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

Agangi, Andrea; Hofmann, Axel; Hegner, Ernst; Xie, Hangqiang; Teschner, Claudia; Slabunov, Alexander und Svetov, Sergei A. (2020): The Mesoarchaean Dominion Group and the onset of intracontinental volcanism on the Kaapvaal craton - Geological, geochemical and temporal constraints. In: Gondwana Research, Bd. 84: S. 131-150

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-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-Pb zircon ages of four felsic samples from different stratigraphic levels yielded the same dates, resulting in a pooled Pb-207/Pb-206 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 epsilon(Nd) 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-Nd isotopic data suggest that the enrichment of incompatible elements and the low epsilon(Nd) 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. (C) 2020 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Geowissenschaften > Department für Geo- und Umweltwissenschaften
• Themengebiete: 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften, Geologie
• ISSN: 1342-937X
• Sprache: Englisch