Proterozoic geology and regional correlation of the Ghanzi-Makunda area, western Botswana

The Ghanzi-Makunda area exposes three main Proterozoic assemblages. The old est rocks belong to the Palaeoproterozoic (Eburnian) Okwa Basement Complex, which consists of porphyritic rhyolitic felsite and granitoids emplaced at 2055 +/- 4 Ma. A volcanic sequence named the Kgwebe volcanic complex consi sts of metarhyolites and metabasalts with interbedded tuff and agglomerate. These metavolcanic rocks represent a bimodal suite of continental tholeiit es and high K rhyolites linked to the evolution of the Mesoproterozoic Kiba ran orogenic system. Siliciclastic and carbonate rock successions of the Ne oproterozoic to early Palaeozoic Ghanzi-Chobe Belt unconformably overlie th e Mesoproterozoic Kgwebe Volcanic complex. The Ghanzi-Chobe Supergroup comp rises the Ghanzi Group and the Okwa Group. In Namibia, felsic lavas with U- Pb zircon ages of ca 750 Ma occur at the top of lithological units correlat ed to the Ghanzi Group. The deposition of the Ghanzi Group occured after 10 20 Ma and before 750 Ma. in the Okwa Group, detrital zircons extracted from Neoproterozoic sedimentary rocks of the Takatswaane Formation yielded the following dates: 1887 +/- 14 Ma, 1246 +/- 4 Ma, 1054 +/- 5 Ma, 627 +/- 6 Ma and 579 +/- 12 Ma. The age of 579 +/- 12 Ma is considered to represent the maximum depositional age of the Okwa Group. Based on the data in this pape r, as well as lithological similarities, the Ghanzi Group is correlated wit h the Nosib Group of the Damara Belt, while the Okwa Group is correlated wi th the Nama Group in Namibia. (C) 2000 Elsevier Science Limited. All rights reserved.