ИСТИНА

Geochemical variations in E-W transect across the Klyuchevskaya Volcanic Group, Kamchatka, are constrained by a compilation of published data complemented by new major and trace element data on rocks from five previously poorly-studied volcanoes: Bolshaya Udina, Malaya Udina, Ovalnaya Zimina, Ostraya Zimina and Gorny Zub. Lavas erupted from these volcanoes are medium-K calcalkaline basaltic andesites to dacites except few low-Mg basalts. On K2O vs SiO2 diagram three trends are distinguished: Trend 1 with low potassium includes lavas from Gorny Zub, Bolshaya Udina, and few samples from Zimina massif; Trend 2 with elevated potassium consists of lavas from Malaya Udina and partly lavas from Zimina massif; Trend 3 with highest potassium is formed by Ovalnaya Zimina lavas. Older basement lavas all belong to the high-K basalt-andesite rocks, suggesting a period of variable in silica high-K volcanism in the KGV during the Middle Pleistocene. Mixing of melts derived from variably enriched/depleted mantle sources and subsequent fractional crystallization can explain all rock variations. The (MgO)5.0 – corrected major, trace elements and trace element ratios in middle-K series show a systematic increase in incompatible, fluid-mobile elements with slab depth from 160 km in the E to 200 km in the W. This zonation is also expressed in increasing LILE, LREE, lower LILE/HFSE ratios from E to W. This zonation is also expressed in increasing LILE, LREE, lower LILE/HFSE ratios from E to W at nearly constant MREE and HREE, which suggests variable contribution of slab components to the mantle source. This research was supported by grants DFG Wo 362/51-1, RFBR # 16-55-12040.