Volatile und Fluide in Subduktionszonen

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.