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

Abstract

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.