The Okwa basement complex, western Botswana: U–Pb zircon geochronology and implications for Eburnean processes in southern Africa

Abstract

The Okwa Basement Complex crops out at the northwestern edge of the Kaapvaal craton within the Okwa Inlier, an isolated exposure of Precambrian basement in the Kalahari Desert. New U–Pb zircon dating was performed on all the major Palaeoproterozoic lithologies of the complex. Results are 2055.3 ± 1.3 Ma for augen gneiss, 2056.3 ± 1.3 Ma for foliated monzogranite and 2057 ± 2 Ma for microgranite. A meta-rhyolite gives an age of 2055 ± 4 Ma, based on one concordant zircon, and contains an inherited zircon with an age of 2101 ± 4 Ma. All precisely dated rocks are indistinguishable in age at 2056 ± 2 Ma. This age can be broadly correlated with Palaeoproterozoic geologic events in the Magondi belt at the northwest margin of the Zimbabwe craton and the Triangle Shear Zone in the Limpopo belt. However, the most precise correlation is with the Bushveld Complex, whose age is indistinguishable from that of the Okwa Basement Complex. This suggests a link between marginal and intra-cratonic Bushveld-age magmatism on the Kaapvaal craton.