Abstract
Vocanic rocks of Karoo age which today cover more than 140,000 km2 of the southern African sub-continent occur as scattered outliers representing eroded remnants of an originally more extensive volcanic province. The rocks are best preserved in central southern Africa including Lesotho, and the continental margin areas of Namibia in the west and Mozambique. Zambabwe, Swaziland and South Africa in the east. Extensive lava fields (yet few volcanoes) dykes, sills, layered intrusions and at least two major dyke swarms characterise the region. Volcano-stratigraphic and geochemical mapping have been used to subdivide the volcanic successions found in the different areas and recently adopted nomenclature is presented. Considerable more variability and complexity occurs in the volcanic succession than was previously recognised: geochemical variations and stratigraphic relationships indicating that four major provinces can be recognised. Rocks from the central Karoo areas are primarily of basaltic composition whereas those from the western and eastern marginal areas include mafic basic, intermediate and acid types. Emplacement of rocks such as carbonatites, nephelinites, and picrite basalts enriched in incompatible elements, indicate that derivation from a heterogeneously enriched source played a significant role in the petrogenesis of a large proportion of the Karoo mafic and basic rocks. Age relationships of the volcanic rocks reveal that vulcanicity extended over a period of 130 m.y. from mid-Triassic to early Cretaceous time.
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Bristow, J.W., Saggerson, E.P. A review of Karoo vulcanicity in Southern Africa. Bull Volcanol 46, 135–159 (1983). https://doi.org/10.1007/BF02597582
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DOI: https://doi.org/10.1007/BF02597582