Synkinematic emplacement of granitoids in a Pan-African shear zone in Central Cameroon

Abstract

The magmatic complex of Koata area that is part of the central Domain of the North Equatorial fold belt outcrops within the Central Cameroon Shear zone (CCSZ). This complex comprises four plutonic groups of rocks: (i) monzodiorites, (ii) quartz-monzodiorites, (iii) quartz-monzonites and (iv) granites. The elongate shape of the plutons, variable orthogneissification and foliation strikes parallel to the CCSZ point to syntectonic magma emplacement. The rocks are metaluminous, high-K, and calc-alkaline to shoshonitic ferro-potassic, with mineralogical and geochemical characteristics of I-type granitoids. The plutonic rocks are characterised by high Sr, moderate ∑REE concentrations and low Ni and Cr contents. They also display chondrite-normalised REE patterns characterised by variable LREE enrichment, moderate to minor HREE fractionation with moderate negative Eu anomalies (Eu/Eu ∗: 0.66–0.93 (quartz-monzonites), 0.77–0.96 (quartz-monzodiorites), 0.76–0.93 (monzodiorites)) and significant positive Eu anomalies (1.27–5.2 (granites)). Trace element distribution patterns show that all these rocks are distinctively depleted in Th, Nb, Ba, Ti and Ta relative to other trace elements and are enriched in LILE compared to HFSE. Each plutonic group shows distinct evolutionary trends and the geochemical data indicate that the groups were derived from different crustal protoliths. The source materials for the four plutonic groups were similar and possibly included amphibolitised high-K calc-alkaline basaltic andesites. The plutonic rocks of Koata 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.