Modelling the non-Arrhenian rheology of silicate melts; numerical considerations

A numerical analysis is presented of the nature and magnitude of correlations inherent in fitting a non-Arrhenian model (e.g. Tamann-Vogel-Fulcher function) to published measurements of melt viscosity. The extent to which the quality and distribution of experimental data can affect covariances between model parameters is demonstrated. The extent of non-Arrhenian behaviour of the melt also affects parameter distribution. This effect is explored using albite and diopside melts to represent strong, nearly Arrhenian melts and fragile, non-Arrhenian melts, respectively. The magnitudes and nature of these numerical correlations tend to obscure the effects of composition and it is therefore, essential to understand them prior to assigning compositional dependencies to fit parameters in non-Arrhenian models.