Deep-rooted “thick skinned” model for the High Atlas Mountains (Morocco). Implications for the structural inheritance of the southern Tethys passive margin

Abstract

A re-interpretation of the deep structure of the High Atlas is presented through integration of geophysical and geological data, highlighting the architectural significance of the southern Tethys palaeomargin. Previous crustal models suggest the occurrence of a flat intra-crustal detachment at a depth of −20 km, a zone where surface thrusts merge and below which the lower High Atlas crust appears continuous. However, within this study seismic refraction data, electrical resistivity surveys and gravity modelling all appear to detect a jump in crustal thickness between the High Atlas and the northern plains. We interpret these data as penetration by thrusts within the “South-Atlasic fault” zone through the lower crust to offset the Moho in accordance with a “deep-rooted thick skinned tectonic model”. The “South-Atlasic fault” zone corresponds to a series of crustal-scale structures inherited from a series earlier orogenic events (Pan-African, Hercynian and Atlasic) and thus is sufficiently weak to create separate crustal blocks in the northern part of the stable African plate. This structural configuration was achieved during Cenozoic plate collision between Africa and Europe culminating in tectonic inversion of Mesozoic extensional basins, linked to the development of Tethys and opening of the Atlantic. The inherited structures typically comprise normal faults and tilted blocks affecting the upper crust, and crustal-scale detachments affecting the lower crust.