Four Pan-African plutonic sets of the Colomines gold district (East-Cameroon): Petrogenesis, K-Ar dating and geodynamic significance

The study of Colomines area (eastern Cameroon) is designed to furnish petrological, mineralogical, geochemical and K-Ar data on granitoids in order to discuss the thermodynamic conditions of crystallization of different magmas, the magma series and differentiation processes, the characteristics of magmas’ sources and the geodynamic implications. The Colomines area is made up of four intrusive sets (heterogeneous granodiorites and their mafic enclaves, mafic plutonic suite (MPS), porphyritic biotite granites, Ms-Bt granites). Mineralogical assemblage is constant in MPS and mafic enclaves (Cpx+Hbl+Bt+Pl+Qtz+Op+Sph+Zrn+Ap), and granodiorite and granites sets (Hbl+Bt+Ms+Pl+Kfs+Op+Sph+Zrn+Ap), except the leucocratic Ms-Bt granites which are amphibole-free. Amphibole in diorite (MPS) and heterogeneous granodiorite has a composition of edenite and ferroedenite, respectively, whereas biotite composition varies with an increase of Fe content from basic to acidic rocks. Concomitantly, plagioclase show an increase of albite component. Crystallization of magmas started at great depths >22 km but the coexistence of heterogeneous granodiorites, MPS plutonic suite rocks, porphyritic biotite-granites and Ms-Bt granites at the same crustal level indicates that magmas migrated upwards and emplaced at a depth