Towards a complete magmatic barcode for the Zimbabwe craton: Baddeleyite U–Pb dating of regional dolerite dyke swarms and sill complexes |
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| Authors: | Ulf Söderlund Axel Hofmann Martin B Klausen Johan R Olsson Richard E Ernst Per-Olof Persson |
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| Institution: | 1. Department of Geology, GeoBiosphere Science Centre, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden;2. School of Geological Sciences, University of KwaZulu-Natal, Private Bag X 54001, Durban, South Africa;3. Ernst Geosciences, 43 Margrave Ave., Ottawa, Canada K1T 3Y2;4. Carleton University, Ottawa, Canada K1S 5B6;5. Laboratory of Isotope Geology, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden |
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| Abstract: | We present baddeleyite U–Pb ages of Neoarchaean to Palaeoproterozoic dyke swarms and the Mashonaland sill province in Zimbabwe. The 2575.0 ± 1.5 Ma age of the Umvimeela dyke is indistinguishable from the 2575.4 ± 0.7 Ma result (Oberthür et al., 2002) for a pyroxenite layer of the Great Dyke and testifies to synchronous emplacement of the Great Dyke and its satellites. Three samples of WNW- to NNW-trending dykes of the Sebanga swarm yielded ages of 2512.3 ± 1.8 Ma, 2470.0 ± 1.2 Ma and 2408.3 ± 2.0 Ma, the latter of which dates the Sebanga Poort Dyke of this swarm. These results suggest that emplacement took place over a protracted period which involved at least three generations of dykes within the swarm and, more importantly, invalidate previous inferences of a genetic link between the Sebanga swarm and the Mashonaland sills. Crystallisation ages of 1877 ± 2.2 Ma, 1885.9 ± 2.4 Ma and 1875.6 ± 1.6 Ma for three dolerite samples of the extensive Mashonaland sills from different parts of the Zimbabwe craton were also obtained. This is the oldest common igneous event that is recorded in the Zimbabwe and Kaapvaal cratons. Collectively with previous published geochronological and petrological evidence in favour of a major 2.0 Ga event within the Limpopo Belt, these results suggest that the Zimbabwe and Kaapvaal cratons did not form a coherent unit (Kalahari) until ca. 2.0 Ga. |
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| Keywords: | Mafic intrusion Kalahari Palaeoreconstruction Superia U&ndash Pb baddeleyite Zimbabwe |
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