OLDEST U-PB CRYSTALLISATION AGE FOR THE WEST AFRICAN CRATON FROM THE OUDALAN-GOROUOL BELT OF BURKINA FASO

Abstract

U-Pb geochronological data from the northern and western extensions of the Oudalan-Gorouol volcano-sedimentary belt (OGB) on 3 samples of granodiorite gneiss (sample BF\_1144), migmatitic gneiss (sample BF\_1299), and granite clast from a metaconglomerate (sample BF_1147) gave the oldest U-Pb crystallisation ages for outcropping Palaeoproterozoic rocks yet identified in the West African Craton (WAC). The U-Pb concordant crystallisation ages of 2253 ± 9 Ma and 2253 ± 15 Ma for samples BF\_1144 and BF\_1299, respectively, likely represent the age of crystallisation of parent granodiorite gneiss and may constrain the age of a gneissic protolith on which the OGB basin was deposited, or an early group of granitoids that was emplaced in the hinterland during formation of the OGB basin. A concordant age of 2255 ± 26 Ma for sample BF_1147 is interpreted as the age of crystallisation of a granite pluton that was eroded from a site nearby before becoming part of the Dembam Member, and constrains the maximum age of the Birimian Supergroup in the OGB. The older Pb-Pb ages on zircons from the granodiorite gneiss, migmatitic gneiss and granite clast are in the range ~2.34 to ~2.27 Ga, and are interpreted as inherited from pre-existing zircon cores. They are similar to Pb-Pb ages reported as inherited zircon ages from the Dabakala tonalitic gneiss (in Cote d’Ivoire).