PETROGRAPHY AND GEOCHEMICAL CHARACTERIZATION OF THE LAME ALKALINE BASALTS (SOUTHWESTERN MAYO KEBBI) IN THE CAMEROON-CHAD VOLCANIC LINE: IMPLICATIONS FOR TECTONIC EVOLUTION AND MANTLE SOURCE

The Lame basalts, located in the Mayo Kebbi massif in southwestern Chad, display petrographic and geochemical features typical of intraplate alkaline magmas. Their homogeneous mineralogical composition (clinopyroxene, olivine, plagioclase, and iron oxides), combined with a relative enrichment in LREE compared to HREE, as well as V, Cr, Mg# contents and Nb/U ratios characteristic of OIB, indicate a HIMU-type mantle source with residual garnet. Variations in major and trace elements show that magmatic differentiation was dominated by fractional crystallization, with no evidence of crustal contamination. These geochemical signatures closely resemble those of alkaline magma observed in the Tibesti, OuaddaI and Lake Chad volcanic provinces, confirming their affiliation with the northern extension of the Cameroon Volcanic Line.