HR: 0830h
AB: Bransfield Strait is a backarc basin situated between the northern Antarctic Peninsula (AP) and the South Shetland Islands (SSI). Multichannel seismic (MCS) reflection studies do not image Moho and lower crustal structure; however, they document extensional structure in the upper crust that suggests: (i) extension propagates from NE-to-SW; (ii) volcanics of the axial neovolcanic zone are more voluminous in the NE than in the SW; (iii) high-amplitude reflections associated with pervasive listric faulting of the AP margin suggest basinwide magmatism (sill-intrusion?) associated with distributed extension; (iv) extension occurs through magmatic inflation followed by collapse involving pervasive listric faulting soling into basinward-dipping detachment systems; (v) detachments may signify basinwide simple-shear extension that is in part responsible for strong basinal asymmetry; (vi) Bransfield Strait is extensively segmented along-strike. These hypotheses have implications for the spatial distribution of crustal thickness and are testable using wide-angle seismic methods. We conducted an ocean bottom seismograph (OBS) experiment in Bransfield Strait in two field phases, one in April-May 2000, the second in October-November 2000. Five strike-oriented and three dip-oriented profiles were collected. Each 2-D profile used 11 OBSs at 15-20 km spacings, recording shots with 185-245 m spacing from a 6-gun, 49 l (3000 cu.in.) source array fired from the RVIB {\it Nathaniel B. Palmer}. Data vary in quality, largely dependent on OBS location. In general, OBSs located on the shallow, ice-scoured SSI shelf are noisy, consistent with poor ground-coupling. OBSs located on sediment cover in the deep basin and the AP margin record cleaner data; coherent arrivals are observed at $>$90 km offset. Preliminary results from inversion of first arrivals in dip profiles suggest that the neovolcanic zone along the basin axis is a fairly discrete, localized high-velocity feature in the shallow crust with possible low velocity zones beneath. The AP margin is underlain by large-scale fault blocks. Crustal thinning is observed, as expected, beneath the basin axis. Profiles paralleling basin strike show clear segmentation into multiple fast and slow blocks that correlate well with volcanic centers along the axis, and horst and graben topography interpreted from MCS data on the AP margin. Structural boundaries appear to correlate with neovolcanic centers suggesting possible across-strike structural control on initial volcanic emplacement.
AN: T61C-19
TI: Crustal Structure of an Active Backarc Basin: Preliminary Results from an OBS Wide-Angle Seismic Experiment, Bransfield Strait, Antarctica
AU: * Barker, D H
EM: danb@ig.utexas.edu
AF: University of Texas Institute for Geophysics, 4412 Spicewood Springs Rd., Building 600, Austin, TX 78759-8500 United States
AU: Christeson, G L
AF: University of Texas Institute for Geophysics, 4412 Spicewood Springs Rd., Building 600, Austin, TX 78759-8500 United States
AU: Austin, J A
AF: University of Texas Institute for Geophysics, 4412 Spicewood Springs Rd., Building 600, Austin, TX 78759-8500 United States
AU: Dalziel, I W
AF: University of Texas Institute for Geophysics, 4412 Spicewood Springs Rd., Building 600, Austin, TX 78759-8500 United States
AU: Nakamura, Y
AF: University of Texas Institute for Geophysics, 4412 Spicewood Springs Rd., Building 600, Austin, TX 78759-8500 United States
AU: Hello, Y
AF: IRD, UMR Geosciences Azur (CNRS), Observatoire Oceanologique de Villefranche, 2 Quai de la Darse, Villefranche-sur-mer, F-06235 France
AU: Yates, B
AF: University of Texas Institute for Geophysics, 4412 Spicewood Springs Rd., Building 600, Austin, TX 78759-8500 United States
DE: 8105 Continental margins and sedimentary basins
DE: 8109 Continental tectonics--extensional (0905)
DE: 9310 Antarctica
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3025 Marine seismics (0935)
SC: T
MN: Fall Meeting 2000