San Jose State University SJSU ScholarWorks Master's Theses Master's Theses and Graduate Research Summer 2017 Construction and Emplacement of Cretaceous Plutons in the Crystal Range, Southwest of Lake Tahoe, California Brad Buerer San Jose State University Follow this and additional works at: https://scholarworks.sjsu.edu/etd_theses Recommended Citation Buerer, Brad, "Construction and Emplacement of Cretaceous Plutons in the Crystal Range, Southwest of Lake Tahoe, California" (2017). Master's Theses. 4837. DOI: https://doi.org/10.31979/etd.eyj9-3w7m https://scholarworks.sjsu.edu/etd_theses/4837 This Thesis is brought to you for free and open access by the Master's Theses and Graduate Research at SJSU ScholarWorks. It has been accepted for inclusion in Master's Theses by an authorized administrator of SJSU ScholarWorks. For more information, please contact [email protected]. CONSTRUCTION AND EMPLACEMENT OF CRETACEOUS PLUTONS IN THE CRYSTAL RANGE, SOUTHWEST OF LAKE TAHOE, CALIFORNIA A Thesis Presented to The Faculty of the Department of Geology San José State University In Partial Fulfillment of the Requirements for the Degree Master of Science by Brad Buerer August 2017 © 2017 Brad Buerer ALL RIGHTS RESERVED The Designated Thesis Committee Approves the Thesis Titled CONSTRUCTION AND EMPLACEMENT OF CRETACEOUS PLUTONS IN THE CRYSTAL RANGE, SOUTHWEST OF LAKE TAHOE, CALIFORNIA by Brad Buerer APPROVED FOR THE DEPARTMENT OF GEOLOGY SAN JOSÉ STATE UNIVERSITY August 2017 Dr. Robert Miller Department of Geology Dr. Jonathan Miller Department of Geology Dr. Dave Andersen Department of Geology ABSTRACT CONSTRUCTION AND EMPLACEMENT OF CRETACEOUS PLUTONS IN THE CRYSTAL RANGE, SOUTHWEST OF LAKE TAHOE, CALIFORNIA by Brad Buerer Three Cretaceous plutons are investigated to determine their construction and emplacement histories, focusing on magmatic foliation patterns and contact relationships with each other and with the Jurassic metasedimentary host rocks of the Sailor Canyon Formation. The earliest Cretaceous Pyramid Peak granite is a leucocratic pluton with extensive co-magmatic diorite and granite-diorite hybrid rock. It contains a single NNW -striking magmatic foliation that probably reflects the regional stress field at the time of crystallization. The granite was constructed by multiple magmatic increments, though internal contacts are scarce in homogeneous parts of the pluton. Emplacement was accommodated by roof uplift, a modest degree of floor sinking, and the brittle transfer of host via stoping. The mid-Cretaceous Wrights Lake granodiorite is largely homogeneous, except near the margin, and has abundant microgranitoid enclaves and schlieren. This granodiorite has two overprinting magmatic foliations: a contact-parallel foliation that is interpreted to reflect filter pressing and/or flow of magma against the margin, and an east-west discordant foliation that reflects regional strain. Xenoliths of Sailor Canyon Formation and Pyramid Peak granite are common near the margin, demonstrating stoping. The markedly homogenous, weakly foliated Tyler Lake granodiorite has poorly exposed contacts and few conclusions could be made about its history, but brittle transfer of host probably played a role. Plutons in the region document a transition in the regional strain field between the early and middle Cretaceous. ACKNOWLEDGMENTS I would like to thank everyone involved in helping me accomplish this task. Thanks to my friends and family for supporting me and encouraging me to get through this thing. Thanks to my trusty field assistants Mireya Berrios, Chris Bonnette, Pablo Cortez, and Monika Leopold for keeping me company in the field, preventing me from dying, and helping find cool stuff in rocks. Thanks to Alphonse Odisho for listening to me whine about the old rock saw and for all the assistance back on campus. Thanks to my thesis committee members, Jonathan Miller and Dave Andersen, for guiding me through my undergrad and grad school adventures and for helping me pull this document together. And thanks to my advisor, Bob Miller, for inspiring me to pursue geology in the first place, many, many (many) years ago, for guiding me through this wild journey of perplexing plutonic puzzles, and for providing endless ideas and suggestions that made this thesis far better than it could have been otherwise. I would also like to thank the Geological Society of America for providing partial funding through a student research grant. v TABLE OF CONTENTS LIST OF FIGURES ........................................................................................................ viii LIST OF PLATES ............................................................................................................. x INTRODUCTION .............................................................................................................. 1 Geologic Setting............................................................................................................ 5 Methods......................................................................................................................... 7 PLUTONS AND HOST ROCKS ....................................................................................... 8 Sailor Canyon Formation .............................................................................................. 8 Pyramid Peak Granite ................................................................................................. 10 Desolation Valley Granodiorite .................................................................................. 16 Wrights Lake Granodiorite ......................................................................................... 16 Tyler Lake Granodiorite ............................................................................................. 25 STRUCTURE ................................................................................................................... 29 Folding of the Sailor Canyon Formation .................................................................... 29 Mineral Fabric Patterns ............................................................................................... 31 Shear Zones ................................................................................................................. 35 Dikes ........................................................................................................................... 39 INTRUSIVE RELATIONSHIPS...................................................................................... 44 Pyramid Peak Granite - Sailor Canyon Formation Contact ........................................ 44 Wrights Lake Granodiorite - Sailor Canyon Formation Contact ................................ 50 Wrights Lake Granodiorite - Pyramid Peak Granite Contact ..................................... 53 Tyler Lake Granodiorite - Pyramid Peak Granite Contact ......................................... 54 DISCUSSION ................................................................................................................... 60 Pluton Construction .................................................................................................... 60 vi Construction of the Pyramid Peak Granite ........................................................... 60 Construction of the Wrights Lake Granodiorite ................................................... 63 Construction of the Tyler Lake Granodiorite........................................................ 65 Pluton Emplacement ................................................................................................... 66 Emplacement of the Pyramid Peak Granite .......................................................... 67 Emplacement of the Wrights Lake Granodiorite .................................................. 70 Emplacement of the Tyler Lake Granodiorite ...................................................... 73 Regional Strain............................................................................................................ 73 CONCLUSIONS............................................................................................................... 75 REFERENCES CITED ..................................................................................................... 77 vii LIST OF FIGURES Figure 1. Simplified geologic map of the Crystal Range and surroundings, modified from Saucedo (2005)......................................................................................... 4 Figure 2. Simplified geologic map of the study area, modified from Saucedo (2005).... 6 Figure 3. Concretion in fractured siltstone of Sailor Canyon Formation......................... 9 Figure 4. Enclave swarms within the Pyramid Peak granite............................................ 13 Figure 5. Features within Pyramid Peak granite enclave swarms.................................... 14 Figure 6. Mingling relationships between standard and leucocratic Wrights Lake granodiorite....................................................................................................... 19 Figure 7. Amorphous 1.8-m-diameter schlieren “blob” in the Wrights Lake granodiorite....................................................................................................... 20 Figure 8. Offset microgranitoid enclaves in the Wrights Lake granodiorite................... 21 Figure 9. Cluster of rounded enclaves in the Wrights Lake granodiorite........................ 22 Figure 10. Enclave accumulations near the margin of the Wrights