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⁴⁰Ar/³⁹Ar age constraints on low-grade metamorphism and cleavage development in the Transvaal Supergroup (central Kaapvaal craton, South Africa): implications for the tectonic setting of the Bushveld Igneous Complex

SUERC, Rankine Avenue, Technology Park, East Kilbride, G75 0QF, United Kingdom, e-mail: P.Alexandre{at}suerc.gla.ac.uk

Marco A.G. Andreoli

South African Nuclear Energy Corporation, P.O. Box 582, Pretoria 0001, South Africa, School of Geosciences, University of the Witwatersrand, P.O. WITS, Johannesburg 2050, South Africa, e-mail: marco{at}necsa.co.za

Antony Jamison and Roger L. Gibson

School of Geosciences, University of the Witwatersrand, P.O. WITS, Johannesburg 2050, South Africa e-mail: tjamison{at}hot.co.za; gibsonr{at}geosciences.wits.ac.za

Rocks of the Palaeoproterozoic Transvaal Supergroup, situated between the Bushveld Igneous Complex and the Vredefort Impact Structure in the central parts of the Kaapvaal craton (South Africa), experienced a regional low-grade metamorphism synchronous with brittle–ductile deformation that formed small- to medium-scale folds, cleavages, monoclines and thrusts in the dolomites, slates, and phyllites. Single-grain ⁴⁰Ar/³⁹Ar step-heating laser probe dating of synkinematic white mica from the phyllites indicates ages of ~2.15 Ga and 2042.1 ± 2.9 Ma (plateaus and pseudo-plateaus, as well as cumulative probability statistics). These ages are clearly distinct from the emplacement age of the Bushveld Igneous Complex (~2.06 Ga) and from the Vredefort impact event (~2.02 Ga), both of which have previously been suggested as possible causes of the deformation. The new data suggest that at ~2.04 Ga, the rocks of the Transvaal Supergroup in the central craton were part of a more extensive fold-and-thrust belt, named here the Transvaalide fold-and-thrust belt. While it is difficult to explain the significance of the ~2.15 Ga ages, the ~2.04 Ga event may be related to orogenic activity along the margins of the Kaapvaal craton at this time.

This article has been cited by other articles:

				B. Rasmussen, I. R. Fletcher, J. R. Muhling, A. G. Mueller, and G. C. Hall Bushveld-aged fluid flow, peak metamorphism, and gold mobilization in the Witwatersrand basin, South Africa: Constraints from in situ SHRIMP U-Pb dating of monazite and xenotime Geology, October 1, 2007; 35(10): 931 - 934. [Abstract] [Full Text] [PDF]

				W.U. Reimold, A. Wittek, and F. Jourdan Comment on 40Ar/39Ar age constraints on low-grade metamorphism and cleavage development in the Transvaal Supergroup (central Kaapvaal craton, South Africa): implications for the tectonic setting of the Bushveld Igneous Complex (South African Journal of Geology, 109, 393 410), by Alexandre et al. (2006) South African Journal of Geology, March 1, 2007; 110(1): 157 - 159. [Full Text] [PDF]

				P. Alexandre, M. A.G. Andreoli, A. Jamison, and R. L. Gibson Response to the Comment by Reimold et al. on 40Ar/39Ar age constraints on low-grade metamorphism and cleavage development in the Transvaal Supergroup (central Kaapvaal craton, South Africa): implications for the tectonic setting of the Bushveld Igneous Complex (South African Journal of Geology, 109, 393 410), by Alexandre et al. (2006) South African Journal of Geology, March 1, 2007; 110(1): 160 - 162. [Full Text] [PDF]