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Plate tectonics, volcanic petrology, and ore formation in the Santa Rosalia area, Baja California, Mexico Item Type text; Thesis-Reproduction (electronic) Authors Schmidt, Eugene Karl, 1947- Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 01/10/2021 01:50:58 Link to Item http://hdl.handle.net/10150/555057 PLATE TECTONICS, VOLCANIC PETROLOGY, AND ORE FORMATION IN THE SANTA ROSALIA AREA, BAJA CALIFORNIA, MEXICO by Eugene Karl Schmidt A Thesis Submitted to the Faculty of the DEPARTMENT OF GEOSCIENCES In Partial Fulfillment of the Requirements For the Degree of MASTER OF SCIENCE In the Graduate College THE UNIVERSITY OF ARIZONA 1 9 7 5 z- STATEMENT BY AUTHOR This thesis has been submitted in partial ful­ fillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, provided that accurate ac­ knowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manu­ script in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author. SIGNED: APPROVAL BY THESIS DIRECTOR This thesis has been approved on the date shown below: Q jjaaIZ! /97.r JOHN GUILBERT Date Professo f Geology f ACKNOWLEDGMENTS Field work in the La Reforma volcanic complex was made possible by a grant from the government of Mexico through Consejo de Recursos Naturales No Renovables. I wish to thank Dr. Guillermo P . Salas, Director General of Consejo de Recursos Naturales No Renovables, for arranging this grant and making available the services of his organization in Santa Rosalia. In the field Lorenzo Aguilar was my guide, packer, boatman, and friend. His skill at maneuvering a string of burros over rugged terrain, landing a small boat in surf, and general knowledge of the area greatly facilitated my field work. I owe special thanks to Dr. John M. Guilbert, my thesis director, for introducing me to the area, arranging funding, and criticizing my thesis. Dr. John Sumner's services as pilot for the initial reconnaissance of the area, helpful advice toward my approach to the field problem, and steady plane handling during aerial photography are appreciated. Dr. B. E. Nordlie, Dr. J. F. Schreiber, Jr., offered constructive criticism of my ideas. Dr. Roy Houston of the Biology Department and Dr. Deitmar Schumacher of the Department of Geosciences identified the genus of several fossils from the Boleo formation. iii iv The Laboratory of Isotope Geochemistry, Department of Geosciences, made available the atomic absorption spec­ trophotometer for chemical analyses. Special thanks are due to Dr. James A. Fonts for his instruction in the use of the atomic absorption spectrophotometer and treatment of the resulting data. Eric Nupen did X-ray fluorescence determination of trace elements on rock samples taken from the La Reforma volcanic complex. The age dates were obtained via Paul E . Damon as "part of a cooperative research project between The University of Arizona, Laboratory of Isotope Geochemistry through N.S.F. Grant GA 31270 and the Consejo de Recursos Naturales No Renovables and have been released for inclu­ sion in this thesis only." I wish to thank Dr. Muhammad Shafiqullah and Kathleen Roe for their patience and per­ severance with the young age and low potassium values in the dated rocks. I greatly appreciate the time spent by my wife, Pat, typing, giving grammatical advice, and assisting on the home front. TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS ............................... viii LIST OF T A B L E S ..................................... xi ABSTRACT ........................................... xii INTRODUCTION ..................................... 1 Purpose and Scope of Investigation i-j cn Location . ....................... in Climate, Vegetation, and Topography Accessibility ..................... REGIONAL TECTONIC SETTING .............................. 8 STRATIGRAPHY ....................................... 11 The Stratigraphy of the Boleo and Lucifer Mining Districts ........ ........ 11 Quartz Monzonite ........................... 12 Comondd Volcanics.............. 12 Boleo Formation . ........................... 13 Gloria Formation ........................... 17 Infierno F o r m a t i o n ....................... , 18 Santa Rosalia Formation..................... 18 Tres Virgenes Volcanics................ 19 Terrace, Gravel Deposits, and A l l u v i u m .......... 19 The Stratigraphy of the La Reforma Volcanic Complex .................. ..... 20 Biotite Quartz Monzonite .................. 