The Cenozoic alkaline magmatism In central-northern Madagascar: a brief overview.

The Cenozoic volcanic rocks of Madagascar were emplaced as lavas, pyroclastic rocks, dykes, and plugs, and range in composition from olivine melilitites, basanites and alkali basalts, to phonolites, trachytes and rhyolites. The ultrabasic-basic lithologies are dominant, in particular basanites and tephrites, with less abundant, mildly evolved, compositions. These rocks form at least three different magma lineages of broadly sodic affinity. Fractional crystallization of the observed phenocryst phases is the most reasonable petrogenetic model for the genesis of the more evolved compositions. The mantle-derived magmas were likely generated by variable degrees of partial melting of incompatible element-enriched mantle sources, possibly located in the deep lithosphere or in the asthenosphere.