VESIcal Part II: A critical approach to volatile solubility modelling using an open-source Python3 engine

Abstract

Accurate models of H2O and CO2 solubility in silicate melts are vital for understanding volcanic plumbing systems. These models are used to estimate the depths of magma storage regions from melt inclusion volatile contents, investigate the role of volatile exsolution as a driver of volcanic eruptions, and track the degassing paths followed by magma ascending to the surface. However, despite the large increase in the number of experimental constraints over the last two decades, many recent studies still utilize the earlier generation of models, which were calibrated on experimental datasets with restricted compositional ranges. This may be because many of the available tools for more recent models require large numbers of input parameters to be hand-typed (e.g., temperature, concentrations of H2O, CO2, and 8--14 oxides), making them difficult to implement on large datasets. Here, we use a new open-source Python3 tool, VESIcal, to critically evaluate the behaviours and sensitivities of different solubility models for a range of melt compositions. Using literature datasets of andesitic-dacitic experimental products and melt inclusions as case studies, we illustrate the importance of evaluating the calibration dataset of each model. Finally, we highlight the limitations of particular data presentation methods such as isobar diagrams, and provide suggestions for alternatives, and best practices regarding the presentation and archiving of data. This review will aid the selection of the most applicable solubility model for different melt compositions, and identifies areas where additional experimental constraints are required

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

“…Even in cases where solubility values (e.g., saturation pressures) are not calculated, the error highlighted above plagues any isobar diagram over which multiple melt compositions are plotted (e.g., Figure 11 0.8 from reservoir to surface, suggesting a scenario approaching closed-system degassing (i.e., melt volatile concentrations are buffered by the co-existing fluid composition). This is discussed in more detail in the companion paper (Wieser et al, 2021).…”

“…We provide these calibrations along with several Jupyter Notebooks in the Supporting Information S1 (Text S3 and S4 and Jupyter Notebooks S1-S7), which allow users to plot their data amongst the calibrations of the different models to assess their suitability for less objective measures (also see Section 3.4). Detailed descriptions of the seven solubility models implemented in VESIcal, including information about their calibration range in terms of melt composition, pressure, and temperature, are given in this manuscript's companion paper Wieser et al (2021).…”

“…While not all solubility models incorporate significant bulk compositional parameters, it has been clearly shown that the composition of a melt plays a strong role in determining the solubility of 2 H E O and 2 CO E in magmas (Moore, 2008;Papale et al, 2006;Ghiorso & Gualda, 2015;Wieser et al, 2021). Thus, compositional variance must be accounted for in any study examining solubility in multiple samples.…”

“…While we certainly advocate for the continued refinement of solubility models, including the completion of new experiments in poorly studied yet critical compositional spaces such as andesites (Wieser et al, 2021), a perhaps more crucial step at this juncture is in the development of a tool that can apply modern computational solutions to making our current knowledge base of volatile solubility in magmas accessible and enduring.…”

“…A detailed history of volatile solubility modeling and the implications of VESIcal are explored in detail in the companion manuscript to this work, Wieser et al (2021).…”