Oxygen Isotope Geochemistry of Oceanic-Arc Lavas

Variations of oxygen isotope ratios in arc-related lavas can constrain trace-element enrichment in a mantle source being fluxed by addition the contributions of subducted crustal igneous rocks, sediments, and of aqueous fluid. Comparison of this model with observed variations fluids to the sub-arc mantle. We have measured oxygen isotope in the geochemistry of lavas from the Vanuatu–Fiji–New Caledonia ratios in 72 arc and back-arc lavas from five ocean–ocean subduction region (the suite of related samples showing the greatest range in zone systems using laser-fluorination analyses of olivine and other dO observed in this study) constrains the amounts and chemical phenocrysts and glass. Eighty percent of our samples have dO and isotopic compositions of slab-derived phases in the sources of values for any given phase (olivine, plagioclase, glass, or biotite) these arc-related lavas. Assuming a dO value of 20‰ for the within 0·2‰ of the average value for that phase in upper-mantle slab-derived fluid, 0·5–1·0 wt % is added to the sources of most peridotites and mid-ocean ridge basalt (MORB); the range for mantle-derived arc magmas; the maximum amount of slab-derived each phase isΖ1·0‰. This result contrasts with previous studies flux in the sources of arc magmas according to our results is 2·5 of whole-rock samples (which are significantly more variable even wt %. after exclusion of samples believed to be altered or fractionated by magmatic differentiation) and demonstrates that most arc-related lavas contain Ζ1–2% of O-enriched crustal oxygen from any