HR: 09:00h
AN: T41A-02    [Abstracts]
TI: Steep Satellite Altimetry Gradients as a Proxy to the Edge of the Continental Crust
AU: * Lawver, L A
EM: lawver@ig.utexas.edu
AF: University of Texas at Austin Institute for Geophysics, 4412 Spicewood Springs Rd. #600, Austin, TX 78759-8500 United States
AU: Gahagan, L M
EM: plates@ig.utexas.edu
AF: University of Texas at Austin Institute for Geophysics, 4412 Spicewood Springs Rd. #600, Austin, TX 78759-8500 United States
AB: Tight-fit plate reconstructions are produced using a global database constrained by marine magnetic anomalies tied to a consistent timescale, paleomagnetic poles, seafloor age dates based on drilling results, and fracture zone and transform fault lineations picked from ship-track and satellite altimetry data. Where a prominent steep gradient in the satellite altimetry data is present near the continental-ocean transition, it is used as a proxy to the continental shelf break [CSB]. Continental block outlines are based on digitization of the steep gradient. In some places, notably off Namibia, there is a very close correlation between that gradient and the ocean-continent boundary deduced from seismic refraction and reflection data. In other regions, there may be some stretched continental crust oceanward of the steep gradient but for reconstruction purposes we assume the crust to be predominantly continental landward of the boundary and oceanic, seaward of the line. Good matchs for conjugate CSBs are found in many places world-wide along passive margins and these will be highlighted. Particularly good matches are observed between the cratonic edges of East Antarctica as determined by sub-ice topographic highs seen along the margins of East Antarctica with respect to Madagascar, Sri Lanka, the southern half of the eastern margin of India, and the region of Australia between 124° E and 133° E along the Great Australian Bight (GAB). There are overlaps of the reconstructed conjugate CSBs, with one overlap between India and East Antarctica (70° E to 85° E) and one between East Antarctica and the western section of the GAB (105° E to 120° E). These two overlaps are coincident with the outer margins of the Lambert Graben - Prydz Bay Basin and the Aurora Subglacial Basin, respectively. It is known that there are substantial glacially-derived sediments prograded off the continental margin onto oceanic crust at Prydz Bay where there may be as much as 200 km in width of Eocene? and younger sediments outboard of the original CSB in the Prydz Bay region. When there is not a good match between conjugate CSBs then post-break up features can frequently be invoked to explain the mismatch. Abroulhos Bank off Brazil is an example of a post-break up [~40 m.y. later] magmatic construction that alters where the steep gradient in the satellite altimetry data is picked. In general, the CSBs are a good proxy to the original continental edge.
DE: 1243 Space geodetic surveys
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8105 Continental margins and sedimentary basins
DE: 8122 Dynamics, gravity and tectonics
DE: 9300 INFORMATION RELATED TO GEOGRAPHIC REGION
SC: Tectonophysics [T]
MN: 2005 Joint Assembly