Zircon U–Pb geochronology and trace-element geochemistry of Paleoproterozoic K-rich Birimian granitoids of northern Ghana, WAC

Abstract

This paper presents the first zircon trace element geochemistry, combined with U-Pb geochronology data, of the Paleoproterozoic K-rich granitoids (KRGs) in the Bole-Nangodi greenstone belt of the West African Craton (WAC) in northern Ghana. The study aimed to constrain the timing of emplacement, magma source characteristics, and petrogenetic processes of the KRGs. The studied KRGs of the Bole-Nangodi Belt include hornblende granite and granodiorite. The zircons from the KRGs contain high abundances of Hf, ΣREE, Pb, Th, and U, indicating a high degree of magmatic evolution, with contemporaneous magmatism occurring between ca. 2120 and ca. 2092 Ma. Chondrite-normalised REE patterns of zircons from the KRGs of the Bole-Nangodi belt show mainly positive Ce anomalies and slightly positive to weakly negative Eu anomalies, suggesting crystallisation under high oxygen fugacity conditions. The studied zircon were derived from magmas of continental crust origin and were subsequently affected by hydrothermal alteration, indicated by their Th/U, (Sm/La)N, Ce/Ce*, Nb/Ta and Hf/Y ratios, weak oscillatory zoning and somewhat metamict patterns, and relative enrichment of light rare earth elements. The evaluation of U-Pb age data suggests that the emplacement of the KRGs was non-systematic. Consequently, there is no distinct age difference or well-defined sequence of emplacement among the granodiorite and granite in the Bole-Nangodi belt. Therefore, the region is characterised as an undifferentiated terrane that underwent contemporaneous pulses of magmatism during the 2.3–2.1 Ga Eburnean events.