UNIVERSITY OF CALIFORNIA Los Angeles Tectonic Reconstruction of the Southern San Andreas Fault System Using Segments of the Chocolate Mountains Anticlinorium in the San Gabriel Mountains, Southern California, U.S.A. A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Geology by Kevin Coffey 2019 © Copyright by Kevin Coffey 2019 ABSTRACT OF THE DISSERTATION Tectonic Reconstruction of the Southern San Andreas Fault System Using Segments of the Chocolate Mountains Anticlinorium in the San Gabriel Mountains, Southern California, U.S.A. by Kevin Coffey Doctor of Philosophy in Geology University of California, Los Angeles, 2019 Professor Raymond V. Ingersoll, Chair The San Gabriel Mountains of southern California contain anticlinoria of schist thought to correlate with one another, and with the Chocolate Mountains anticlinorium to the east. These correlations provide cumulative-slip estimates for the Punchbowl and southern San Andreas faults, respectively; however, the validity of these correlations, as well as the original orientations of these anticlinoria, is debated. This dissertation presents four related studies, each addressing a different aspect of this problem. Chapter 1 presents sedimentologic and structural data verifying that the two anticlinoria of the San Gabriel Mountains were continuous prior to 40-50 km of dextral slip on the Punchbowl fault, and casting doubt on the 80-110 km of dextral ii slip on the San Francisquito-Fenner-Clemens Well fault suggested by some prior studies. Chapter 2 presents structural data from the schist of the larger anticlinorium of the San Gabriel Mountains, which supports its correlation with the Chocolate Mountains anticlinorium, and thus estimates of approximately 240 km of dextral slip on the southern San Andreas fault. New data are combined with previously published structural and paleomagnetic data, which have been interpreted as implying different architectures for the anticlinorium, suggesting a model reconciling the datasets, and implying an originally linear, approximately northeast/southwest trend of the anticlinorium. Chapter 3 proposes a strain-partitioning model for the anomalously oriented Mojave segment of the southern San Andreas fault, in which slip south of this segment is partitioned within this segment into a strike-slip component along the San Andreas fault itself, and a shortening component beside it. This model, together with a previous study’s insight, brings otherwise contradictory cumulative-slip estimates of approximately 240 km and 160 km for the southern San Andreas fault into agreement. Chapter 4 presents new fault-kinematic data, and sequential reconstructions of the San Gabriel block as maps and cross sections, suggesting that the anticlinorium is in the hanging wall of a detachment fault, rather than the exhumed footwall as previously suggested. New geochronologic and geochemical data support correlation of the anticlinoria and constrain the onset of extension to ca. 26-25 Ma. iii The dissertation of Kevin Coffey is approved. An Yin Kevin D. McKeegan Gilles F. Peltzer Raymond V. Ingersoll, Committee Chair University of California, Los Angeles 2019 iv DEDICATION I dedicate this dissertation to my parents, Paula Sullivan Coffey and Lewis Coffey. Throughout my life, they encouraged and supported me in my pursuit of anything that I found interesting. Geology was one of those things, and, although it was not itself important to either of them, once I began to develop a passion for it, they made sure I had every opportunity to explore it. When administrators at the local community college tried to deny me entry to a geology course because of my young age, my mother researched and wrote a counterargument grounded in education law, and my father took the class with me. This was only the first of countless examples, big and small, from then through the present. I would never have achieved this without them. Thank you, mom and dad. v TABLE OF CONTENTS: Page: ABSTRACT ii APPROVAL PAGE iv DEDICATION v LIST OF FIGURES x LIST OF TABLES xiv LIST OF APPENDICES xv LIST OF SUPPLEMENTARY MATERIALS xvi ACKNOWLEDGMENTS xvii VITA xix FOREWORD 1 REFERENCES CITED 3 CHAPTER 1: STRATIGRAPHY, PROVENANCE, AND TECTONIC 6 SIGNIFICANCE OF THE PUNCHBOWL BLOCK, SAN GABRIEL MOUNTAINS, CALIFORNIA, U.S.A. ABSTRACT 6 INTRODUCTION 8 GEOLOGIC BACKGROUND 8 Oligocene-Miocene Basins 8 Potential Source Rocks 13 Tectonic Reconstructions of the Southern San Andreas Fault System 14 GEOLOGY OF THE PUNCHBOWL BLOCK 15 vi Stratigraphy 15 Sediment Composition 20 Structure 30 DISCUSSION 34 Basin Development 34 Regional Stratigraphic Correlations 36 Regional Tectonic and Paleogeographic Reconstructions 41 CONCLUSIONS 47 REFERENCES CITED 51 CHAPTER 2: RECONCILING