Petrogenesis of migmatites from Liman Katagum area (Bauchi) North-East Nigeria: Constraints from U-Pb and Lu-Hf isotopic data

Abstract

This study investigates the petrogenesis and tectonic evolution of migmatites from the Liman Katagum area in northeast Nigeria. In-situ Lu-Hf isotopic analyses of zircon reveal a complex source history, with εHf(t) values ranging from −13.43 to +8.95 at different ages (482 ± 120 Ma, 582.2 ± 9.0 Ma, and 498 ± 43 Ma). These values suggest contributions from both ancient reworked and juvenile crustal materials, spanning the Chondrite Uniform Reservoir (CHUR) and various crustal domains, indicating significant crustal recycling and juvenile additions. High zircon U/Yb ratios, along with elevated Y and Hf, reflect a strong continental arc affinity, supporting a crustal origin for the migmatites. Geochemical and morphological evidence, including enriched heavy rare earth elements (HREEs) and variable Th/U ratios, indicate both magmatic and metamorphic origins for the zircons, consistent with early Silurian arc magmatism. U-Pb zircon ages of 582.2 ± 9.0 Ma, 498 ± 43 Ma, and 482 ± 120 Ma correspond to distinct tectonic events, including the Pan-African orogeny. The earliest stage, at 582.2 Ma, shows significant juvenile crustal input during continental arc magmatism in the Neoproterozoic. By 498 Ma, tectonic reactivation led to partial melting and zircon crystallization, while the final stage at 482 Ma is linked to high-pressure metamorphism and crustal thickening during the collision of the West African Craton and the Tuareg Shield. Two distinct zircon age groups (582.2 ± 9.0 Ma and 498 ± 43 Ma) reflect the reworking of the Paleoproterozoic and Mesoproterozoic crust, with substantial juvenile input. This tectonic evolution, initiated around 482 Ma, involved crustal thickening, metamorphism, and partial melting, forming migmatites. Continued tectonic activity around 582 Ma caused shear zone development and crustal reworking, while reactivation at 498 Ma led to the crystallization of new zircons and the formation of migmatites. This study, similar to migmatite studies across Africa, elucidates the dual-source history of the Liman Katagum migmatites, with contributions from both reworked and juvenile crustal materials during the late Neoproterozoic and Early Paleozoic, highlighting episodes of partial melting and magma intrusion associated with the breakup of Rodinia and the assembly of Gondwana.