Archean Foreland Basin tectonics in the Witwatersrand, South Africa

Abstract

The Witwatersrand Basin of South Africa is the best‐known of Archean sedimentary basins and contains some of the largest gold reserves in the world. Sediments in the basin include a lower flysch‐type sequence and an upper molassic facies, both of which contain abundant silicic volcanic detritus. The strata are thicker and more proximal on the northwestern side of the basin which is, at least locally, bound by thrust faults. These features indicate that the Witwatersrand strata may have been deposited in a foreland basin and a regional geologic synthesis suggests that this basin developed initially on the cratonward side of an Andean‐type arc. Remarkably similar Phanerozoic basins may be found in the southern Andes. We suggest that the continental collision between the Kaapvaal and Zimbabwe Cratons at about 2.7 Ga caused further subsidence and deposition in the Witwatersrand Basin. Regional uplift during this later phase of development placed the basin on the cratonward edge of a collision‐related plateau, now represented by the Limpopo Province. Similarities are seen between this phase of Witwatersrand Basin evolution and that of active basins north of the Tibetan Plateau (e.g., the Tarim and Tsaidam Basins). The geologic evidence does not appear so compatible with earlier suggestions that the Witwatersrand strata were deposited in a rift or half‐graben. Copyright 1986 by the American Geophysical Union.