Petrology of lherzolite xenoliths of Hosséré Sédé volcano (Adamawa plateau, Ngaoundéré area, Cameroon)

Abstract

Numerous mantle xenoliths 6–12 cm in size and sub-angular to rounded in shape occur within Mio-Pliocene basanite lavas of the monogenic volcano of Hosséré Sédé in the Adamawa plateau. Xenoliths of spinel lherzolite exhibit protogranular, equigranular or porphyroclastic texture. Microprobe chemical analyses show that olivine is highly magnesian (Fo_88-90), clinopyroxene crystals are diopside and augite (Wo_41.6–49.6 En_45.3–53.7 Fs_4.2–6.2), orthopyroxene crystals are enstatite (Wo_1.4–1.5 En_88.6–89.0 Fs_9.6–9.9) and spinel crystals are mainly Al-spinel associated to minor Cr-spinel. Estimated temperatures and pressures through empirical formulas show that Hosséré Sédé xenoliths have equilibrated between 1085 and 1204 °C and 1.08 to 1.57 GPa, corresponding to sampling depths of 36 and 52 km. Detailed petrographical and mineral chemistry of Hosséré Sédé xenoliths evidences the complex nature and composition of the subcontinental lithosphere under the Adamawa plateau. This may involve a probable uplift of the whole area after a limited extensional event, possible metasomatism through melt infiltration during shearing of the lithospheric mantle along the Pan African strike-slip fault system.