EPISODIC MAFIC MAGMATISM DURING THE MESOARCHEAN TO PALEOPROTEROZOIC ON THE KAAPVAAL CRATON: IMPLICATIONS FOR CRATONIC RECONSTRUCTIONS

Archean cratons host numerous swarms of mafic dykes and sills. These short-lived mantle-generated magmatic events are of great importance in the determination of spatial and temporal barcodes which are useful in paleotectonic reconstructions, as most are associated with crustal extension and breakup.

The Archean Kaapvaal Craton in South Africa is one of the oldest, best preserved cratons in the world. It is host to a complex array of mafic dyke swarms of varying ages. They can be found where granitoid-greenstone basement and Mesoarchean to Paleoproterozoic supracrustal successions are exposed. These dyke swarms record major episodic extensional events which can be associated with the breakup of supercratons during the past, as these same events can be shown to be duplicated on numerous fragments of cratonic crust around the world [Olsson et al., 2010]. This includes a 2.95 Ga dyke event associated with the volcanic rocks of the Pongola Supergroup, whose trend was also followed by the Usushwana Complex dykes and sills at 2.87 Ga. Another event of similar age is the Hlagothi Complex. The next event occurred at 2.65 Ga, associated with Ventersdorp Supergroup extension, and a 1.90 Ga post-Bushveld Complex dyke event associated with the Waterberg, Soutpansberg and Olifantshoek groups, formed during the final stabilisation of the Kaapvaal Craton. Other possible dyke events on the Kaapvaal Craton may be associated with the Ongeluk/Hekpoort and Rooiberg volcanic rocks of 2.22 Ga and 2.06 Ga respectively.

These recognized dyke swarms form three episodes of mafic magmatism at 2.90 Ga, 2.65 Ga and 1.90 Ga on the Kaapvaal Craton, and have been noted on other cratons. A exception is a 2.50 to 2.40 Ga event which can be found on numerous other cratons including the Zimbabwe, Kola-Karelia, Yilgarn and Superior which form part of the Superia supercraton [Bleeker and Ernst, 2006]. This would suggest that the Kaapvaal Craton was separate when the other cratons were connected during this time. The Kaapvaal Craton may however be linked to the Pilbara Craton as part of the larger craton Vaalbara, as both these cratons share a similar magmatic barcode. Also, the Kaapvaal Craton and Zimbabwe Craton have a similar barcode after the 1.90 Ga dyke event, prior to this, their barcodes are different, suggesting a link only at 1.90 Ga for the two cratons.