidence suggests that they formed at different times. As noted above, the easternmost exposures of the pluton in Hall Canyon show minor recrystallization and no recognizable fabric. Schists and conglomerates of the Kingston Peak that exhibit strong L-S fabrics have been intruded by these undeformed rocks. Hall Canyon dikes in the area which cross-cut the lineation also show only weak solid state deformation, whereas the country rocks remain strongly lineated. In addition, the country rock lineations and pre emplacement folding die out together to the east (Labotka and others, 1980; Albee and others, 1981). This is also the case in regions to the south of the study area (M. Cichanski, pers. comm.) and implies a genetic tie between the two. These relationships imply that country rock lineations predate pluton emplacement, whereas the shear zone lineation deforms the pluton and thus must be a post-emplacement fabric. 68 High-angle faults Two high-angle faults with westward dips are present in the eastern portion of the study area (Fig. 11; Plate 1). These two faults were mapped from Hall Canyon to the north (through Jail Canyon in the case of the western fault) and are either poorly expressed, or die out to the south of Hall Canyon (Fig. 11). Where exposed, the fault zones show brittle textures and range from sharp, single surfaces to brittle zones a few tens of meters across. Dips on the eastern fault are ~60°, whereas the western fault dips roughly 75°. Previous mapping suggests that these faults are part of a larger set of faults that are common in the western Panamints (Labotka and others, 1980; Albee and others, 1981). Although it has been suggested that this set of faults is Precambrian in age (Labotka and Albee, 1980), they were clearly active after folding in the area as they cut the limbs and axial surfaces of large scale, D3-D4 folds. Their timing relative to other events in the area is not clear. Current exposures do not show if the faults cross-cut the pluton, the shear zone, or the Tertiary hypabyssal dikes that are discussed below. The simplest explanation is that these features are Tertiary normal faults. This interpretation accounts for their brittle nature in that if the faults are older, they would have operated at greater depth and, thus, might be expressed in a similar manner as the late Cretaceous, ductile shear zone. Kinematic indicators for the faults are absent, even in the best exposures. Where the faults cut the 69 axial surface of large scale D3 folds, as illustrated in Figure 13, some down-to-the-west component of faulting may be inferred. This would imply a displacement on the order of 250 meters for each of the faults. However, matching these features should not be considered a unique solution in rocks that are as heterogeniously folded as the Kingston Peak in this area. It is also possible that some component of strike slip brought the axial surfaces in the two panels into their present positions. Labotka and others (1 9 8 0 ) suggest the possibility that these are wrench faults with different segments of individual faults showing normal and reverse slip. Hypabyssal dikes A sparse set of hypabyssal, diabase dikes cut through the study area. Textures in the dikes are aphanitic to porphyritic. Their mineralogy is characterized by abundant plagioclase, partially resorbed olivine and hornblende, and late biotite. The dikes can be seen cross-cutting both the pluton and the country rocks. They clearly post-date D5 deformation as they remain undeformed while cutting through mylonitized Hall Canyon pluton. Although these rocks have not been dated, they are similar to intrusives found just to the north of the study area. Cross cutting relationships to the north suggest an age of Early to Middle Tertiary (Hodges, pers. comm.). 70 The Emigrant fault The Tertiary Emigrant fault system marks the limits of the field area to the west, north, and south (figs. 7 and 11). The fault has disrupted rocks of the footwal! and the hanging wall to the extent that it is difficult to determine a single fault surface. Footwall rocks contain numerous small displacement faults in all orientations, but are preferentially aligned along Jurassic foliations. Rocks of the hanging wall are brecciated, although some contacts between units have remained intact. Defining the fault zone is further complicated by the fact that both the footwall and the hanging wall are members of the Kingston Peak Formation. To the west of the area studied, the fault region would be easier to study in that it places Kingston Peak rocks on top of Hall Canyon pluton. Nonetheless, the overall dip of the fault system is clearly shallow, at 5-25°. DISCUSSION Mesozoic History of the West-Central Panamint Mountains The data presented above has implications for several aspects of the Mesozoic history of the west-central Panamint Range. A generalized timeline of major events in the area is given in Figure 26. Timing of the earliest episodes of deformation, D1 and D2, is poorly constrained. These events may have occurred as 71 ????'