Abstract
Abstract The oldest crust in the Ukrainian Shield occurs in the Podolian and Azov domains, which both include Eoarchaean components. U–Pb age data for Dniestr–Bug enderbites, Podolian Domain, indicate that these are c. 3.75 Ga old, and Lu–Hf isotope data indicate extraction from chondritic to mildly isotopically depleted sources with ɛ Hf up to c. +2. Nd model ages support their Eoarchaean age, while model ages for Dniestr–Bug metasedimentary gneisses indicate that these also include younger crustal material. Most of the Hf-age data for metasedimentary zircon from the Soroki greenstone belt, Azov Domain, reflects Eoarchaean primary crustal sources with chondritic to mildly depleted Hf isotope signatures at 3.75 Ga. A minor portion is derived from Mesoarchaean crust with a depleted ɛ Hf signature of c. +4 at 3.1 Ga. U–Pb zircon ages from Fedorivka greenstone belt metasediments are consistent with the Soroki age data, but also include a 2.7–2.9 Ga component. Nd whole rock model ages provide support for a younger crustal component in the latter. Both domains have been subject to Neoarchaean, c. 2.8 Ga, and Palaeoproterozoic, c. 2.0 Ga, metamorphism. The spatial distribution indicates that the Podolian and Azov domains evolved independently of each other before the amalgamation of the Ukrainian Shield.
Highlights
Key evidence about both ancient and modern crustal formation processes is provided by isotopic age determinations combined with Nd, Hf, Pb and O isotopic data from whole rock samples, and the Hf and O isotope compositions of dated zircon crystals (e.g. Hawkesworth & Kemp 2006)
The East European Craton, with its three segments Sarmatia, Volgo –Uralia and Fennoscandia (Bogdanova 1993), comprises a significant fraction of the Archaean crust exposed at the Earth, including Palaeo- and Eoarchaean components (Fig. 1)
We demonstrate that two separate domains in the Ukrainian Shield include significant components of rocks and metasedimentary detrital minerals which are up to 3.75 Ga in age
Summary
Key evidence about both ancient and modern crustal formation processes is provided by isotopic age determinations combined with Nd, Hf, Pb and O isotopic data from whole rock samples, and the Hf and O isotope compositions of dated zircon crystals (e.g. Hawkesworth & Kemp 2006). The East European Craton, with its three segments Sarmatia, Volgo –Uralia and Fennoscandia (Bogdanova 1993), comprises a significant fraction of the Archaean crust exposed at the Earth, including Palaeo- and Eoarchaean components (Fig. 1) Much of this crust has been strongly reworked during the Palaeoproterozoic. The Ukrainian Shield, a central part of Sarmatia, includes Eoarchaean components as well as younger Archaean and Proterozoic rocks (Claesson et al 2006; Bibikova et al 2010) In this contribution we present U –Pb and Hf zircon results and Sm –Nd whole rock data from enderbites and metasedimentary rocks, which provide new information about the origin and complex Archaean and Palaeoproterozoic evolution of this old segment of crust. From the Podolian Domain, U – Pb dating of zircon from granulite-facies granitoids (enderbites) from the Dniestr– Bug Series has yielded ages up to 3.65 Ga, and indications of material up to 3.75 Ga old (Claesson et al 2006)
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