The oldest crust in the Ukrainian Shield – Eoarchaean U–Pb ages and Hf–Nd constraints from enderbites and metasediments
S. Claesson, E. Bibikova, L. Shumlyanskyy, B. Dhuime, C. J. Hawkesworth, 2015. "The oldest crust in the Ukrainian Shield – Eoarchaean U–Pb ages and Hf–Nd constraints from enderbites and metasediments", Continent Formation Through Time, N. M. W. Roberts, M. Van Kranendonk, S. Parman, S. Shirey, P. D. Clift
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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 ɛHf 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 ɛHf 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.
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The continental crust is our archive of Earth history, and the store of many natural resources; however, many key questions about its formation and evolution remain debated and unresolved:
What processes are involved in the formation, differentiation and evolution of continental crust, and how have these changed throughout Earth history?
How are plate tectonics, the supercontinent cycle and mantle cooling linked with crustal evolution?
What are the rates of generation and destruction of the continental crust through time?
How representative is the preserved geological record?
A range of approaches are used to address these questions, including field-based studies, petrology and geochemistry, geophysical methods, palaeomagnetism, whole-rock and accessory-phase isotope chemistry and geochronology. Case studies range from the Eoarchaean to Phanerozoic, and cover many different cratons and orogenic belts from across the continents.