Abstract

Deep seismic reflection profiles have been collected across the conjugate margins of the North Atlantic Ocean. The eastern North Atlantic margin is traversed in the Goban Spur region, and the western North Atlantic margin is crossed in the vicinity of Flemish Cap in the Grand Banks region. These seismic profiles allow us to examine the deep structures and mode of extension in crust that was once contiguous. The Flemish Cap and Goban Spur margins have different structural styles: thick and relatively unfaulted crust is present on the Flemish Cap margin west of the continent-ocean boundary, whereas the Goban Spur margin exhibits a zone of extensional faulting and thinned continental crust. The restored rift zone displays overall symmetry in which a bridge of thin crust (< 15 km thick), about 60 km wide, joins the two crustal blocks of normal continental thickness (∼28 km). The configuration of the Moho, the geometry and distribution of the lower crustal reflections, and the overall symmetry of the rift zone favor pure-shear stretching in the lower lithosphere, although either pure or simple shear could accommodate crustal extension.

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