HR: 0830h
AN: T31E-0885    [PDF]
TI: Continent- Ocean Transition Across the Alarcon Basin, Gulf of California from Seismic Reflection and Refraction Data.
AU: * Sutherland, F H
EM: fi@ucsd.edu
AF: IGPP, Scripps Institution of Oceanography, UCSD, 9500 Gilman Drive, MC 0225, La Jolla, CA 92093-0225 United States
AU: Harding, A J
EM: aharding@ucsd.edu
AF: IGPP, Scripps Institution of Oceanography, UCSD, 9500 Gilman Drive, MC 0225, La Jolla, CA 92093-0225 United States
AU: Kent, G M
EM: gkent@ucsd.edu
AF: IGPP, Scripps Institution of Oceanography, UCSD, 9500 Gilman Drive, MC 0225, La Jolla, CA 92093-0225 United States
AU: Lizarralde, D
EM: danl@eas.gatech.edu
AF: Georgia Tech, 311 Ferst Drive, Atlanta, GA 30332-0340 United States
AU: Holbrook, W S
EM: steveh@uwyo.edu
AF: Univeristy of Wyoming, P.O. Box 3006, Laramie, WY 82071-3006 United States
AU: Gonz lez-Fern ndez, A
EM: mindundi@cicese.mx
AF: CICESE-Departamento de GeologĦa, Carr. Tijuana-Ensenada, km 107, Ensenada, BC C.P. 22830 Mexico
AU: Fletcher, J M
EM: jfletche@cicese.mx
AF: CICESE-Departamento de GeologĦa, Carr. Tijuana-Ensenada, km 107, Ensenada, BC C.P. 22830 Mexico
AU: Umhoefer, P J
EM: paul.umhoefer@nau.edu
AF: Northern Arizona University, P. O. Box 4099, Flagstaff, AZ 86011-4099 United States
AU: Axen, G J
EM: gaxen@ess.ucla.edu
AF: University of California, Los Angeles, 595 Charles Young Drive East, Box 951567, Los Angeles, CA 90095-1567 United States
AB: A transect of seismic reflection and onshore/offshore refraction data was collected across the Alarcon Basin, Gulf of California in Fall 2002 as part of the MARGINS Rupturing Continental Lithosphere (RCL) initiative. The dataset consists of ~600 km of seismic reflection data together with data from 53 ocean-bottom seismometers and 11 land seismometers along a coincident ~900 km refraction line. This transect crosses the entire conjugate rift system from continent to the thinned and faulted crust of the transition zone, and then to oceanic crust with an active seafloor spreading center. The Alarcon Rise is the southernmost spreading segment in the Gulf of California, separated from the East Pacific Rise by the Tamayo transform fault. Extension in the gulf began about 12 Ma and rifting was initiated at the mouth of the Gulf at the now inactive Magdalena spreading ridge about 5 Ma. Magnetic anomalies reveal that the Alarcon Rise has been spreading at an intermediate rate since 3.6 Ma. The current ridge crest is about 10 km wide, 150 m high and with a small axial valley. The data quality from the ocean-bottom seismometers is excellent, with first arrivals to at least 75 km offset, and past 100 km on many instruments. Land seismometers also produced excellent results- first arrivals are typically observed out to 200 km offset. Pg/Pn crossover distances are around 40 km in the oceanic crust of the Alarcon basin, increase to about 60-75 km in the transition zone and reach a maximum of about 100km for the continental land instruments. The total width of oceanic crust created at the Alarcon Rise, as determined from reflection profiles and initial refraction processing is about 130 km, which agrees with the bathymetric data. The transition zone is characterized by normal faulting- synrift faulting created sedimentary basins, which were later modified by additional normal faulting. The rifted margin appears to be symmetric, with about 180 km of transition zone on either side. However the southern margin is complicated by the fossil Magdalena spreading ridge, which lies about 150 km southeast of the Alarcon rise. We will present MCS results and an initial velocity model across the Alarcon basin.
DE: 3025 Marine seismics (0935)
DE: 7220 Oceanic crust
DE: 8105 Continental margins and sedimentary basins
DE: 8150 Plate boundary--general (3040)
DE: 9350 North America
SC: Tectonophysics [T]
MN: 2003 Fall Meeting