? 7? 77 7777? D1 and D2 Deformation ?? IZZZZZZ3 D3-D4 deformation ? 7 \ / / ' / / ZZZZ1 ?? [ZZZZZZ Metamorphism Pluton Emplacement D5 (Shear Zone) Deformation •??EZZ3 High Angle Faulting 7????’????’???? Hypabbysal Dikes ?????-???????? Jurassic Cretaceous T ertiary 200 150 100 Figure 26. Timeline showing ages of important events. earlier phases of D3-D4 deformation, and thus be of similar age, or could predate this folding event and be as old as Eocambrian, the age of the rocks involved. The first events for which good timing constraints have been established are the Jurassic metamorphism and folding. Previous workers in the area concluded that the folding is Cretaceous and synchronous with pluton emplacement (e.g., Labotka and others, 1985). However, there are several lines of evidence that suggest a Jurassic age. The truncation of D3-D4 structures along the contact with the Hall Canyon pluton illustrates that folding predates final emplacement, but it could be argued that the folding occurred in the early phases of emplacement and that stoping, late in the emplacement history, resulted in the truncation of structures that developed only a short time earlier. Other lines of evidence, however, do indicate a Jurassic age. As discussed earlier, Ar-Ar release patterns showed two episodes of metamorphism, the first in the Jurassic and a second in the Cretaceous (Labotka and others, 1985). This study concluded that the Cretaceous Ar-Ar plateaus in the central Panamints were associated with folding and pluton emplacement, whereas Jurassic ages were preserved from an earlier foliation. Extensive microstructural observations of the Kingston Peak schists during the present study, and the recognition of the wide Cretaceous shear zone that effected a portion of the area, suggest alternate explanations. In thin section, the dominant mineral fabric cross-cuts D2 layers and is axial planar to D3-D4 folding. The pervasive nature of such textures suggests that the 73 preservation of Ar ratios in minerals that predate folding would likely be very rare or absent (e.g., Kligfield and others, 1986). One might point to earlier deformations (D1 and D2) that are recognized in the present study to dispute this conclusion. However, microstructures associated with D1 are far too rare and minor in percentage of minerals to account for a consistent Ar signature, and D2 is defined by compositional banding which is often oblique to and overprinted by dominant mineral alignments. Subsequently, the earliest preserved (Jurassic) Ar signature in the Kingston Peak Formation is most likely associated with D 3 /D 4 folding. Cretaceous ages are considered to be the result of a more static heating that partially reset argon systematics. Regional considerations provide another line of evidence for a Jurassic age of folding. To the south of the present study area, folding appears to predate the intrusion of the Jurassic Manly Peak pluton (Miller, 1983, as sited in Labotka and Albee, 1988). The folding is also present in regions between the Hall Canyon and Manly Peak plutons, but clear timing relationships are absent in this area (M. Cichanski, pers. comm.). Another line of evidence comes from Snow and Wernicke (1 9 8 9 ) who suggest a correlation between Mesozoic folding in the Panamints and similar structures known as the Argus anticline, which lie to the northwest of the area. This study claims that the Argus anticline developed synchronously with the intrusion of a 181 Ma pluton. The evidence, therefore, supports the reinterpretation of folding in the west-central Panamints as having occurred in the 74 Jurassic. The cause of west-vergent folding is unknown. Limited exposures of west-vergent folding are in evidence in other portions of the southern Basin and Range (Snow, 1992). A number of studies have attributed these west-vergent structures to backthrusting in an overall east-vergent thrust system (e.g., Wernicke, 1 9 8 8 ). Another possibility is to tie the folding to extension. Several studies have offered arguments for Mesozoic extension (e.g., Miller and others, 1988; Hodges and Walker, 1992), but without