Le Protérozoïque supérieur d'Imiter, Saghro oriental, Maroc: Un contexte géodynamique d'arrière-arc

The Upper Proterozoic (PII) of Imiter shows a large amount of turbiditic greywackes which are organized into deep sea fans. They were deposited at the foot of the continental slope in an extensional basin prior to the Pan-African orogeny. The extension is associated with mafic volcanism (MORB) enriched into light REE by crustal contamination. Petrological and geochemical data show that the greywackes are immature (23 to 42% feldspars, 11 to 24% lithic fragments) with high concentrations of Na2O, Ba, Co, Cr and Ni. All these features are consistent with an active back-arc environment, the arc itself being situated to the south of the Saghro mountains. However, the source of the sedimentary infill of the basin shows continental characteristics with calc-alkaline affinities. Furthermore, this material comes from the northeast, which is a direction opposite to the arc. The REE pattern is characteristic of an active domain. This domain would correspond to a marginal or back-arc basin, supplied with sediment from two opposing directions.