PECULIARITIES OF CHEMICAL COMPOSITION OF KLYUCHEVSKOY VOLCANO MELTS INSIGHT FROM MELT INCLUSIONS STUDY IN OLIVINES Mironov N.L.1,2, Portnyagin M.V.2, Pletchov P.Yu.1 1 - Geological department of Moscow State University. 2 - Vernadsky Institute of geochemistry and analytical chemistry RAS e-mail: nikita_mir@rambler.ru key words: olivines, melt inclusions, Klyuchevskoy volcano, basalts, melts. In order to characterize composition and evolution of parental melts of Kluchevskoy volcano, melt inclusions in olivine phenocrysts (Fo91-67) were studied. The olivines were picked from well dated lava samples of old cones Bulochka and Luchitskogo (2500-4000 y.a.), Ochki (1500-2000 y.a.) and of historic eruptions Tuyla (1932 y.), Apakhonchich (1946), Bylinkinoy (1951), Vernadskogo (1953) and Piipa (1966). Samples represent all geochemical varieties of Kluchevskoy volcano rocks: Bulochka and Luchitskogo lavas (MgO=11.2-12.1 wt.%) are high magnesian basalts, Ochki and Tuyla lavas (MgO=8.7-8.8 wt.%) are magnesian basalts, Apakhonchich, Bylinkinoy, Vernadskogo and Piipa lavas (MgO=4.4-5.9 wt.%, Al2O3=16.6-18.1 wt.%) are high alumina basalts (Fig.1,2) (rock types as in [1]).The data obtained provide comprehensive information about melts existed at Kluchevskoy volcano over the recent 4000 years of its volcanic activity. Partially recrystallised melt inclusions (most of melt inclusions studied) were experimentally rehomogenised. For this purpose heating stage with visual control of Sobolev-Slutsky construction [2] was used. The heating occured in atmosphere of pure He under atmospheric pressure. The inclusions were partially homogenized (melt + fluid phase) and quenched. Glasses of such inclusions and glasses of naturally quenched melt inclusions were analyzed by microprobe. The peculiarity of the melt inclusion compositions is low FeO content. We suggest this is due to the process of Fe-loss from inclusions after their entrapment. In order to recover the initial melt compositions, special calculation method developed by L. Danyushevsky [3] was used. This method allows to take into account the effect of Fe-loss and restore initial melt composition. Initial FeO content in melt was assumed to be 8.5 wt.% This value was taken from the average FeO content of Klyuchevskoy volcano rocks. It is important to note that unlike other oxides FeO content is rather constant in different types of Klyuchevskoy volcano rocks. This makes our assumption acceptable for all melts studied. The most of the melts obtained from the melt inclusions composition show significantly lower SiO2 and higher CaO, Al2O3 compared to the composition of host rocks at given MgO (Fig.1,2)