Existence of old doleritic dykes of continental tholeiite composition, in the Cameroon Line alkaline province. Implication to the geodynamical context.

In the Adamawa Plateau (Northern Cameroon), doleritic dykes belong to a mag matic activity which predated the Cenozoic alkaline volcanism of the Camero on Line. They have the chemical composition of continental tholeiites with Nb-Ta- and Ti-negative anomalies. This magmatism is interpreted as being de rived from a sub-continental lithospheric source, which may have bean conta minated during a former subduction event, linked to the Pan-African converg ence. It is related to an early stage of continental break-up, which was co ntemporaneous or predated the Cretaceous tholeiitic magmatism of predominan tly asthenospheric origin, which indicates a lithospheric thinning. (C) 200 1 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.