ALONG STRIKE VARIATION AND THE ROLE OF FAULT PROPAGATION FOLDING IN GENERATION OF STRUCTURAL RELIEF IN THE KOCHKOR VALLEY, TIEN SHAN, KYRGYZSTAN by KATHRYN TERESA PAULSON A THESIS Presented to the Department of Geological Sciences and the Graduate School of the University of Oregon in partial fulfillment of the requirements for the degree of Master of Science September 2013 THESIS APPROVAL PAGE Student: Kathryn Teresa Paulson Title: Along Strike Variation and the Role of Fault Propagation Folding in Generation of Structural Relief in the Kochkor Valley, Tien Shan, Kyrgyzstan This thesis has been accepted and approved in partial fulfillment of the requirements for the Master of Science degree in the Department of Geological Sciences by: Samantha Hopkins Chair Ray Weldon Advisor Marli Miller Member and Kimberly Andrews Espy Vice President for Research and Innovation; Dean of the Graduate School Original approval signatures are on file with the University of Oregon Graduate School. Degree awarded September 2013 ii © 2013 Kathryn Teresa Paulson iii THESIS ABSTRACT Kathryn Teresa Paulson Master of Science Department of Geological Sciences September 2013 Title: Along Strike Variation and the Role of Fault Propagation Folding in Generation of Structural Relief in the Kochkor Valley, Tien Shan, Kyrgyzstan The southern margin of the Kochkor Basin in the Kyrgyz Tien Shan is actively shortening. The South Kochkor Fault, a reverse fault that places Paleozoic granite on Neogene sediments, varies in displacement from 0-2 km while the structural relief across the basin margin is 4 km. North of the fault, a 2 km thick panel of steeply-dipping to overturned sediments exhibits flexural shearing. This steep section is bounded by limbs of gently-dipping beds to the north and south. Northward, Neogene section is thrust over late Quaternary deposits in two younger episodes of faulting: the Akchop Hills Fault and the Aigyrdzal Hills Fault. Through 1:25,000 scale mapping I have demonstrated that of structural relief in the area is shared by fault propagation folding and faulting on a steep, reverse fault that shallows into a detachment. A complete geologic map of Kochkor, Kyrgyzstan is included with this thesis as a supplemental file. iv CURRICULUM VITAE NAME OF AUTHOR: Kathryn Teresa Paulson GRADUATE AND UNDERGRADUATE SCHOOLS ATTENDED: University of Oregon, Eugene University of Washington, Seattle DEGREES AWARDED: Master of Science, Geology, 2013, University of Oregon Bachelor of Science, Geology, 2011, University of Washington AREAS OF SPECIAL INTEREST: Structural Geology PROFESSIONAL EXPERIENCE: Graduate Teaching Fellow, University of Oregon, Sept 2011-Sept 2013 Teaching Assistant, University of Washington, Jan 2010-Jun 2011 GRANTS, AWARDS, AND HONORS: Travel Grant, Masters field work, University of Oregon, 2012 North Seattle Lapidary and Mineral Club Scholarship, University of Washington, 2010 A. Woolley and J.W. Crooks Scholarship, University of Washington, 2010 University of Washington Dean’s List Annual Dean’s List: 2006 – 2007 academic school year Spring 2008 Winter/Spring/Summer 2010 v ACKNOWLEDGMENTS I would like to acknowledge and thank the Kyrgyz aids who helped me in the field, Kanatbek Abdrakhmatov, Imankulov Segyn, Atyr Djumabaeva and Azat Said; they made my time in Kyrgyzstan run smoothly and feel like home. Thank you to Nyle Weldon, for his help in the field and great attitude. I thank my committee members, Samantha Hopkins, Marli Miller and advisor Ray Weldon for feedback, support and encouragement. Special thanks to my cohorts and office mates, Ashley Streig, James McNabb and Lauren Austin, who helped with brainstorming, technology concerns and emotional support and encouragement. This project was a pleasure to be a part of and everyone who has contributed made it that much better. vi TABLE OF CONTENTS Chapter Page I. INTRODUCTION .................................................................................................... 1 Geologic Setting..................................................................................................... 6 Lithology .......................................................................................................... 6 Tectonics .......................................................................................................... 14 Methods............................................................................................................ 15 II. RESULTS................................................................................................................ 18 Map Data ................................................................................................................ 18 Structural Results ................................................................................................... 22 III. DISCUSSION ........................................................................................................ 32 Structural Implications .......................................................................................... 32 Comparison to Other Work ................................................................................... 37 Conclusion ............................................................................................................ 46 REFERENCES CITED ................................................................................................ 48 SUPPLEMENTAL FILE COMPLETE GEOLOGIC MAP vii LIST OF FIGURES Figure Page 1. Map of India-Eurasia boundary indicating direction of relative plate motion. Landsat image of Issyk-Kul region of the central Tien Shan ................................ 2 2. Major faults of the central Tien Shan .................................................................... 3 3. Simplified map of field area showing primary faults and fold hinges. .................. 5 4. Small scale cross section adapted from Abdrakhmatov et al. (2001) .................... 6 5. Coarse-grained, feldspar-rich Paleozoic granite .................................................... 7 6. Unconformable contact between Paleozoic granite and Neogene sediments ......................................................................................... 9 7. Coarse, well-bedded sandstones from lower Bjer Formation ................................ 10 8. Beds of fine-grained mud, silt and sandstone of the lower Djuanarik Formation .................................................................................... 11 9. The contact between upper Chu equivalent and Sharpyldak ................................ 13 10. Field assistants Azat and Nyle measure attitudes in the upper Shamsi equivalent ........................................................................................ 16 11. Tight, nearly isoclinal parasitic folds in upper Shamsi equivalent ........................ 19 12. The South Kochkor Fault east of the Djuanarik River .......................................... 20 13. Two map localities of triple fold hinges splaying out from a single fold ................................................................................................... 21 14. Examples of narrow fold hinges ............................................................................ 22 15. Simplified area map showing locations of the three cross section transects ............................................................................................ 23 viii Figure Page 16. Cross section A-A’ ................................................................................................. 24 17. Schematic illustration of the temporal relationships between major structures ...................................................................................................... 26 18. Cross section B-B’ ................................................................................................. 28 19. Cross section C-C’ ................................................................................................. 30 20. Russian maps and cross sections............................................................................ 39 21. Terrace profiles along the west side of the Djuanarik River ................................. 41 22. A cross section from the southern margin of the Issyk-Kul Basin ........................ 46 ix CHAPTER I INTRODUCTION The Tien Shan mountain range (“Heavenly Mountains” in Chinese) is an actively deforming zone within the Eurasian plate (Figure 1). This intercontinental orogeny is caused by the collision of India with Eurasia and currently accommodates about half of the shortening generated by the plate boundary (Abdrakhmatov et al. 1996; Holt et al. 2000). The Tien Shan consists of alternating uplifting ranges, built by thick-skinned faulting and basement-involved folding and intermontane basins filled with syntectonic sediments. Faults along the South Kochkor Basin margin account for around 15% of this total shortening within the central Tien Shan (Abdrakhmatov et al. 2001). Throughout the central Tien Shan, similar structural basins have been studied (Figure 2). The three we will discuss here are the Chu Basin (Bullen et al. 2003), Naryn Basin (Burbank et al. 1999) and the Issyk-Kul Basin (Burgette, 2008). These basins are all basement-bounded and contain steep reverse faults, but accommodate shortening with slight variations in structures and structural relationships (Figure 2). The relatively young Tersky Ala-Too range forms the southern margin of the Kochkor Basin (Figure 2) bounding a thick (~3.5-4 km) section