Article ID Journal Published Year Pages File Type
4679597 Earth and Planetary Science Letters 2008 12 Pages PDF
Abstract

The viscosity of silicate melts controls magma transport dynamics, eruption style and rates of physicochemical processes (e.g., degassing, crystallization) in natural magmas. Thus a comprehensive viscosity model for magmatic liquids has long been a goal of earth scientists. Here we present a model that predicts the non-Arrhenian Newtonian viscosity of silicate melts as a function of T and melt composition, including the rheologically important volatile constituents H2O and F. Our model is based on > 1770 measurements of viscosity on multicomponent anhydrous and volatile-rich silicate melts. The non-Arrhenian T-dependence of viscosity is accounted for by the VFT equation [log η = A + B / (T(K) − C)]. The optimization assumes a common, high-T limit (A) for silicate melt viscosity and returns a value for this limit of − 4.55 (+ 0.2) (e.g., log η ~ 10− 4.6 Pa s). All compositional dependence is ascribed to the parameters B and C and is accounted for by an additional 17 model coefficients. Our model is continuous in composition- and temperature-space and predicts the viscosity of natural volatile-bearing silicate melts (SiO2, Al2O3, TiO2, FeOtot, CaO, MgO, MnO, Na2O, K2O, P2O5, H2O, F2O− 1) over fifteen log units of viscosity (10− 1– 1014 Pa s). The model for viscosity can also predict other transport properties including glass transition temperatures (Tg) and melt fragility (m). We show strong systematic decreases in Tg and m with increasing volatile content. This pattern has implications for predicting styles of volcanic eruption and understanding silicate melt structure. Our model transforms a quarter-century of experimental study of melt viscosities, into a parameterisation having a predictive capacity that makes it relevant to diverse fields of research including: volcanology, geophysics, petrology and material sciences.

Related Topics
Physical Sciences and Engineering Earth and Planetary Sciences Earth and Planetary Sciences (General)
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