Oxygen Isotope Geochemistry of Oceanic-Arc Lavas 论文

摘要

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 18 O observed in this study) constrains the amounts and chemical phenocrysts and glass. Eighty percent of our samples have 18 O 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 18 O value of 20 for the within 02 of the average value for that phase in upper-mantle slab-derived fluid, 05-10 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 is 10. This result contrasts with previous studies flux in the sources of arc magmas according to our results is 25 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 1-2% of 18 O-enriched crustal oxygen from any KEY WORDS: oxygen isotopes; arc volcanism source (i.e. assimilation or subducted contributions). Elevations in 18 O that do occur in these basic, arc-derived magmas relative to values most common for mantle-derived lavas are associated both with 'enriched' radiogenic isotope signatures and, even more strongly,