Crustal modelling from Pan-African granites of the Colomine Gold District, SE Cameroon: Insights from zircon U-Pb dating and Lu-Hf isotope systematics

Abstract

The Neoproterozoic Pan-African Orogeny in the Adamawa-Yadé domain (AYD) of Cameroon is characterized by intense magmatism of metaluminous to weakly peraluminous I-type granites spatially associated with transcurrent shear zones. This domain provides a critical geological record that is important for unravelling the regional tectonic evolution and geodynamic setting. We present new zircon U-Pb ages and Lu-Hf isotope data from pre-collisional biotite granite and porphyritic K-feldspar granite of the gold-producing Colomine district. Zircon U-Pb ages of biotite granite samples suggest emplacement at 727 ± 8 Ma and at 671 ± 6 for the porphyritic K-feldspar granite. Metamorphic-hydrothermal events between 600 and 550 Ma resulted in Pb-loss of most dated zircons. Lu-Hf isotope data of zircon grains form the porphyritic K-feldspar granite with ϵHf(t) values of −28.7 to −22.6 and TDMc ages of 2.4–2.1 Ga overlap with those of the biotite granite (ϵHf(t) values of −29.4 to −19.6; TDMc ages of 2.5–1.9 Ga). Depleted mantle model ages and ϵHf(t) values suggest that the granites were derived from crustal reworking of older Archean to Paleoproterozoic crust with minor mixing from a juvenile component during the Pan-African. The formation of these pre-collisional granites is interpreted as related to accretion tectonics that started around 750 Ma and incorporating tectonic domains of the Central African Fold belt, namely, the NW Cameroon domain, Mayo-Kebbi domain and the Adamawa-Yade domain.