INTEGRATED GEOPHYSICAL MODELING OF A GIANT, COMPLEX IMPACT STRUCTURE - ANATOMY OF THE VREDEFORT STRUCTURE, SOUTH-AFRICA

Only three very large, confirmed impact structures are known on Earth: the Chicxulub Crater (Mexico), 65 Ma, ca. 180 lan wide; the Sudbury S tructure (Canada), 1.85 Ga, 200 lan in diameter; and the Vredefort Str ucture in South Africa, 2.02 Ga. While extensive data on large impact structures have been obtained by remote sensing studies of such featur es on other planetary bodies, only this small number of large terrestr ial impact structures can provide data crucial to understanding these catastrophic impact processes on Earth. Integrated modelling of gravit y and magnetic data, constrained by geological as well as refraction a nd reflection seismic data, accomplished the reconstruction of the Vre defort impact structure in South Africa, approximately 250 km wide. Th e original Vredefort impact structure covered the whole extent of the Archaean Witwatersrand Basin, distinguished by enormous gold resources , as it is structurally preserved today. In fact, it is clear that the preservation of vast volumes of economically important Witwatersrand strata is the direct result of the formation of the ring basin around the central uplift (the Vredefort Dome) of the impact structure. This study is the first attempt to create an integrated and geophysically w ell-constrained model of this very large, complex impact structure. (C ) 1998 Elsevier Science B.V. All rights reserved.