STRUCTURAL AND PALEO MAGNETIC 73 DATA TO CONSTRAIN EVOLUTION OF THE CHOCOLATE MOUNTAINS ANTICLINORIUM ALONG THE SAN ANDREAS FAULT SYSTEM, SOUTHERN CALIFORNIA, U.S.A. ABSTRACT 73 INTRODUCTION 74 GEOLOGIC BACKGROUND 76 The Chocolate Mountains Anticlinorium 76 Penetrative Lineations 77 Paleomagnetic Declinations 78 METHODS 79 RESULTS 81 Mount Pinos 81 Sierra Pelona 83 vii Crafton Hills 86 DISCUSSION 89 Decoupling-Surface Model 90 Origin of Penetrative Lineations Within the Schist 92 NNW-Lineations Model 93 Comparison of the Two Models 94 Formation of NNW/SSE-Oriented Penetrative Lineations 104 Possible Relationship to Nacimiento Fault 106 Origin of Neogene-Quaternary Clockwise Vertical-Axis Rotations 107 Implications of the NNW-Lineations Model 109 CONCLUSIONS 110 REFERENCES CITED 113 CHAPTER 3: STRAIN PARTITIONING EXPLAINS DISPARATE CROSS- 134 FAULT CORRELATIONS ALONG THE SAN ANDREAS FAULT, SOUTHERN CALIFORNIA, U.S.A. ABSTRACT 134 INTRODUCTION 135 STRAIN-PARTITIONING MODEL 138 CONCLUSIONS 144 REFERENCES CITED 146 CHAPTER 4: CONSTRAINING THE GEOMETRY AND TIMING OF 155 NORMAL FAULTING AND ASSOCIATED VOLCANISM IN THE SAN GABRIEL MOUNTAINS AND ITS CROSS-FAULT CORRELATIVES, viii SOUTHERN CALIFORNIA, U.S.A. ABSTRACT 155 INTRODUCTION 156 SIERRA PELONA AND ASSOCIATED NORMAL-FAULT SYSTEM 158 Kinematics of the Pelona Fault 160 SEQUENTIAL RECONSTRUCTION OF THE SAN GABRIEL BLOCK 164 Ca. 5 Ma Reconstruction 164 Ca. 14 Ma Reconstruction 165 Ca. 18 Ma Reconstruction 165 Ca. 26 Ma Reconstruction 171 TIMING OF NORMAL FAULTING AND ANTICLINORIUM 172 DEVELOPMENT K-Ar Dating of Volcanic Flows (Previous Work) 172 Zircon U-Pb Dating of Volcanic Flows and Domes 173 Geochemistry of Volcanic Flows and Domes 176 CONCLUSIONS 182 REFERENCES CITED 183 AFTERWORD 196 REFERENCES CITED 198 APPENDICES 200 ix LIST OF FIGURES Page: Chapter 1 Figure 1-1: Regional map showing Punchbowl block, and Tejon, Soledad, and Orocopia 7 regions. Figure 1-2. Time-stratigraphic chart showing approximate ages of deposition of 9 Oligocene-Miocene strata of Punchbowl block, and of Tejon, Soledad, and Orocopia regions. Figure 1-3. Geologic map of central Punchbowl block. 17 Figure 1-4: Cross sections along section lines of Figure 1-3. 18 Figure 1-5: Schematic composite stratigraphic sections of Oligocene-Miocene strata (A) 21 south and (B) north of Blue Ridge in Punchbowl block. Figure 1-6: Sandstone composition of Oligocene-Miocene strata of Punchbowl block. 24 Figure 1-7: Relative-probability distributions of detrital-zircon U-Pb ages from 27 Oligocene-Miocene strata of Punchbowl block (A) south and (B) north of Blue Ridge. Figure 1-8: Schematic cross section showing hypothesized positive flower structure 33 along Punchbowl fault: (A) in its initial geometry, and (B) in its present, deformed geometry. Figure 1-9: Comparison of sandstone composition of Vasquez Formation of Punchbowl 37 block and Vasquez Formation of Soledad region, which are likely correlative. Figure 1-10: Schematic composite stratigraphic sections for Oligocene-Miocene strata of 38 Punchbowl block, and Tejon, Soledad, and Orocopia regions. Figure 1-11: Comparison of sandstone composition of Paradise Springs formation of 40 x Punchbowl block and Tick Canyon strata of Soledad region, which are likely correlative. Figure 1-12: Schematic representation of interpreted paleogeography, source rocks, and 46 depositional systems of Tejon-Soledad-Punchbowl-Orocopia regions. Chapter 2 Figure 2-1: Regional map and schematic restorations, showing present and restored 74 locations and schematic extents of exposures of Pelona, Orocopia, Rand, and related schists, and relevant faults. Figure 2-2: Field photos showing lineations on foliation surfaces exposed at Sierra 79 Pelona. Figure 2-3: Map of Mount Pinos area, showing measurements of A: foliation within 81 schist and mylonitic gneiss, and B: tilt-corrected penetrative and crenulation lineations within schist, and penetrative lineations within mylonitic gneiss. Figure 2-4: Foliation and lineation data from Mount Pinos area 82 Figure 2-5: Map of Sierra Pelona, showing measurements of A: foliation within schist 83 and mylonitic gneiss, and B: tilt-corrected penetrative and crenulation lineations within schist, and penetrative lineations within mylonitic gneiss. Figure 2-6: Foliation and lineation data from schist of Sierra Pelona. 84 Figure 2-7: Map of northeastern Crafton Hills, showing measurements of A: foliation 86 within schist and mylonitic gneiss, and B: tilt-corrected penetrative and crenulation lineations within schist, and penetrative lineations within mylonitic gneiss. Figure 2-8: Foliation and lineation data from northeastern Crafton Hills. 87 xi Figure 2-9: Paleotectonic reconstruction of exposures of Pelona, Orocopia, Rand,