Polyphase tectonics, fault kinematics and metallogenic implications at the fringe of a craton (Anti-Atlas, Morocco)

Abstract

At the northern border of the West African Craton (WAC), the Saghro massif of the Moroccan Anti-Atlas belt is renowned for its tectonic complexity inherited from Pan-African, Variscan, and Alpine orogenic cycles. This makes it an ideal area to investigate the tectonic evolution of the northern fringe of the WAC from Precambrian to present times. In this study, remote sensing structural mapping and extensive field observations and measurements have been integrated to decipher the tectonic style and fault kinematic history in the Precambrian-Cambrian and Cenozoic outcrops of the southwestern Saghro massif. The structural analysis shows three fault systems, namely N–S to NNE-SSW, NE-SW to E-W, and NNW-SSE to NW-SE. Extensive and transpressive/compressive tectonics reactivated the NE to ENE major faults, while most of the NW-SE pan-African structures are tectonically aborted. This fault pattern played a major role in the thick-skinned Variscan tectonics of the area and the origin of the present-day reliefs of the Saghro massif. The thin-skinned deformation style characterizes the superimposed Ouarzazate foreland basin, accommodated by deep detachment faults and fault-propagation folds favored by multiple post-Variscan incompetent levels. The increased fracture frequency with increasing rock strength and deformation intensity has a significant implication in the fault distribution over the basement and cover outcrops. The resulting structural map allows the revision and updating of existing geological maps and helps to understand the tectonic correlations between the southern orogenic border of the High Atlas and the Anti-Atlas fold and thrust belt.