Thermodynamic equilibrium in multicomponent gas-melt systems is characterized by complex non-linear distributions of species concentrations, especially when different oxidation states are possible. Such distributions affect all the physico-chemical properties and largely drive the dynamics of magmatic systems. In order to simulate the saturation surface of CO2-H2O-SO2-H2S-silicate melt systems, we have combined different modeling approaches based on classical Gibbs thermodynamics and Toop-Samis polymeric treatment of silicate melts. The model is developed according to more than 2,500 experimental data from the literature on saturation contents of H2O, CO2, S, and iron oxidation state, in silicate melts with compositions from two-component synthetic to natural, and in wide P-T ranges. Model applications to natural systems reveal that simple trends characterizing one-component gas phases can be deeply modified due to the multicomponent nature of the equilibrium. The theoretical S-solubility minimum commonly observed in laboratory experiments at fixed fSO2 can be totally hidden in the multicomponent system, a feature which has puzzled the interpretation of natural samples. Maxima and minima in the concentration of volatile components in the melt and gas phases can characterize depressurization paths, depending on the specific redox state of the system. Critical experiments aimed at revealing such complex patterns can be defined with the aid of multicomponent modeling. In this way, an efficient feedback between experimental and theoretical investigations provides the means to understand and reproduce the complex behaviors of volatiles in natural magmas.
MODELING THE COMPLEX SATURATION SURFACE OF CO2-H2O-SO2-H2S-SILICATE MELT SYSTEMS: TWO-WAY LINK BETWEEN EXPERIMENTS AND THEORY
MORETTI, Roberto;
2004
Abstract
Thermodynamic equilibrium in multicomponent gas-melt systems is characterized by complex non-linear distributions of species concentrations, especially when different oxidation states are possible. Such distributions affect all the physico-chemical properties and largely drive the dynamics of magmatic systems. In order to simulate the saturation surface of CO2-H2O-SO2-H2S-silicate melt systems, we have combined different modeling approaches based on classical Gibbs thermodynamics and Toop-Samis polymeric treatment of silicate melts. The model is developed according to more than 2,500 experimental data from the literature on saturation contents of H2O, CO2, S, and iron oxidation state, in silicate melts with compositions from two-component synthetic to natural, and in wide P-T ranges. Model applications to natural systems reveal that simple trends characterizing one-component gas phases can be deeply modified due to the multicomponent nature of the equilibrium. The theoretical S-solubility minimum commonly observed in laboratory experiments at fixed fSO2 can be totally hidden in the multicomponent system, a feature which has puzzled the interpretation of natural samples. Maxima and minima in the concentration of volatile components in the melt and gas phases can characterize depressurization paths, depending on the specific redox state of the system. Critical experiments aimed at revealing such complex patterns can be defined with the aid of multicomponent modeling. In this way, an efficient feedback between experimental and theoretical investigations provides the means to understand and reproduce the complex behaviors of volatiles in natural magmas.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
