Abstract

Local zones of compressional deformation, spatially coincident with the ocean-continent transition. occur in the NE Atlantic off western Iberia, on the northern margin of the Bay of Biscay and in the southern Rockall Trough. The deformation zones are typically broad oceanward-facing monoclines several tens of kilometres in width. The amount of shortening is small, although the structures may also accommodate some strike-slip motion. Deformation peaked during the Mid-Late Eocene in Biscay. off Galicia Bank and in Rockall Trough, and in the mid-Miocene off western Iberia. These deformation pulses were contemporary with the Pyrenean and Betic Orogenies in western Europe and may have resulted from structural reorganizations within the evolving orogens driven by changes in plate motion. Possible mechanisms which might concentrate deformation at the ocean-continent transition include slip within serpentinized peridotite underlying the transitional region and reactivation of a pre-existing detachment fault within the thinned continental crust. Our observations may imply that rifted continental margins, when reactivated, can develop into new sites of plate subduction.

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