A buried Paleoarchean core of the Eastern Sarmatia, Kursk block: U-Pb, Lu-Hf and Sm-Nd isotope mapping and paleotectonic application

Abstract

Zircon U-Pb and Lu-Hf isotope analyses along with whole-rock Sm-Nd isotope studies shed a light on distribution of the Paleoarchean crust in the Kursk block, Eastern Sarmatia. It has been revealed that this domain consists of two provinces with different crust ages: the Paleoarchean Kursk-Besedino granulite-gneiss domain (KBd) and the Mesoarchaean Mikhailovsky granite-greenstone area (Mgga). The KBd encompasses TTG orthogneisses and pelite, BIF, and mafic volcanics (sills) metamorphosed in the granulite facies. The orthogneiss protolith was formed ca 3.55 Ga (U-Pb SHRIMP data) from a juvenile source. In the metapelites, U-Pb detrital zircon ages cluster in three groups, 3535–3556, 3464–3472, and 3334–3384 Ma. The latter one suggests post-Middle Paleoarchean age of the protoliths deposition. Sm-Nd and Lu-Hf isotope characteristics of the volcanic-sedimentary rocks suggest the leading role of Paleoarchean crustal material in their protoliths. The age of metamorphic zircon is ca 2.8 Ga in all the KBd rocks.The Mgga consists of TTG and volcanic-sedimentary units. The ages of the TTG, felsic volcanics and metasediments fall in a narrow range of 2.96–3.12 Ga. They have juvenile isotope-geochemical characteristics (εNd(t) = +0.3 – + 4.0; εHf(t) = -0.3 – + 5.8) without any contribution of Paleoarchean crust. High-temperature 2.8 Ga-old metamorphism is not recorded in the Mgga.Pronounced differences in the age of crust-forming events in the KBd and Mgga indicate that these continental blocks had a different geological history, hence were distant from each other during most of the Archean Eon, probably up to 2.8 Ga. The Paleoproterozoic Trosnyanskaya intrusion in the Mgga bears signs of the KBd Paleoarchean crust. This suggests a collision of these Archean blocks with the Mesoarchean being thrust over the Paleoarchean rocks possibly at ca 2.8 Ga.