The Jurassic-Cretaceous basaltic magmatism of the Oued El-Abid syncline (High Atlas, Morocco): physical volcanology, geochemistry and geodynamic implications.

Basaltic lava flows, dykes and sills, interbedded within red clastic continental sedimentary sequences (the so called "Couches Rouges") are widespread in the Oued El-Abid syncline. They represent the best candidates to study the Jurassic-Cretaceous magmatism in the Moroccan High Atlas. The volcanic successions were formed during two pulses of volcanic activity, represented by the Middle to Upper Jurassic basaltic sequence B1 (1 to 4 eruptions) and the Lower Cretaceous basaltic sequence B2 (3 eruptions). Whether belonging to the B1 or B2, the lava flows present morphology and internal structures typical of inflated pahoehoe. Our geochemical data show that, at least for Jurassic magmatism, the coeval dykes, and sills cannot be considered as strictly representing the feeders of the sampled lava flows. The Middle to Upper Jurassic pulse is moderately alkaline in character, while the Lower Cretaceous one is transitional. Crustal contamination plays a minor role in the petrogenesis of these magmas, which were generated by variable partial melting degrees of a garnet-bearing mantle source. Magmatism location was controlled by re-existing Hercynian fault systems reactivated during a Middle to Upper Jurassic-Cretaceous rifting event. The associated lithospheric stretching induced melting by adiabatic decompression of enriched low-solidus infra-lithospheric domains.