Crustal modelling from Pan-African granites of the Colomine Gold District, SE Cameroon: Insights from zircon U-Pb dating and Lu-Hf isotope systematics. (March 2022) - Ngatcha, Ralain Bryan
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 T DM c ages of 2.4–2.1 Ga overlap with those of the biotite granite (ϵHf(t) values of −29.4 to −19.6; T DM c 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. Highlights: U–Pb, Lu–Hf isotope data from Colomine zircons presented. Biotite granites and porphyritic K-feldspar granite were emplacement at ca. 727 ± 8 Ma and ca. 671 ± 6, respectively. Model Hf ages for the zircons grains ranges from 2.5 to 1.9 Ga. The granites were derived from crustal reworking of older Paleoproterozoic crust with mixing from a juvenile component. Accretion tectonics started around 750 Ma incorporating tectonic domains of the Central African Fold belt.