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Late Cenozoic-Recent Tectonics of the Southwestern Margin of the Tibetan Plateau, Ladakh, Northwest India

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Late Cenozoic-Recent Tectonics of the Southwestern Margin of the Tibetan Plateau, Ladakh, Northwest India Late Cenozoic-recent tectonics of the southwestern margin of the Tibetan Plateau, Ladakh, northwest India by Wendy Bohon A Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Approved April 2014 by the Graduate Supervisory Committee: Kip Hodges Ramon Arrowsmith Arjun Heimsath Kelin Whipple Stephen Reynolds ARIZONA STATE UNIVERSITY May 2014 DEDICATION This work is dedicated to my grandmother, Eunice Waterfield Boyette, who was a model of perseverance and dedication, and to my parents, Dean and Linda Bohon, who always believed I could do anything. i ACKNOWLEDGMENTS First, I need to give a sincere and hearty thank you to my advisors, Ramon Arrowsmith and Kip Hodges. You have both been incredible sources of inspiration and support, and I am grateful for your guidance during this processes. I would also like to thank my committee, Kelin Whipple, Arjun Heimsath, and Steve Reynolds for providing mentorship and support for the last several (or more!) years. I must also give a special acknowledgement to Matthijs van Soest and Jo-Anne Wartho for their patience and mentorship in the laboratory. I would also like to thank Thijs for many informative and helpful discussions about my data. I must also thank the JMARS team, especially Chris Edwards and Scott Dickenshied, for their help with all aspects of the ASTER remote sensing. My advisors and other mentors have been amazing, but my fellow graduate students also deserve special recognition for the integral part they have played in my educational journey. Many thanks to all of the students in the Hodges and Arrowsmith research groups- and to the larger surfaces processes crew- especially the folks in Room 603. Special thanks to Matt Jungers and Matt Rossi for help with CRN lab work and data processing. Many thanks to Byron Adams for all of his codes, and for hundreds of hours at the board talking about geothermal gradients. My deepest and sincerest thanks go to Aka Tripathy-Lang for all of the things-without you I wouldn’t be here. I would also like to thank the Wednesday night crew for providing much-needed stress-relief, friendship and laughter. ii Working in remote parts of the world requires special planning, and I would like to thank C.P. Dorjay for his assistance in organizing our trips and keeping us safe. I would also like to acknowledge all of the wonderful drivers, cooks and helpers who made our fieldwork so safe and enjoyable. Additionally, many thanks to Nathaniel Borneman, Alka Tripathy, Kip Hodges and Ramon Arrowmsith for help in the field. Special thanks to Nateki and Ramon for digging all of the holes! I would also like to acknowledge the Graduate and Professional Student Association at ASU, Sigma Xi and Kip Hodges for funding my fieldwork, and Kip Hodges and Ramon Arrowsmith for funding my lab work. Finally, I would like to acknowledge my family. Thank you to my mom, dad and sister for always believing in me, no matter what crazy road I decide to travel. Thanks especially to my dad, for inspiring my curiosity about the nature world. A huge thank you is due to my husband, Scott Clarey, and my daughter, Abigail Clarey, for their love and support during this long (and sometimes trying) process. I appreciate all of the sacrifices you’ve had to make to allow me the time to finish this work. I love you. iii ABSTRACT The Himalayan orogenic system is the youngest and most spectacular example of a continent-continent collision on earth. Although the collision zone has been the subject of extensive research, fundamental questions remain concerning the architecture and evolution of the orogen. Of particular interest are the structures surrounding the 5 km high Tibetan Plateau, as these features record the collisional and post-collisional evolution of the orogen in this area. In this study we examine structures along the southwestern margin of the Tibetan Plateau, including the Karakoram (KFS) and Longmu Co (LCF) faults, and the Ladakh, Pangong and Karakoram Ranges. New low-temperature thermochronology data collected from across the Ladakh, Pangong and Karakoram Ranges improved the spatial resolution of exhumation patterns adjacent to the edge of the plateau. These data show a southwest to northeast decrease in cooling ages, which we believe a wave of increased exhumation due to north-south shortening. We also posit that this shortening is responsible for the orientation of the LCF in India. Previously, the southern end of the LCF was unmapped. We used ASTER remotely sensed images to create a comprehensive lithologic map of the region, which allowed us to map the LCF into India. This mapping shows that this fault has been rotated into parallelism with the Karakoram fault system as a result of N-S shortening and dextral shear on the KFS. Additionally, the orientation and sense of motion along these two systems implies that they are acting as a conjugate fault pair, allowing the eastward extrusion of the Tibet. Finally, we identify and quantify late Quaternary slip on the Tangtse strand of the KFS, which was previously believed to be inactive. Our study found that this fault strand iv accommodated ca. 6 mm/yr of slip over the last ca. 33-6 ka. Additionally, we speculate that slip is temporally partitioned between the two fault strands, implying that this part of the fault system is more complex than previously believed. v TABLE OF CONTENTS Page CHAPTER 1 INTRODUCTION .................. ... .................................................................................. 1 1. Motivation .............................................................................................. 1 2. Outline of Chapters 2-5 .......................................................................... 3 3. References .............................................................................................. 6 2 LITHOLOGY FROM SPACE: USING ASTER REMOTE SENSING TO MAP REMOTE TERRESTRIAL AREAS ......................................................... 10 1. Abstract ................................................................................................ 10 2. Introduction .......................................................................................... 11 3. Background .......................................................................................... 12 3.1 ASTER .......................................................................................... 12 3.2 Geologic setting of Ladakh ........................................................... 13 4. ASTER image analysis ........................................................................ 15 4.1 Data acquistion .............................................................................. 16 4.2 Data exclusion masks .................................................................... 17 4.3 Image processing .......................................................................... 18 4.4 Laboratory spectra ........................................................................ 19 5.Creating a lithologic map ...................................................................... 21 5.1 Decorrelation stretch and analysis ................................................ 22 5.2 Spectral averaging (pixel averaging) ............................................ 22 5.3 Comparing laboratory spectra and ASTER spectra ..................... 23 vi 6. Discussion ............................................................................................ 25 7. Conclusions .......................................................................................... 27 8. References ............................................................................................ 28 9. Figures .................................................................................................. 35 3 REFINING ESTIMATES OF QUATERNARY SLIP ALONG THE KARAKORAM FAULT SYSTEM, LADAKH, NORTHWEST INDIA 43 1. Abstract ............................................................................................ …43 2. Introduction ...................................................................................... …46 3. The Karakoram fault system in Ladakh and adjacent Tibet ............... 48 4. Late Quaternary slip on the Tangtse strand ......................................... 49 5. Methods ................................................................................................ 53 6. Constraints on the timing of late Quaternary activity ......................... 53 7. Implications .......................................................................................... 56 8. Conclusions .......................................................................................... 57 9. References ............................................................................................ 57 10. Figures ................................................................................................ 63 11. Tables ................................................................................................. 70 4 MIOCENE EXHUMATION HISTORY OF THE CENTRAL LADAKH BATHOLITH, NW INDIA ......................................................................... 71 1. Abstract ................................................................................................ 71 2. Introduction .......................................................................................... 72 3. Geologic setting ................................................................................... 73 4. Previous work on Ladakh
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