3D imaging of the rifting and breakup west of Spain and the nature of the S detachment

Abstract

American Geophysical Union Fall Meeting, 12-16 December 2016, San FranciscoThe west Galicia margin (NW Spain) is a magma-poor margin with limited sedimentary cover, providing ideal conditions to study the processes of continental extension and break-up through seismic imaging. In 2013, we collected a 65km x 20km 3D multi-channel seismic dataset extending from the edge of the Galicia Bank over the feather edge of the continental crust to beyond the Peridotite Ridge to the west. The volume has been processed through to 3D prestack time migration and 3D depth conversion and provides 3D images of the hyper-extended continental crust, consisting of well-defined but internally intensely deformed rotated faults blocks with associated syn-kinematic sedimentary wedges. The rotated fault blocks contain possible low-angle normal faults that in places appear to define and elsewhere to offset top basement; we interpret them as early faults that predate the formation of the fault blocks. The early faults are in places cut and offset by the later block-bounding faults that appear to detach downwards onto a bright reflection, the S reflector, a detachment fault and locally the crust-mantle boundary. S is corrugated on both depth and time structure maps, with the corrugations sweeping in an arc from E-W proximally to ESE-WNW towards the ocean. We interpret the corrugations as forming during slip on S and representing the displacement (and hence extension) direction on the detachment leading to breakup. Early synrift sediment within the most recent faults blocks are intensely deformed, representing the internal deformation of the fault blocks. However, in places simple synrift wedges can be seen to thicken towards the block-bounding faults. The angular relationship of the top of these wedges to the block-bounding faults demonstrates that they were deposited during slip on the faults and low-angle slip on the underlying S detachment. Although beneath the continental crust S appears continuous and shows only minor distortion in the vicinity of the block-bounding faults, just east of the Peridotite Ridge, S appears to have been offset by landward-dipping faults associated with the development of the Ridge. We conclude that rifting to breakup was a complex, time variant, 3D process involving slip at low-angles, multiple generations of faults and the unroofing of mantle along later landward-dipping structuresPeer Reviewe