Abstract

Author:
Oyeshomo, A.V

Doi: 10.26480/gsrj.02.2024.120.123

This is an open access article distributed under the Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

The Gneisses around Ikare consists of varieties such as grey, granite, charnockitic, pelitic and biotite gneiss. This area is underlain by both igneous and metamorphic rocks intruded by the charnockitic and Pan African granitoids. Essential minerals are microcline, plagioclase, quartz, biotite, hornblende and orthoclase, while ilmenite, apatite, zircon and magnetite are the accessory minerals. Major trend of foliation is NW direction and typified by parallel alignment of mafic and quartzo-feldspathic bands of varying dimension. The geochemical analysis showed major oxides such as SiO2 in the range of 62.10 – 71.50 wt%, Al2O3 vary in content from 12.90 – 16.70 wt %, Fe2O3 has between 5.15 – 8.43 wt %, Na2O content is between 2.55 – 3.64 wt%, while K2O vary between 3.02 – 4.82 wt %. The gneisses are sub alkaline and metaluminous, except one sample of granite gneiss which is peraluminous. This may be due to contamination of the parent source rock. The average K/Rb ratios of 193ppm suggested that the gneisses were formed through internal differentiation of archetypal TTGs through intra crustal melting. All the gneisses are enriched in Ba, Sr, Zr, but depleted in Rb. Absence of minerals like sillimanite, kyanite and cordierite foreclosed sedimentary origin for the gneisses. Geochemical variations suggest igneous precursors for the gneisses in Ikare area.