An Investigation of the carbonatites of the Kaapvaal Craton and their tectonic context

Abstract

Carbonatites are exotic rocks which usually occur in discrete intrusions. Considering the association of carbonatites with rifting environments, this dissertation proposes that: carbonatites occur in extensional tectonic settings and therefore carbonatite occurrence can be used to constrain an extensional setting for related occurrences. In order to give context in which to consider this hypothesis, the formation of carbonatites is reviewed. This work favours the direct mantle melting model as it is most relevant and consistent with observations of Kaapvaal Craton carbonatites. However the liquid immiscibility model cannot be entirely rejected with current knowledge. The hypothesis is applied to the Bushveld Igneous Complex after providing evidence of the rift-carbonatite association. The Bushveld Igneous Complex is considered to have been emplaced in the same tectonic setting as carbonatites. Therefore the Bushveld Igneous Complex was emplaced in an extensional tectonic setting. Finally the carbonatites which are part of the Pilanesberg Alkaline Province are considered in order to test the hypothesis. This work finds that the Pilanesberg carbonatites do occur with other rift related magmatism during the break-up of Nuna (Columbia) and therefore the hypothesis is not rejected. This work offers reviews of basic carbonatite background, formation models and carbonatite occurrences on the Kaapvaal Craton.