Water Speciation and Viscosity of Hydrous Melts

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ZhangEAR-0125506Viscosity of hydrous silicate melts plays a critical role in bubble growth, magma fragmentation and volcanic eruptions. This proposal requests funding to develop a new and long-term project for viscosity measurement using a novel technique developed over the years in my lab. It is based on the equivalence between glass transition temperature and the apparent equilibrium temperature of the hydrous species reaction in silicate melt. In order to obtain viscosity using this method, the equilibrium of the hydrous species reaction must also be characterized. Such data are important in their own right in understanding melt structure, water solubility and diffusion in magma, and D/H fractionation between water vapor and melt. In the three years of the grant period, we will concentrate on the following: a) speciation and viscosity at high pressures for hydrous rhyolitic melt up to 8 GPa; b) speciation equilibrium in hydrous dacitic melts and the viscosity of such melts to high dissolved H2O content (up to 8 wt% dissolved H2O); and c) development of more accurate viscosity models for hydrous rhyolitic and dacitic melts. The new viscosity model will be applied to re-evaluate previous results of bubble growth and magma fragmentation.