Rifting and subsidence of the northern continental margin of the Bay of Biscay.

Abstract

In the northeast Atlantic, DSDP drilling results, combined with intensive geophysical surveys, permit a proposed model of the structural evolution of a starved, passive continental margin. Environment and tectonics of the rifting phase have been established. Active rifting took place in Early Cretaceous time in a pre-existing marine basin in contrast to many subaerial rift systems. The overall tectonic style is characterized by a series of tilted fault blocks (20-30o) along listric faults reduced the thickness of the upper continental crust from 6 to 8km to 4 to 5km. Close to the near horizontal bse of the listric faults, a strong horizontal reflector corresponding to the 6.3 and 4.9 km/s refraction interface has been interpreted as the boundary between the upper brittle and the lower ductile continental crusts. The Moho discontinuity, 25km deep in the vicinity of the shelf break, is 12km deep in the lower part of the margin. In this area the ductile part of the crust (6.3 km/s) is only 3km thick.-Authors