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RESEARCH PRODUCT

Polyphased mesozoic rifting from the Atlas to the north-west Africa paleomargin

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24 pages; International audience; Based on the interpretation of geological maps, seismic reflection and well data complemented with a bibliographic compilation and field work in the Rif, we investigate the factors that control the rift initiation, its development and the formation of oceanic crust in NW Africa. From SE to NW, we examine the Western Sahara Atlas, the Tendrara, the Guercif, and the Rif basins, to establish their geodynamic evolution in relation with the Mesozoic formation of the Central Atlantic and Maghrebian Tethys oceans, respectively. The Triassic extension was diffuse and developed over Lower Carboniferous horst-and-graben structures formed in the NW passive margin of Gondwana and involved in the subsequent late Carboniferous – early Permian Variscan orogenic system; suggesting that, at the onset of the Triassic rifting, the lithosphere was thermally re-equilibrated and replaced by more fertile lithospheric mantle. Afterwards, extension resumed in the Atlas system during middle to late Pliensbachian and finished during Toarcian. In the Rif and Guercif basins, the extension began later, mainly during the Toarcian, climaxing during Middle Jurassic times with the exhumation along low-angle extensional faults of CAMP gabbroic bodies and the final mantle exhumation during Upper Jurassic in the Rif. The study evidences the prominent role of the Variscan structural and thermal inheritance on the subsequent deformation events. Accordingly, the Paleozoic inverted basins and horsts localized the Triassic extension. From that, the opening of the Central Atlantic and Maghrebian Tethys oceans activated, respectively, the SE (Atlas) and NW (Tethys) rifted segments of the weakened continental crust where the Jurassic extension was gradually distributed. This led to the final formation of an oceanic domain in the NW paleomargin of Africa.