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Geological Society, London, Special Publications; 1987; v. 33; p. 315-325;
DOI: 10.1144/GSL.SP.1987.033.01.21
© 1987 Geological Society of London

Proterozoic Volcanic Suites of Africa

Fundamental uniformity in the trace element patterns of the volcanics of the Kaapvaal Craton from 3000 to 2100 Ma: evidence for the lithospheric origin of these continental tholeiites

R. E. Myers, R. G. Cawthorn & T. S. McCarthy

Department of Geology, University of the Witwatersrand, Johannesburg, South Africa

C. R. Anhaeusser

Economic Geology Research Unit, University of the Witwatersrand, Johannesburg, South Africa

In order to examine the nature of the mantle beneath the Kaapvaal Craton in southern Africa, data from thirteen volcanic sequences ranging in age from 3000 to 2100 Ma have been examined in this study. Variations in Nb, La, Ce, P, Zr, Ti, and Y have been evaluated using a niobium-normalized spidergram which minimizes variations due to fractional crystallization and clearly illustrates mantle source variations. Using this diagram a pattern, showing strong LREE enrichment of source relatively depleted in niobium and titanium, has been identified which remains quantitatively the same throughout this time period, indicating that it is the result of a reproducible equilibrium process. Melting of an incompatible element enriched (modally metasomatized) subcontinental lithosphere in which renewable metasomatic phases, such as diopside, are residual during melting can explain the quantitative uniformity and the time independence of this pattern.