- © 2003 Geological Society of South Africa
Geochronological comparisons of large datasets are facilitated by the use of structured databases. Data for the Precambrian of South Africa, Swaziland, Lesotho and Botswana have been compiled in a DateView database and linked to chronostratigraphy and GIS databases to produce a series of ‘time-slice’ maps illustrating the development of the Kaapvaal Craton. Linking geochronological data to GIS coverages provides a valuable visual perspective on the development of the southern African lithosphere.
The oldest preserved rock formation dates occur south of the Barberton Greenstone Belt in South Africa and Swaziland. Subsequent scattered development of new crust occurred in the south eastern, eastern and northern Kaapvaal Craton before being ‘stitched’ together by extensive granitoid intrusions at ~3.25 Ga and ~3.1 Ga. Coeval development of new crust occurred in what would later become the central zone of the Limpopo Belt. The patterns of igneous activity from ~3.1 Ga to ~2.8 Ga, outboard of major cratonic lineaments (Colesberg lineament in the west and Thabazimbi-Murchison lineament in the north) may indicate that these lineaments represent suture zones along which the younger domains were accreted during formation of the Kaapvaal Craton.
By ~3 Ga the lithosphere was sufficiently rigid to support development of the Dominion, Witwatersrand and Pongola sedimentary basins, followed by extensive volcanism during the Ventersdorp and concomitant granitoid activity throughout the Craton. Subsequent geological activity, not necessarily evident in the available geochronological record, was concentrated on craton with the development of the widespread Transvaal Supergroup followed by essentially coeval extrusion of the Rooiberg felsites and intrusion of the Bushveld Complex at ~2.06 Ga. Deposition of sediments comprising the Waterberg and Soutpansberg Groups followed.
Igneous activity along the south-western edge of the Kaapvaal Craton terminated at ~1.93 Ga with formation of the Hartley basalts, Olifantshoek Supergroup. Post-Olifantshoek Supergroup and pre-Volop Group tectonism has been reported from the western margin of the Kaapvaal Craton. There is currently no geochronological evidence for major igneous or metamorphic activity post-dating formation of the Olifantshoek Supergroup until the early stages of the Namaqua-Natal Belt subsequent to ~1.4 Ga i.e. there is no geochronological evidence for a major late-Palaeoproterozoic ‘Kheisian orogeny’. Off-craton, new crust formed in the Richtersveld Sub-province at ~1.8 Ga but was presumably only accreted to the Kaapvaal Craton some 700 million years later during the Namaqua-Natal orogenesis.