Abstract

Conglomerates and associated finer-grained sedimentary rocks, from Neoproterozoic to Lower Paleozoic successions in southern Africa (Kaigas and Numees Formations of the Gariep Belt; Nooitgedagt Member and Vaartwell Formation from the Kango Inlier in the Saldania Belt), were selected for provenance determination. The studied supracrustal rocks are dominated by material derived from the upper continental crust, and display a moderate weathering trend, as derived from the chemical index of alteration, and upper crustal Th/U ratios. Samples characterized by an influence of less fractionated material may be derived from a volcanic arc or from an alkaline source. A volcanic arc component that has been identified in the Kaigas Formation (~770 Ma) detritus is interpreted as eroded from the underlying Meso- to Palaeoproterozoic Orange River Group and/or Vioolsdrift Suite. Alternatively it may represent an undiscovered, unknown arc terrane. Stronger fractionated material identified within samples is reworked and are thought to have formed in a passive margin setting. Detrital material, from a source with a continental arc signature, was observed in both the Nooitgedagt Member and the Vaartwell Formation of the Kango Inlier, but is difficult to substantiate. It has been shown that various local source areas supplied the detrital material to the studied successions. The heterogeneity and the lack of age constraints from the different sources inhibit the modelling of palaeogeographic settings until the entire basin evolution is understood. Correlation of sedimentary successions between isolated outcrops should thus be avoided or treated with greatest caution.

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