RIFTING-RELATED MAGMATIC EPISODES OF SOUTH-WESTERN MALAGASY (MORONDAVA BASIN)

Greater India and Malagasy underwent a southwards lateral displacement along the Davie ridge. Then, separation between Greater India and Mal agasy occurred during the Upper Cretaceous. A voluminous magmatism has been evidenced during or after th is rifting, in different parts of t he island particularly in the Morondava basin, in the western part of the island. In this basin, Cretaceous lavas are mostly basalts (45-54 % SiO2) of two types: Ti-rich (TiO2 > 2 %) and Ti-poor (TiO2 < 2 %), o f tholeiitic to transitional affinities. A Sew gabbroic intrusions and doleritic veins outcrop too. Later, during the Upper Miocene, basic l avas of transitional to alkaline affinities erupted south of the basin . Several mantellic sources are evidenced which explain the geochemica l diversity of studied lavas: EM I, EM II, and moreover a source close to those described in Etendeka in Namibia. The Cretaceous volcanism s eems to have been linked to the activity of the Marion hot spot. (C) A cademie des sciences/Elsevier, Paris.