A long-duration experiment on hydrous species geospeedometer and hydrous melt viscosity

A 2.4-year controlled-cooling-rate experiment was carried out to investigate the dependence of hydrous species concentrations in rhyolitic melt on cooling rate. The experiment allows us to obtain speciation for a cooling rate of 1.68 × 10−6 K/s, extending previous experimental data by two orders of magnitude. Furthermore, a viscosity as high as 1017.2 Pa s is inferred for this hydrous rhyolitic melt with 0.85 wt% total H2O at 671 K. The results are applied to examine whether a geospeedometry model and four viscosity models may be extrapolated to slower cooling rates or lower temperatures. Two of the viscosity models and the geospeedometry model can be extrapolated by two orders of magnitude upwards in terms of viscosity or downwards in terms of cooling rate.