Geophysical dataset integration of the vredefort dome, South Africa

D.R. Cowan; G.R.J. Cooper

doi:10.1071/ASEG2009ab095

ISSN: 2202-0586
E-ISSN:

oa Geophysical dataset integration of the vredefort dome, South Africa
Authors D.R. Cowan^a and G.R.J. Cooper^b
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^a Cowan Geodata ServicesSchool of Earth and Geographical Sciences at the University of Western Australia,, [email protected], ^b School of Geosciences, University of the Witwatersrand, , [email protected]
Publisher: Australian Society of Exploration Geophysicists
Source: ASEG Extended Abstracts, Volume 2009, Issue ASEG2009 - 20th Geophysical Conference, Dec 2009, p. 1 - 5
DOI: https://doi.org/10.1071/ASEG2009ab095
- Published online: 01 Dec 2009

Abstract

Introduction

The Vredefort Structure is a deeply eroded, complex impact structure, located near the centre of the Kaapvaal Craton with an age of 2.02 Ga. Estimates of the original diameter of the impact structure range from 250-380 km, making it the largest known terrestrial impact. The Vredefort Dome, the central uplift, has a diameter of approximately 80 km and consists of a core of uplifted Archaean migmatites and granulites of 3.1-3,2 Ga, with an 20 km wide outer collar zone of supracrustals of the Archaean to Palaeoproterozoic Witwatersrand, Ventersdorp and Transvaal Supergroups. In the northwest, there is good outcrop and the collar sequence can be seen to dip steeply towards the center of the dome or are overturned. To the south and east, overlying Karoo sediments obscure the geology. The morphology of the central uplift has been modified by post-impact deformation

The Archaean core consists of an outer annulus of heterogenous amphibolite facies migmatites of the Outer Granite Gneiss (OGG) around the central Inlandsee Leucogranofels (ILG) terrain of granulite facies metamorphic grade. Stepto (1990) recognizes a threefold concentric zoning, with the Steynkraal Formation between the OGG and ILG.

Previous work (Corner at al (1990), Muundjua et al, 2007, Stepto, 1990) have mainly analysed aeromagnetic and gravity data separately. Henkel and Reimold (1998) carried out profile modelling of magnetic and gravity data. Antoine et al (1990) imaged aeromagnetic and gravity data. We have investigated the remanent magnetization problem and used similarity images and cross grey level coocurrence matrix texture transforms to analyse and compare aeromagnetic, gravity and SRTM DEM data to provide a clearer picture of the Vredefort Dome.

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References

Antoine, T.A.G., Nicolaysen, L.O. & Niccol, S.L. 1990, Processed and enhanced gravity and magnetic images over the Vredefort structure and their interpretation: Tectonophysics, 171,63-74.
Bisschoff, A. A. 2000 The geology of the Vredefort Dome(Explanation of Geological Sheets 2627CA, CB, CC, CD, DA, DC, and 2727AA, AB, BA, 1:50000 scale). Council for Geoscience, Pretoria, 49pp. and map 1:50000 scale.
Cooper, G.R.J., and Cowan, D.R., 2003, Feature detection using sunshading: Extended abstracts, ASEG 16th Geophysical Conference and Exhibition, February 2003, Adelaide.
Corner, B. Durrheim, R.J. and Nicolaysen, L.O. 1990 Relationships between Vredefort structure and the Witwatersrand basin within tectonic framework of Kaapvaal craton as interpreted from regional gravity and aeromagnetic data. Tectonophysics, 171, 49-61.
Davis, J.C., 1973, Statistics and Data Analysis in geology: John Wiley & Sons, 550p.
ASEG 20tn Geophysical Conference and Exhibition, February 2009, Adelaide
Henkel, H. Reimold, W.U. 1998 Integrated geophysical modelling of a giant, complex impact structure: anatomy of the Vredefort Structure, South Africa. Tectonophysics, 287, 1-20.
Muundjua, M., Hart, R.J., Gilder, S.A., Carporzen, L and Galdeano, A., 2007, Magnetic imaging of the Vredefort impact crater, South Africa: Earth & Planetary Sci. Letters 261, 456- 468.
Roest, W.R. and Pilkington, M., 1993, Identifying remanent magnetization effects in magnetic data: Geophysics 58, 653-659.
Stepto, D. 1990 The geology and gravity field in the central core of the Vredefort structure. Tectonophysics, v. 171, pp. 75-103

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Article Type: Research Article

Keyword(s): Archaean core; collar sequence; GLCM; pole reduction; similarity; SRTM

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Abstract

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