Les basaltes éocènes à affinité transitionnelle du plateau Bamoun, témoins d’un réservoir mantellique enrichi sous la ligne volcanique du Cameroun

Abstract: Transitional basalts of Eocene age crop out on the western part of the Bamoun Plateau. Basalts of this type are rather scarce in the Cameroon Volcanic Line (LVC). These olivine-free basalts (BSO) lack olivine and have the oldest ages (51.8±1.2Ma) of the entire LVC. They differ from the olivine-bearing basalts (BAO, 46.7±1.1Ma) on the same plateau, as well as from the typical alkali basalts found elsewhere on the LVC. They closely resemble the rocks of the East-African rifts and Kerguelen Island. They are characterized by the scarcity of modal olivine, a relatively high Y/Nb ratio (1), but low LaN/YbN (10) and CeN/YbN (7) ratios. Moreover, 87Sr/86Sr (0.7044) and 143Nd/144Nd (0.5126) isotopic ratios of BSO are respectively higher and lower than those of BAO (0.7034 and 0.5128) are. These data indicate a source in an enriched lithospheric mantle (EM) that produced the transitional basalts, in contrast to a source closer to HIMU, which could have produced alkali basalts. [Copyright &y& Elsevier]