A DEEP SEISMIC ANALYSIS OF THE FLEMISH CAP CONTINENTAL MARGIN OFF NEWFOUNDLAND, CANADA

Abstract

The crustal structure of the NE Flemish Cap margin off Newfoundland, Canada has been determined along a 460-km-long wide-angle reflection seismic transect (FLAME Line). The westward section crossing Flemish Cap displays an up to 32-km-thick continental crust. The thick crust thins to a 6-km-thick crust over a distance of only 40 km, which then continues seaward for an additional 100 km. S-wave velocities favor a thin crust of continental composition. Beneath the thin crust velocities infer that the upper mantle is partially serpentinized. The seaward-most end of the model displays velocities and thicknesses typical of oceanic crust. The raw multichannel seismic (MCS) reflection data of Line 85-3, coincident with the FLAME Line, were reprocessed. Results were combined with the velocity model and then compared with similar results across the conjugate Goban Spur margin (NE Europe). Previous stud- ies had suggested a model of symmetric pure shear extension followed by asymmetric breakup. The new results indicate that asymmetric structures are formed during all stages of rifting, breakup, and transition to oceanic spreading. The differing nature of the two transition zones is particularly striking. For Flemish Cap, the reprocessed image of the MCS profile shows tilted fault blocks beneath syn-rift sediment packages, consistent with a wide region of highly thinned continental crust suggested by P- and S-wave velocities. In contrast, the Goban Spur transition zone consists primarily of exhumed serpentinized mantle. To define potential variations along-strike of the mar- gin, the raw MCS data of Line 87-4 to the north of Flemish Cap were reprocessed. Interpretation of the image indicates a different crustal structure along the profile in comparison to Line 85-3. Fault blocks with a roughly NW-SE rift direction are indicated in the landward region of Line 87-4, followed seaward by a block indicating complex 3D rifting. The basement morphology farther seaward indicates crust of an oceanic affinity. In light of the results of the reprocessed images, Erable lines (E43, E44, E46-E52) situated between Lines 87-4 and 85-3 were re-interpreted. The results together with gravity data indicate along-strike variations both in rifting as well as mantle serpentinization on the NE Flemish Cap margin.