Jurassic tectonic and paleogeographic evolution of the junction zone between the Middle Atlas and High Atlas (Morocco)

The Middle Atlas (MA) and High Atlas (HA) chains are considered intraplate basins developed during the Mesozoic Era. The Jurassic structural evolution of the junction between MA-HA recorded three successive tectonic events beginning with a NE-SW extensional tectonic regime responsible for the differentiation between a nearshore environment to northwest with sandstone and pelite deposits, the platform domain with its metric carbonate marls, and a basin domain filled with black marls and limestones with an euxinic character during the Toarcian. In this episode, the sedimentary thickness is controlled by High Atlas trending faults (N120-N110). The second tectonic event corresponds to a tectonic extension regime with an NW-SE to NNW-SSE directed σ3 axis, causing subsidence towards the southeastern part delimited by the Middle Atlas direction faults (NE-SW). The sedimentary series indicates an evolution from a continental environment in the northwest (conglomerates and sandstones) to platform and basin sedimentation in the southeast, noted by the intercalation of marls and bioclastic limestones of the Aalenian–Bajocian age. During the third tectonic event (Bathonian–Barremian), the sedimentary series becomes continental lagoonal deposits represented by marls with limestones, grading into sandstone and gypsum marl, and conglomerates overlain by marls and sandstones of the "Red beds". This evolution associated with by the establishment of a transpressional tectonic regime with NNE-SSW compression σ1 axis responsible for uplift using High Atlas direction faults (E-W to ENE-WSW), caused marine regression; this compression is accompanied by WNW-ESE extension σ3 axis responsible for subsidence towards the southern part with the establishment of basalt lava flows and gabbroic dykes of the Bathonian–Barremian magmatism complex.