Viscosities of hydrous leucogranitic melts: a non-Arrhenian model

Abstract

An equation is presented for the calculation of the shear viscosity of hydrous (0-12.5 wt.% H2O) leucogranitic melts from 102 to 1013 Pa.s. The equation is a multiple nonlinear least-squares regression of a data set of 111 viscosity determinations in the literature. It is based on the Vogel-Fulcher-Tammann (VFT) form and thus accounts for the very important non-Arrhenian temperature dependence of the viscosity. This is possible because of the inclusion of data obtained recently in the high-viscosity region. The equation includes a logarithmic dependence of the three adjustable parameters of the VFT equation on the H2O content of the melt. The root-mean-standard deviation for the 111 data points included is 0.46 log10 units. In comparison with earlier methods based on the Arrhenian approximation of the temperature dependence of viscosity, the present method provides significant improvement in the accurate prediction of viscosity.