evidence for the presence of an extensional fault in the vicinity, this possibility seems unlikely; extension in the Death Valley area has only been adequately documented for the Tertiary. Cretaceous events include metamorphism, intrusion of the Hall Canyon pluton, and formation of a mylonitic, dextral shear zone (D5). As noted earlier and shown in Figure 26, Ar-Ar plateaus associated with Cretaceous metamorphism indicate cooling ages over a span of approximately 25 Ma. It seems unlikely that all of this metamorphism is a result of the Hall Canyon pluton alone, as cooling around an individual pluton is usually assumed to occur in a much shorter time span (e.g., Furlong and others, 1991; Paterson and Tobisch, 1992). Metamorphism can therefore be interpreted as resulting from the gradual cooling of the Cretaceous arc as a whole. Deformation in the shear zone (D5) may also account for some portion of the spread in ages because it was intense enough to have reset the argon systematics. The youngest date (55 M.a.) attained by Labotka and others (1 9 8 5 ) was in intensely mylonitized pluton. It is possible that other samples could have been effected 75 by eastern splays of the shear zone, contributing to the broad range on closure ages. The presence of a major right-lateral shear zone that runs along the western margin of the Panamints adds a previously unrecognized facet to the Mesozoic history of the area. As exposed in the Hall Canyon area, the zone is a minimum of several kilometers wide and strikes roughly north-south. As noted, right lateral S-C fabrics have also been found in the South Park Canyon pluton to the south and lie roughly on trend with the shear zone as mapped in this study (Cichanski and Crossland, 1994). With the restoration of some Tertiary tilt, the attitude of the shear zone approaches vertical and is consistent with the interpretation that it represents a strike-slip fault. Emplacement of the Hall Canyon pluton Although the Mesozoic history of the west-central Panamint Range is complex, none of the episodes of deformation recorded in the vicinity of the Hall Canyon pluton made significant space for the pluton's emplacement. To summarize, west-vergent folding of the basement and Pahrump Group strata predates intrusion. Fold limbs, axial surfaces, and all features associated with D2 to D4 are sharply truncated at the intrusive contact and this deformation is approximately 100 M.y. older than the pluton. The D5 shear zone directly overprints pre-pluton country rock structures, the pluton 76 itself, and was most likely not active until a fte r pluton emplacement. These relations allow for the elimination of a number of emplacement mechanisms for this pluton, and place some constraints on the mechanisms of vertical and horizontal material transfer. If the Hall Canyon pluton had been emplaced by in situ expansion (ballooning) or by flow around an ascending diapir, the roof rocks examined in this study should exhibit coeval flattening strains parallel to the contact. None are seen. Models of emplacement by horizontal extension or the infilling of an extensional pull-apart may also be ruled out. As noted, these models require the presence of a fault at the roof contact or large scale extension in the roof. The roof of the Hall Canyon pluton is not a fault and contains only two brittle faults that are best interpreted as Tertiary in age, thus post-dating emplacement. Furthermore, even if these brittle faults had been active during emplacement, displacements on the faults were on the scale of only a few hundred meters, allowing for the dismissal of significant space making. The presence of the D5 shear zone might initially invoke thoughts of space making in a pull-apart along a fault. Although it was clearly active after emplacement, since it deforms the pluton in the solid state, it is possible to argue that the shearing began during emplacement and continued until after crystallization and cooling. This possibility is discounted by microstructural and geometrical arguments. Thin section analyses of the pluton using, 77 the criteria given by Paterson and others (1 9 8 9 ), show no indication of deformation while in the magmatic state or in the transition to the solid state. With regards to geometry, two points should be made. First, the placement of the fault is inconsistent with pull-apart infilling. Undeformed plutonic rock exposed in Hall Canyon lies to the east of the main shear zone, although minor splays of the zone do effect this area. The second point is tied to the massive character of the pluton and the rate