Stratigraphy and petrology of the Archaean Nsuze Group,northern Natal and southeastern Transvaal,South Africa

The Nsuze Group is the lower, dominantly volcanic, division of the Pongola Supergroup that accumulated on a sialic basement between 3.1 and 2.9 Ga. The Nsuze Group is subdivided into a lower sedimentary unit (800 m thick), a middle volcanic unit (± 7500 m thick) and an upper volcaniclastic-sedimentary unit (5–600 m thick). The predominant sediments in the lower unit are immature, medium- to very coarse-grained quartz wackes with thin intercalated lenses of quartz and arkosic arenites, and minor conglomeratic wackes. These sediments were deposited in a distal braided stream environment.There followed a major period of volcanism during which lavas showing a continuous spectrum of compositions from basalt to rhyolite were extruded subaerially. Flows of both different and similar compositions are complexly interfingered on both regional and local scales. As volcanism waned, pyroclastic and sedimentary rocks became dominant in the upper unit. The Nsuze Group is gently dipping and is metamorphosed to low greenschist grade.The Nsuze Group is significant in that it provides evidence for the existence of high-standing continental sialic crust in the southeastern part of the Kaapvaal province at ca. 3.0 Ga. Volcanism and sedimentation in the Pongola Supergroup are more typical of Proterozoic basins than of Archaean environments, despite their age. Komatiitic and high-Mg basalts were, however, being extruded in Zimbabwe contemporaneously with the Nsuze lavas.