Petrogenesis, tectonic setting and geodynamic implications of Ouaden, Doumba Bello, and Ngoura granitic plutons (Eastern Cameroon): Constraints from elemental and Sr−Nd−Hf isotopic data and zircon U−Pb ages

Abstract

The Ouaden, Doumba Bello, and Ngoura granitic plutons, eastern Cameroon, comprise segments of the Central African Fold Belt (CAFB) situated along the northern edge of the Congo craton. A geochemical, isotopic and geochronological study was carried out on these three plutons to determine their petrogenesis and tectonic environment of formation. Granodiorites and granites (SiO2 of 65–73 wt%, Mg# of 14–46) of these plutons are potassic and weakly peraluminous with A/CNK ratios of 0.99–1.10. On primitive-mantle normalized trace element diagrams, all intrusives are depleted in Nb, Ta, and Ti. LA-ICP-MS zircon U − Pb dating indicate that the Ouaden, Doumba Bello and Ngoura granitic plutons were emplaced coevally at 640 ± 3 Ma, 641 ± 3 Ma, and 638 ± 4 Ma, respectively. The granodiorites and granites have variable 87Sr/86Sr(i) ratios of 0.71117–0.71831, relatively unradiogenic whole-rock εNd(t) values of −9.6 to −6.3, and zircon εHf(t) values ranging from −10.1 to −2.1; the occurrence of mafic microgranular enclaves suggests mixing with mantle-derived magmas, and such mixing possibly resulted in the scattering of zircon Hf data. Two-stage Nd-Hf model ages of 2115–1856 Ma and 2218–1708 Ma, and ΔFMQ of +5.3 − +2.1 indicate that the studied granitoids were derived from partial melting of Paleoproterozoic crust under variable oxidizing conditions. All granitoids yield inherited zircon ages (736–685 Ma), indicating contamination of Early Neoproterozoic crust during ascent. A combined examination of the geological record, bulk rock chemistry and isotope signatures suggests that the granodiorites and granites formed by mixing of mantle-and crust-derived melts during a late-subduction early-collision setting between the Metacraton and the Congo craton.