Statistics – Computation
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.v23g2217r&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #V23G-2217
Statistics
Computation
8400 Volcanology, 8429 Lava Rheology And Morphology
Scientific paper
We recently published a model for predicting the non-Arrhenian Newtonian viscosity of silicate melts as a function of temperature (T) and melt composition (X), including the volatile constituents H2O and F (Giordano et al. 2008). The non-Arrhenian T-dependence is accounted for by the VFT equation [log η = A + B/(T(K) -C)] and the model is calibrated on > 1750 measurements of melt viscosity. All compositional dependence is accommodated by 17 model coefficients embedded in the parameters B and 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) making for a total of 18 model coefficients. The effects of pressure on the silicate melt viscosity are not accounted for in this model, however, the model has the following attributes: a) it covers over fifteen log units of viscosity [10-1 to 1014 Pa s], b) it spans most of the compositional range found in naturally-occurring volcanic rocks, c) it is computationally continuous across the entire compositional and temperature spectrum of the database, and d) it is capable of accommodating both strong (near-Arrhenian T-dependence) and fragile (non-Arrhenian T-dependence) behaviour of silicate melts. Lastly, the model for melt viscosity can be used to predict other transport properties including glass transition temperatures (Tg) and melt fragility (m). Volcanic regimes feature constantly changing T-X melt conditions and, in many instances, these small changes generate strong non- linear variations in melt viscosity. The GRD model allows for accurate, continuous prediction of melt properties as a function of temperature and melt composition and, thus, is ideal for modelling transport properties in dynamic natural systems. Below we demonstrate the utility of this model with three volcanological applications: (A) We track variations in viscosity along liquid lines of descent predicted by MELTS (Ghiorso et al. 1995) and discuss the overall implications for differentiation processes, (B) We explore the rheological (η, m, and Tg) consequences of mixing between hot, dry mafic melts and cooler, hydrous, felsic melts, whilst also accounting for issues of thermal equilibration and volatile saturation, and (C) We couple the GRD model to that of Caricchi et al.'s (2007) model for viscosity of crystal-rich melts and explore changes in magma rheology attending the 2007 eruption of Stromboli. These eruptions featured a variety of eruption styles and produced nearly isochemical eruptive products that varied in crystallinity and vesicularity (e.g., from dark holocrystalline scoria to aphyric pumice). Caricchi, L., Burlini, L., Ulmer, P., Gerya, T., Vassalli, M., Papale, P. (2007) Earth and Planetary Science Letters 264 : 402-419. Giordano, D. Russell, J.K. and Dingwell, D.B. (2008) Earth and Planetary Science Letters 271: 123-134. Ghiorso, M.S., and Sack, R.O. (1995) Contributions to Mineralogy and Petrology 119: 197-212.
Dingwell Donald B.
Giordano Daniele
Russell Ken
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