Fractionation of Rare-earth Elements in Surface Streams of Baransky Volcano (Etorofu, Southern Kuriles)

Baransky is an active volcano, located in southern Kurile arc, on the subduction zone between Okhot and Pacific plates. Being active during the last 50 years, it is still a threat to locals and air transport. Geochemical study of hydrothermal system of Baransky volcano gives us an opportunity to understand processes occurring in volcanic structure. Thermal springs of the Kipyaschiy creek basin were studied for major ions, micro and rare-earth elements. Hydrothermal springs are characterized with T = 90-100°C, pH = 1.2 -1.9, Cl = 1.8g/l and SO4 = 4g/l. These conditions have a strong influence on water of Kipyaschiy creek. During fluids/surface water interaction we see fractionation of rare-earth element as indicators of changing physico-chemical parameters of the creek. Solfatars are enriched in trivalent Gd and Lu, bivalent Eu, Tm and Yb and depletion in tetravalent Ce, Tb, Dy and trivalent Ho and Er. Hydrothermal fluids are enriched in all REEs with trend to HREE accumulation, but minimum changes in Ce and Gd.