arguments of Paterson and Tobisch (1 9 9 2 ) and Paterson and Fowler (19 93 b ). With typical fault rate maxima on the scale of centimeters per year, emplacement o f a pluton by pull- apart infilling should result in a series of sub-vertical dikes (or in this case, possibly west-dipping dikes, depending on the extent of Tertiary tilting). Neither of the phases of the Hall Canyon Pluton appears to have been emplaced in this incremental fashion. The lower, biotite-bearing phase is fairly homogenous chemically, and the upper, muscovite phase shows compositional gradients from the roof to the contact with the lower phase (Nibler, 1991) -- indicating that both existed as large chambers. The absence of deformation associated with the pluton suggests emplacement mechanisms such as assimilation and stoping. Indications of assimilation are limited to local rims along the contact and around stoped blocks. Although the amount of assimilation is not quantifiable without detailed geochemistry, it can not account for more than a fraction of a percent of the space occupied by the pluton at this structural level. Furthermore, based 78 on Sr and Nd isotopes in a single sample of Kingston Peak schist, Nibler (1 9 9 1 ) concluded that the upper phase of the pluton could not have resulted from the mixing of the lower phase and melted Kingston Peak formation. This is not surprising as the volume of Kingston Peak Formation that is "missing" is, in fact, small compared to that of underlying units — and the majority of rock from this unit was likely transferred to lower levels by the sinking of stoped blocks. It is possible, however, that assimilation or partial melting of stoped blocks effected pluton compositions at a lower structural level. As noted, irregular jogs in the contact are suggestive of stoping at a scale of tens to hundreds of meters. Blocks of this size are only found in the brittlely deformed rocks of lower Jail Canyon, but models of stoping suggest that blocks greater than 10 m in diameter would quickly sink in a granitic melt, and thus be removed from view (Marsh, 1982). Smaller pieces of country rock are common along the contact and found occasionally further into the pluton. It should also be reiterated that although the roof contact of the pluton lies wholly within the Kingston Peak Formation, rare, small stoped blocks of Beck Spring Dolomite are also found in the area, implying at least some ascent by stoping through this unit as well. Lower units, such as the Crystal Spring Formation and underlying basement, are not found included in the pluton, but preservation of such blocks would be very unlikely in that they would have to float or be carried upwards by magma 79 convection in order to be preserved at higher levels — as was presumably the case with the rare blocks of Beck Spring Dolomite. Given these features, the sharp truncation of previous structures, and the lack of evidence for any emplacement-related deformation, stoping may account for nearly 100% of the space making at this structural level. Material transport is, therefore, largely directed downward. No evidence was found in the country rocks to support a case for material transport upwards or horizontally. Yet, these conclusions face some qualification. This study has dealt exclusively with the roof of the intrusion; exposures of intrusive wall contacts are not in evidence. As a result, the three dimensional shape of the pluton remains unknown, and constraints on the nature and extent of deformation around its sides remain unaddressed. It is possible, for instance, that processes such as marginal return flow, or some component of flattening along steep contacts, played a role in the transfer of material that made space for the pluton. Precedents for plutons with undeformed roofs and deformed walls are found in a number of studies (e.g., Buddington, 1959; Pitcher, 1979; Fowler, 1994; Paterson and Miller, 1994). This could be the result of either different processes being active in the different settings, or the removal of deformed roof rocks by stoping. Studies of strain in steep walls of plutons have shown that, on average, margin parallel deform ation accounts for approximately 30% of the space taken up by the pluton (Paterson and Fowler, 1993a). In a study of deflected marker units around 32 80 steep-walled pluton exposures, Fowler (1 9 9 4 ) showed that similar amounts of space making result from the restoration of deflections - although a range from 0% to 60% of the pluton space was found to be common. It is quite possible, therefore, that margin parallel shortening, return