Volatiles and Fluids in Subduction Zones

Volatile fluxes

Magma mass fluxes are converted to K2O mass fluxes, and mass fluxes of the various volatile species are then calculated from analyzed volatile/K2O ratios. We note that H2O and Cl input fluxes derived from geophysical estimates of slab hydration (and assuming seawater composition) are 10-20 times higher than the output at the arc; this clearly needs further studies. Eruptive Cl fluxes into the atmosphere are only a small fraction (5-20%) of the respective fluxes from the mantle; most of these volatiles remain stored in the ash and are potentially recycled into subduction by forearc erosion. Fluorine is fractionated with apatite such that felsic and mafic melt F-contents are similar; inclusion-matrix glass comparison does not reveal any significant F degassing during eruptions. Sulfur has largely exsolved from all felsic magmas prior to eruption; the atmospheric release can only be estimated by comparison with mafic-rock data (collaboration with C2). Such comparisons, however, suggest that some plinian CAVA eruptions discharged >200 Mt SO2 into the stratosphere and should have had a significant climatic effect. Additionally we can first quantify significant bromine and iodine flux into the stratosphere by using SYRFA analyses of melt inclusions and matrix glasses.