HR: 08:00h
AN: T51E-01 INVITED     [Abstracts]
TI: Gulf of California Rift Structure and Magmatism: Guaymas Basin and Comparison With Southern Basins
AU: * Lizarralde, D
EM: danl@whoi.edu
AF: Woods Hole Ocng. Inst., MS#22, Woods Hole, MA 02543 United States
AU: Axen, G J
EM: gaxen@ees.nmt.edu
AF: New Mexico Tech, Dept. Earth and Env. Sci., Socorro, NM 87801 United States
AU: Fletcher, J M
EM: jfletche@cicese.mx
AF: CICESE, Dept. of Geology, Ensenada, BA 22860 Mexico
AU: Fernandez, A G
EM: mindundi@cicese.mx
AF: CICESE, Dept. of Geology, Ensenada, BA 22860 Mexico
AU: Harding, A J
EM: aharding@ucsd.edu
AF: Scripps Inst. Ocng, IGPP, La Jolla, CA 92037 United States
AU: Holbrook, W S
EM: steveh@uwyo.edu
AF: Univ. of Wyoming, Dept. of Geology, Laramie, WY 82071 United States
AU: Kent, G M
EM: gkent@ucsd.edu
AF: Scripps Inst. Ocng, IGPP, La Jolla, CA 92037 United States
AU: Umhoefer, P J
EM: paul.umhoefer@NAU.EDU
AF: N. Ariz. Univ., Dept. of Geology, Flagstaff, AZ 86011 United States
AU: Brown, H
EM: hbrown@uwyo.edu
AF: Univ. of Wyoming, Dept. of Geology, Laramie, WY 82071 United States
AU: Paramo, P
EM: paramo@uwyo.edu
AF: Univ. of Wyoming, Dept. of Geology, Laramie, WY 82071 United States
AU: Sutherland, F
EM: fsutherl@ucsd.edu
AF: Scripps Inst. Ocng, IGPP, La Jolla, CA 92037 United States
AB: We present a detailed seismic velocity model of the crust from margin to margin across the Guaymas Basin and compare this model with basins in the southern Gulf of California. These results are based on data from a 2002 crustal-scale, active-source seismic experiment, where multi-channel and wide-angle seismic data were acquired along three flow-line transects across Guaymas Basin, Alarcon Basin, and between Puerto Vallarta and Cabo San Lucas. Each of these transects was instrumented with ocean-bottom seismometers spaced 10-15 km apart and similarly spaced seismometers on land recording the offshore shots. The seafloor morphology of the Gulf has suggested to many that the mode of extension transitions from localized extension followed by seafloor spreading (a narrow rift) in the southern Gulf to a wide-rift mode of distributed extension in the north. This is not the case, however. The thickly sedimented Guaymas basin is a narrow rift. Lithospheric necking occurred after ~150 km of extension, and a subsequent ~300 km of extension has been accommodated by the formation of new lithosphere. The spreading center has been robustly magmatic, forming new igneous crust 7 to 10 km thick. To the south, the Alarcon basin is a wider rift, experiencing ~290 km of extension, including rift relocations, prior to the onset of seafloor spreading (~160 km of extension), which produces crust ~6 km thick. Thus, total extension for these two basins is similar (~450 km), but the mode of extension and manifestation of magmatism are very different. Differences in sedimentation may provide an explanation for the variation in magmatism between these basins, with the thicker sediments in the north providing a thermal blanket that enables more complete melt extraction from the mantle. Magmatism does not provide a sufficient explanation for the difference in rift width, however, since rifting between Cabo San Lucas and Puerto Vallarta, just one segment south of Alarcon, was particularly narrow and amagmatic. These observations indicate that a continuous, along-axis transition in rift mode does not to exist in the Gulf of California. Rather, the mode of extension seems best correlated with geologic provinces on the Baja peninsula.
DE: 3025 Marine seismics (0935, 7294)
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8109 Continental tectonics: extensional (0905)
SC: Tectonophysics [T]
MN: Fall Meeting 2005