flow, or other processes effected the walls of the Hall Canyon pluton and account for some percentage of emplacement at presently exposed levels, or at some point during ascent. Without wall exposures these possibilities can not be evaluated and conclusions as to operative space-making processes are necessarily incomplete. Nonetheless, there are ways by which we may begin to constrain the distance that the pluton ascended by stoping. One of the traditional arguments against significant amounts of stoping is that the blocks would fill the pluton due to their loose packing. For example, Marsh (1 9 8 2 ) concluded that a body could only rise approximately one body radius by stoping before the blocks choked the melt. The radius and three dimensional shape of the Hall Canyon pluton is unknown. Current exposures give a north-south length of greater than 7 km, an east-west length of roughly 3 km and a minimum height of 1 km. Although modeling possible ascent distances using Marsh's calculations is not possible with given exposures, a minimum of 2-3 km is reasonable. Melting or partial melting of stoped blocks at deeper levels would also allow for greater distances of ascent by stoping as the clogging of the magma would become less of an issue - although the amount of block melting would be thermally limited. 81 A second approach to bracketing distances of ascent by stoping involves the removal of rocks effected by possible diapirism or radial expansion. Cruden (1 9 8 8 ) showed that deformation above an ascending diapir would extend to at least four body radii above the intrusion (see Fig. 2). If the early portion of ascent was by diapirism, the Hall Canyon pluton would again have had to ascend a minimum of 2-3 kilometers (and likely considerably more if the pluton extends to any depth) by stoping in order for the effects of the diapirism to be obliterated. This is, admittedly, an oversimplification as both processes (or other processes) would likely have operated at the same time instead of in sequence, but it does offer some loose constraint. Traditionally, stoping has been considered to be a minor process, or one that is operative only at quite shallow levels in the crust where temperature differences between melt and country rock are high (Buddington, 1959; Marsh, 1982). Evidence from the Hall Canyon pluton adds to a growing body of evidence that suggests that stoping may be important at deeper levels as well. A recent study of the Sage Hen Flat pluton, a granite in the White Mountains of California, concluded that the body was emplaced by stoping at a depth of roughly 8 km (Bilodeau and Nelson, 1993). The Mount Stuart batholith of Washington also shows evidence for stoping at a depth of - 1 0 km (Paterson and Miller, 1994). The depth of emplacement of the Hall Canyon Pluton is not as well constrained as for the pluton’s in these studies, but it must have been emplaced at a depth of at least several kilometers as it is 82 overprinted by a ductile shear zone, and could have been intruded as deep as these other examples. 83 REFERENCES Armstrong, R. L. and Suppe, J., 1973, Potassium-Argon geochronometry of Mesozoic igneous rocks in Nevada, Utah, and southern California: Geological Society of America Bulletin, v. 84, p. 1375-1392. Barton, M. D., 1990, Cretaceous magmatism, metamorphism, and metallogeny in the east-central Great Basin, in Anderson, J. 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P., ed., Basin and Range extensional tectonics near the latitude of Las Vegas, Nevada: Geological Society of America Memoir 176, p. 377-390. 85 Hodges, K. V. and Walker, J. D., 1992, Extension in the Cretaceous Sevier orogen, North American Cordillera: Geological Society of America Bulletin, v. 104, p. 560-569. Hutton, D. H. W., 1982, A tectonic model for the emplacement of the Main Donegal granite, NW Ireland: Journal of the Geological Society of London, v. 139, p. 615- 631. Hutton, D. H. W., 1988, Granite emplacement mechanisms and tectonic controls: inferences from deformation studies: Transactions of the Royal Society of Edinburgh, v. 79, p. 245- 255. Hutton, D. H. W., 1992, Strike-slip tectonics and granite petrogenesis: Tectonics, v. 11, 5, p. 960-967. Kerrick, D.M., Lasaga, A.C., and Raeburn, S.P., 1991, Kinetics of heterogeneous reactions, in Kerrick, D. M., ed., Contact Metamorphism: Mineralogical Society of America Reviews in Mineralogy, v. 26, p. 583-671. 