HR: 0800h
AN: S31A-03    [Abstracts]
TI: Crustal Structure of Southern Baja California Peninsula, Mexico, and its Margins
AU: * Gonzalez, A
EM: mindundi@cicese.mx
AF: Division de Ciencias de la Tierra CICESE, Km 107 Carretera Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: Robles-Vazquez, L N
EM: lunarov@gmail.com
AF: Division de Ciencias de la Tierra CICESE, Km 107 Carretera Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: Requena-Gonzalez, N A
EM: requenan72@yahoo.es
AF: Division de Ciencias de la Tierra CICESE, Km 107 Carretera Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: Fletcher, J
EM: jfletche@cicese.mx
AF: Division de Ciencias de la Tierra CICESE, Km 107 Carretera Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: Lizarralde, D
EM: dlizarralde@whoi.edu
AF: Woods Hole Oceanographic Institution, Clark 260B, MS #22, Woods Hole, MA 02543, United States
AU: Kent, G
EM: gkent@ucsd.edu
AF: Scripps Institution of Oceanography, Institute of Geophysics and Planetary Physics, UCSD, 9500 Gilman Drive, La Jolla, CA 92093, United States
AU: Harding, A
EM: aharding@ucsd.edu
AF: Scripps Institution of Oceanography, Institute of Geophysics and Planetary Physics, UCSD, 9500 Gilman Drive, La Jolla, CA 92093, United States
AU: Holbrook, S
EM: steveh@uwyo.edu
AF: University of Wyoming, Department of Geology and Geophysics, Laramie, WY 82071, United States
AU: Umhoefer, P
EM: paul.umhoefer@nau.edu
AF: Northern Arizona University, Department of Geology, P.O. Box 4099, Flagstaff, AR 86011, United States
AU: Axen, G
EM: gaxen@ees.nmt.edu
AF: New Mexico tech, Department of Earth and Environmental Science, MSEC 208, 801 Leroy Place, Socorro, NM 87801, United States
AB: Data from 6 deep 2D multichannel seismic (MCS) lines, 1 wide-angle seismic transect and gravity were used to investigate the crustal structure and stratigraphy of the southern Baja California peninsula and its margins. An array of air guns was used as seismic source shooting each 50 m. Each signal was recorded during 16 s by a 6 km long streamer with 480 channels and a spacing of 12.5 m. Seismic waves were also recorded by Ocean Bottom Seismometers (OBS) in the Pacific and the Gulf of California and by portable seismic instruments onshore southern Baja California. MCS data were conventionally processed, to obtain post-stack time-migrated seismic sections. We used a direct method for the interpretation of the wide-angle data, including ray tracing and travel times calculation. In addition to the gravity data recorded onboard, satellite and land public domain data were also used in the gravity modeling. The combined MCS, wide-angle and gravity transect between the Magdalena microplate to the center of Farallon basin in the Gulf of California, crossing the southern Baja California Peninsula to the north of La Paz, allows to verify the existence of the Magdalena microplate under Baja California. We have also confirmed an extensional component of the Tosco-Abreojos fault zone and we have calculated crustal thicknesses. We have also observed the continuation to the south of the Santa Margarita detachment. The MCS seismic sections show a number of fault scarps, submarine canyons and grabens and horsts associated to normal faults offshore southern Baja California peninsula. The normal displacement observed in the Tosco-Abreojos fault zone and some basins in the continental platform, as well as the presence of faulted acoustic basement blocks, evidence that not all extension was accommodated by the Gulf Extensional Province during the middle to late Miocene. Part of the extension was (and is) accommodated in the Baja California Pacific margin. This confirms the observations from previous seismic lines that suggest that the peninsula is a tectonic block not completely transferred to the Pacific plate. In agreement with the seismic facies and the correlations with the available stratigraphic columns of Deep Sea Drilling Program 471 and 474, we generally identify at least three seismostratigraphic units over the acoustic basement. The lower unit reflectors dip towards the palaeo-trench. We identified a Bottom Simulating Reflector (BSR) probably associated to the presence of gas hydrates, which extends at least 200 km along three seismic lines.
DE: 0905 Continental structures (8109, 8110)
DE: 1219 Gravity anomalies and Earth structure (0920, 7205, 7240)
DE: 3025 Marine seismics (0935, 7294)
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8106 Continental margins: transform
SC: Seismology [S]
MN: 2007 Joint Assembly