Pan-African Granitoids Revisited: The Igarra Pluton as A Case Study for Crustal Recycling and Hybrid Magmatism in Orogenic Belts

Abstract

The Igarra granitic pluton forms part of the Pan-African granitoid suite of the Nigerian Basement Complex and records important aspects of late Neoproterozoic crustal evolution within the Dahomeyide Belt. Petrographic observations reveal hypidiomorphic granular textures and locally developed syn-tectonic microstructures, indicating emplacement contemporaneous with regional deformation. Major-element geochemistry shows calc-alkaline affinity and predominantly metaluminous compositions, consistent with granitoids emplaced in convergent orogenic settings. Trace-element and rare earth element (REE) geochemistry provide key constraints on magma source and evolution. Chondrite-normalized REE patterns are characterized by strong enrichment of light rare earth elements relative to heavy rare earth elements, together with weak to moderate negative Eu anomalies. Primitive-mantle–normalized trace-element patterns show enrichment in incompatible elements and relative depletion in high-field-strength elements such as Ta. These geochemical signatures closely resemble those of Pan-African granitoids from the Ilesha, Idanre, Kabba–Lokoja–Igarra, and Egbe–Isanlu schist belts. The combined petrographic and geochemical characteristics indicate that the Igarra granite was derived predominantly from partial melting of continental crust during crustal thickening associated with the Pan-African orogeny, with magma evolution controlled by fractional crystallization. Although limited interaction with more mafic magmas during emplacement cannot be ruled out, the available data do not support a dominant juvenile mantle contribution. The Igarra pluton therefore represents a typical syn- to late-collisional Pan-African granitoid that documents significant crustal reworking during the assembly of the Nigerian Basement Complex.