Geochemistry of Precambrian gneisses in the eastern part of the Ohan massif, Southeastern Nigeria

Abstract

The basement of the eastern Oban massif is composed of a wide range of texturally and mineralogically different types of gneissic rocks. Migmatitic gneisses are characterized by high contents of silica and related trace elements while granite and biotite-hornblende gneisses have relatively lower values of these elements. Geochemical variation diagrams suggest that the gneisses evolved from a calc-alkaline magma of quartzdiorite to granodiorite composition. This demonstrates that orthogneisses exist in the basement complex of Nigeria.