Tholeiitic and alkaline magmatisms of the Early-Cretaceous half-grabens ofMayo Oulo-Lere and Babouri-Figuil (Northern Cameroon-Southern Chad) in extensional structural settings.

Two major dykes of basalts, microgabbros, olivine dolerites (continental th oleiites), and of camptonites and benmoreites (alkaline rocks) are respecti vely exposed in the Mayo Oulo-Lere and Babouri-Figuil Early Cretaceous half -grabens (Northern Cameroon-Southern Chad). The tholeiites were probably de rived from an asthenospheric source in connection with a lithospheric thinn ing occurring between Santonian and Eocene times. In contrast, the alkaline rocks may be derived from a deeper metasomatized mantle source. (C) 2001 A cademie des sciences editions scientifiques et medicales Elsevier SAS.