Structure and origin of the imbricated wedge of the Gulf of Cadiz from MCS images

Abstract

We present new insights on the structure and origin of the imbricated wedge of the Gulf of Cadiz based on ~3000 km of multichannel (MCS) profiles acquired off NW Moroccan margin. Seismic images indicate that the imbricated wedge is bounded between the Gulf of Cadiz Margin (North), the Rharb Margin (East) and the Kenitra Margin (South). It is imaged as a sedimentary body, with semi-chaotic facies and variable seismic amplitude, which is structured by imbricated thrust sheets similar to an accretionary prism. This wedge thins toward the centre of the gulf, where it is buried by ~0.3 twts of sedimentary deposits, indicating that it is currently not growing. Probably it stops its activity at ~5-6 Ma. No evidences for a gravitational (olistostrom) origin have been found. The imbricated wedge is overlaid by sedimentary sequences whose oldest unit is uppermost Tortonian. Plate convergence is currently causing active faulting deformation, mainly along strike-slip faults and minor thrusting. Mud diapirism was also imaged intruding the prism and the overlaying sediments. Regarding the prism boundaries, the Kenitra Margin, located at the southernmost area of the gulf, is an extended continental or probably continent-ocean transitional crust margin that extends under the prism. The age of margin extension is probably Triassic-Jurassic, and we propose it as the conjugated margin of the Gulf of Cadiz. Off NW Moroccan margin, MCS profiles image high-amplitude continent-verging reflections corresponding to pervasive normal faulting. This extended terrain, named Rharb Margin, acts as the backstop of the wedge to the west, and it is over-thrusted by Prebetic/Flysh sequences to the east, off the Strait of Gibraltar. Plate convergence is currently causing active faulting deformation mainly along strike-slip faults and minor thrusting that internally deforms it in a diffuse manner. Also, mud diapirism was imaged intruding the imbricated wedge and the overlaying sediments