Tectonic evolution of the Western High Atlas of Morocco: oblique convergence, reactivation and transpression

The High Atlas of Morocco is a double-vergent mountain belt developed by Cenozoic shortening and inversion of a Triassic-Jurassic rift. The structural setting, the morphometric features, and the patterns of exhumation through time and space change remarkably both along and across the strike. Here we combine structural data with revised thermochronological data to unravel the kinematic and evolution of the western High Atlas. Our results show that the structural grain of the western High Atlas is defined by two main groups of faults, namely, thrust and oblique-slip faults, which mainly strike subparallel from W-E to NE-SW. The slip direction of the thrust structures is NNW-SSE to NW-SE oriented, and the slip direction of the oblique-slip faults is WSW-ENE to NW-SE oriented. Pieces of thermochronological and geological evidence indicate that in the last 10 Ma the exhumation rate increased during the activity thrusts and oblique-slip faults. The coexistence of these two fault systems also suggests partitioning of deformation under a transpressive regime. In the western High Atlas, we estimate a displacement of 12 km on the frontal thrusts and of at least 22 km on the axial oblique-slip structures. Thrusts and oblique-slip structures together result in a total cumulative displacement of 25 km, which represents about half of the Africa-Eurasia convergence.