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G., ed., Metamorphism and crustal evolution, western conterminous United States: Englewood Cliffs, New Jersey, Prentice-Hall, Ruby Volume 7, p. 714-736. Labotka, T. C. and Albee, A. L., 1990, Uplift and exposure of the Panamint metamorphic complex, California, in Wernicke, B . P., ed., Basin and Range extensional tectonics near the latitude of Las Vegas, Nevada: Geological Society of America Memoir 176, p. 345-362. Labotka, T. C., Albee, A. L., Lamphere, M. A., and McDowell, S. D., 1980, Stratigraphy, structure, and metamorphism in the central Panamint Mountains (Telescope Peak Quadrangle), Death Valley area, California: Geological Society of America Bulletin, v. 91, part II, p. 843-933. Lamphere, M. A., Waserburg, G. J. F., Albee, A. L. and Tilton, G. R., 1964, Redistribution of Sr and Rb isotopes during metamorphism, World Beater Complex, Panamint Range, California, in Craig, H., Miller, S. L. and Waserburg, G. J. F., eds., Isotopic and cosmic chemistry: Amsterdam, North Holland Publishing Company, p. 269-320. Mahood, G.A., Nibler, G.E., and Halliday, A.N., in press, Zoning patterns and petrologic processes in peraluminous magma chambers: Hall Canyon pluton, Panamint Mountains, California: Geological Society of America Bulletin. Marsh, B. D., 1982, On the mechanics of igneous diapirism, stopping, and zone melting: American Journal of Science, v. 282, p. 808-855. McKenna, L. W. and Hodges, K. V., 1990, Constraints on the Kinematics and timing of late Miocene-Recent extension between the Panamint and Black Mountains, southeastern California, in Wernicke, B . P., ed. ., Basin and Range extensional tectonics near the latitude of Las Vegas, Nevada: Geological Society of America Memoir 176, p. 363-376. 87 Miller, C. F., and Bradfish, L. J., 1980, An inner Cordilleran belt of muscovite bearing plutons: Geology, v. 8, p. 412-416. Miller, E. L., and Gans, P. B., 1989, Cretaceous crustal structure and metamorphism in the hinterland of the Sevier thrust Belt: Geology, v. 17, p. 59-62. Miller, E. L., Gans, P. B., Wright, J. E., and Sutter, J. F., 1988, Metamorphic history of the east-central Basin and Range province; tectonic setting and relationship to magmatism, in Ernst, W. G., ed., Metamorphism and crustal evolution, western conterminous United States: Englewood Cliffs, New Jersey, Prentice-Hall, Ruby Volume 7, p. 649-682. Miller, J. G., 1985, Glacial and syntectonic sedimentation: The upper Proterozoic Kingston Peak Formation, southern Panamint Range, eastern California: Geological Society of America Bulletin, v. 96, p. 1537-1553. Nibler, G.E., 1991, Origin of mineralogical and compositional zonation in the peraluminous Hall Canyon pluton, Panamint Mountains, California [MS Thesis]: Stanford University, 66 p. Paterson, S. R . and Fowler, T. K., 1993a, Re-examining pluton emplacement mechanisms: Journal of Structural Geology, v. 15, p. 191-206. Paterson, S. R . and Fowler, T. K., 1993b, Extensional pluton- emplacement models: Do they work for large plutonic complexes?: Geology, v. 21, 6, p. 781-784. Paterson, S. R and Miller, R . B., 1994, Porphyroblast-matrix relations around the Mt. Stuart Batholith, Washington: Are they compatible with P-T data?: Geological Society of America, Program with Abstracts, Cordilleran section, v. 26, 2, p. 80. Paterson, S. R . and Tobisch, 0. T., 1992, Rates of processes in magmatic arcs: Implications for the timing and nature of pluton emplacement and wall rock deformation: Journal of Structural Geology, v. 14, p. 291-300. Paterson, S.R., Vernon, R.H., and Tobisch, O.T., 1989, A review of criteria for the identification of magmatic and tectonic foliations in granitiods, Journal of Structural Geology, v. 11, 349-363. Paterson, S. R., Vernon, R. H., and Fowler, T. K., 1991, Aureole Tectonics, in Kerrick, D. M., ed., Contact Metamorphism: Mineralogical Society of America Reviews in Mineralogy, v. 26, p. 673-722. Pitcher, W. S. and Bussell., M. A., 1977, Structural control of batholithic emplacement in Peru: a review: Journal of the Geological Society of London, v. 133, p. 249-256. Saleeby, J. B., and Busby-Spera, C., 1992, Early Mesozoic tectonic evolution of the western U.S. Cordillera, in Burchfield, B. C., Lipman, P. W., and Zoback, M. L., ed., The Codilleran Orogen: Conterminous U.S.: Geological Society of America, The Geology of North America, G-3, p. 107-168. Schemeling, H., Cruden, A. R., and Marquart, G., 1988, Finite deformation in and around a fluid sphere moving through a viscous medium: implications for diapiric ascent: Tectonophysics, v. 149, p. 17-34. Silver, L. T., McKinney, C. R. and Wright, L. A., 1961, Some Precambrian ages in the Panamint Range, California (abstract): Geological Society of America - Special Paper 68, p. 55. Snoke, A. W., and Miller, D. M., 1988, Metamorphic and tectonic history of the northeastern Great Basin, in Ernst, W. G., ed., Metamorphism and crustal evolution, western conterminous United States: Englewood Cliffs, New Jersey, Prentice-Hall, Ruby Volume 7, p. 606-648. Snow, J. K., 1992, Large-magnitude Permian shortening and continental-margin tectonics in the Southern Cordillera: Geological Society of America Bulletin, v. 104, p. 80-105. 