Geologicheskii Vestnik

This article presents the results of studying the compositions of rock-forming and accessory ultrama c minerals of the southern part of the ophiolitic massif of Nurali. It is shown that the chemical composition of Nurali ultrama c minerals form stable relationships with the mineral composition of the rocks they form. Thus, in a series of lherzolite – garzburgite – dunite increases magnesia and nickel content in the olivine, in chromium spinelids increases chromium and decreases vanadium content, the joint increase in iron and chromium content forms a trend. The most chromium-rich varieties of spinelids are found in dunite. It was shown that ultrama tes of the massif were formed in the process of partial melting of the original mantle substrate — about 20–30% for peridotites, about 30–40% for dunite. Closing of exchange reactions in chromespinelide – olivine pairs from peridotites occured at temperatures 580–830°C, in the same pairs from dunites — at temperatures 770–840°C. According to the calculations of two-pyroxene thermometers, the closure of exchange reactions in pyroxenite veins occured at temperatures 1000–1150°C. The obtained temperatures of reaching chemical equilibria in the minerals, as well as the melting degrees of the initial mantle matter during the formation of mantle ultrama cs of Nuraly massifs are consistent with the data on other ophiolitic ultrama c rocks of the Urals.

ultrama c rocks of Nurali, olivine-spinel geothermometry, double-pyroxene thermometry, peridotite, dunite, pyroxenite

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