U-Pb zircon age of the upper Palapye group (Botswana) and regional implications

The Palapye Group is exposed in central-eastern Botswana at the northern margin of the Kaapvaal Craton, north of the Zoetfontein/Palala Fault. The Lechana and Sunnyside faults bound it. The Palapye Group comprises five formations: Selika (oldest), Moeng, Tswapong, Lotsane and Shoshong (youngest) of red to lilac siliciclastic sedimentary rocks (conglomerates, sandstones, and shales) and minor volcanic tuffs and rhyolitic lavas. The Lotsane and Shoshong Formations are lateral correlatives and show a gradational lateral transition. The Palapye Group overlies nonconformably the Mahalapye Granite. The U-Pb zircon age of the Mahalapye Granite (2023 ± 7 Ma) is the maximum deposition age for the Palapye Group sedimentary rocks. New ion microprobe U-Pb dating of igneous zircons from a volcanic tuff located in the Lotsane Formation yielded the following weighted mean ²⁰⁷Pb/²⁰⁶Pb ages: 2594 ± 14, 2034 ± 8 and 1604 ± 33 Ma (this paper). The last date sets the age of extrusion of the tuff. A sandstone above the volcanic tuff bed yielded a major group of detrital zircons within the range 2.1-2.0 Ga (weighted mean age of 2049 ± 4 Ma) and two groups with old mixture modelling component ages of 2841 ± 14 Ma and 2688 ± 7 Ma. Zircons younger than ≈2 Ga include a main group with a mixture modelling component age of 1635 ± 14 Ma and minor groups at 1953 ± 26 Ma and 1858 ± 14 Ma. Detrital zircons with the youngest mean date of 1635 ± 14 Ma from the sandstone were sourced from the local volcanic tuff bed. The date of 1635 ± 14 Ma sets the age of deposition of the Lotsane Formation and at the same time sets the age of deposition of the uppermost part of the Palapye Group. The major group of detrital zircons from the sandstone at 2049 ± 4 Ma is, within analytical error, identical to the age of the Bushveld-age magmatism in South Africa and Botswana. The concordant inherited zircon of 2035 ± 8 Ma from the volcanic tuff is similar to the age of the Mahalapye Granite, which is inferred to be their source. The near-concordant detrital zircons of 2.84-2.69 Ga could have been sourced from the Archaean Limpopo Belt and/or the adjacent Kaapvaal Craton. The data in this paper are used to constrain the regional correlation of post-Bushveld Paleoproterozoic sedimentary basins (Palapye, Waterberg, Soutpansberg Groups and Olifantshoek Supergroup) in southern Africa. The lower Waterberg, Olifantshoek and Soutpansberg rocks were deposited during the same time frame and are >200 Ma older than the uppersedimentary units of the Palapye Group.