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Variscan deformation at the northern border of the West African Craton, eastern Anti-Atlas, Morocco: compression of a mosaic of tilted blocks

¹ Ministère de l’Energie et des Mines, BP 6208, Rabat Agdal, Maroc, e-mail : raddiyoussef{at}mem.gov.ma.
² Département de Géologie, Faculté des Sciences Aïn Chok, BP 5366, Casablanca Maarif, Maroc, e-mail lbaidder{at}yahoo.fr.
³ Laboratoire de Géologie, Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris cedex 05, e-mail : andremichard{at}wanadoo.fr.

North of the Saharan cratonic domain, the Anti-Atlas mountains correspond to the foreland, external fold belt of the Variscan orogen which extends in the Meseta block to the north, and Mauritanides to the southwest. The Anti-Atlas was uplifted during the Mesozoic-Cenozoic, and display several basement culminations ("boutonnières") amidst the folded Palaeozoic cover. Recent studies in western Anti-Atlas emphasized the basement implication in the shortening process (thick skinned structure). Hereafter we investigate the cover-basement relations in eastern Anti-Atlas south of the Ougnat culmination, based on mapping at scale 1:50,000. The Palaeozoic sequence is much thinner than in the west, and the décollement levels are less important. Flexural slip folds are concentrated along the faults (en échelon folds) and within some rhombic domains crushed between major faults (e.g. Angal-Gherghiz Lozenge), whereas other areas are monoclinal. The main shortening direction deduced from the fold axes trend is directed ~N045°E as in the Ougarta range further to SE. At a regional scale, this shortening direction interferes with a N-S trending one. A sketch map of the top of the basement makes visible a mosaic of S- to SE-ward tilted blocks. The faults between these blocks are inherited from paleofaults which formed during extensional events during the Cambrian, late Ordovician, and (mainly) Middle-Late Devonian. The paleofault array is indicative of a proximal passive margin setting at the northern border of the metacratonic domain. The fault inversion and their dominant strike-slip throw occurred during a late Variscan (Stephanian-Permian) compression event, postdating the NNW-SSE collision of the Meseta block.

Key Words: Foreland fold belts • Variscan • Paleofaults • Inversion tectonics • Anti-Atlas • Morocco

This article has been cited by other articles:

				L. Baidder, Y. Raddi, M. Tahiri, and A. Michard Devonian extension of the Pan-African crust north of the West African craton, and its bearing on the Variscan foreland deformation: evidence from eastern Anti-Atlas (Morocco) Geological Society, London, Special Publications, January 1, 2008; 297(1): 453 - 465. [Abstract] [Full Text] [PDF]