Redox control of sulfur degassing in silicic magmas

摘要: Explosive eruptions involve mainly silicic magmas in which sulfur solubility and diffusivity are low. This inhibits exsolution during magma uprise as compared to more mafic such basalts. Silicic can nevertheless liberate large quantities of shown by the monitoring SO 2 recent explosive arc settings, invariably have displayed an excess relative that calculated from melt degassing. If this is stored a fluid phase, it implies strong preference for over under oxidized conditions, with fluid/melt partition coefficients varying between 50 2612, depending on composition. Experimentally determined dacite bulk composition confirm trend show volcanic displaying gaseous sulfur, were probably fluid-saturated at depth. The experiments reduced magmas, those coexisting only pyrrhotite, coefficient decreases dramatically values around 1, because pyrrhotite locks up nearly all magma. Reevaluation yields some major historical light these results shows presence 1-5 wt % may indeed account differences observed petrologic estimate yield constrained ice core data. very magnitude but involving cool Toba or Bishop events, release minor amounts could consequently negligible long-term (years centuries) atmospherical effects. redox control diminishes becomes less temperature increases, both factors favor efficient degassing owing increased silicate melts conditions.