The Geometry and Emplacement Mechanics of a Bushveld Complex Peridotite Body, South Africa

Abstract

The Apiesdooringdraai peridotite is a syn-Bushveld Complex, dominantly harzburgitic intrusion of Lower Zone parentage. Detailed mapping and three-dimensional modeling shows the intrusion to comprise several discordant segments linked by concordant, silllike segments. Deformation in the contact aureole is strongly partitioned adjacent to the discordant segments of the intrusion and is detectable at distances from the contact on the order of the intrusion width. In contrast, areas above and below the intrusion, and at greater distances from the discordant intrusive segments, are effectively undeformed. The geometry of structural features suggests that the peridotite is a variably structurally-evolved stepped-sill system that was emplaced as kilometre-scale magma fingers from the northwest to the southeast, a trend heavily utilised by the mafic-ultramafic magmas of the Bushveld Complex. Deformation in the country rock was affected by the lateral expansion of the magma fingers at high postulated strain rates, and linkage of offset fingers formed prominent steps in the intrusion. Emplacement-related country rock deformation is postdated by a shallow dipping foliation that records compaction and crustal loading during contact metamorphism. Figure 5. Simplified geological map of the Burgersfort-Steelpoort area, showing the transgressive nature of the ADP with respect to its country-rock stratigraphy.

A preliminary survey of the diversity of soil algae and cyanoprokaryotes on mafic and ultramafic substrates in South Africa

“…Ohrigstad sites (Sites 1 and 2, which were siliciclastic rocks and Silverton Formation) were situated on the metasediments of the Paleoproterozoic Transvaal Supergroup that forms the floor to the mafic-ultramafic Rustenburg Layered Suite of the Bushveld Igneous Complex (Clarke et al 2009). The Bushveld Complex was formed 2000 million years ago when enormous volumes of magma intruded the upper levels of the earth crust (Clarke et al 2009). Steelpoort sites (Sites 3 and 4) were situated on the ultramafic pyroxenite hills of the Vlakfontein Subsuite of the Rustenburg Layered Suite and the Burgersfort sites (Sites 5 and 6) on mafic hills of Kolobeng norite.…”