The crustal architecture of the Kaapvaal crustal block South Africa, between 3.5 and 2.0 Ga

Abstract

Following terrane amalgamation of early oceanic lithosphere, the southern and central parts of the Kaapvaal Craton were a coherent unit by 3.1 Ga. Juxta-position of the northern and western granitoid-greenstone terranes including the Murchison Island Arc was the result of terrane accretion that started at 3.1 Ga. The culmination of these events was the collision of the Kaapvaal Craton, the pre-cratonic Zimbabwe block and the Central Zone to generate the Limpopo granulite gneiss terrane. Coeval with these orogenic events the central Kaapvaal Craton underwent extension to accommodate the development of the Dominion, Witwatersrand/Pongola and Ventersdorp basins. The craton scale Thabazimbi-Murchison Lineament development during the 3.1 Ga accretion event and continued to influence the tectonic evolution of the Kaapvaal block throughout the period under review as indicated by the syn-sedimentary tectonics of the > 2.64 Ga Wolkberg Group, overlying Black Reef Formation and the Transvaal Sequence. The Transvaal and Griqualand West basins developed in the Late Archaean (> 2.55 Ga) with basin dynamics influenced by far field stresses related to the Limpopo Orogeny. During this period the Thabazimbi-Murchison Lineament lay close to the northern margin of the depository. Reactivation of the Lineament between 2.4 and 2.2 Ga resulted in inversion of the Transvaal Basin and formation of the northward verging Mhlapitsi fold and thrust belt. The half-graben setting envisaged for the deposition of the Pretoria Group was influenced by the Thabazimbi-Murchison Lineament as was the emplacement and subsequent deformation of the Bushveld Complex.