Magma Mixing and Metasomatic Reaction in Silicate-Carbonate Liquids at the Kruidfontein Carbonatitic Volcanic Complex, Transvaal

L. B. Clarke and M. J. Le Bas
Department of Geology, University of Leicester, LE1 7RH, UK

Abstract: The Kruidfontein volcanic complex is a Proterozoic collapsed carbonatitic caldera structure, the inner caldera of which is filled with carbonatitic bedded volcaniclastic rocks cut by carbonatite dykes, and the outer with bedded silicate tuffs. As well as numerous fragments of phonolitic pumice in the silicate tuffs, there are unusual banded fragments composed of alternating silicate and carbonate compositions which appear to have been originally glasses, and which give evidence for mechanical mixing of magmas which may originally have been magmas separated by liquid immiscibility. The fragments have also been strongly fenitized with the introduction of K and the replacement of Al by Fe.

Keywords: carbonatite • Kruidfontein • South Africa • magma mixing • metasomatic reaction

Mineralogical Magazine; March 1990 v. 54; no. 374; p. 45-56; DOI: 10.1180/minmag.1990.054.374.04
© 1990, The Mineralogical Society
Mineralogical Society (