The South-Western Branch of the Variscan Belt: Evidence from Morocco

This work is based on the compilation and re-evaluation of the most significant data, either personal or from the literature, concerning the Moroccan Variscides. The latter constitute the only, moderately disturbed or even undisturbed part of the South-Western Branch of the Variscan Belt, facing directly NW Gondwana. They include two orogenic segments, namely the northern Mauritanides and the Meseta Domain exposed in the Saharan and Atlas-Meseta regions respectively, and a foreland belt cropping out essentially in the Anti-Atlas. The eastward thrust units of Saharan Morocco (Oulad Dlim) mostly originate from the West African Craton (WAC) border in an area of thin Palaeozoic sedimentation. Thin-skinned fold-thrust foreland arcs develop progressively northward (Zemmour) at the expense of the increasingly thick Palaeozoic series, whereas thick-skinned deformation characterizes the inverted proximal paleomargin in the Anti-Atlas Domain. As suggested by the Meseta and Anti-Atlas stratigraphic similarities, the Meseta Domain corresponds to a collage of moderately displaced, thinned crustal blocks from the distal Gondwana paleomargin. Variscan deformation is dominated by NW-verging thrusts, and metamorphism developed in the thickened tectonic prism in relation with crustal anatexis at depth. The Meseta-Anti-Atlas boundary is a major, ENE-trending transpressional dextral fault referred to as the South Meseta Fault (SMF). Discussing the correlations between the Variscan segments of Morocco and SW Iberia allows us to suggest that a latitudinal transform zone similar to the SMF separated these segments during the Late Palaeozoic. Subduction of the Rheic Ocean crust would have been directed SE-ward along both the Iberian and Moroccan Meseta, and NW-ward south of the SMF, i.e. along the WAC.