Isotopic evidences of magmatic nature of the dolomite-calcite bodies of the Ilmeny mountains and the Plastovsky district of the South Urals

The data obtained for the first time on the isotopic composition of oxygen and carbon of calcites and graphites of dolomitecalcite rocks of the Ilmeny Mountains and dykes of a similar composition in the Plastovsky district have confirmed their magmatic genesis. The temperature of formation of carbonate bodies (590-1000 °C), determined from the isotopic ratios of C and O in calcite and graphite, corresponds to the temperature range (600-900 °C) of the formation of carbonatite associations. According to the same ratios of isotopes in calcites, the protoliths of carbonate rocks are located within thecarbonatite fields of the folded regions and in the transition zone to carbonates of marine origin. This is probably due to the fact that these rocks are a product of carbonate magma during remelting of sedimentary carbonate rocks in subduction zones, or under theinfluence of the heat of granite intrusions.