The isotopic composition of subduction fluid: High-, low-, or normal δ^(18)O?

Abstract

The oxygen isotopic composition of subduction zone fluids has been hypothesized to have high-δ^(18)O derived from the high-δ^(18)O upper portions of the slab's top and sediments. We report oxygen isotope analyses of olivine and other phenocrysts from four arcs that appear to have unusually large fluid contributions (ca >5-10wt%): Mt. Shasta, California, Kluchevskoy, Kamchatka, ten samples of high-^(226)Ra lavas from the Tonga Kermadec arc, and lavas from Central American arc. Other fluid-sensitive trace element ratios (Ba/La) and mass balance approaches were used to constrain the amount of fluid added.

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