Petrology of highly evolved Pan-African two-mica granites from the Nkambe area, West Cameroon

Abstract

Two-mica granites from the Nkambe area (West Cameroon) comprise two-mica granite and magnetite-rich two-mica granite. They are composed of K-feldspar, phengite, biotite and quartz. Megacrysts of magnetite surrounded by pink-colored patches are present locally. They are peraluminous with a ferroan affinity and exhibit normative corundum. These two-mica granites were generated at the minimum temperature and pressure of crystallization of 640 °C/600 MPa and later on evolved in the late stage of differentiation to give magnetite-rich two-mica granite. During the differentiation, hydrothermal events took an important role and led to the genesis of megacrysts of magnetite and leaching of alkalis, calcium, iron and magnesium out of some minerals. However the substitution of Fe 3+ by Al vi has been more prominent in magnetite-rich two-mica granite than in two-mica granite leading the formation of muscovite adversely to celadonite during the hydrothermal process. This process lasted about 50 m.y and was associated to the cooling path that reached lower pressures with the formation of chlorite at temperatures below 400 °C.