HR: 10:35h
AN: T22A-02    [Abstracts]
TI: Detachment Faulting and Hanging-wall Segmentation in the Gulf Extensional Province, Baja California
AU: * Seiler, C
EM: c.seiler@pgrad.unimelb.edu.au
AF: School of Earth Sciences, The University of Melbourne, Melbourne, VIC 3010, Australia
AU: Fletcher, J M
EM: jfletche@cicese.mx
AF: Departamento de Geología, CICESE, Km107 Carr. Tijuana-Ensenada, Ensenada, BC 22800, Mexico
AU: Quigley, M C
EM: mquigley@unimelb.edu.au
AF: School of Earth Sciences, The University of Melbourne, Melbourne, VIC 3010, Australia
AU: Gleadow, A J
EM: gleadow@unimelb.edu.au
AF: School of Earth Sciences, The University of Melbourne, Melbourne, VIC 3010, Australia
AU: Kohn, B P
EM: b.kohn@unimelb.edu.au
AF: School of Earth Sciences, The University of Melbourne, Melbourne, VIC 3010, Australia
AB: The opening of the Gulf of California, caused by the re-localization of the Pacific -- North America plate boundary, is a premier example of an incipient passive margin. The San Felipe area in northern Baja California comprises a typical basin and range-style topography, produced by Neogene extension affecting the Gulf Extensional Province (GEP). The > 100 km long Sierra San Pedro Mártir (SSPM) escarpment is defined by an east-down normal fault system, separating the unextended western part of the peninsula from the GEP. The hanging-wall of the SSPM fault is characterized by several fault-bound blocks that have been rotated around both vertical and horizontal axes. The Las Cuevitas and the Santa Rosa detachments are two major fault systems in the Sierra San Felipe that are responsible for segmentation of the hanging-wall of the SSPM fault. The curvilinear, NE to NNW striking Las Cuevitas Detachment extends for more than 43 km and brings Neogene volcanics and sediments in contact with the Mesozoic basement of the footwall. The detachment dips at 15-50° and accommodates more than 4-6 km of east-down displacement. Faulting appears to preferentially occur at the contact of Mesozoic metamorphics to granitoid intrusives with transfer faults translating deformation between the faulted contacts. Fission track and (U-Th)/He thermochronology constrain the initiation of deformation on the Las Cuevitas detachment to the latest Miocene. The > 45 km long and equally curvilinear Santa Rosa Detachment system consists of a low-angle normal fault system (15-35° dip) with transfer zones facilitating the transfer of strain between individual segments of the detachment fault. The slip direction varies between top-to-the-east and top-to-the-south, a possible explanation for the change in strike from NW to NE to NW. The roughly 4-5 km offset of Neogene volcanic and sedimentary deposits has created the necessary space for syntectonic deposition in the Santa Rosa Basin. The onset of deformation is loosely constrained to postdate the 12.6 Ma Tuff of San Felipe, but (⁴⁰Ar/³⁹Ar), fission track, (U-Th)/He and cosmogenic nuclide dating in progress will refine the timing of deformation.
DE: 8010 Fractures and faults
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8109 Continental tectonics: extensional (0905)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting