HOST LAVA PETROLOGY AND LHERZOLI MINERAL PHASE CHEMISTRY

Alkaline basalts encrust enclaves of peridotites, most of which are spinel lherzolites. They have been discovered on the Adamaoua plateaux and in the Liri region (south of the Kapsiki plateau). The basalts have a porphyritic microlitic texture and the enclaves have a protogranular texture, consisting of olivine, orthopyroxene, clinopyroxene and spinel crystals. The forsterite (Fo89-91) and NiO (0.30-0.44) contents in olivine crystals, the Mg# (¿ 94) number of orthopyroxene and the low titanium contents in clinopyroxene (TiO2 < 0.9) and spinel crystals (TiO2 < 0, 5 %) are within the range of values reported for the peridotites of the "Cameroon Volcanic Line", indicating that the peridotites of the Liri and Adamaoua region represent the residues of partial melting of the primitive mantle. The host basalt (Liri) has a porphyritic microlitic texture with phenocrysts of olivine, clinopyroxene and microlites of plagioclase, ilmenite and titanomagnetite. The equilibrium temperature for the Liri samples varies between 842 - 1136°C and 825 - 1245°C for those from the Adamaoua Plateau.