HR: 11:35h
AN: T11E-06    [PDF]
TI: On the formation of ultra-thick sedimentary basins on rifted margins: a comparison of the Scotian and Labrador margins
AU: * Louden, K
EM: Keith.Louden@Dal.Ca
AF: Department of Oceanography, Dalhousie University, Halifax, NS B3H 4J1 Canada
AU: Funck, T
EM: tf@dlc.ku.dk
AF: Danish Lithosphere Centre, Oester Voldgade 10L, Copenhagen, DK-1350 Denmark
AB: Sedimentary basins that form on rifted continental margins exhibit a great variety of shapes and sizes. In particular, the total sediment thickness can vary significantly and in certain sub-basins can approach 15-20 km. The deeper structure of these ultra-thick basins is typically not well resolved by seismic reflection profiles due to poor penetration within the thickest parts of the basin. Wide-angle seismic reflection/refraction profiles can help resolve these deeper features. We compare two such sub-basins that occur on the eastern Canadian margins, where reflection and refraction profiles are able to define the complete sedimentary and crustal structures: the Sable sub-basin on the northeast Nova Scotian margin and the Hopedale sub-basin on the central Labrador margin. We compare the development of these basins by converting the sediment refraction velocities to density and back-stripping assuming local isostasy. Although these basins formed during completely different episodes of rifting on different types of continental crust, we find a surprising similarity in the characteristics of crustal thinning across each margin, especially for the lower crust. Initial thinning of the crust by 50-60% occurs within 50 km followed by more gradual thinning over the subsequent 100 km. This leaves a tongue of lower continental crust extending 150 km seaward of the unstretched continental crust. This outer region becomes the location of the thickest initial sediment deposition, followed by up-building and out-building of the shelf. The local form of this deposition differs between the two margins: with much larger syn- and immediately post-rift sediments on the Scotian margin and thicker recent deposition on the Labrador margin, probably controlled by the local availability of sediment fill. Comparison with previous models of rifting based on borehole observations for the Scotia margin compare well with the overall width of the rifting (150 km), but our results suggest more rapid initial crustal thinning. By comparison, the conjugate margins of SW Greenland and Morocco are much narrower, do not have the broad region of thinned lower continental crust and have much smaller sediment thicknesses primarily located seaward of the continental shelf and slope. These features are all evidence for asymmetric rifting during late stages of extension.
DE: 3025 Marine seismics (0935)
DE: 8105 Continental margins and sedimentary basins
SC: Tectonophysics [T]
MN: 2003 Fall Meeting