Initial Cenozoic magmatic activity in East Africa: new geochemical constraints on magma distribution within the Eocene continental flood basalt province

Abstract The initial interaction between material rising from the African Large Low Shear Velocity Province and the African lithosphere manifests as the Eocene continental large igneous province (LIP), centred on southern Ethiopia and northern Kenya. Here we present a geographically well-distributed geochemical dataset comprising flood basalt lavas of the Eocene continental LIP to refine the regional volcano-stratigraphy into three distinct magmatic units: (1) the highly alkaline small-volume Akobo Basalt (49.4–46.6 Ma), representing the initial phase of flood basalt volcanism derived from the melting of lithospheric–mantle metasomes; (2) the primitive and spatially restricted Amaro Basalt (45.2–39.8 Ma), representing the early main phase of flood basalt volcanism derived from the melting of the upwelling thermochemical anomaly; and (3) the spatially extensive Gamo–Makonnen magmatic unit (38–28 Ma), representing the mature main phase of flood basalt volcanism that has undergone significant processing within the lithosphere and resulted in relatively homogeneous compositions. The focused intrusion of these main phase magmas over 10 myr preconditioned the African lithosphere for the localization of strain during subsequent episodes of lithospheric stretching. The focusing of strain into the region occupied by this continental LIP may have contributed to the initial extension in SW Ethiopia that is associated with the East African Rift.