Petrological Features and Geochemical Characterization of Igneous Rocks in Ado-Ekiti, Southwestern Nigeria

Abstract

This research investigates and report petrological features and geochemical characteristics of igneous rocks in Ado-Ekiti, Southwestern Nigeria. Exhaustive geological fieldwork reveals Ado-Ekiti is underlain by migmatite-gneiss, quartzite, granite (porphyritic and fine-grained) and charnockite. Petrographic investigation revealed overwhelming presence of quartz, biotite and plagioclase in all the rocks while microcline and opaque minerals occur in subordinate amounts. Average SiO2 content in porphyritic granite (74.56 %) is marginally higher than charnockite (73.51%) and fine-grained granite (70.41%). These values correlate well with previous works in the study area and agrees with similar rocks in other parts of the country. Analytical results using Phillips Panalytical PW1480 X-ray Fluorescence Spectrometer with Rhodium Tube as the X-ray source revealed the siliceous nature of the rocks. The binary plot (Na2O+K2O) vs SiO2 established the rocks are granitic with all the samples plotting within granite field. AFM ternary diagram shows the rock have calc-alkaline affinity. Geochemical classification by (Na2O + K2O-CaO) vs SiO2 diagram reveals the rocks are “Calc-alkalic and calcic”. The elevated K2O (average of 4.41%) in the data signaled High-K calc-alkaline type on K2O vs SiO2 binary diagram. Alumina Saturation Index (ASI) showed the rocks are metaluminous while Al2O3 / (Na2O + K2O) vs Al2O3/ (Na2O +K2O +CaO) plot suggest the rocks have mantle origin