The layered sequence of the Potgietersrus Limb of the Bushveld Complex

Abstract

The Potgietersrus limb, occupying a buffalo-horn-shaped area of approximately 2,000 km 2 , constitutes one of the compartments of the Bushveld Complex in South Africa. The Layered Sequence occupies roughly the eastern half of the area and consists of the Basal, Critical, Main, and Upper zones. A platiniferous horizon forms the base of the Main Zone.Gravimetric and field observations suggest a north-striking trough-shaped body almost at longitude 29 degrees , with a feeder just west of Potgietersrus. The south part of the body is dike-like; the wider north part has the shape of a sheet. The body appears to be a separate compartment of the Bushveld Complex.According to detailed field work, the stratigraphy as well as the thickness of the sequence differs from that of the rest of the Bushveld Complex. The south part of the complex appears to have been emplaced concordantly on a floor of the Magaliesberg Stage. Northward and northwestward, the complex transgresses and fingers into the Transvaal Supergroup until the complex rests on a floor made up of the Archean Granite Complex. The so-called Basal Zone is developed as satellitic bodies and as an inclusion within the main body proper. Two major transgressions occur within the Layered Sequence. Differentiation indices suggest that the magma chamber had at least four major influxes of fresh, undifferentiated magma.