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

Abstract

The Ghanzi-Makunda area exposes three main Proterozoic assemblages. The oldest 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 consists of metarhyolites and metabasalts with interbedded tuff and agglomerate. These metavolcanic rocks represent a bimodal suite of continental tholeiites and high K rhyolites linked to the evolution of the Mesoproterozoic Kibaran orogenic system. Siliciclastic and carbonate rock successions of the Neoproterozoic to early Palaeozoic Ghanzi-Chobe Belt unconformably overlie the Mesoproterozoic Kgwebe volcanic complex. The Ghanzi-Chobe Supergroup comprises 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 correlated to the Ghanzi Group. The deposition of the Ghanzi Group occured after 1020 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 paper, as well as lithological similarities, the Ghanzi Group is correlated with the Nosib Group of the Damara Belt, while the Okwa Group is correlated with the Nama Group in Namibia.