Petrochemistry of Charnockitic Rocks of Awo-Osuntedo Area, southwestern Nigeria

Abstract

The petrochemistry of charnockitic rocks from the Awo-Osuntedo area of southwestern Nigeria were investigated with the objectives of presenting their petrogenesis and geotectonic setting at the time of their emplacement. The rocks were mainly found within the migmatitic gneiss country rock and associated pegmatites. They occurred as small intrusive bodies and are composed mainly of orthopyroxene, clinopyroxene, quartz, biotite, secondary amphibole, plagioclase and alkaline feldspars with a small compositional range between basic and intermediate respectively for Awo and Osuntedo rocks. The small Eu* anomalies (0.9-1.47) with an average of 1.2 combined with elemental signatures indicate that the rocks were derived from an enriched mantle with some crustal contamination and emplaced in an environment similar to the arc region of tectonic setting. Though, the rocks have dry mineral assemblages, there is no geochemical evidence to suggest they were derived from melting that was associated with granulite facies metamorphism rather the small sizes of the plutons and the geochemical signatures particularly high magnesian and calc-alkaline nature are typical of the Caledonian type charnockite formed during delamination of thickened continental crust after collisional orogeny.