89 Snow, J. K. and Wernicke, B., 1989, Uniqueness of geological correlations: An example from the Death Valley extended terrain: Geological Society of America Bulletin, v. 101, p. 1351-1362. Tikoff, B. and Teyssier, C., 1992, Crustal-scale, en-echelon "P- shear" tensional bridges: A possible solution to the batholithic room problem: Geology, v. 20, 10, p. 927-930. Tullis, J., 1983, Deformation in feldspars, in Ribbe, P. H., ed., Feldspar Mineralogy: Mineralogical Society of America Reviews in Mineralogy, 2, p. 297-323. Tullis, J., 1990, Experimental studies of deformation mechanisms and microstructures in quartzo-feldspathic rocks, in Barber, D.J., and Meredith, P.G., eds., Deformation processes in minerals, ceramics, and rocks, Unwin Hyman, London, p. 197- 227. Tullis, J. and Yund, R.A., 1977, Experimental deformation of dry Westerly granite, Journal of Geophysical Research, v. 82, p. 5705-5718. Tullis, J. and Yund, R.A., 1980, Hydrolytic weakening of experimentally deformed Westerly granite and Hale albite rock, Journal of Structural Geology, v. 2, p. 439-451. Tullis, J. and Yund, R.A., 1987, Transition from cataclastic flow to dislocation creep of feldspar: mechanisms and microstructures, Geology, v. 15, p. 606-609. Wernicke, B. P., 1990, Cenozoic extensional tectonics of the U.S. Cordillera, in Burchfield, B. C., Lipman, P. W. and Zoback, M. L., eds., The Cordilleran Orogen: Coterminous United States: Boulder, Geological Society of America, The Geology of North America, G3, p. 556-583. Wernicke, B. P., Axen, G. J. and Snow, J. K., 1988, Basin and Range extensional tectonics at the latitude of Las Vegas, Nevada: Geological Society of America Bulletin, v. 100, p. 1738-1757. 90 Zen, E-an, 1988, Tectonic significance of high pressure plutonic rocks in the western Cordillera of North America, in Ernst, W. G., ed., Metamorphism and crustal evolution, western conterminous United States: Englewood Cliffs, New Jersey, Prentice-Hall, Ruby Volume 7, p. 714-736. 91 PLEASE NOTE: Oversize maps and charts are filmed in sections in the following manner: LEFT TO RIGHT, TOP TO BOTTOM, WITH SMALL OVERLAPS The following map or chart has been refilmed in its entirety at the end of this dissertation (not available on microfiche). A xerographic reproduction has been provided for paper copies and is inserted into the inside of the back cover. Black and white photographic prints (17” x 23") are available for an additional charge. UMI 3>VJ-L c A /'iV oM ..... * ■ , x w j K c ' (64 . yu 4 V - d i ^ ( 3 0 ° / y X 7 ~ Beck Spring Dolomite X Country rock foliation (D2) tSTFI Kingston Peak Formation 0 Horizontal foliaton (D2) i L fl r V . A V « -h Key: Beck Spring Dolomite X Country rock foliation (D2) 0 :? vn Kingston Peak Formation (conglomerate) Kingston Peak Formation 0 X Horizontal foliatori (D2) Vertical foliation (D2) (schist) X "C" surfaces (D5) n Hall Canyon Pluton Vertical "C" surfaces (D5) □ □ Cenozoic Breccia Quaternary Sediment • • Unfoliated plutonic rock \ '.' /' O o >\ - v - r o ° o “ -fy \ \ i t \ - m o / 5 3 /' ■ J IT 3 0 v V - yM ^ l- CanY ov .\S ( ■ ■ S' r. V <> r A - ' " - ^ Q y o°°0o % ^ p J 3 ^ x < V ° C \V 'U < ' - / O f - - . ■ ■ - ' 1 ') S .° " U A V r 0 oV ? f< - ■ ■ > IV j .... v I Lr v V» » ® tJ V _ ^ ' j , * > “ I ^ 1 * " 3 ,\ b« i ■’ ■ '■ J V 5 V A w/ .• \\ .• : . V ;: ■ ■ ■ .; V » 3 a ^ '/£?k ^ ■ ' -c- \ ... \ 5 f > 4 . < v ,J t i l .. . 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UMI Beck Spring Dolomite / o D O \ r r ^ i W ^ i i ^MfoW ' • < i ' / ' f l f l ' - ’ " _ o 0 1 _ n , o,-. r ) iV ^ C ; • Q C (} ’ 'V " S c ’ O p O C ^ < r V ; c - Q " ? cv* ■ # ® ;.;; ^ ;/v;-t? j > o~ Key: Quaternary Sediment Hall Canyon Pluton Cenozoic Breccia Kingston Peak Formation (schist) Kingston Peak Formation (conglomerate) Beck Spring Dolomite Horizontal lineation (D3-4) Horizontal lineation (D5) 05 lineation D3-4 lineation it ■ p \ r. v . J A b s i " 1 " , ■ n ^ y ^ Y 4) -r -r - N - - - 1 ' V n O w V / ^ ! / ^ Y ^ ? . o / ■ V\u ~ d / „ j o * 7 ■ • A > Jy, < ■ • V “ : { / Y Y Y V Y V A t i o A A # 7 t 5^ rcu-} o Y i / ) c / ^ : ■ i i ■ ■ ■ ■ ' . : : . • : : V /? A ° n . L > r\ S , , o ^ °y*c P r\ (7 ,,0 -dA / P ^ ; > A A A A - - A - V • ' 't ’ , - . v. 0^ < > ; S / o ° r y = rK . U V- ' ' 0 • > ,, C \ ° 0 - - j r,(y-J *d.