VESIcal Part I: An Open‐Source Thermodynamic Model Engine for Mixed Volatile (H₂O‐CO₂) Solubility in Silicate Melts

Abstract

Understanding the solubility and degassing of volatiles in silicate melts is a crucial component of modeling volcanic systems. As dissolved components, volatiles (primarily 2 H E O and 2 CO E) affect magma viscosity, rheology, and crystal growth. In addition, due to the strong dependence of volatile solubility on pressure, measured volatile concentrations in preserved high-pressure melts (i.e., melt inclusions: liquid magma trapped within crystals at high pressure, then brought to the surface during an eruption) can be used to determine preeruptive magmatic storage pressures, and thus depths. Importantly, volatile exsolution-driven overpressure of a magmatic system is likely the trigger of many explosive volcanic eruptions (Blake, 1984; Stock IACOVINO ET AL.

Explosive activity on Kīlauea’s Lower East Rift Zone fuelled by a volatile-rich, dacitic melt

“…For Cl and F, models A and B produce very similar trajectories, as these models predict similar amounts of solid fractionated. The solubility of pure CO2 and H2O calculated using the MagmaSat solubility model (Ghiorso and Gualda, 2015) implemented in VESIcal (Iacovino et al, 2021) for a best-fit to the observed major element path (see Supporting Fig. S11) is shown with a blue dashed line.…”

“…6. a-c) Example degassing paths for three fissures, with open and closed system degassing paths calculated using MagmaSat (Ghiorso and Gualda, 2015) in VESIcal (Iacovino et al, 2021) for specific melt inclusions overlain. Vectors for different processes are shown in a).…”

“…While the upper limit of melt inclusion volatile contents follow MELTS model B, a number of melt inclusions plot to lower CO2 and H2O concentrations. The cause of this spread is best evaluated using plots of H2O vs. CO2, with degassing paths for specific melt inclusions overlain (calculated using the solubility model MagmaSat implemented in VESIcal; Ghiorso and Gualda, 2015;Iacovino et al, 2021;Fig. 6).…”

“…We use the solubility model MagmaSat (Ghiorso and Gualda, 2015) implemented in the Python3 tool VESIcal (v.0.01;Iacovino et al, 2021) to calculate entrapment pressures from PEC-corrected major element, H2O, and CO2 contents of each melt inclusion, and a temperature estimated using the Helz and Thornber (1987) MgO thermometer. We choose MagmaSat because this model provides the best fit of available models to experimental data with basaltic to dacitic compositions, as a result of its thermodynamic nature and extensive calibration dataset (P. Wieser et al, 2021).…”

The sulfur solubility minimum and maximum in silicate melt

“…This exercise is comparable to when T, fO2, and Y = w m ST are taken as independent variables in a silicate melt + vapour assemblage and the dependent variable Z = P is calculated (e.g., Figure 4c). The effect of dissolved S is currently not included in such calculations, which include only H2O and CO2 (e.g., Newman and Lowenstern 2002;Papale et al 2006;Iacono-Marziano et al 2012;Ghiorso and Gualda 2015;Allison et al 2019;Iacovino et al 2021). Also, the effect fO2 on volatile speciation in the silicate melt and vapour is mostly ignored (but see Scaillet and Pichavant 2004;Wetzel et al 2015).…”