Age relationships between greenstone belts and “granites” in the Rhodesian Archaean craton |
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| Authors: | CJ Hawkesworth S Moorbath RK O&#x;Nions JF Wilson |
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| Institution: | Department of Geology and Mineralogy, University of OxfordEngland;Department of Geology, University of Rhodesia, Salisbury Rhodesia |
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| Abstract: | Whole-rock Rb-Sr age measurements on rocks from the Rhodesian Archaean craton of Southern Africa demonstrate that (a) the Mashaba area gneisses, which are typical of the Rhodesian Basement Complex, are approximately 3600 m.y. old, (b) volcanic rocks from the main greenstone belts, assigned to the Bulawayan Group, were extruded approximately 2600–2700 m.y. ago, (c) a cross-cutting pluton, the Sesombi tonalite, was emplaced2690 ± 70 m.y. ago, (d) the Gwenoro Dam migmatites, which field evidence suggests could be older than the main greenstone belts, were emplaced2780 ± 30 m.y. ago.The initial87Sr/86Sr ratios of most of the rock units of groups b, c and d are in close agreement at about 0.701, suggesting that the later granitic (sensu lato) and andesitic rocks so far analysed were not produced by remelting of, or contamination with, ancient gneissic basement. |
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