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 °Ñ), determined from the isotopic ratios of C and O in calcite and graphite, corresponds to the temperature range (600—900 °Ñ) of the formation of carbonatite associations. According to the same ratios of isotopes in calcites, the protoliths of carbonate rocks are located within the carbonatite 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 the influence of the heat of granite intrusions.

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—Chaotically localized isolated small bodies of metaultrabasic rocks have been found in the quartzite-schist strata of the Ilmeny metamorphic complex in the South Urals. These are metamorphosed rootless blocks and lumps of serpentinite melange within the so-called Urazbaevo olistostrome. Sometimes they contain lumpy inclusions of massive anorthite gabbroids with gabbro, ophitic, and cumulative textures, free of crystallization schistosity, and of different mineral compositions. The rocks have abnormally high contents of Al2O3, CaO, MgO, and REE and low contents of SiO2 and are characterized by weak secondary alteration. Seldom, inclusions of hornblendites, along with anorthite, spinel, apatite, enstatite, diopside, and rutile, are present. Some gabbroid and hornblendite bodies have abnormally high contents of REE, with a strong predominance of LREE (81–93% of the total REE). The maximum contents of REE have been established in zoisite amphibolites (170–850 ppm) and apatite–garnet hornblendites (up to 450 ppm). The conclusion has been drawn that the rocks formed in the basement of the Earth’s crust and got with protrusions of serpentinite melange to the surface.