-l '■>A-vt ! --v> 7-0 a* K m X X f - - 5o a , r r L j . O O a if/ O T A tL . C M iY f'V . . N 6li_ ' o = C 0 ' ,V - « ■ ■ 1 .0 ^ 0 “/ t - f V- v - ;: H .............. V« J, ' ■ ' ■ '< ’' - r - • ■ . v c .• 5. ^ y , i _ •_ •/ r. u ( , o v - ‘ , V-:-:: : < 7Id ■ < : ■ h-i? C l tU - Q .; o . ^ - - — X -S IS ■ ^ js m ■ .op.tltfs- 0 . ° U or O -°0°. v : G ^ Q ? q 0 i r s , f S n ° C ' r - Q r “x ?vK - > “.c; V -> > V P = ••1 y t- ' ) 0 r A X i ; ~ j <>''h> • • r > \ i ,0 5 ’V C * ^ v V S O n < r s o : ■ ' J O o C j\-v — s r d d ^ d n ‘d:<d ^ Key: S Beck Spring Dolomite r Country rock foliation (D2) [ETf] Kingston Peak Formation 0 Horizontal foliaton (D2) &CU (conglomerate) x Vertical foliation (D2) E l Kingston Peak Formation (schist) x "C" surfaces (D5) E l Hail Canyon Pluton 0 Vertical "C" surfaces (D5) □ Cenozoic Breccia Unfoliated plutonic rock □ Quaternary Sediment >~>\Q ^.on-VPAiO^C N /f Beck Spring Dolomite X Country rock foliation (D2) [sni Kingston Peak Formation 0 Horizontal foliaton (D2) £ b 'l (conglomerate) X Vertical foliation (D2) Kingston Peak Formation Lu— I (schist) X ”C" surfaces (D5) { Z 3 Hall Canyon Pluton # Vertical ”C" surfaces (D5) □ Cenozoic Breccia *.• Unfoliated plutonic rock □ Quaternary Sediment ig-§°S 'o ^ „ wavy/ ' Q‘o - ‘ * ’ ’ /0/ •/O •_ : r ^ S ^ f . J c z - r o • ^ o P ^ T V O • • ° * / I , / r \ c?^v£ r^?-°:01 l.*lO -;ll O^ r -v C J ’o- oq'O'&o -Z *£:*•&'&. J & & - «S d o ° - W « c > ^ : 6 V • “ ~ / s;u ^ ~r* . e^/v* o ^ v -C s1 •^ T : '> :.:c i < • • • ■ • ytS • •■■•.■>■■■■■-••• ° : 'e> r ^~= ^ i 9HytJ •■•■■■S o-i.m # ■ > ^ v g > o ^ o £'S T* m m i i S I > V,% .Vx - ' i'-i!" '~ -' X'J- - < :> - ■■/•7':,r< 1 V> ; r - > '- re / -' - • , '- .f T - I 7 i •','/ '-O O ' ' C ' - ' ■ » / -, -\i\~c* 7 ' , . ' - ' '■ r - ' - 7~ i ! 7 T ' . , ' - , r N ' - - ; I ' , \ " . " ' • , _ ' s < > ■ • - ', ■ '. - •'. ' 17 ‘ J ' 1 - ' > ■•'-'• 7,7 7 | . i ' 7- - , 1 -~ ' 7 ■ ';' -" :7 • • ' 7 - 1 ' '-/ ' ' 7> - ' -/■ 1'. : 7 ■ ' . ,: 7 - ' , \ i. / - ' J - “ ’-. ' 1 - 7 , i: ' - , 7 '7 ' , s' ■'. i 73-' "-7 1 ' ^ ■ ' ' v ‘ ‘ ^ ‘ y ■ ' ' / > . ' / v •* - N - < i / ’ / ’**' ' " '" ’i - > ■ 7 7 -, 7 7.' - v / V '; ' ' b V ' ; ^ v ; '- \-'7 vT -'r'A '. 7>'-'; ' V,-V{ >4 ' ’ u-'v'"' \ ‘ C /"i • ’•'77' 1 l-'1 c % • ’ ' c r ' 1 Crossland, Andy 1378408 c 1996 L f . o o° Key: Beck Spring Dolomite Kingston Peak Formation (conglomerate) Kingston Peak Formation (schist) Hall Canyon Pluton D3-4 lineation D5 lineation ^ Horizontal lineation (D3-4) Horizontal lineation (D5) Key: □ □ Beck Spring Dolomite Kingston Peak Formation (conglomerate) Kingston Peak Formation (schist) Hall Canyon Pluton • Cenozoic Breccia Quaternary Sediment ' D3-4 lineation D5 lineation Horizontal lineation (D3-4) - a - 0 , Horizontal lineation (D5) I « O’- O ' ■'^■oo9r?n M ,ko»c3 o o < - " • * . ■ > o v*. o .<0' ■ ! • ? ° i = > t . ; ° & os J n:Q/77 ^V»^A?c-c 'r^i ‘ rrtO^- j3 S s S f e § a p % » ^ r n m m r n m m m m & ^ £ § f e 3 " rN ' - ■ > ■ ' - > cy r-^ u w m m . o * r ~ ~ i r y ' ' ' V d ~ ' ■ r r* > <T: \ ( 0^“ ^Oj&W - ’ LLf * if ’a? c S ^ ^ o W o PQ Q>° ° n o A°r^c '3->p>» ■»;«y O o ^ .0 „• »-P 0 V >. ^ c - > ° -V c V * o0 ,?'.^ !^ :2 r*t? r)0 aa . o - . o '> tC <0r‘ch,0 \Stt&b?xs ■°'0-<n S^- i ’ ; i ! T O l ^ W ! | ! 1 * ? r Crossland, Andv 1378408 c 1996 INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. LJMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type o f computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send U M I a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. 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Asset Metadata
Creator
Crossland, Andy
(author)
Core Title
The Hall Canyon pluton: implications for pluton emplacement and for the Mesozoic history of the west-central Panamint Mountains
School
Graduate School
Degree
Master of Science
Degree Program
Geology
Degree Conferral Date
1995-08
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
geology,OAI-PMH Harvest
Language
English
Contributor
Digitized by ProQuest
(provenance)
Advisor
Paterson, Scott R. (
committee chair
), Davis, Gregory A. (
committee member
), Morrison, Jean (
committee member
)
Permanent Link (DOI)
https://doi.org/10.25549/usctheses-c18-7588
Unique identifier
UC11357659
Identifier
1378408.pdf (filename),usctheses-c18-7588 (legacy record id)
Legacy Identifier
1378408-0.pdf
Dmrecord
7588
Document Type
Thesis
Rights
Crossland, Andy
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
Tags
geology