Synkinematic ferro-potassic magmatism from the Mekwene-Njimafofire Foumban Massif, along the Foumban-Banyo shear zone in central domain of Cameroon Pan-African fold belt

Abstract

The ferriferous high-K calc-alkaline intrusive of the Mekwene-Njimafofire Foumban Massif, Central Cameroon, were synkinematically emplaced in a sinistral strike-slip shear zone of Pan-African age. The rock sequences consist of orthogneisses with abundant coarse- to medium-grained quartz monzodiorite, medium- to fine-grained quartz monzonite, granodiorite, and fine-grained biotite granite composition and cover a range of about 60 to 76 wt.-% SiO2. They display characteristics of shoshonitic and high-K calc-alkaline series. Quartz monzodiorite, quartz monzonite and granodiorite are metaluminous, whereas biotite-amphibole granite is moderately peraluminous (1≤ A/CNK £ 1.1) and plot in the field of I-type granitoids. Major and trace element composition and the Rb/Sr isotopic data of the granitoids indicate that the source materials 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 andesite in the central domain of the PANEFB (Pan-African North Equatorial Fold Belt). The plutonic rocks of Mekwene-Njimafofire area resemble other Neoproterozoic high-K calc-alkaline syntectonic plutons in western and central Cameroon. They also display strong similarities with high-K calc-alkaline plutons of eastern Nigeria and of the Borborema Province in NE Brazil. Key words: Metaluminous and peraluminous granitoids, orthogneisses, ferriferous series, I-type granite, high-K calc-alkaline rocks, crustal source, Pan-African fold belt, Cameroon.