Tectonic Evolution of the Eastern Moroccan Meseta: From Late Devonian Forearc Sedimentation to Early Carboniferous Collision of an Avalonian Promontory

Abstract

The deformed Paleozoic succession of the Eastern Moroccan Meseta crops out in relatively small and isolated inliers surrounded by Mesozoic and Cenozoic rocks. Two of the largest inliers (Mekkam and Debdou) are characterized by a monotonous succession of slates and greywackes affected by polyphasic folding that occurred at low- to very low grade metamorphic conditions. New U-Pb ages on detrital zircon grains from the Debdou-Mekkam metasediments constrain the maximal depositional age as Late Devonian, interpreted to be close to the true sedimentation age. Furthermore, the εHf values of the Devonian detrital zircons, together with the presence of a series of scattered zircon grains with ages between c. 0.9 and c. 1.9 Ga, suggest provenance from a subduction-related magmatic arc located on the Avalonian margin. The Debdou-Mekkam massif is characterized by an Early Carboniferous first deformational event (D1), which gave way to a pervasive cleavage (S1) associated with plurikilometric-scale, tight to isoclinal, overturned to recumbent folds. Later events (Dc) occurred at Late Carboniferous time and generated variably developed crenulation cleavages (Sc) associated with variously oriented metric- to kilometric-scale folds, which complicate the pattern of both D1 intersection lineations (L1) and axial traces. The restoration of this pronounced curved pattern yields originally SW-NE-oriented D1 fold axes with regional SE-vergence. This important Early Carboniferous shortening and SE-directed tectonic transport can be explained by closure of the Rheic Ocean and the first phases of the collision between the northern passive margin of Gondwana and an Avalonian promontory.