U-Pb zircon geochronology of the Dete-Kamativi Inlier, NW Zimbabwe, with implications for the western margin of the Archaean Zimbabwe Craton

Abstract

We report new in-situ U-Pb zircon ages which were obtained from a variety of lithologies within the Dete-Kamativi Inlier of western Zimbabwe using both LA-ICP-MS and SIMS. These include igneous or metamorphic zircon grains from granitoids and granitic gneisses as well as detrital zircon grains from a number of paragneisses. The oldest ages are from two highly deformed migmatitic granitoid orthogneisses, which yielded Neoarchaean concordia ages of 2723 Ma and 2694 Ma, which are interpreted to be crystallisation ages. These are the first Archaean ages from the Dete-Kamativi Inlier, indicating that the Archaean Zimbabwe Craton extends much farther west than previously recognised. Our new maximum ages of deposition of 2.31, 2.0 and 2.07 Ga for the Malaputese, Inyantue and Tshontanda Formations, respectively, match closely with previously determined maximum ages of 2.29, 2.07 and 2.16 Ga for the Deweras, Lomagundi and Piriwiri Groups, thus supporting the lithostratigraphic correlation of the Dete-Kamativi Inlier with the Magondi Supergroup. Foliated and unfoliated K-feldspar megacrystic granites and granodiorites have yielded concordia ages ranging from 2.08 to 2.01 Ga. They contain abundant Archaean inherited zircon grains ranging in age from 3.34 to 2.66 Ga, implying the involvement of Archaean crust in their petrogenesis. These results suggest the formation of a calc-alkaline continental magmatic arc on the western edge of the Archaean Zimbabwe Craton, some 80 Ma prior to the onset of the Palaeoproterozoic Magondi Orogeny.