Petrography and geochemistry of amphibolites from the Fomopéa Pluton (West Cameroon): Origin and geodynamic setting

Abstract Petrographic and geochemical investigations were carried out on amphibolites from the Fomopea pluton (FP) in order to determine their origin and geodynamic setting. The geology of the FP consists of granitoids (granites, monzogranites, syenogranites and diorites), intruded in the basement rocks (gneiss and amphibolites). In the N and NE parts, the pluton was partially recovered by basalts while the SE parts was mylonitized. The amphibolites are represented in the pluton body by stretched, sub-rounded or elongated xenoliths. They are cumulate, massive or banded. The main minerals are amphibole, plagioclase and biotite while accessory minerals are pyroxene, quartz, K-feldspar, calcite and oxides. Amphibolites display magmatic heterogranular to granoblastic heterogranular textures. They are ortho-amphibolites, gabbroic in nature, calc-alkaline and metaluminous. The Nb/Ta ratio (12.5–18.5) is characteristic of arc-type basalts. Rare earth element (REE) profiles show negative Ce anomalies that are more significant in cumulate amphibolites (samples TN74 and TN78), suggesting a possible enrichment of the source by pelagic sediments. Our results are consistent with those of previous studies in the Central African Fold Belt (CAFB) in Cameroon thus, followed the same evolution during the Proterozoic.