Imaging a lithospheric detachment at the continent–ocean crustal transition off Morocco

The SISMAR seismic survey on the Moroccan Atlantic Margin recorded deep penetration images of the continent–ocean boundary. This paper focuses on the 3D observation of a landward dipping reflector, overlaid by a layered unit. The deep part of the reflector plunges towards the continent beneath thinned continental crust whereas its upper part finishes at the top of the basement in a transition zone where likely volcanics dipping reflectors are visible and where a magnetic anomaly named S1 marks the continent–ocean boundary location. As the landward dipping reflector crosses the Moho, it is interpreted as a lithospheric detachment with associated volcanic material originating from the asthenospheric mantle. Observations are used (i) to build a 2D model to explain the mechanisms of the lithospheric breaking off between Moroccan margin and its conjugate Canadian margin, the landward dipping reflector allowing mantle exhumation; (ii) to propose an ENE–WNW trend for the initial rifting extension in this part of Atlantic during late Triassic, direction compatible with that of the southern Grand Banks transform margin.