A review of the geochronological constraints on the evolution of the Kaapvaal Craton, South Africa

All the published U–Pb geochronological data from zircon, titanite, sphene and monazite, and Pb–Pb evaporation data applicable to the Palaeoarchaean-to-Neoarchaean geology of the Kaapvaal Craton are employed to reconstruct the history and crustal architecture of the ca. 3600–2500 Ma cratonic basement in South Africa. Only data interpreted as representative of the age of crystallisation, or the 207Pb/206Pb ages from zircon xenocrysts, have been considered in constructing graphs of cumulative probability versus age of rock formation. In this manner, it has been possible to identify the main magmatic events that have contributed to the assembly of the craton. For convenience of data handling, the Kaapvaal Craton has been subdivided into eastern, central, northern and western geographic domains. These domains are not intended as discrete geological terranes although each one has its own geological and chronological character, although consanguinity of events is also evident. The oldest rocks so far recognised are located in the Swaziland–Barberton areas where ages >3600 Ma have been recorded. The early stages of shield development are best exposed in the Barberton Mountain Land where it is now apparent that continent formation took place by magmatic accretion and tectonic amalgamation of small protocontinental blocks. At Barberton, several diachronous blocks, formed between 3600 and 3200 Ma, have been identified, each of which represents a cycle of arc-related magmatism and sedimentation. This phase of crustal development was followed by a period of Mesoarchaean cratonic magmatism, particularly prevalent between approximately 3100–3000 Ma, and marked by the development of a major, crescent-shaped, juvenile arc that was accreted onto the northern and western margins of the evolving Kaapvaal Shield. Cratonisation was accomplished by the emplacement of major granitoid batholiths, which thickened and stabilised the continental crust during the early stages of this cycle. Subsequent evolution of the craton, between 3000 and 2700 Ma, was associated with continent–arc collision, during which time the Witwatersrand Basin and its correlatives were deposited as foreland sequences, followed by episodic extension and rifting, when the Gaborone–Kanye and Ventersdorp sequences were developed.