Wehrlite xenoliths and petrogenetic implications, Hosséré Do Guessa volcano, Adamawa plateau, Cameroon

Abstract

Peridotite xenoliths of wehrlite composition, scarcely known in Adamawa plateau, Cameroon, were sampled by Mio-Pliocene basanites from Hosséré Do Guessa volcano. Their origins are discussed and elucidated trough petrography and mineral chemistry. Studied wehrlites exhibit poikilitic or protogranular textures and are composed of four main mantle phases (high Mg-olivine, augite, enstatite and Al-spinel). Petrographic and microprobe (Camebax SX100) chemical data (Fo90.8-91.4 olivine, Wo39.4-42.0 augite, En90.5-91.1 enstatite and Al-spinel) suggest a mantle origin for the Hosséré Do Guessa wehrlites. Hence, these rocks could not be considered cumulate. They have been equilibrated between 1,140 and 1,220°C, at pressures of 1.5–2.0 GPa, at 50–66 km deep, below the crust-mantle boundary. Wehrlites might result in reactions with carbonate/carbonatite melt, accompanying CO2 degassing and metasomatism by fluid phases. They suffered transpressional tectonics, during movement at Tertiary times of Pan-African strike-slip-faults, after solid-state tectonic relaxation.