Petrography and geochemistry of migmatite-gneisses from Nassarawan Eggon and environs, north-central Nigeria

Nassarawan Eggon and its environs in north-central Nigeria are predominantly underlain by rocks of the Migmatite-Gneiss Complex, Jurrasic Younger Granite (JYG) and  minor occurrences of pegmatite veins and dolerite dykes. To understand the petrological and geochemical significance of these rock units, detailed geological mapping and geochemical investigations were carried out. The study aimed to characterize the migmatite-gneiss to establish its relationship with the regional geology of Nigeria, and evaluate its implications for the Pan-African Orogenic event. The migmatite-gneiss compsied of metatexite and diatexite. Geochemical results indicate both metatexite and diatexite display similar affinities, characterized by high-K calc-alkaline compositions and weakly magnesian to ferroan signatures. The metatexite and diatexite are interpreted as orthogneisses of igneous origin, derived through partial melting of metatonalite and metagraywacke protoliths. Geochemical discrimination further suggests that they exhibit affinities with syn-collisional granitoids, indicating that their emplacement was likely associated with the main deformational phase (D2) during the climax of Pan-African magmatism. The basement rocks may have subsequently undergone metamorphism that transformed the original quartzo-feldspathic (granitic) protolith into gneissic rocks during the late- to post-collisional deformation phase (D3). These findings provide valuable insights into the evolution of the Nigerian Basement Complex and its relationship to the Pan-African tectonothermal event.