Spinel-Bearing Lherzolite Xenoliths from Hosséré Garba (Likok, Adamawa-Cameroon): Mineral Compositions and Geothermobarometric Implications

Abstract : Spinel-bearing lherzolite xenoliths from the Hosséré Garba (1272 m.a.s.l) volcano on the Adama-wa Plateau, is located in Likok village, at about 35 km to WSW of Ngaoundéré. These xenoliths (~11 cm size) have been sampled into the host basaltic lava flows from the NE flank of the Hosséré Garba volcano. These xenoliths characterized by porphyroclastic texture consisted of olivine (~55 vol.%), orthopyroxene (~19 vol.%) and clinopyroxene (~21 vol.%) crystals. Spinel crystals (~5 vol.%) are red brown and interstitial between the crystals of olivine and pyroxenes. CaO contents are low (<0.08 wt%) in olivine and similar to those estimated (CaO: 0.05 -0.1 wt%) for the mantle origin. The values of Al VI /Al IV ratio range between 1.1 and 1.3 for the Cr-diopside crystals from Hosséré Garba xenoliths. The constant value of the volumes V(Cell) and V(M1) for clinopyroxene compositions, indicates the similar pressures. Hosséré Garba represents a residual sequence is-sued from partial melting of a mantle source. Similar compositions have been recorded in miner-als of ultramafic xenoliths from other ultramafic xenoliths domains of the Cameroon Line and the Adamawa Plateau.