Abstract

The Rustenburg Layered Suite of the Bushveld Complex has been considered to result from intrusion, either discordantly across the sedimentary layering of the Pretoria and Rooiberg Groups, or along a regional unconformity at the boundary between these two groups. The latter model is based on the observation that the thickness of sedimentary rocks of the Pretoria Group in the roof of this intrusive body is much less than that eliminated from the floor by the intrusion. This conclusion is only valid if the emplacement of the intrusive body was parallel to the layering of the sedimentary rocks. A geometrical analysis shows that if there is an angular discordance between the sedimentary rocks and the intrusive body, a considerable thickness of apparently missing strata is predicted without there having been any erosion. These strata are preserved, but are truncated beneath the intrusive body. It is calculated from the known dips and discordances between the sedimentary rocks and the intrusive body in the eastern and Potgietersrus limbs of the Bushveld Complex that 3.5 and 6.5 km, respectively, of strata will not be preserved at surface. These figures match the thicknesses of apparently eliminated strata in these two areas. It is therefore considered unnecessary to appeal to a major period of pre-Rooiberg Group erosion, as discordant emplacement of the mafic rocks of the Bushveld Complex into the Transvaal Supergroup and Rooiberg Group adequately explains the observed field relationships.

You do not currently have access to this article.