Daniel I. Omoruyi

This project presents a detailed petrographic and geochemical study of granitic rocks in the IgarraUgbogbo area of Edo State Nigeria, within the Nigerian Basement Complex. In order to characterize the mineralogical composition, and interpret their petrogenesis and tectonic setting. To address the significant knowledge gaps in the understanding of this segment of the Pan-African orogenic belt using integrated field mapping with laboratory analysis, Five representative fresh samples (SJ01–SJ05) were collected and subjected to polarizing microscopy for petrographic study and X-ray fluorescence (XRF) spectrometry for whole rock major and trace element geochemistry. Petrographic analysis reveals that the granites are medium to coarse grained with a hypidiomorphic granular texture, indicating slow plutonic cooling. Modal composition is dominated by quartz (21- 31%), plagioclase (31-35%), and microcline (20-26%), with biotite (7-10%) as the main mafic mineral. Minor hornblende, muscovite, and accessory zircon and opaque minerals are present. Textural features such as undulose extinction in quartz and sericitization of feldspars indicate post crystallization deformation and hydrothermal activity. Geochemical data classify the rocks as metaluminous to weakly peraluminous (ASI = 0.98-1.05), high-silica (69.23-71.44 wt. % SiO₂) granites with calc-alkaline affinity. They are enriched in Large Ion Lithophile Elements (LILE: e.g., Rb, Ba) and depleted in High-Field-Strength Elements (HFSE: e.g., Nb, Ta, Y), a signature characteristic of crustal-derived magmas. Trace element discrimination diagrams consistently plot the samples in the syn collision to post-collision granite fields. The integrated results lead to the conclusion that the Igarra granites are I-type granitoids formed primarily by partial melting of pre-existing crustal igneous rocks during the Pan-African Orogeny and their emplacement occurred in a post-collisional tectonic environment, accompanied by minor deformation and hydrothermal alteration. This study provides a crucial petrogenetic framework for the Igarra basement and contributes valuable data for understanding crustal evolution and mineral exploration potential in southwestern Nigeria.