ThermotopesC_DEW, a Python GUI application to automate thermodynamic computations for fluid-rock interactions

Fluid-rock interactions are one of the most important processes on Earth and play an important role in many metamorphic systems, especially during fluid migration. Research during the past three decades have provided many new software and thermodynamic databases for both mineral and fluids. Yet, in the metamorphic community, the fluid phase is usually modelled using molecular fluids such as pure H₂O or  H₂O-CO₂ mixtures. This may be a limiting factor since aqueous fluids containing dissolved ionic species are involved leading to metasomatic reactions. The Deep Earth Water (DEW) model allows modeling complex fluid-rock interactions involving ionic species at pressure and temperature conditions up to 6 GPa and 1200 °C ¹. However, its use through software packages such as EQ3/6 ² may be time-consuming.

 

ThermotopesC_DEW is a Python application with a user-friendly graphical user interface (GUI) that allows automation of thermodynamic computations with the EQ3/6-DEW software package. The application uses the capability of the EQ3 and EQ6 to compute the chemical speciation of a fluid in equilibrium with a user-defined mineral assemblage, and the reaction of this fluid with a new rock, respectively. ThermotopesC_DEW allows the user to compute batches of EQ6 calculations with different fluid-rock ratios set by the user, or to batch process EQ6 computations with different proportions for 3 minerals within a ternary diagram, for a given fluid-rock ratio. The application then allows the user to create customized plots of the computation results in 2D and 3D, for each option and for each variable.

 

In this contribution, we explore the capabilities of ThermotopesC_DEW to investigate fluid-peridotite interactions at subduction zone pressure and temperature conditions, for over 30 000 individual EQ6 runs. Different fluid compositions, reacting assemblages, and fluid-rock ratios were considered.

 

Over the wide range of conditions of these runs, modes of hydrous phases, relative proportions of the different phases, pH and log f_O2 vary widely, highlighting the complexity of fluid-rock interaction processes in the subduction zone and warrant the use of simple fluid formulation to model such processes. We believe that user-friendly applications such as the one presented here will allow more petrologists to introduce fluid speciation into their metamorphic projects.

 

1. Sverjensky, D. A., Harrison, B. & Azzolini, D. Water in the deep Earth: The dielectric constant and the solubilities of quartz and corundum to 60kb and 1200°C. Geochim Cosmochim Ac 129, 125–145 (2014).

2. Wolery, T. J. EQ3/6, a software package for geochemical modeling of aqueous systems: Package overview and installation guide (Version 7.0). doi:10.2172/138894.

This work is part of project that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 864045).