Nature of and controls on volcanism in the ca. 2.32-2.06Ga Pretoria Group, Transvaal Supergroup, Kaapvaal Craton, South Africa

摘要: Abstract The time of deposition the Pretoria Group between 2.32 and 2.06 Ga on South Africa's Kaapvaal Craton was characterized by first major increase in atmospheric oxygen. It accompanied extrusion significant thicknesses volcanic deposits, namely Bushy Bend lavas Timeball Hill Formation, Hekpoort Formation Machadodorp Volcanic Member Silverton marking three events within Transvaal Supergroup which are thought to be precursors succeeding Bushveld Complex magmatism. Lava is subaqueous basaltic–andesitic fissure eruptions with fumarolic activity probably minor subaerial explosive hinterland basin. volcanism appears have been dominated a preponderance lava flows locally important pyroclastic material. Intermittent hiatuses were marked local lacustrine shale deposition. Finally, can interpreted as deposits several seamounts aligned along fissure, an extensional environment. geodynamic control inferred for evolution basin encompasses two cycles prerift uplift, subsequent mechanical rifting long lived thermal subsidence. limited extent south depository attests likelihood that accompanying event short-lived. In contrast, second cycle postulated has strong association widespread large scale Hekpoort–Ongeluk flood basalts, may plume-related. its importance influencing upper part basin-fill underlined volcanism, related hot spot Ongeluk–Hekpoort plume waned.