20 Comondu Volcanics .................. 24 Boleo Formation . ........................... 25 Gloria Formation ............................. 32 Re forma Andesite F l o w s ................... 32 Punta Arena Andesite Flows and Dikes .... 33 Canyon Diablo Diorite Porphyry ............... 36 Borrego Intrusive Sequence ......... 42 Gypsum ..... .......... ....... 56 v vi TABLE OF CONTENTS (Continued) Page Palmas Terrestrial Conglomerate ............... 58 Aro Volcanics.................................. 59 Recent Arroyo Sediments ............ .... 62 Tres Virgenes Volcanics ....................... 63 Present Arroyo Sediment and Beaches ........... 68 Regional Correlation of Stratigraphy in the Santa Rosalia A r e a ......................... 69 STRUCTURAL GEOLOGY .................................... 79 Description of Structures . ........ ..... 80 Late Miocene F a u l t s ......................... 80 Middle to Late Pliocene Faults ....... 80 Tectonic B l o c k s ........................... 83 Late Pliocene Internal Deformation of Tectonic B l o c k s ......................... 90 Structural Interpretation ......................... 90 Application of Stress Ellipsoid ............... 92 Structural Hypothesis ......................... 95 PETROLOGY AND GEOCHEMISTRY ........................... 98 Petrographic Analysis........................ 101 Description of Rocks ............ ..... 101 Interpretation of Petrography ................. 106 Whole Rock A nalysis............................... 114 Presentation and Discussion of D a t a .......... 114 Interpretation of Major Element A n a l y s i s ................................. 120 Trace Element Analysis .............. ..... 129 Presentation and Discussion of D a t a .......... 129 Interpretation of Trace Element A n a l y s i s ................................... 134 Conclusions....................................... 136 VOLCANOLOGY......................................... 139 ECONOMIC GEOLOGY ................................... 154 Description of Ore Deposits . ..................... 154 Mechanism of Boleo Ore Formation— A Hypothesis 160 Vll TABLE OF CONTENTS (Continued) Page GEOLOGIC SYNTHESIS ................................. 178 Geologic History and Conclusions About the Volcanic C o m p l e x .................. 178 Regional Interpretation ......................... 185 APPENDIX A; CALCULATION OF THE AMOUNT OF COPPER CONTAINED IN THE BOLEO T U F F .......... 188 SELECTED BIBLIOGRAPHY ............................... 190 LIST OF ILLUSTRATIONS Figure Page 1. Photograph of Cerro de La Reforma viewed from the w e s t .................... 3 2. Location map of the area studied........ 4 3. Photograph of a tinaja in biotite quartz monzonite ......................... 6 4. Geologic map of the La Reforma volcanic complex, Baja California, Mexico ........ In pocket 5. Geologic cross sections of the La Reforma vol­ canic complex,* Baja California, Mexico . In pocket 6. Generalized stratigraphy of the La Reforma volcanic complex ................ 21 7. Photograph of tuff of the Bpleo forma­ tion facing south at the base of the Arroyo de Punta Arena .................. 26 8. Photograph of the cliff south of Arroyo de Punta A r e n a ........................... 30 9. Photograph of the Punta Prieta cinder cone facing s o u t h ....................... 64 10. Photograph of the Tres Virgenes tuff in Arroyo de Punta A r e n a ................ 64 11. Photograph of columnar jointed Tres Virgenes basalt which forms Punta P r i e t a ...................... 66 12. Stratigraphic columns showing correla­ tion between the Boleo Basin and the La Reforma volcanic complex ............ 71 13. Basement blocks in the La Reforma , volcanic complex ......................... 84 viii ix LIST OF ILLUSTRATIONS (Continued) Figure Page 14. Photograph of slickensides on the Cerro de La Re forma b l o c k .............. 85 15. Timing of events in the La Reforma volcanic complex ......................... 91 16. Schmidt net showing major stress direction ............................... 94 17. Variations in mineralogy between in­ trusive and volcanic rocks .............. 104 18. Mafic mineral stability with varying amounts of water ......................... 108 19. Solubility of water in igneous melts . 110 20. Mineral stabilities in rocks of granodiorite composition ................ 113 21. Major element variations in Pliocene and Recent

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