Geochemistry of Ferriferous, High-K Calc-Alkaline Granitoids from the Banefo-Mvoutsaha Massif (NE Bafoussam), Central Domain of the Pan- African Fold Belt, Cameroon

摘要

The ferriferous high-K calc-alkaline rocks of the Banefo-Mvoutsaha Massif, Pan-African Belt, Central Cameroon, were synkinematically emplaced in a sinistral strike-slip shear zone of Pan-African age. The rock sequences consist of orthogneises made of coarse-grained granites, quartz-monzonites, and medium- to fine-grained granodiorites, ranging from ca. 55 to 75 wt.-% SiO2. They display characteristics of shoshonitic and high-K calc-alkaline series. Orthogneises are metaluminous to peraluminous and show characteristics of I-type granitoids from a ferriferous series. Trace element distribution patterns reveal rocks enriched in LILE when compared to HSFE and distinctively depleted in Th, Nb, Ba, Sr, Ti and Ta. The data indicate that this granitic rock assemblage did not result from the simple differentiation of a common parental magma, but show that Banefo-Mvoutsaha plutonic rocks were derived from different crustal protoliths. Major and trace element composition are consistent with the magmatism which may have involved remelting of (1) a composite metagreywackes protolith in the upper crust and (2) amphibolitised high-K calc-alkaline basaltic andesites in the central domain of the PANEFB (Pan-African North Equatorial Fold Belt). The plutonic rocks of Banefo-Mvoutsaha area resemble other Neoproterozoic high-K calc-alkaline syntectonic plutons in Western Cameroon. They also display strong similarities with high-K calc-alkaline plutons of the Pernambuco shear zone in NE Brazil and Eastern Nigeria.