Petrogenesis of the Middle Jurassic Intraplate Mafic Magmatism in the Imilchil Syncline (Central High Atlas, Morocco)

Following the Early Liasic tholeiitic CAMP magmatism, there was an extensive transitional to alkali mafic magmatism in the Central High Atlas from the Middle Jurassic (B1 event) to Lower Cretaceous (B2 event). These magmas consist of shallowly differentiated intrusions (gabbro, diorite, and syenite) outcropping in numerous narrow anticlinal ridges, while doleritic dykes and basaltic lava flows intersect Middle Jurassic–Upper Cretaceous continental deposits forming large synclines. In this study, we use petrological and geochemical investigations to characterize the magmatic affinity of dolerites and basalts (B1 event) in the Imilchil syncline and constrain their genesis. We primarily discuss mantle source, crustal contamination, and tectonic setting. The alkali basalts and dolerites of the Imilchil syncline (B1 event) have moderate alkali affinity and OIB-like geochemical signatures. They are formed by low-degree (5–10%) partial melting of a deeper mantle source in the garnet stability field, presumably in the asthenosphere with low continental crustal contamination. B1 Alkaline magmatism in the Central High Atlas marked a rift-drift transition phase in which intraplate extension gave way to the breakup between the African and American plates and the Central Atlantic seafloor spreading.