Zircon Geochemical Constraints on the Evolution of Pan-African Post-Collisional Granitoids in Katchuan and Boje, Southeastern Nigeria Basement Complex

Abstract

We present the first LA-ICP-MS trace element data for zircons from two Pan-African post-collisional granitoids of the southeastern Nigerian Basement Complex: the Katchuan granodiorite and the Boje biotite granite. Whole-rock geochemistry classifies both suites as peraluminous, calc-alkaline S-type granitoids derived from melting of continental or reworked arc crust. Zircons from Boje are enriched in ΣREE, Th, U, and Pb relative to Katchuan, reflecting crystallization from a more evolved melt. Both populations exhibit HREE enrichment with positive Ce and negative Eu anomalies, but many grains show atypically high LREE contents. Most zircons record Th/U ≥ 0.5, supporting an igneous origin. Discrimination plots (LaN–PrN, (Sm/La)N–La, Ce/Ce*–(Sm/La)N) indicate dominantly magmatic signatures for Katchuan zircons, whereas Boje zircons occupy fluid-influenced domains. Elevated Ca, correlating with P, suggests local interference from apatite inclusions. Ti-in-zircon thermometry yields mean crystallization temperatures of ~670 and ~750°C for Boje and Katchuan granites respectively, while zircon saturation temperatures exceed these by 100–140°C. Overall, zircon chemistry reveals magmatic growth with hydrothermal overprinting at Boje, processes that likely promoted rare-metal mobility (Be, Nb, Ta).