Geochemical Characteristics and Petrogenesis of Basement Rocks in Idoani Area, Ondo State, Southwestern Nigeria

Abstract

Idoani area of Ondo State is an extension of the Upper Proterozoic Igarra Schist Belt of the Southwestern Nigerian Basement Complex. The area comprises mainly of metasedimentary rocks with subordinate amount of intrusives. Quartz-mica schist, phyllite, quartzite and banded gneiss are the dominant rock types in the area. These metasediments are intruded by the Older granite and other minor intrusives (pegmatite, aplite, dolerite dyke, quartz vein). Idoani rocks, as revealed by petrographic studies, are rich in quartz, alkali and plagioclase feldspars and mica with a low amount of opaque minerals. Geochemical studies and petrochemical variation diagrams show that the rocks are sub-alkaline, medium-K calc-alkaline to shoshonitic, peraluminous, and characterized by intermediate-high silica content and low-moderate amount of mafic oxides. Petrological and geochemical studies revealed that the quartz-mica schist and phyllite are metapelites while the quartzite is a meta-arkose, derived from a granitic – quartz-monzonitic source. The banded gneisses were probably derived from a hybrid sedimentary–igneous protoliths while the granite is of magmatic origin.