New geochronological constraints on the middle Archean Shurugwi greenstone belt toward an understanding of the crustal evolution of the Zimbabwe Craton

Abstract

The Shurugwi greenstone belt (SGB) in the central Zimbabwe Craton is one of the major volcano-sedimentary belts in the craton, but its formation age and tectonic history have not been well constrained. For revealing the evolution of SGB, this study performed in-situ U–Pb dating of zircons from meta-sedimentary rocks of the Wanderer and Mont d’Or formations in SGB, granitoids/orthogneisses around SGB, and also whole-rock Re–Os isotopic analysis of chromitite in an ultramafic unit in SGB. Igneous zircons from granitoids which intruded into SGB were dated ca. 2.91 Ga, whereas those from the orthogneiss were dated ca. 3.01 Ga. The Re–Os isotopic analysis provided an intrusive age of ca. 3.0 Ga for the ultramafic unit that is unconformably covered by the Wanderer Formation. These ages indicate that the Wanderer Formation was deposited between 3.0 and 2.91 Ga and the SGB was tectonically emplaced over the basement with 3.01 Ga orthogneiss. By ca. 2.91 Ga. The depositional age of the Mont d’Or Formation is constrained between ca. 3.59 Ga and 3.0 Ga nonetheless the age range is still large. The age spectrum of the detrital zircons from the Mont d’Or Formation resembles that of the Wanderer Formation, sharing a dominant age cluster at ca. 3.59 Ga. For the Wanderer Formation, a significant time gap of nearly 600 million years between the depositional age and the 3.59 Ga major cluster in detrital zircon age spectra suggests that the SGB had a remarkable provenance which prevented large-scale supply of young detrital grains from tectono-magmatically active region.