A seismic reflection and GLORIA study of compressional deformation in the Gorringe Bank region, eastern North Atlantic

Abstract

Seismic reflection and GLORIA side-scan sonar data obtained on RRS Charles Darwin cruise CD64 reveal new information on the styles of deformation in the Gorringe Bank region, at the eastern end of the Azores-Gibraltar plate boundary. Previous studies suggest that Gorringe Bank was formed by the overthrusting of a portion of the African plate upon the Eurasian plate. The new seismic data show, however, that the most intensely deformed region is located south of Gorringe Bank, on the northern flanks of a NW-SE-trending submarine ridge which includes the Ampere and Coral Patch seamounts. The deformation is expressed as long-wavelength (up to 60 km), large-amplitude (up to 800 m) folds in the sediments and underlying acoustic basement, which in places are associated with one or more reverse faults, and as a fabric of short-wavelength folds (up to 3 km) with a NE trend. In contrast, the same sedimentary units when traced beneath the flanking plains are undeformed, except for some fauults with a small throw (~30 m), some of which offset the seafloor. GLORIA data show that recent deformation is broadly distributed over the region. Structural trends rotate from 45°in the west to 70°in the east of the region, nearly perpendicular to the NW-verging plate motion vectors as determined from plate kinematic models. Flexure modelling suggests that a portion of Gorringe Bank has loaded 152 Ma oceanic lithosphere and that a maximum of 50 km of shortening has occurred at Gorringe Bank since the mid-Miocene. Our observations support a model in which there is no single plate boundary in the region, rather that the deformation is distributed over a 200-330 km wide zone.