HR: 0800h
AN: S31A-02    [Abstracts]
TI: Variable styles of rifting expressed in crustal structure across three rift segments of the Gulf of California
AU: * Lizarralde, D D
EM: danl@whoi.edu
AF: Woods Hole Oceanographic Inst., 360 Woods Hole Rd, Woods Hole, MA 02543, United States
AU: Axen, G J
EM: gaxen@ees.nmt.edu
AF: New Mexico Tech, Department of Earth & Environmental Sciences, Socorro, NM 87801, United States
AU: Brown, H E
EM: hbrown@uwyo.edu
AF: Univ. Wyoming, Dept. of Geology and Geophysics, Laramie, WY 82071, United States
AU: Fletcher, J M
EM: jfletche@cicese.mx
AF: CICESE, Departamento de Geologia, Ensenada, BC 22860, United States
AU: Fernandez, A G
EM: mindundi@cicese.mx
AF: CICESE, Departamento de Geologia, Ensenada, BC 22860, United States
AU: Harding, A J
EM: aharding@ucsd.edu
AF: Scripps Inst. Ocng, IGPP, La Jolla, CA 92092, United States
AU: Holbrook, W S
EM: steveh@uwyo.edu
AF: Univ. Wyoming, Dept. of Geology and Geophysics, Laramie, WY 82071, United States
AU: Kent, G M
EM: gkent@ucsd.edu
AF: Scripps Inst. Ocng, IGPP, La Jolla, CA 92092, United States
AU: Paramo, P
EM: paramo@uwyo.edu
AF: BP Exploration Op. Co., Thrashers Lane, Corte Castle Wareham, Dorset, LN BH20 5JR, United Kingdom
AU: Sutherland, F H
EM: fionahsutherland@gmail.com
AF: BP Exploration Op. Co., Thrashers Lane, Corte Castle Wareham, Dorset, LN BH20 5JR, United Kingdom
AU: Umhoefer, P J
EM: Paul.Umhoefer@NAU.EDU
AF: N. Ariz. Univ., Department of Geology, Flagstaff, AZ 86011, United States
AB: We present a summary of results from a crustal-scale seismic experiment conducted in the southern Gulf of California. This experiment, the PESCADOR experiment, imaged crustal structure across three rift segments, the Alarcon, Guaymas, and San José del Cabo to Puerto Vallarta (Cabo-PV) segments, using seismic refraction/wide-angle reflection data acquired with airgun sources and recorded by closely spaced (10-15 km) ocean-bottom seismometers (OBSs). The imaged crustal structure reveals a surprisingly large variation in rifting style and magmatism between these segments: the Alarcon segment is a wide rift with apparently little syn-rift magmatism; the Guaymas segment is a narrow, magmatically robust rift; and the Cabo-PV segment is a narrow, magmatically "normal" rift. Our explanation for the observed variability is non-traditional in that we do not invoke mantle temperature, the factor commonly invoked to explain end-member volcanic and non-volcanic rifted margins, as the source of the considerable, though non-end-member variability we observe. Instead, we invoke mantle depletion related to pre-rift arc volcanism to account for observed wide, magma-poor rifting and mantle fertility and possibly the influence of sediments to account for robust rift and post-rift magmatism. These factors may commonly vary over small lateral spatial scales in regions that have transitioned from convergent to extensional tectonics, as is the case for the Gulf of California and many other rifts. Our hypothesis suggests that substantial lateral variability may exist within the uppermost mantle beneath the Gulf of California today, and it is hoped that ongoing efforts to image upper mantle structure here will provide tests for this hypothesis.
DE: 3025 Marine seismics (0935, 7294)
DE: 3075 Submarine tectonics and volcanism
DE: 8109 Continental tectonics: extensional (0905)
SC: Seismology [S]
MN: 2007 Joint Assembly