Abstract:
The volcanic rocks of the Rooiberg Group represent the uppermost unit in the Palaeoproterozoic Transvaal
Supergroup and form one of the largest provinces of silicic volcanic rocks in the world. Although stratigraphically
associated with the Transvaal basin-fill, the Rooiberg Group is petrogenetically linked with
the larger Bushveld magmatic event for which emplacement was preceded by the extrusion of the vast
Rooiberg lava flows in the northern part of the Kaapvaal Craton. Like many silicic-dominated Large
Igneous Provinces (LIPs), which are increasingly recognised in the rock record, the Rooiberg Group
volcanics are intracontinental, subaerial, and are dominated by voluminous lava flows. Originally, the
Rooiberg Group is inferred to have covered an area of more than 200,000 km2 of which, after erosion, an
area of 50,000–67,000 km2 remains. The lava flows form a stratigraphic succession up to 6 km thick, and
are divided into four formations in ascending order: Dullstroom, Damwal, Kwaggasnek and Schrikkloof.
Due to a scarcity of reliable geochronological data, the temporal span of the Rooiberg Group is poorly
understood. The Rooiberg Group consists of basaltic to rhyolitic lava erupted from fissural volcanism with
estimated eruption temperatures of the rhyolitic lavas exceeding 1000 ◦C. Minor explosive eruptions are
represented by pyroclastic rocks, and subordinate sedimentary interbeds originated from sandy fluvial
and lacustrine processes. The rocks are essentially undeformed and have not been buried so that their
original textures are well preserved. The Bushveld Complex and the associated Rooiberg Group lava flows
are proposed to have formed as a result of partial melting of subcontinental lithosphere and lower crust
by a mantle plume. This thorough review of the geochronology, physical volcanology, and geochemistry
of the Rooiberg Group enables construction of a geodynamic model.
