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Three major east-trending structures in Southern Africa are described. They are referred to as the 16°, 23°, and 29° S. lat belts, and they correspond in part to what are commonly referred to in Southern African literature as the Zambesi, Limpopo, and Orange River belts. It is shown that the crustal blocks defined by these belts have displayed a more or less independent mobility at intervals through much of geologic time, and that the belts themselves have acted as loci for periodic volcanism. It is proposed that the belts are analogous to present-day oceanic fracture zones and played a part in the fragmentation of Gondwanaland.

An extension of the African Rift System through South West Africa is postulated on the basis of some modern seismic activity and a line of Cretaceous alkaline volcanic centers. Opening of this rift in late Precambrian time provided a site for the accumulation of the Swakop Facies of the Damara System, and the extreme folding and thrusting of these rocks is related to closing in the Paleozoic. Rifting along the present west coast probably occurred simultaneously, leading to the formation of a proto-Atlantic Ocean. Subsequent closure of this proto-ocean is registered by intensely deformed and metamorphosed marginal facies of platform sediments underlying the Damara System.

Further, it is suggested that the hydrothermal activity responsible for ore mineralization at Tsumeb is related to these events.

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