Transvaal Supergroup inliers: geology, tectonic development and relationship with the Bushveld complex, South Africa

Abstract

Several deformed Transvaal Supergroup inliers occur in the Bushveld complex. The most prominant are the Crocodile River dome and the Rooiberg fragment in the western Transvaal basin and the Dennilton-Marble Hall dome and Stavoren fragment in the eastern Transvaal basin. Several other smaller Transvaal Supergroup inliers are situated in the Bushveld complex to the east and west of the central inliers. The geology and tectonic relationship of these inliers with the Bushveld complex imposed important constraints on the tectonic evolution of the Transvaal basin and the subsequent distribution of the Bushveld complex. The central inliers are subdivided into two groups. The Crocodile River, Marble Hall and Dennilton domes consist of highly deformed, lower Transvaal strata that were subjected to low-grade metamorphism. The domes were formed by interference folding that was accentuated by the intrusion of the Bushveld complex. They acted as physical barriers to the emplacement of the mafic rocks of the Bushveld complex in the centre of the Transvaal basin. The Rooiberg and Stavoren fragments are synforms of upper Transvaal strata. The strara that comprise them are less deformed than those in the domes. These fragments were subjected to low-grade metamorphism because of the intrusion of Bushveld granite beneath them. They acted as roof pendants to the emplacement of the Bushveld complex. Other smaller Transvaal Supergroup inliers in the Transvaal basin are shown to be either attached or detached structures, depending on their tectonic setting and relation to the Bushveld complex.