The Paleoproterozoic Rooiberg Group, Kaapvaal Craton, South Africa: new insights into the formation of silicic large igneous provinces (SLIPs)

摘要: 3 2 With an estimated erupted volume of 300,000 km and areal extent of ca. 200,000 km (Fig. 1), the Paleoproterozoic (2.06 Ga) silicic volcanics of the Rooiberg Group (Kaapvaal Craton) in northern South Africa form one of the largest and oldest silicic large igneous provinces (SLIPs) known. These rocks can be sub-divided into four formations: the Dullstroom, Damwal, Kwaggasnek and Schrikkloof formations. Despite the uniqueness of these rocks and their scientific importance regarding the formation of SLIPs worldwide, the Rooiberg Group received little attention in the past. Therefore, a geochemical and petrological study was initiated to further investigate the petrogenesis of the Rooiberg Group, provide constraints on the magma-forming processes and to come up with an explanation for the wide extent of its rhyolitic lava flows.The Loskop Dam area, Mpumulanga Province, ca. 120 km east of Pretoria, and one of the type localities for the Rooiberg Group, was found suitable as a study area because of its good outcrop conditions and the fact that most of the formations can be found here (Fig. 2). For this study 44 volcanic samples were collected for chemical analysis, based on location and apparent freshness. Major element oxides were determined by XRF analyses at the University of Pretoria. Trace elements and REE were analyzed at the University of Cape Town.