Granite gneisses form one of the major felsic lithologies occurring in the gneiss-migmatite-quartzite unit of the Nigerian basement complex within which Supare-Akoko lies. The rock in the area occurs mainly in association with quartzo-feldspathic gneiss and is severally truncated by dolerite, swarms of pegmatite and quartz vein/veinlets. They are medium grained in texture and have quartz, plagioclase, orthoclase/microcline and biotite as major minerals, with pyroxene, hornblende and opaque minerals sometimes occurring. Modal analysis shows that the rock is mainly granitic in composition. Geochemical studies show the preponderance of crustal traits in the evolutionary history as illustrated by sedimentary origin shown on all the discrimination diagrams and the peraluminous features obtained from molecular Al2O3/(CaO + Na2O + K2O) ratio. Other traits like slight metaluminous character, absence of sedimentary index minerals and the linear variation trend of oxides with SiO2 point towards crystallization from a melt. Consequently, it is thought that anatexis must have played a major role in the formation of the magma that produced the granite gneiss of the area.
PAPER TITLE :THE PETROGENESIS OF THE GRANITE GNEISS OF SUPARE-AKOKO AREA, SOUTHWESTERN NIGERIA
JOURNAL Of SUSTAINABLE TECHNOLOGY | VOLUME 3 NUMBER 1 2012
- Author(s) : ADEYEYE, O.A. and ADEMESO, O.A