Abstract
The westernmost part of the Senegalese basin in West Africa is characterized by an extensive magmatic event, exposed in the form of sills and dykes, mainly during the Quaternary but beginning in the Tertiary (35 + 0.1 Ma (Miocene) to 0.8 + 0.1 Ma (Pleistocene)). The main exposures are located in the Cap-Vert Peninsula and Thiès Plateau to the East of Dakar. This magmatic event postdated the opening of the Central Atlantic and displays chemical similarities to the Tertiary-Quaternary magmatic centres within the African plate. Two main facies are distinguished among the flows: microporphyric and doleritic textured olivine-rich alkaline basalts, the former often containing spinel-lherzolite mantle inclusions. The alkaline sodic affinity of the volcanic series and the Ti, K + Na, Nb, P 2O 5 and Zr content of the lavas are typical of magmas generated in a within-continent plate tectonic setting. This volcanism appears to have resulted from an active mantle hotspot, over which the African plate migrated as the central Atlantic Ocean opened, using reactivated faults (contemporaneous with Central Atlantic opening) as magmatic pathways.
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