The magmatic evolution at the Moroccan outboard of the West African craton between the Late Neoproterozoic and the Early Palaeozoic

Abstract

Abstract The Late Neoproterozoic Ouarzazate Group crops out on the north margin of the West African craton (WAC). In this group an important post-collisional magmatism is characterized by a great diversity in plutonic and volcanic rock types of the high-K calc-alkaline series. This series evolved mainly by crystal fractionation and by an important crustal contamination from an anomalous mantle source. The Early Cambrian magmatism began at the same time on both sides of the Anti-Atlas Major Fault, the southwestern side (Kerdous region) and northeastern side (Ouarzazate-Agdz region), interbedded in the Early Cambrian Basal Series and spread later to the Western High Atlas of the Morocco northern WAC outboard areas. This magmatism changes from a continental tholeiitic series (HPT and LPT) at the beginning to an alkaline series at the top (Adoudou and ‘Lie de vin’ formations). Fractional crystallization and pelagic or crustal contamination were the most important processes in the magma differentiation. The geochemical inversion from calc-alkaline to tholeiitic magmatism between the Late Neoproterozoic and the Early Cambrian is documented, as is the major extension of the tholeiitic activity on both sides of the South Atlas Fault. This geochemical variation indicates a transition of the tectonic regime from compressive to extensional. The late local Jbel Boho alkaline magmatism indicates the sink of the source and the mitigation or closure of the extensional cycle at this time.