HR: 1330h
AN: T12A-0430    [PDF]
TI: Evidence for asymmetric rifting at the Newfoundland margin from SCREECH Transect 2 wide-angle data and numerical modeling
AU: * Van Avendonk, H J
EM: harm@ig.utexas.edu
AF: University of Texas Institute for Geophysics, 4412 Spicewood Springs Road, Austin, TX 78759 United States
AU: Lavier, L L
AF: University of Texas Institute for Geophysics, 4412 Spicewood Springs Road, Austin, TX 78759 United States
AU: Nunes, G T
AF: University of wyoming, Dept. of Geology and Geophysics, P.O. Box 3006, Laramie, WY 82071 United States
AU: Holbrook, W S
AF: University of wyoming, Dept. of Geology and Geophysics, P.O. Box 3006, Laramie, WY 82071 United States
AU: Shillington, D J
AF: University of wyoming, Dept. of Geology and Geophysics, P.O. Box 3006, Laramie, WY 82071 United States
AU: Tucholke, B E
AF: Woods hole Oceanographic Institution, 372 Woods hole road, Woods Hole, MA 02543
AU: Louden, K E
AF: Dalhousie University, Dept. of Oceanography, 1355 Oxford St., Halifax, NS NS B3H 4J1 Canada
AU: Hopper, J R
AF: Danish Lithosphere Centre, Oester Voldgade 10, Copenhagen, DK1350 Denmark
AU: Larsen, H C
AF: Danish Lithosphere Centre, Oester Voldgade 10, Copenhagen, DK1350 Denmark
AB: Recent geophysical investigations on the nonvolcanic margins of the North Atlantic have shown us that the basic structure of the two conjugate ocean-continent transitions (OCTs) is remarkably different. The evolution of the Iberian margin seems to have been controlled by a shallow low-angle fault, and mantle exhumation clearly preceded the onset of mid-ocean spreading. In contrast, no evidence for large crust-penetrating faults have been found on the Newfoundland margin, and slow-spreading oceanic crust appears to abut the edge of continental crust. These observations have been explained by development of a concave-downward detachment fault in a late stage of the continental rifting, with the Newfoundland margin representing the hanging wall of the detachment. Numerical modeling of this scenario shows that lithospheric thinning brings up hot asthenospheric mantle beneath the Newfoundland margin crust shortly before break-up. During this last phase, ductile flow of the lower crust may have formed a weld between the Newfoundland margin and incipient oceanic crust. Results from a tomographic inversion of seismic refraction data of SCREECH Transect 2 are consistent with such a sequence of events. The thinned continental crust is characterized by seismic velocities ranging from 5.4 km/s below basement to 7.0 km/s in the lowermost crust. A 3 km thick lower crustal layer pinches out towards the OCT, where upper crustal seismic velocities reach 6.4 km/s over a width of ~10 km. This high velocity anomaly may be the result of lower crustal diapirism in the wake of break-up of the continental lithosphere.
DE: 3025 Marine seismics (0935)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8164 Stresses--crust and lithosphere
SC: Tectonophysics [T]
MN: 2003 Fall Meeting