Geochronology of Gaborone Granite Complex extensions in the area north of Mafikeng, South Africa — Reply

Abstract PbPb age determinations of zircons, using the evaporation technique, have been undertaken on three phases of the Kgale Granite (granite, granophyric granite and spherulitic microgranophyre) and on rhyolite of the Kanye Volcanic Formation in the area north of Mafikeng, western Transvaal, South Africa. The lithologies analysed are considered to be eastern extensions of the Gaborone Granite Complex, the bulk of which is located farther west, in Botswana. The zircon data indicate indistinguishable crystallisation ages close to the weighted mean date of 2780.6 ± 1.8 Ma for each of the units analysed, although metamict zircon populations in the granite phase of the Kgale Granite provide younger dates, suggesting Pb loss in its early geological history. The 2.78-Ga age is slightly lower than an previously published UPb zircon age of 2.83 Ga for the Gaborone Granite Complex in the Kubung area, Botswana. The zircon PbPb data emphasise the coeval nature of the various phases of the Kgale Granite and the Kanye Volcanic Formation and support cogenetic models for the origin of these rocks.