Crustal structure variations along the NW-African continental margin: a comparison of new and existing models from wide angle and reflection seismic data

Friday, 19 December 2014: 5:45 PM
Youssef Biari1, Frauke Klingelhoefer1, Mohamed Sahabi2, Daniel Aslanian1, Philippe Schnurle1, Keith E Louden3, Kai Berglar4, Maryline Moulin1, Khalid Mehdi2, David Graindorge5, Mikael Evain1, Massinissa Benabellouahed1 and Christian J Reichert4, (1)IFREMER, Plouzané, France, (2)University of Chouaïb Doukkali, Department of Geology, El Jadida, Morocco, (3)Dalhousie University, Halifax, NS, Canada, (4)BGR Federal Institute for Geosciences and Natural Resources, Hannover, Germany, (5)University of Western Brittany, Brest, France
Deep seismic data represent a key to understand the geometry and mechanism of continental rifting. The passive continental margin of NW-Africa is one of the oldest on earth, formed during the Upper Triassic–Lower Liassic rifting of the central Atlantic Ocean over 200 Ma. We present new and existing wide-angle and reflection seismic data from three study regions along the margin located in the North Moroccan salt basin, on the central continental margin offshore Safi and in the south, offshore Dakhla. In each of the study areas several combined wide-angle and reflection seismic profiles perpendicular and parallel to the margin have been acquired and forward modelled using comparable methods. The thickness of unthinned continental crust decreases from 36 km in the North to about 27 km in the South. In the North Moroccan Basin continental crust thins from originally 36 km to about 8 km in a 150 km wide zone. The basin itself is underlain by highly thinned continental crust. Offshore safi thinning of the continental crust is confined to a 130 km wide zone with no neighboring sedimentary basin underlain by continental crust. In both areas the zone of crustal thinning is characterised by the presence of large blocks and abundant salt diapirs. In the south crustal thinning is more rapid in a zone of 90 km and asymmetric with the upper crust thinning more closely to the continent than the lower crust, probably due to depth-dependent stretching and the presence of the precambrian Reguibat Ridge on land. Oceanic crust is characterised by a thickness of 7-8 km along the complete margin. Relatively high velocities of up to 7.5 km/s have been imaged between magnetic anomalies S1 and M25, and are probably related to changes in the spreading velocities at the time of the Kimmeridgian/Tithonian plate reorganisation. Volcanic activity seems to be confined to the region next to the Canary Islands, and is thus not related to the initial opening of the oceanic, which was related to no or only weak volcanism.