Zircon ~(207)Pb/~(206)Pb evaporation ages of Panafrican metasedimentary rocks in the Kombe-II area (Bafia Group, Cameroon): Constraints on protolith age and provenance

摘要

The Kombe-II area belongs to the southern part of the Cameroonian Panafrican belt. It is made up of different gneisses, amphibolites and quartzites of the Bafia Group. This volcano-sedimentary rock sequence became polyphasely deformed and metamorphosed during the Panafrican orogeny. It was thrust in SSW-ward direction, parallel to the L2 stretching lineation, over the Congo Craton. Zircon morphology and ~(207)Pb/~(206)Pb evaporation ages (2289-2351 Ma) show that the gneissic metasediments contain detritus of Paleoproterozoic plutonic rocks. In addition to existing data, our zircon ages and Nd model ages (generally in the range of 2.4-3.4 Ga) indicate that the sedimentary sequence derived from material which was added to the crust between the Archean and the Mes-oproterozoic era. A garnet-amphibole paragneiss, however, has a Nd model age of 1.5 Ga demonstrating the contribution of younger mafic material in the sediment source. Our results strengthen earlier suggestions that NE Brazil and Central Africa followed the same evolution during the Proterozoic.