Age of nephrite-bearing dikes of the Uzunkyr Belt (South Urals): Local U-Pb isotope analysis of zircon and Sr-Nd isotope data of rock-forming minerals

Through local U-Pb isotope analysis of zircon and Sir-Need data on rock-forming minerals, the age of nephrite-bearing monzonite-diorite dikes of the Uzunkyr Belt has been determined. The derived datings coincide with known geological events that took place in the Phanerozoic on the territory of the South Urals. Xenogenic zircons prove the participation of the Upper Ordovician units in the tectonic structure of the studied area. Devonian zircons are associated with assimilation of subvolcanic rocks which are middle and basic in composition and whose formation time correlates with the appearance of the subduction zone with the Magnitogorsk island arc above it. Early Carboniferous datings indicate the relationship between dike formation and formation of the continental arc-shaped structure to which the Syrostan massif (monzodiorite-granite formation) belongs. The age range of the Uzunkyr nephrite-bearing dikes coincides with that of intrusives (350–336 Ma) of the Magnitogorsk Belt, where formation of gabbro series was also changed by formation of subalkali and alkali igneous rocks. According to the analogous data on zircon datings from metamorphic rocks of the Il’menogorskii Complex, the given territory later evolved as a whole.