U–Pb and Hf isotope data of detrital zircons from the Barberton Greenstone Belt: constraints on provenance and Archaean crustal evolution

Abstract

Combined U–Pb and Hf isotope analyses of detrital zircons from the Fig Tree and Moodies Groups of the Barberton Greenstone Belt, South Africa, yield similar Hf isotope compositions and age populations, thus pointing to a similar provenance. Zircon populations of Fig Tree Group greywacke and Moodies Group quartzarenite are both dominated by age clusters at 3.53, 3.47, and 3.28 Ga, and a minor cluster at 3.36 Ga. The Moodies quartzarenite sample additionally contains a younger age population at 3.23–3.19 Ga. Hafnium isotope data indicate that the source area of both sediments was affected by new crust formation from depleted mantle sources at 3.53, 3.47, and perhaps at 3.36 Ga (ϵHf t between −1.7 and +4.5), accompanied by partial reworking of an Eoarchaean crustal component as old as 3.75–3.95 Ga. In contrast, crustal reworking was the predominant process between 3.28 and 3.22 Ga (ϵHf t between −6.0 and +0.9), probably related to subduction and collision of terranes along the Inyoka Fault system. The zircon U–Pb and Hf isotope datasets favour a southern provenance for the Fig Tree and Moodies sediments, comprising granitoids in the vicinity of the southern Barberton Greenstone Belt and in Swaziland. This finding is in contrast to the sedimentary record of the Moodies Group, which mostly suggests a northern and along-strike provenance. This discrepancy may be due to reworking of sediments during extensive syn- and postorogenic strike-slip faulting and high uplift or subsidence between 3.26 and 3.19 Ga. Supplementary material Results of in situ U–Pb and Lu–Hf isotope zircon analyses are available at www.geolsoc.org.uk/SUP18561 .