ORIGIN OF OLIVINE PHENOCRYSTS AND MANTLE SOURCE OF MAGNESIAN BASALTS FROM THE KHARCHINSKY VOLCANO ( <i>Central Kamchatka depression</i> )

The article presents new data on the formation conditions of basalt and basaltic andesite of the Kharchinsky Volcano (Central Kamchatka Depression, CKD). It is shown that the liquidus association is represented by olivine (Fo91) and Cr-spinel, which crystallized in oxidized conditions NNO+0.4 – NNO+1.5 at temperatures of 1,110–1,210 °C. The study of melt inclusion in olivine phenocrysts allows us to reconstruct compositions of parental melts for basalt and basaltic andesite. These melts have Mg-high (Mg# ≈ 76), Al-low and Ca-low basic compositions enriched in volatiles. Water content in melts could have reached up to 5.5 wt.%. These melts formed from a peridotite source, sometimes with slight admixture of pyroxenite component. Crystallization of melts could have occurred in several intermediate chambers (up to 1.5, at 5–7 and 11–13 kbar).