Mineralogical and Geochemical Characterization of Migmatites in Wonu-Apomu, Southwestern Nigeria

Abstract

The outcrops of migmatites occur in the western part of Wonu-Apomu area, which were studied to unravel the petrogenetic affinity of the migmatite and determine its petrotectonic setting using its petrography, geochemical data. Samples of the migmatites were collected and prepared into thin sections for petrographic analysis and also pulverized for geochemical analyses. Major and trace element was carried out, using X-ray Fluorescence Spectrometry. The petrographic analysis revealed the presence of microcline, plagioclase feldspar, quartz, biotite, and hornblende as the main minerals and muscovite (?5 %) occurs in minor amount, while zircon, rutile, titanite, ilmenite and magnetite are accessory phases. The geochemical data revealed high concentrations of SiO₂ (67.48 - 70.29 wt.%), Al₂O₃  (14.15 - 16.95 wt.%), Fe₂O₃ (2.72 – 4.03% wt.%), CaO  (2.02 – 3.01 wt.%), K₂O  (2.40 - 3.96 wt.%) and Na₂O  and (3.77 – 5.54 wt.%) while MgO  (0.73% wt.%), MnO (0.06 wt.%), TiO₂  (0.56 wt.%) are generally low,  The plot of  Na₂O/Al₂O₃ vs. K₂O/Al₂O₃ revealed the protoliths of the migmatite are both sedimentary and igneous. The chemical classification of the protolith using the sum alkalinity plot (Na₂O+K₂O) vs. SiO₂ diagram indicated that the migmatite has subalkaline granite affinity. The K₂O vs. SiO₂ diagram evidently showed the influence of oceanic crustal material in the generation of the migmatite protolith. The geochemical results revealed the ancestry of the migmatites in Wonu-Apomu  to be of calc-alkaline magmatic suite in contact with oceanic crustal material in a syn-collisional tectonic setting.