Age and Lu-Hf isotope systematics of zircon from metapelite granulites of the Kursk-Besedino Domain: evidence of the Paleoarchean crust within the Kursk Block of Sarmatia

Abstract

Introduction: In the southern segment of the East European Craton (Sarmatia), the Paleoarchean crust has long been known on the Ukrainian Shield. In the eastern part of Sarmatia (the Kursk Block), the Oboyan complex rocks were belonged to the Early Archean, despite the absence of precise isotope age dating. Sm-Nd and Lu-Hf isotopic data suggest that the Kursk Block comprises rocks with a Paleoarchean crustal prehistory. The aim of our research is to reveal the episodes of the Paleoarchean crust growth based on isotopic U-Pb dating and isotopic Lu-Hf systematics of zircon from metapelite granulites of the Kursk-Besedino Domain. Methodology: The age and Lu-Hf isotopic composition of zircon from metapelitic granulites of the Kursk-Besedino domain was determined, as well as the content of petrogenic, minor, and rare elements in the rocks. Results and discussion: Different ages of the zircon overgrowths and cores have been determined. The outgrowths age is about 2.8 Ga and is interpreted as the age of granulite metamorphism. The Paleoarchean ages were determined in the zircon cores cluster at: 3535 ± 13, 3464 ± 9, and 3334–3384 Ma, apparently recording episodes of crustal growth and indicating the heterogeneous nature of the provenance source. Although the Lu-Hf isotope system in zircon shows wide variations in the Hf isotopic composition, all T Hf(DM) model ages are Paleoarchean, Eoarchean, and even Hadean. The Paleoarchean sediments represented by immature pelites, psammites apparently deposited in marine basins. Their provenance sources were mainly Paleoarchean felsic rocks. Conclusion: The Paleoarchean crust comprised an older tonalite-trondhjemite-granodiorite basement, covered by volcanic-sedimentary units of pelites, psammites, chemogenic banded iron formations, and injected with basite sills. Such a supracrustal association suggests their formation in a passive margin setting. These rocks were transformed into orthogneisses, metapelite and mafic granulites of the Kursk-Besedino Domain as a result of ca. 2.8 Ga metamorphsm. U-Pb zircon dating of metapelite granulites, permitted recognition of several episodes of crustal growth: 3535–3556, 3464–3472 and 3334–3384 Ma. The zircons have been derived from fragments of the Paleoarchean nucleus of Sarmatia that had a long-lasting crustal prehistory with Eoarhean and even Hadean sources of matter. Zircons provenance source of the third, younger group, is unbeknown, though its age limits a time of the metapelite protolith deposition.