Paleozoic Age of Metaterrigenous Sequences of the Maksyutov Metamorphic Complex (Southern Urals): Results of U–Pb Dating of Detrital Zircons

© 2020, Pleiades Publishing, Ltd. Abstract: The first U–Pb (LA–ICP–MS) isotope dating of detrital zircons from quartzites of two strata of the Maksyutov metamorphic complex (Southern Urals) was performed. Zircon grains from the Galeevo quartzites are well rounded. The concordant zircon ages fall into the ranges of 529–594, 956–2144, and 2709–2781 Ma; the main age peaks are 544, 551, and 1491 Ma. Zircon grains from the Yumaguzino quartzites are idiomorphic and weakly rounded. The concordant zircon ages fall into the ranges of 497–640 and 957–1027 Ma, forming distinct age peaks of 514, 548, and 605 Ma. The U–Pb ages obtained and their comparison with similar data on the other sequences of the Southern Urals and the Caspian Sea Region indicate the Ordovician age of the protolith of the studied quartzites of the Maksyutov complex

Early Palaeoproterozoic granulite-facies metamorphism and partial melting of eclogite-facies rocks in the Salma association, eastern Fennoscandian Shield, Russia

The Salma-type Archaean eclogites exposed along the northwestern boundary of the Belomorian Eclogite Province in the eastern Fennoscandian Shield formed as a result of the Mesoarchaean–Neoarchaean subduction and collision. The common protoliths of the Salma-type subduction-related eclogites were oceanic layered gabbro and volcanic-sedimentary assemblage. The eclogite-facies pillow lavas and associated alumina-siliceous sediments that fill interpillow space and intercalate with lava flows are the main objects of our work. The kyanite-garnet–phengite–quartz rocks formed after alumina-siliceous sediments contain fluid inclusions trapped in large relic quartz grains. The fluid inclusions yielded an isochore that corresponds to PT-conditions of a beginning of the Salma oceanic rock subduction from the seafloor level that generally confirms the sedimentary provenance of these rocks. The alumina-siliceous sediments underwent the eclogite-facies metamorphism at pressure no lower than 21 kbar and temperatures of 650–750 °C and transformed into kyanite-garnet–phengite–quartz rocks. During exhumation under granulite-facies conditions at temperatures up to 900 °C and pressure down to 9 kbar, eclogite facies metasediments underwent partial melting accompanied by disequilibrium breakdown of phengite + quartz association with formation complex polymineralic pseudomorphs consisting of feldspars, biotite, muscovite, kyanite, corundum, and dumortierite. U-Pb dating of Th-rich igneous zircon from melted metasedimentary and mafic rocks using the LA-ICP-MS and TIMS methods yielded the time of granulite facies event accompanied by partial melting processes at ~2.45 Ga. After this, zircon underwent fluid-induced alteration, causing partial dissolution followed by precipitation of new Th–poor zircon and zircon rims around ancient grains at ~1.9 Ga ago © 2021 Elsevier B.V