CALIFORNIA STATE UNIVERSITY, NORTHRIDGE GEOLOGY AND DIKE SWARMS OF THE HOMER MOUNTAIN AREA, SAN BEP~ARDINO COUNTY, CALIFORNIA A thesis submitted in partial satisfaction of the requirements for the degree of Master of Science in Geology by Kit H. Custis January, 1984 i The Thesis of Kit H. Custis is approved: D. Carlisle, University of California, Los Angeles P.L. hllg, State Un1vers1ty, Los Angeles Un1vers1ty, G. { .3() California State University, Northridge California State University, Northridge ii ACKNOWLEDGEMENTS The author gratefully acknowledges the advice and review by the thesis committee. Dr. G.C. Dunne is especially thanked for his guidance and suggestions. Dr. P.W. Weigand is thanked for his tireless effort to keep the XRF computer running. Dr. D. Carlisle is thanked for suggesting the project. Dr. P.L. Ehlig is thanked for his reviews and field instruction. Special thanks to Dr. M.J. Walawender, San Diego State Universit~ for allowing me access to the SDSU XRF. The California State University Foundation, Northridge Students Project Committee, is gratefully acknowledged for providing funding for the K-Ar age dating and plate graphics. Peter Ertman and Albert Endo, Bureau of Land Management, River­ side, California, are thanked for arranging the loan of the air photos. Torn Anderson and Eugene Hsu, California Division of Mines and Geology, Los Angeles, California, are thanked for their effors to include my data in the Kingman 2° Geologic Sheet. Yaw Agyakawa, University of California, Los Angeles, provided helpful discussions on the dikes of the New York Mountains. Bob Griffis, California State University, Northridge is especially thanked for developing the computer programs for the geochemical analysis and plotting. iii Q ' TABLE OF CONTENTS ABSTRACT~ ..... 1:1 "' ••••• So • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • X • INTRODUCTION. 1. Location . ... ·· ................................. ., . 1. Purpose and Scope. • • • • • • • • • • • • • • • • • • • • • • • • • • • e • e 1. Methodology ... • • • 0 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 4 . Previous Work . ............................ " . 5. GEOGRAPHY ............... 7. Surface and Cultural Features................... 7. Climate and Vegetation. 9. Pioneer Settlements .... 10. GEOLOGY • ......•.•...••••••••..•••••••••••••• 11. Regional Geologic and Tectonic Setting. 11. Geochemical Analysis ..... 20. Analytical Procedure. 20. Rock Classification. 24. Results of Geochemical Analyses ............ 24. Plutonic Rocks ..... 26. Volcanic Flows and Breccias. 29. Dikes of Mafic and Intermediate Composition ........... 29. Felsic Dikes and Sills. 40. K-Ar Age Dating ............................ 43. Litho logy . ........................ 43. Precambrian and Hesozoic-Early Tertiary Plutonic Rocks ...•.... 43. General Statement. 43. Precambriam Granitoid Gneiss. 47. iv Q • Teutonia Quartz Monzonite Pluton............................ 49. Homer Mountain Quartz Monzonite Pluton .......................... ~~~~.... 51. Leucocratic and Mesocratic Aplite Dikes . ................... ~~ . 52. Quartz Veins and Pegmatite Dikes ..........•. 55. Altered Crystalline Rock of the Detachment Terrane ...............•...•.• 59. Tertiary Volcanic Flows and Breccias ............ 61. Mafic and Intermediate Composition Flows ..........................• 61. Eastern Rhyolitic Dikes and Breccias . ............. ~~~ . .. 65. Tertiary Hypabyssal Dikes .......••.......•....•. 66. General Statement ........•.................. 66. Altered Quartz Gabbro Dikes •............•... 68. Altered Quartz Andesite Dikes ............... 69. Granophyric Rhyodacite Porphyry Dikes and Sills ..............•..•.. 72. Quartz Andesite to Quartz Andesite Porphyry Dikes..................... 73. Hornblende Quartz Andesite Porphyry Dikes.............................. 74. Biotite Rhyodacite Porphyry Dikes.. 76. Quartz-Orthoclase Porphyritic Rhyodacite Dikes ...............•........•... 78. Quartz Rhyodacite Porphyry Dikes .......••... 81. Reddish Rhyodacite and Rhyodacite Porphyry Dikes. • . • . 8 2. v Tertiary Sedimentary Units................. 83. Homer Mountain Conglomerate........... 83. Quaternary Sedimentary Units... 85. General Statement..................... 85. Consolidated Alluvium (Qc) ...•......•. 86. Older Alluvium (Qoal)................. 89. Recent Alluvium {Qal) . • . 90. Structures. 90. Foliations and Mylonitic Zones .•.... ~...... 90. Joints ..................................... 94. East-West-Trending Joints............. 94. North-Trending Secondary Joints ....................•. 101. Faults..................................... 101. Northwest- and Northeast- Trending Faults ....................... 101. Low-Angle Normal (Detachment) Faults................... 