Subduction Influence on Oxygen Fugacity and Trace and Volatile Elements in Basalts Across the Cascade Volcanic Arc

Fluids or melts derived from a subducting plate are often cited as a mechanism for the oxidation of arc magmas.What remains unclear is the link between the fluid, oxygen fugacity, and other major and trace components, as well as the spatial distribution of the impact of those fluids. To test the potential effects of addition of a subduction-derived fluid or melt to the sub-arc mantle, olivine-hosted melt inclusions from primitive basaltic lavas sampled from across the central Oregon Cascades (438^458N) have been analyzed for major, trace and volatile elements and fO2. Oxygen fugacity was determined in melt inclusions from sulfur speciation determined by electron microprobe and from olivine^chromite oxygen geobarometry. The overall range in fO2 based on sulfur speciation measurements is from 5 ̂ 025 log units toþ19 log units (DFMQ, where FMQ is fayalite^magnetite^quartz buffer). Oxygen fugacity is positively cor-related with fluid-mobile trace element and light rare earth element