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Volume 56 Supplement 2

Special Issue: Special section for IUGG workshop: Lithospheric Structure of a Supercontinent:Gondwana

Variations in the thickness of the crust of the Kaapvaal craton, and mantle structure below southern Africa

Earth, Planets and Space volume 56, pages 125–137 (2004)Cite this article

Abstract

Estimates of crustal thicknesses using Pn times and receiver functions agree well for the southern part of the Kaapvaal craton, but not for the northern region. The average crustal thicknesses determined from Pn times for the northern and southern regions of the craton were 50.52 ± 0.88 km and 38.07 ± 0.85 km respectively, with corresponding estimates from receiver functions of 43.58 ± 0.57 km and 37.58 ± 0.70 km. The lower values of crustal thicknesses for receiver functions in the north are attributed to variations in composition and metamorphic grade in an underplated, mafic lower crust, resulting in a crust-mantle boundary that yields weak P-to-SV conversions. P and S wavespeeds in the uppermost mantle of the central regions of the Kaapvaal craton are high and uniform with average values of 8.35 and 4.81 km/s respectively, indicating the presence of depleted magnesium-rich peridotite. The presence of a low wavespeed zone for S waves in the upper mantle between depths of 210 and about 345 km that is not observed for P waves was inferred outside the Kaapvaal craton. The 410 km discontinuity shows similar characteristics to that in other continental regions, but occurs slightly deeper at 420 km. There is no evidence for a discontinuity near 520 km depth. The 660 km discontinuity also appears to be slightly deeper than average (668 km), and is poorly defined for P waves, but clear for S waves.

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Author notes

  1. R. E. Simon

    Present address: Department of Physics, University of Botswana, Private Bag UB704, Gaborone, Botswana

  2. E. M. Kgaswane

    Present address: Council for Geoscience, Private Bag X112, Pretoria, 0001, South Africa

  3. T. K. Nguuri

    Present address: PREPCOM CTBTO, Vienna International Centre, P.O. Box 1250, A-1400, Vienna, Austria

Affiliations

  1. Bernard Price Institute of Geophysical Research, School of Geosciences, University of the Witwatersrand, Private Bag 3, Wits, 2050, South Africa

    C. Wright, M. T. O. Kwadiba, R. E. Simon, E. M. Kgaswane & T. K. Nguuri

  2. Department of Geological Survey, Private Bag 14, Lobatse, Botswana

    M. T. O. Kwadiba

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  1. C. Wright
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  4. E. M. Kgaswane
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Correspondence to C. Wright.

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Wright, C., Kwadiba, M.T.O., Simon, R.E. et al. Variations in the thickness of the crust of the Kaapvaal craton, and mantle structure below southern Africa. Earth Planet Sp 56, 125–137 (2004). https://doi.org/10.1186/BF03353397

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Key words

  • Gondwanaland
  • Kaapvaal craton
  • crust and mantle structure