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.