The Pre-Pan-African rifting of Saghro (Anti-Atlas, Morocco): example of the middle Neoproterozoic basin of Boumalne.
Résumé
In the Anti-Atlas, the Boumalne basin includes 3,000 m of Middle Neoproterozoic sediments. It consists of turbiditic deposits folded during the major Pan-African event ca 685 Ma. A syn-sedimentary basaltic pile of lava flows is interbedded in the upper part of the lower formation. These lavas show an initial rift tholeiite (IRT) chemical signature. Petrographical analysis of sediments and typology of detrital zircons indicate a continental margin sedimentation, without any volcano-sedimentary supply from a close volcanic arc. It is concluded that the Boumalne Basin formed in a continental passive margin evolving from an intracontinental rift. This interpretation differs clearly from that of a back-arc basin which is commonly accepted. Hence, the opening of this basin is related to the pre-Pan-African Saghro rift synchronous to the Central Anti-Atlas oceanization, and not to the demise of this oceanic domain along an active margin.