Abstract

Mantle plumes that precede continental break-up have been postulated to exert a major influence on continental drainage patterns. In this model, a radial drainage develops away from the centre of the plumes, while failed arms of the associated rift system provide conduits for rivers from the continental interior towards the newly formed ocean. This paper summarises drainage evolution in southern Africa from the Permo-Carboniferous to the lower Cretaceous in order to test this model. A major reorganisation of the river system occurred at the time of eruption of the Karoo volcanics, or during subsequent fragmentation of Gondwana. The Karoo and Paraná Plumes imposed a first-order imprint on the drainage pattern. The superimposition of the Paraná plume pattern on the earlier Karoo plume drainage is responsible for the dominant eastward drainage system from the Early Cretaceous to the present-day. The post-Gondwana river network has been modified by at least three other major factors: structural controls, exhumed ancient land surfaces, and post-Gondwana epeirogenic flexing of the sub-continent and resulting river capture. Understanding the factors responsible for initiation and evolution of continental–scale drainage patterns has important economic implications - for example, the identification of primary sources of diamond placers.

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