Extensive reworking of Archaean crust within the Birimian terrane in Ghana as revealed by combined zircon U-Pb and Lu-Hf isotopes

Located in the southeastern parts of the BaouléMossi domain of the West African Craton,the Birimian terrane in Ghana is known to consist of predominantly juvenile crust emplaced during the Eburnean orogeny.Here we present novel coupled zircon U-Pb and Lu-Hf isotope data from nine Birimian granitoids intruding different domains from northwestern,western and southeastern Ghana.Sub-chondriticε_(Hf)-values indicating reworking of Archaean crust are recorded in zircon from both northwestern and southeastern Ghana.As a conservative estimate 71%of all analysed zircon grains spanning in age from2220 Ma to 2130 Ma require contribution from a reworked Archaean source,contradicting the common belief that the Birimian terrane consist of predominantly juvenile crust.A minimumε_(Hf)-value of-10.5 at2139 Ma suggests a Palaeoarchaean to late Mseoarchaean component as the contributing ancient source.Combined with previously reported heavy zirconδ^(18)O signatures from Birimian river zircon in Ghana,our new data suggests reworking of Archaean aged sediments during subduction initiated crustal growth in the vicinity of one,or possibly in between two Archaean aged cratons.

Located in the southeastern parts of the Baoule Mossi domain of the West African Craton, the Birimian terrane in Ghana is known to consist of predominantly juvenile crust emplaced during the Eburnean orogeny. Here we present novel coupled zircon U-Pb and Lu-Hf isotope data from nine Birimian granitoids intruding different domains from northwestern, western and southeastern Ghana. Sub-chondriticε_(Hf)-values indicating reworking of Archaean crust are recorded in zircon from both northwestern and southeastern Ghana. As a conservative estimate 71% of all analysed zircon grains spanning in age from2220 Ma to 2130 Ma require contribution from a reworked Archaean source, contradicting the common belief that the Birimian terrane consist of predominantly juvenile crust. A minimum ε_(Hf)-value of-10.5 at2139 Ma suggests a Palaeoarchaean to late Mseoarchaean component as the contributing ancient source.Combined with previously reported heavy zircon δ^(18)O signatures from Birimian river zircon in Ghana,our new data suggests reworking of Archaean aged sediments during subduction initiated crustal growth in the vicinity of one, or possibly in between two Archaean aged cratons.