Oluwatoyin, O. Akinola, Olusola, A. OlaOlorun* and Olatayo L. Afolagboye

This paper investigates and report field relationship and structural features of the basement rocks in Ekiti, southwestern Nigeria. Systematic geological mapping reveals that Ekiti is underlain by migmatite-gneiss, quartz schist, quartzite, granite, and charnockite. These lithologies were intruded by series of aplite, dolerite, and pegmatite dykes. Structural deformations attributable to polycyclic orogenic activities manifested in all the basement rocks. Migmatite and its gneissic subunits form the country rock and exhibits complex folds, abundant quartz veins and haphazardly emplaced dykes. Foliation and lineament are oriented N-S, strike values range between N5oE -N18oE with westerly dip of 72º to 84º. Quartzite and quartz schist exhibits distinctive joint and fracture system which runs parallel to one another while minor ones are oblique. The polymetamorphic terrain has older tectonic fabrics massively overprinted by younger ones. The gneiss units are porphyroblastic to granoblastic, xenoliths of varying sizes are embedded within the granite bodies indicating the magmatic liquid was forcefully injected into the country rock. The presence of parallel fractures in fine-grained granite indicate Ekiti area is a shear zone. The occurrence of dykes of heterogenous lithologies on single granite outcrop suggests pluton assemblage occur as discrete pulses during the intrusive phases. Contact relationship indicate age decreases from migmatite to granite-charnockite to microgranite while dykes are the youngest. Deformation, metamorphism, and intrusive phases are the dominant geodynamic features of Ekiti area while the regional and local changes in rocks resulted from environmental constraints of pressure, temperature, and fluid activity. The plutonic activities which accompanied orogenic events resulted in deformation which is genetically related to evolution and geodynamic setting of Ekiti area.

Keywords: Ekiti, field relationship, orogenic activities, polymetamorphic terrain, geodynamic setting.

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