Volume 60, Issue 334, January - April 2024

Mineral chemistry and Geothermobarometry of intrusivecharnockitic rocks around Ikare, Southwestern Nigeria

Anthony Victor Alaba Oyeshomo^♦

Department of Earth Sciences, AdekunleAjasin University, Akungba-Akoko, Nigeria

^♦Corresponding author
Department of Earth Sciences, AdekunleAjasin University, Akungba-Akoko, Nigeria

ABSTRACT

Charnockite of igneous origin outcropping around Ikare area, southwestern Nigeria have been investigated in this work. Two representative samples of the intrusive charnockites were prepared into thin and polished sections for petrographic and electron micro-analysis to determine their mineralogy and mineral chemistry. The mineral assemblages observed were quartz, plagioclase feldspar, alkali feldspar, orthopyroxene, clinopyroxene, hornblende and biotite while the accessory minerals are apatite, zircon, ilmenite, magnetite and opaque ores. Electron microprobe analysis carried out on the two samples showed that the average compositional range of plagioclase feldspar can be expressed as An28Ab75 for core composition which indicate andesine to oligoclase. Alkali feldspar expressed asOr86Ab13An1 was mainly microcline to orthoclase. Hornblende in the intrusive charnockite are Mg-rich pargasite while orthopyroxene were mainly hypersthene to ferro-hypersthene in composition. The clinopyroxene is augite. Geothermobarometric calculations using two-pyroxene thermometer show that the crystallization temperature of the intrusive charnockites range from 8060C to 8890C with assumed pressure of 5 kbars suggesting that these rocks are high temperature, low pressure types of charnockitic rocks. The charnockite showed evidence of melting. Dynamic recrystallization of mesoperthitic feldspar and residual alkali feldspar or quartz in biotite relicts are features related to high metamorphic temperatures.

Keywords: Intrusive charnockites, electron microprobe, post crystallization, ductile deformation, low pressure

Discovery, 2024, 60, e13d1421

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DOI: https://doi.org/10.54905/disssi.v60i334.e13d1421

Published: 30 March 2024