The Mesoarchaean Dominion Group and the onset of intracontinental volcanism on the Kaapvaal craton – Geological, geochemical and temporal constraints

Andrea Agangi, Axel Hofmann, Ernst Hegner, Hangqiang Xie, Claudia Teschner, Alexander Slabunov, Sergei A. Svetov

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)

Abstract

The ca. 3.07 Ga volcanic rocks of the Dominion Group, South Africa, represent the oldest example of intracontinental, rift-related volcanism on the Archaean Kaapvaal craton. The volcanic assemblage comprises a >2 km-thick succession of mafic-intermediate lavas interlayered with felsic lavas and pyroclastic rocks. Textural and geological features indicate emplacement in a subaerial environment probably in an incipient intracontinental rift. We report SHRIMP U[sbnd]Pb zircon ages, elemental and Nd-isotope bulk-rock analyses of drill core samples and interpret their petrogenesis in the context of a Mesoarchaean continental setting. The U[sbnd]Pb zircon ages of four felsic samples from different stratigraphic levels yielded the same dates, resulting in a pooled 207Pb/206Pb age of 3074 ± 5 Ma. Primitive mantle-normalised incompatible trace element concentrations show enriched patterns with fractionated rare earth elements over high field-strength elements and negative anomalies of Nb and Ta relative to La. Initial εNd values for mafic and felsic rocks from −1.0 to −0.2 indicate melting of sources comprising time-integrated incompatible element-enriched mantle. The combined trace element and Sm[sbnd]Nd isotopic data suggest that the enrichment of incompatible elements and the low εNd values in the most primitive basalt samples (Mg# of 65–67) can be explained with contamination of asthenosphere-derived melts with crustal material or melting of an incompatible element-enriched upper mantle. The chemical compositions of the Dominion Group and Pongola Supergroup represent a significant petrogenetic departure from earlier Archaean (>3.6–3.1 Ga) magmatism as recorded in the Kaapvaal craton, which was dominated by komatiite-basalt volcanism and tonalite-trondhjemite-granodiorite intrusions. This change reflects the transition from a “greenstone belt type” tectonic setting to a failed intracontinental rift setting shortly after stabilisation of the Kaapvaal craton.

Original languageEnglish
Pages (from-to)131-150
Number of pages20
JournalGondwana Research
Volume84
DOIs
Publication statusPublished - Aug 2020

Keywords

  • Archaean
  • Dominion Group
  • Intracontinental magmatism
  • Kaapvaal craton
  • Witwatersrand basin

ASJC Scopus subject areas

  • Geology

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