MICROSTRUCTURAL INTERPRETATION OF THE GARNET-SILLIMANITE- BEARING GRANITE GNEISS OF IKARE AREA, SOUTHWESTERN NIGERIA
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Oziegbe, E. J.
Ife Journal of Science
This study presents microstructures from the granite gneiss of the Basement complex of southwestern Nigeria. The granite gneiss of Ikare area comprises of the mineral assemblage; garnet, biotite, K-feldspar, quartz, plagioclase, sillimanite and opaque minerals. K-feldspar porphyroblasts have cuspate interstitial quartz grains, also quartz grains are included in K-feldspar. Most K-feldspar grains are highly strained and in some cases are fractured. Prismatic and fibrolite-type sillimanite are both present. Biotite is closely associated with fibrolite-type sillimanite. Sillimanite was observed to mimic the foliation produced by biotite. K-feldspar is the dominant mineral and could have formed by the dehydration reaction of biotite + plagioclase + quartz + sillimanite ==> garnet + K-feldspar + melt. Microscopic structures such as strained feldspar grains, micro-fractures in K-feldspar, simple twinning in K-feldspar, myrmekite, mimicking textures, microperthitic intergrowth and cuspate volumes of quartz surrounding K-feldspar are indicative of melt-bearing and solid-state deformation of regional metamorphic rocks.
Oziegbe, E.J. and Oziegbe, O., 2023. Microstructural interpretation of the garnet-sillimanite-bearing granite gneiss of Ikare area, southwestern Nigeria. Ife Journal of Science, 25(1), pp.035-044.