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Paleomagnetic Quantification of Neogene Block Rotations Within an Active Transtensional Plate Boundary, Baja California Sur, Mexico

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Paleomagnetic Quantification of Neogene Block Rotations Within an Active Transtensional Plate Boundary, Baja California Sur, Mexico Ludwig-Maximilians-Universität München Paleomagnetic Quantification of Neogene Block Rotations within an Active Transtensional Plate Boundary, Baja California Sur, Mexico Inaugural-Dissertation zur Erlangung des Doktorgrades der Fakultät für Geowissenschaften der Ludwig-Maximilians-Universität München vorgelegt von Josef Weber am 21. Mai 2012 1. Berichterstatter: Prof. Dr. V. Bachtadse 2. Berichterstatter: Prof. Dr. H. C. Soffel Tag der mündlichen Prüfung: 13.07.2012 Table of contents Table of contents List of figures ............................................................................................................ 3 List of tables .............................................................................................................. 5 Glossary ..................................................................................................................... 6 Abstract ..................................................................................................................... 8 1. Introduction ......................................................................................................... 11 1.1 State of the art........................................................................................................ 13 1.2 Scientific aims and study areas.............................................................................. 16 2. Tectonic evolution of the Gulf of California ..................................................... 19 2.1 Subduction of the Farallon Plate and arc-related volcanism (30-12 Ma).............. 19 2.2 Proto-Gulf stage of rifting (12 – 8-6 Ma) – two-phase kinematic model.............. 25 2.3 Alternative model of proto-Gulf development – one-phase kinematic model ...... 27 2.4 Oblique-divergent stage (8-6 Ma – present).......................................................... 30 2.5 Amount of displacement (one-phase vs. two-phase kinematic model)................. 33 2.6 Present day setting................................................................................................. 37 3. Geology of the study areas .................................................................................. 42 3.1 San José del Cabo Basin and Sierra La Trinidad .................................................. 42 3.1.1 San José del Cabo Basin evolution.................................................................. 42 3.1.2 Geological units in the San José del Cabo Basin and Sierra La Trinidad........ 46 3.1.2.1 La Calera Formation...........................................................................................46 3.1.2.2 Trinidad Formation.............................................................................................47 3.1.2.3 Refugio Formation..............................................................................................48 3.1.2.4 Los Barriles Formation.......................................................................................48 3.1.2.5 El Chorro Formation...........................................................................................49 3.1.2.6 Igenous rocks......................................................................................................49 3.2 Bay of La Paz area................................................................................................. 50 3.2.1 Tectonics.......................................................................................................... 50 3.2.2 Geology............................................................................................................ 52 3.3 San José and San Francisco Island........................................................................54 Table of contents 4. Vertical-axis block rotation and previous studies ............................................ 56 5. Field and laboratory methods ............................................................................ 60 6. Paleomagnetic results ......................................................................................... 62 6.1 San José del Cabo Basin and Sierra La Trinidad .................................................. 63 6.1.1 La Calera Formation........................................................................................ 63 6.1.2 Trinidad Formation.......................................................................................... 68 6.1.3 Refugio Formation........................................................................................... 69 6.1.4 El Chorro Formation........................................................................................ 70 6.1.5 Igneous rocks................................................................................................... 71 6.1.6 Summary.......................................................................................................... 74 6.2 Bay of La Paz area ................................................................................................ 77 6.2.1 La Paz area....................................................................................................... 77 6.2.2 Summary of La Paz area data.......................................................................... 81 6.2.3 San Juan de la Costa........................................................................................ 84 6.2.4 Summary of San Juan de la Costa data............................................................ 87 6.3 San José and San Francisco Island........................................................................ 89 6.3.1 San José Island........................................................................................... 89 6.3.2 San Francisco Island................................................................................... 90 6.3.3 Summary.................................................................................................... 92 7. Rockmagnetic studies ......................................................................................... 95 7.1 Methods................................................................................................................. 95 7.2 Results................................................................................................................... 95 7.2.1 San José del Cabo Basin and Sierra La Trinidad ........................................... 96 7.2.2 Bay of La Paz area........................................................................................... 98 7.2.3 San José and San Francisco Island .................................................................. 98 8. Discussion and conclusion ................................................................................ 100 References .............................................................................................................. 110 Acknowledgments ................................................................................................. 137 List of figures List of figures 1.1 Comparison of orthogonal and oblique-divergent rifting.................................. 12 1.2 Overview of the Baja California Peninsula Borderland .................................... 15 1.3 Overview of the study areas .............................................................................. 17 2.1 Tectonic setting in the region of present Baja California 29 Ma ago.......................................................................................................... 20 2.2 Tectonic setting in the region of present Baja California 24–25 Ma ago.................................................................................................... 21 2.3 Tectonic setting in the region of present Baja California between 20 and 12 Ma ago................................................................................ 23 2.4 Tectonic setting in the region of present Baja California at 12 Ma................... 24 2.5 Protogulf phase of rifting (two-phase kinematic model)................................... 26 2.6 Alternative kinematic model ............................................................................. 29 2.7 Tectonic setting in the region of present Baja California about 8 Ma ago.................................................................................................. 30 2.8 Tectonic setting in the region of present Baja California about 3.6 Ma ago............................................................................................... 31 2.9 Illustration of the two-phase kinematic model.................................................. 34 2.10 Illustration of the one-phase kinematic model .................................................. 36 2.11 Present day tectonic setting in the Gulf of California region ............................ 38 2.12 Map of accommodation zones in Baja California Sur....................................... 40 2.13 Tectonic setting of Baja California Sur............................................................. 41 3.1 Geological map of the San José del Cabo Basin and the Sierra La Trinidad........................................................................................ 43 3.2 Overview of stratigraphic units in the San José del Cabo Basin and the Sierra La Trinidad........................................................................................ 45 3.3 Geological map of the Bay of La Paz area........................................................ 51 3.4 Volcanic facies model of Baja California Sur................................................... 53 3.5 Geological
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