Le massif tertiaire du Nkogam (Ouest Cameroun): caractéristiques principales et géochronologie Rb/Sr sur roches totales

Abstract

The Nkogam massif is exposed over an area of about 140 km². It is located on the ‘Cameroun Line’ and is one of the tertiary massives along this structure. It is composed of three units: (1) basalts; (2) ignimbrites; and (3) acid plutonic rocks. The first two are alkalic, the third one is peraluminous. Rb/Sr radiometric analysis on whole rocks yields an age of 67 Ma for the granites. The fact that two parallel isochrons are obtained shows possible slightly different origins.