MICROSTRUCTURAL INTERPRETATION OF THE GARNET-SILLIMANITE-BEARING GRANITE GNEISS OF IKARE AREA, SOUTHWESTERN NIGERIA
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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 fibrolitetype
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 Kfeldspar,
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.
Keywords
QH Natural history, QH301 Biology, QR Microbiology