Tectonic styles in the Marrakesh High Atlas (Morocco): The role of heritage and mechanical stratigraphy

The Moroccan High Atlas is an intra-continental orogen formed during the Cenozoic in response to crustal shortening and thermal processes. In this study, we focus on the Marrakesh High Atlas (MHA), characterized by the abundance of Paleozoic or older rocks and giving an opportunity for a direct observation of the deep geometry of the chain. We propose an overview of the tectonic style and discuss the role of the heritage on the mechanical stratigraphy. Important variations in the sedimentary pile explain the wide variety of structures related to the activation of various décollement levels. In the southern part of the study area, the main detachment level is situated in the Cambrian series triggering the development of a wide triangle zone. Westward, in the Souss Basin, the Senonian silts and evaporites favour the development of secondary folds. Such structures can also be observed in the north-western part of the MHA, in the western Haouz Basin, where the Cambrian series form the core of the main anticlines. In the south-eastern part of the MHA, the Senonian silts and evaporites become the main detachment. Northeast of the MHA, the Upper Triassic salt acted as a major décollement level. However, this décollement is folded during the activation of a deeper detachment level in the Visean flyschs and cut out by late basement faults. A basal rigid group is distinguished, including Precambrian rocks and locally Paleozoic and Triassic rocks. Finally, we propose the first complete balanced cross-section of the belt in the MHA. The timing of the deformation is addressed: two main compressive tectonic events are highlighted and their relative importance is discussed.