COMPRESSIONAL DEFORMATION AT THE OCEAN CONTINENT TRANSITION IN THE NEATLANTIC

Local zones of compressional deformation, spatially coincident with th e ocean-continent transition, occur in the NE Atlantic off western Ibe ria, on the northern margin of the Bay of Biscay and in the southern R ockall Trough. The deformation zones are typically broad oceanward-fac ing monoclines several tens of kilometres in width. The amount of shor tening is small, although the structures may also accommodate some str ike-slip motion. Deformation peaked during the Mid-Late Eocene in Bisc ay, off Galicia Bank and in Rockall Trough, and in the mid-Miocene off western Iberia. These deformation pulses were contemporary with the P yrenean and Betic Orogenies in western Europe and may have resulted fr om structural reorganizations within the evolving orogens driven by ch anges in plate motion. Possible mechanisms which might concentrate def ormation at the ocean-continent transition include slip within serpent inized peridotite underlying the transitional region and reactivation of a pre-existing detachment fault within the thinned continental crus t. Our observations may imply that rifted continental margins, when re activated, can develop into new sites of plate subduction.