Crustal structure of the SW Moroccan margin from wide-angle and reflection seismic data (the Dakhla experiment). Part B - The tectonic heritage

摘要

The Dakhla 2002 experiment on the Northwest African margin obtained deep penetration, multichannel reflection (MCS) and wide-angle seismic (OBS) data. These results were combined with total magnetic intensity data, kinematic reconstructions and geological field studies to decipher the early tectonic and sedimentary history of the South Moroccan margin, adjacent to the Reguibat Shield. The structural study of this margin shows that the crust thins, from about 28 km beneath the un-thinned continental domain, to less than 10 km over a lateral distance of about 120 km. The Dakhla margin differs from the structural scheme of the adjacent African margin segments. There, the Moho rise, generally observed just above the deepening of the top of the basement, is achieved with an offset of around 50 km (with respect to the latter). In Early Jurassic time, the break-up of continental crust in what is now the Central Atlantic led to the formation of two basins, one on either side of the Reguibat, which correspond to the older parts of segments of the Late Palaeozoic Hercynian orogen. The Dakhla segment appears as a Precambrian cratonic zone, squeezed between two orogenic segments, which have remained unaffected by break-up processes; and the lower crust of this particular domain has behaved differently from all other neighbouring Appalachian (North America) and Mauritanide domains. This observation points to the important role of tectonic inheritance in the structural development of passive continental margins.