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Geological Society, London, Special Publications; 1998; v. 138; p. 121-135;
DOI: 10.1144/GSL.SP.1996.138.01.08
© 1998 Geological Society of London

Regional metamorphism due to anorogenic intracratonic magmatism

Roger L. Gibson1 & Gary Stevens2

1 Department of Geology, University of the Witwatersrand, Private Bag 3, PO WITS, Johannesburg 2050, South Africa
2 Economic Geology Research Unit, University of the Witwatersrand, Private Bag 3, PO WITS, Johannesburg 2050, South Africa

The Vredefort Dome, the central uplifted portion of the c. 300 km diameter, 2.02 Ga Vredefort Impact Structure, exposes a c. 20 km deep profile through the crust of the Kaapvaal Craton of southern Africa which displays evidence of greenschist- to granulite-facies low-pressure metamorphism. Reaction textures in the medium- to high-grade metamorphic rocks indicate an anticlockwise isobaric cooling P-T evolution, and peak metamorphic temperatures consistent with a mid- to upper-crustal geotherm of 40–50°C km–1. The metamorphism is attributed to craton-wide intraplating of mantle-derived magmas into the deep crust during the 2.05–2.06 Ga Bushveld Event. Felsic volcanic rocks and high-level intrusions in the Bushveld Complex represent anatectic derivatives from the deeper, high-grade parts of the metamorphic terrane. The intracratonic setting, the absence of evidence of concomitant orogenic deformation, and the preservation of the pre-existing diamondiferous lithospheric root beneath the craton, suggest that the thermal event was triggered by the transient positioning of the Kaapvaal Craton over a mantle plume.





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C. L. Hayward, W. U. Reimold, R. L. Gibson, and L. J. Robb
Gold mineralization within the Witwatersrand Basin, South Africa: evidence for a modified placer origin, and the role of the Vredefort impact event
Geological Society, London, Special Publications, 2005; 248: 31 - 58.
[Abstract] [PDF]