Transpressional tectonics in the Marrakech High Atlas: Insight by the geomorphic evolution of drainage basins

The Ouzzelarh Massif extends across the Marrakech High Atlas (MHA) and forms the highest elevated mountain belt. To better understand the evolution of collision-related topography, we present the results of a geomorphological study in which elevation changes generated by reactivated pre-Alpine (Variscan and Triassic–Jurassic) faults drive a landscape evolution model. We aim to evaluate the relationship between the geometry of the drainage network and the main fault systems in this region. New insight into geomorphological changes in drainage patterns and related landforms is based on geological fieldwork combined with DEM analysis. To quantitatively measure landscape features we used several classical geomorphic indices (spacing ratio, hypsometric curves and integral, stream frequency drainage, stream length-gradient). The Ouzzelarh Massif is bounded to the north by the Tizi N'Test Fault Zone (TTFZ) and to the south by the Sour Fault Zone (SFZ). These faults delimit a pop-up structure. By using the above geomorphic parameters, we ascertained that the Ouzzelarh Massif is affected by a high spatial variability of uplift. The actual landscape of the Ouzzelarh Massif reveals remnants of an uplifted ancient erosional surface and the heterogeneity of exposed rocks in the range explaining the possibility that the topographic asymmetry between north and south flanks is due to differences in lithology-controlled resistance to erosion. Drainage, topography and fault pattern all concur to show uplifted rhomboidal-shaped blocks. It exhibits high stream frequency drainage and uplift in separate tectonically-uplifted blocks such as Jebel Toubkal which is characterized by asymmetric drainage basins.