Geophysical dataset integration of the vredefort dome, South Africa

Abstract

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.