107. High-Angle Normal (Basin and Range) Faults ......•.....•. 116. Quaternary Faults ....................• 121. Dike Structures ...................•.•••.... 123. Economic Geology . , . .. 124. Mineralization in the Surrounding Region ..................•.....• 124. Mineralization in the Homer Mountain Area ...............•.......• 125. Transverse Structures of the Southern Cordillera............................ 12-a. SUMMARY. • . • • • • • . • • • . • . • • • . • • • • • • • • . • . • • . • • • • • • • • • • 13 8 • vi References ................... ~. & • • • • • • • • • • • • • • • • • 144-154. APPENDICES APPENDIX A Table A-1: Major Oxides and Normative Minerals ...•..•..............•.... 155-165. APPENDIX B Loss On Ignition Values ...................•.. 166-168. ILLUSTRATIONS Figure Number 1. Index Map . ............................. 2-3. 2. Normative Mineral QAP Plots of Plutonic Rocks .....•........... 27-28. 3. Normative Mineral QAP Plots of Andesitic Flows and Rhyolitic Breccias .. 30-31. 4. Normative Mineral QAP and AFM Plots of Mafic and Intermediate Composition Dikes ...................... 33-34. 5. Classification Diagrams of Tertiary Mafic, Intermediate, and Felsic Dikes ... 35-36. 6 . Harker Diagrams of Tertiary Mafic, Intermediate, and Felsic Dikes ... 37-38. 7. Normative Mineral QAP and AFM Plots of Felsic Dikes .................. 41-42. 8. Plots of Leucocratic Aplite dikes, Rose and Schmidt Net ..........•......... 53-54. 9. Plots of Quartz Veins, Rose and Schm.id t Net . ................•....•...... 57-58. 10. Plots of Andesitic and Quartz Andesite Flow Layering, Schmidt Net ............•• 63-64. vii 11. Plots of Mafic and Intermediate Dikes, Rose and Schmidt Net .•.•••....•.. 70-71. 12. Plots of Felsic Dikes, Rose and Schmidt Net ............•..•.....•... 79-80. 13. Plots of Foliations and Mylonite Lineations, Schmidt Net ...........•.••.. 92-93. 14. Plots of East-West-Trending Joints, Rose and Schmidt Net ..........••.....•.• 96-97. 15. Joints Commonly Found in Folded Rocks and Pinnate Fractures............. 98-99. 16. Plots of North-Trending Secondary Joints, Rose and Schmidt Net.. 102-103. 17. Plots of Northwest- and Northeast Trending Paul ts, Rose and Schmidt Net... 105-106. 18. Plots of Detachment Faults, Schmidt Net. 109-110. 19. Graphic Calculations of Amount of Granophyric Rhyodacite Dike Displacement by Detachment Fault ........ 113-114. 20. Plots of High-Angle Basin-Range Style Faults, Rose and Schmidt Net ...... 117-118. 21. Transverse Structures of the Southern Cordillera, Western United States ....... 134-135. TABLES Table Number 1. Tertiary Dike Swarms-Lower Colorado River Region .............. .............. 21-23. 2. Summary of Rock Classifications Based on Geochemical Analyses •.....•.••. 25. 3. Potassium-Argon Dates on Igneous Rocks From the Horner Mountain Area ...•.. 44. 4. Transverse Structures................... 129-133. viii 5. Summary of Regional and Local Tectonic Event~ •..•......•.•.•••.••.. 139. PLATES Plate Number 1. Geologic Map and Sections of the Horner Mountain Area, San Bernardino County, California ...........•.•..... in pocket 2. Dike Swarms of Horner Mountain Area, San Bernardino County, California..... in pocket ix Q • A B S T R A C T GEOLOGY AND DIKE SWARMS OF THE HOMER MOUNTAIN AREA, SAN BERNARDINO COUNTY, CALIFORNIA by Kit H. Custis Master of Science in Geology Homer Mountain is located in the northern portion of the eastern Mojave Desert Province. Basement rock exposed in the 250 km 2 study area consists of Precambrian large K-spar granitoid gneiss which is intruded by two Late Cretaceous peraluminous quartz monzonite plutons (Teutonia and Homer Mountain plutons). These plutons are similiar to the Mid Hills adamellite of the Teutonia batholithic complex of the New York Mountains. Developed within the eastern portion of the Precambrian basement, prior to the late Mesozoic plutonism, are a small number of thin, north-trending , east-dipping mylonitic zones. An early Tertiary or older system of generally north­ trending altered tholeiitic quartz gabbro dikes are exposed in the central portion of the study area and intrude these basement rocks. Northwest- to northeast­ trending conjugate leucocratic aplite dikes are inter~ preted to have been intruded along with scattered mineralized quartz veins during the final stage of Late X @ • Cretaceous plutonism. Late Cretaceous to early Tertiary (?) submarginally economic molybdenium-copper-tungsten mineralization in the western portion of the study area accompanied em­ placement of the quartz veins along a northwest-trending shear zone and east-west-trending joints. Younger middle Tertiary age hydrothermal mineralization appears to have accompanied the intrusion of numerous east-west-trending felsic dikes. A similar pattern