Hydrated sub-arc mantle: a source for the Kluchevskoy volcano, Kamchatka/Russia

Oxygen isotope ratios of olivine and clinopyroxene phenocrysts from the Kluchevskoy volcano in Kamchatka have been studied by CO2 and ArF laser techniques. Measured delta(18)O values of 5.8-7.1 parts per thousand for olivine and 6.2-7.5 parts per thousand for clinopyroxene are significantly heavier than typical mantle values and cannot be explained by crustal assimilation or a contribution of oceanic sediments. Positive correlations between delta(18)O and fluid-mobile elements (Cs, Li, Sr, Rb, Ba, Th, U, LREE, K) and a lack of correlation with fluid-immobile elements (HFSE, HREE) suggest that O-18 was introduced into the mantle source by a fluid from subducted altered oceanic basalt, This conclusion is supported by radiogenic isotopes (Sr, Nd, Pb). Mass balance excludes simple fluid-induced mantle melting. Instead, our observations are consistent with melting a mantle wedge which has been hydrated by O-18-rich fluids percolating through the mantle wedge. O-18-enriched fluids are derived from the subducted oceanic crust and the Emperor seamount chain, which is responsible for a particularly high fluid flux. This hydrated mantle wedge was subsequently involved in are magmatism beneath Kluchevskoy by active intra-are rifting. (C) 2000 Elsevier Science B.V. All rights reserved.