The major Adassil-Medinet fault; a complex evolution of high angle transpressive Variscan shear zones (Western High Atlas, Morocco)

Abstract

The Western High Atlas is one of the most important sectors of the Variscan foldbelt in Morocco and also of its Alpine intracontinental orogen. Its tectonic evolution is thus essential for the understanding, not only of the Moroccan geology, but also of the interaction between successive orogenic cycles which is one of the focus of this article. Furthermore, as the Moroccan Variscides must be seen in the context of the complex dextral collision between Laurasia and Gondwana, this is also a contribution to the comprehension of the complexity of transpressive regimes and strain partitioning processes.

New data show that WNW-ESE sinistral Variscan shear zones (mainly the Addouz-Adassil-Anamrou one - AAAsz), although secondary to the main orogenic scale ENE-WSW dextral shear zones, must be considered in order to understand the Late Paleozoic deformation and its Alpine reactivation. In fact, the concentration of the last stages of the Variscan ductile deformation in the steep and irregular AAAsz played an important role in the initiation and localisation of the minor magmatic events and influenced the geometry and kinematics of the Late Variscan WNW-ESE sinistral shear zones. Furthermore, during the Alpine inversion, the orientation of the AAAsz and related major anisotropies tend to be reactivated, with a major reverse component, giving rise to the irregular Adassil-Medinet fault zone, one of the most important structures of the Western High Atlas.