Zimbabwe Craton - Ca. 2.5 Ga Wedza and Chilimanzi Suites, South-eastern Zimbabwe Craton

Ca. 2.5 Ga Wedza and Chilimanzi Suites, South-eastern Zimbabwe Craton

The final stage of the cratonization process of the Zimbabwe craton is marked by emplacement of large volumes of monzogranitic and granodioritc material at 2.6-2.4 Ga. Monzogranitic and granodioritic granitoids and gneisses of the Wedza and Chilimanzi suites form large intrusive complexes in the south-eastern part of the Zimbabwe craton, between the Mutare-Odzi greenstone belt and the Northern Marginal Zone of the Limpopo Belt. The older units of the Wedza suite are of syn-kinematic origin, while the younger Chilimanzi suite was emplaced late- to post-kinematically. Internal differentiation of the major elements indicates similar paths of magmatic evolution for both suites. Comparison with the major element distribution of older granodioritic/tonalitic intrusives within the Mutare greenstone belt suggests an overall magmatic evolution from primitive, tonalitic towards monzogranitic compositions.

The model ages mark a discrete and well established Archean crust forming event in Africa. Small observed variations may indicate minor contribution of juvenile crust. U/Pb isotopic multigrain analyses of distinctly zoned zircons revealed highly discordant ages of 2.507-2.585 Ga for the Wedza and 2.402-2.448 Ga for the Chilimanzi suite. These ages confirm the intrusion age of about 2.6 Ga for the Wedza suite. However, the age of 2.4 Ga for the posttectonic Chilimanzi suite conflicts with the timing of the Great Dyke emplacement into an already consolidated crust. The geochemical and radiometric investigations suggest a dynamic crust forming process initialised at ca. 3.2-2.9 Ga with the formation of a crustal protolith. The final stage of this process is marked by emplacement of large volumes of monzogranitic/granodioritc material at 2.6 to 2.4 Ga.