Several lines of evidence suggest that simple shear rifting of the continental crust, in the form<br/>of low-angle detachment faulting, occurred during the final stages of continental breakup<br/>between West Iberia and the Grand Banks. The primary evidence for such faulting is the<br/>occurrence of low-angle, high amplitude reflectors within the basement adjacent to the ocean–<br/>continent transition zone. Here we present a series of intersecting, depth migrated seismic<br/>reflection profiles that image one such reflector, the H-reflector, located on the southern edge<br/>of Galicia Bank. ‘H’ lies beneath several boreholes drilled during ODP Legs 149 and 173,<br/>in a region where the oceanward extent of extended continental crust steps at least 150 km<br/>westward from its location in the southern Iberia Abyssal Plain to its location off the relatively<br/>shallow Galicia Bank. In our profiles ‘H’ appears to define a surface that extends over a region<br/>of at least 200 km2 and that dips down ?19? to the north, towards Galicia Bank. The profiles<br/>show that a close affinity exists between ‘H’ and the most seaward continental crust. Based on<br/>geophysical data and ODP drilling results, we infer that the basement above ‘H’ is composed<br/>of continental crust deformed by extensional faults into a series of wedge-shaped blocks and<br/>thin slivers. These basement wedges have a complex 3-D geometry. ‘H’ rises to the basement<br/>surface on a number of the seismic profiles and appears to define locally the oceanward extent<br/>of continental fault blocks
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