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

Oxygen isotope ratios of olivine and clinopyroxene phenocrysts from the Klu chevskoy volcano in Kamchatka have been studied by CO2 and ArF laser techni ques. 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 altere d 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 bee n hydrated by O-18-rich fluids percolating through the mantle wedge. O-18-e nriched fluids are derived from the subducted oceanic crust and the Emperor seamount chain, which is responsible for a particularly high fluid flux. T his hydrated mantle wedge was subsequently involved in are magmatism beneat h Kluchevskoy by active intra-are rifting. (C) 2000 Elsevier Science B.V. A ll rights reserved.