The Mushandike granite: further evidence for 3.4 Ga magmatism in the Zimbabwe craton

The conflict between independently published ages for the Mushandike Granit e, Zimbabwe (2.92 +/- 0.17 Ga and 3.35 +/- 0.13 Ga) has been resolved in fa vour of the older age by SHRIMP U-Pb analyses of zircon. Two samples yield indistinguishable estimates of 3374 +/- 7 and 3368 +/- 11 Ma for the crysta llization age of the magma. Together with published data from elsewhere in southern Zimbabwe, the results imply a widespread magmatic event at about 3 .35 Ga. A single zircon core giving 3.46 Ga, together with the granite's pr eviously measured Nd model age, suggests that the Mushandike ma,sma could h ave incorporated remobilized basement similar to the c. 3.5 Ga Tokwe gneiss es which crop out 30 km to the west. The published Rb-Sr and Pb-Pb datasets show evidence of late Archaean disturbance of Sr and Pb isotope systematic s. In the absence of exposed contacts between the Mushandike granite and th e neighbouring Mushandike stromatolitic limestone, the new U-Pb emplacement age suggests that the limestone is unconformable on the granite.