HR: 11:15h
AN: T42A-03    [Abstracts]
TI: Depth-Imaging the Transfer Boundary Between the Galicia Bank and Iberia Abyssal Plain Rifted Margin Segments, Integrating MCS and OBS Data
AU: * Clark, S A
EM: stoney@rice.edu
AF: Dept of Earth Science, Rice University, 6100 Main St, MS-126, Houston, TX 77005 United States
AU: Sawyer, D S
EM: dale@rice.edu
AF: Dept of Earth Science, Rice University, 6100 Main St, MS-126, Houston, TX 77005 United States
AB: We present multi-channel seismic reflection data and coincident wide-angle ocean-bottom seismometer (OBS) data from the non-volcanic rifted margin west of Iberia. Profile ISE-9 runs 270 km north-south, 200 km west of the Portuguese coast, imaging the physiographic transition between Galicia Bank in the north (500-3000 m water depths) and the Iberia Abyssal Plain in the south (4000-5500 m water depths). Underlying Galicia Bank the crust is 13-16 km thick (from OBS modeling), indicating a continental origin with relatively minor thinning. To the south, from the flank of Galicia Bank into the Iberia Abyssal Plain, the crust thins significantly, reaching a thickness of less than 1 km in a region where crust has been previously characterized as transitional between oceanic and continental, and where mantle in places may have been exhumed. Atop Galicia Bank, 10-20 km-wide sedimentary basins are separated by near-seafloor basement highs. In contrast, sediments in the Iberia Abyssal Plain are laterally continuous and up to 4500 m thick. Relatively flat-lying stratigraphy unconformably overlies tilted stratigraphy, but there is no apparent thickening of any sedimentary packages. Strong intra-crustal reflections, occasionally coinciding with Moho, suggest complex extensional faulting along the margin apparently orthogonal to the widely accepted east-west direction of rifting. We have migrated and depth -converted the reflection data utilizing a combination of stacking velocities (for lateral resolution) and OBS-modeled velocities (for time-depth accuracy) as a starting velocity field. The resulting seismic profile accurately depicts the structural geometries along strike of the margin, but the relationship of these faults to the west-dipping normal faults of intersecting profiles remains ambiguous. Two possibilities could explain the apparent south-dipping faults: 1) they are southwest-dipping faults which have been imaged obliquely by north-south and west-east profiles, or 2) they are south-dipping faults distinct from the west-dipping faults. In either case, crustal extension oblique or perpendicular to the east-west rifting is not necessarily indicative of full lithospheric extension driven by asthenospheric flow. Instead, gravity-induced mass wasting may cause the north-south, rift-axis-parallel component of extension.
DE: 3025 Marine seismics (0935)
DE: 7218 Lithosphere and upper mantle
DE: 8105 Continental margins and sedimentary basins
SC: Tectonophysics [T]
MN: 2005 Joint Assembly