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Karroo basalts of southern Malawi and their regional petrogenetic significance

Published online by Cambridge University Press:  05 July 2018

R. Macdonald ,
R. Crossley  and
K. S. Waterhouse
R. Macdonald
Affiliation:
Department of Environmental Sciences, University of Lancaster, Lancaster LA1 4YQ
R. Crossley
Affiliation:
Department of Earth Sciences, Chancellor College, PO Box 280, Zomba, Malawi
K. S. Waterhouse
Affiliation:
Department of Environmental Sciences, University of Lancaster, Lancaster LA1 4YQ
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Abstract

Karroo basaltic lavas of southern Malawi are divided into two groups on the basis of stratigraphy, petrography, and the data from 20 newly analysed rocks. A lower group of porphyritic lavas is notably rich in plagioclase phenocrysts and has contents of K, Ti, P, Ba, and Zr unusually high for tholeiitic basalts. They are overlain by an upper group of aphyric or sparsely microphyric lavas whose chemistry is more normal for tholeiites and is comparable with that of the Karroo dolerite dykes in Malawi. Though they outcrop in the northern part of the Karroo province, the lavas and dykes have chemical characteristics more similar to southern province rocks, adding some complexity to the concept of geochemical provinces established by earlier workers. Inter-suite variations in incompatible trace element contents and ratios indicate that the basalts of each group were derived from heterogeneous mantle sources.

Type
Research Article
Information
Mineralogical Magazine , Volume 47 , Issue 344 , September 1983 , pp. 281 - 289
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1984

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