LINK BETWEEN THE GRANITIC-ROCKS AND VOLCANIC-ROCKS OF THE BUSHVELD COMPLEX, SOUTH-AFRICA

Until recently, it was proposed that the Bushveld Complex, consisting of the extrusive Rooiberg Group and the intrusive Rashoop Granophyre, Rustenburg Layered and Lebowa Granite Suites, evolved over a long peri od of time, possibly exceeding 100 Ma. Most workers therefore consider ed that the various intrusive and extrusive episodes were unrelated. R ecent findings suggest that the intrusive, mafic Rustenburg Layered Su ite, siliceous Rashoop Granophyre Suite and the volcanic Rooiberg Grou p were synchronous, implying that the Bushveld igneous event was short -lived. Accepting the short-lived nature of the complex, the hypothesi s that the granites are genetically unrelated to the other events of t he Bushveld Complex can be reconsidered. Re-examination of the potenti al Rooiberg Group/Lebowa Granite Suite relationship suggests that the granites form part of the Bushveld event. Rhyolite lava, granite and g ranophyre melts originated from a source similar in composition to upp er crustal rocks. This source is interpreted to have been melted by a thermal input associated with a mantle plume. Granite intruded after e xtrusion of the last Rooiberg rhyolite, or possibly overlapped in time with the formation of the youngest volcanic flows. (C) 1997 Elsevier Science Limited.