AN: T52C-1220
TI: Crustal Structure of the Continent-Ocean Boundary Zone Using Seismic Refraction and Reflection Data, Exmouth Plateau, Northwest Australia
AU: * Tischer, M
EM: mtischer@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, Route 9W, Palisades, NY 10964 United States
AU: ten Brink, U
AF: U.S. Geological Survey, Quissett Campus, 384 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Karner, G
AF: Lamont-Doherty Earth Observatory, Columbia University, Route 9W, Palisades, NY 10964 United States
AU: Goodliffe, A
AF: SOEST, University of Hawaii, 1680 East-West Rd, Honolulu, HI 96822 United States
AU: Sugimoto, M
AF: SOEST, University of Hawaii, 1680 East-West Rd, Honolulu, HI 96822 United States
AU: Taylor, B
AF: SOEST, University of Hawaii, 1680 East-West Rd, Honolulu, HI 96822 United States
AU: Driscoll, N
AF: Scripps Institution of Oceanography, UCSD, 8602 La Jolla Shores Drive, La Jolla, CA 92037 United States
AU: Sutherland, F
AF: Scripps Institution of Oceanography, UCSD, 8602 La Jolla Shores Drive, La Jolla, CA 92037 United States
AU: Babcock, J
AF: Scripps Institution of Oceanography, UCSD, 8602 La Jolla Shores Drive, La Jolla, CA 92037 United States
AU: Hollinshead, C
AF: Scripps Institution of Oceanography, UCSD, 8602 La Jolla Shores Drive, La Jolla, CA 92037 United States
AU: Ryan, D
AF: Geoscience Australia, GPO Box 378, Canberra, ACT 2601 Australia
AB: We present new seismic refraction data collected on R/V Ewing cruise EW0113 during November 2001. The purpose of the cruise was to study continental extension and breakup of the northwestern Australian margin from Greater India. Approximately 2200 kilometers of reflection data were collected together with gravity and magnetics. In addition, 400 km and 300 km-long Ocean Bottom Seismometer (OBS) refraction lines were acquired across the Exmouth Plateau and the Cuvier margin, respectively, using a total of 20 OBSs for each transect. We have analyzed the refraction data together with the corresponding gravity, magnetic, and seismic reflection data to constrain the crustal structure of the continent-ocean boundary zone across the western edge of the Exmouth Plateau. The Exmouth Plateau transect imaged the complete continent-ocean boundary zone across the margin. The boundary zone has a width of about 200 km and is flanked on the ocean side by a somewhat normal oceanic crustal section of approximately 7 km thickness topped by a 1 km thick layer consisting possibly of volcanic flows. The continental side of the transect shows a crustal thickness of about 25 km. The upper crust in this area is about 17 km thick and shows seismic p-wave velocities ranging from 4.5 km/s to 6.1 km/s. The upper crustal layer starts to thin at the beginning of the eastern edge of the continent-ocean boundary zone and reaches a thickness of about 5 km in the west. Below the upper crust, we identified a layer with a characteristic p-wave velocity of 7.1 km/s to 7.6 km/s and thickness of 5 km on the continental side that thins to about 2 km with a p-wave velocity of 7.1km/s to 7.3 km/s in the west. Previous workers have suggested the presence of an underplated layer in this region with p-wave velocities of 7.0-7.2 km/s. However, the high p-wave velocities as well as the thinning of the layer towards the ocean side offers a preliminary alternative interpretation in terms of a highly thinned and magmatically intruded lower crustal layer. Such an interpretation is consistent with extension partitioning of the crust during Mesozoic rifting.