The crustal structure of the NW-Moroccan Continental Margin for Wide-angle and Reflection Seismic Data

Abstract

The Atlantic margin off Morocco with its neighbouring Jurassic oceanic crust is one of the oldest on earth. It is conjugate to the Nova Scotia margin of North America. The SISMAR marine seismic survey acquired deep reflection seismic data as well as wide-angle seismic profiles in order to image the deep structure of the margin, characterize the nature of the crust in the transitional domain and define the geometry of the synrift basins. We present results from the combined interpretation of the reflection seismic, wide-angle seismic and gravity data along a 440-km-long profile perpendicular to the margin at 33-34°N, extending from nearly normal oceanic crust in the vicinity of Coral Patch seamount to the coast at El Jadida and approximately 130 km inland. The shallow structure is well imaged by the reflection seismic data and shows a thick sedimentary cover that is locally perturbed by salt tectonics and reverse faulting. The sedimentary basin thickens from 1.5 km on the normal oceanic crust to a maximum thickness of 6 km at the base of the continental slope. Multichannel seismic (MCS) data image basement structures including a few tilted fault blocks and a transition zone to a thin crust. A strong discontinuous reflection at 12 s two-way travel-time (TWT) is interpreted as the Moho discontinuity. As a result of the good data quality, the deep crustal structure (depth and velocity field) is well constrained through the wide-angle seismic modelling. The crust thins from 35 km underneath the continent to approximately 7 km at the western end of the profile. The transitional region has a width of 150 km. Crustal velocities are lowest at the continental slope, probably as a result of faulting and fracturing of the upper crust. Upper-mantle velocities could be well defined from the ocean bottom seismometer (OBS) and land station data throughout the model