This code calculates the speciation and volume of a volcanic gas phase erupting in equilibrium with it's parent magma. Models can be run to calculate the gas phase in equilibrium with a melt at a single pressure, or the melt can be decompressed from depth rising to the surface as a closed-system case. Single pressure and decompression can be run for OH, COH, SOH, COHS and COHSN systems, and outputs include:

• Gas phase weight and volume fraction within the system
• Gas phase speciation as mole fraction or weight fraction across H2O, H2, O2, CO2, CO, CH4, SO2, S2, H2S and N2.
• Volatile content of the melt at each pressure
• Melt density
• fO2 of the system
• Total volatile contents as ppm atomic H, O, C, S and N

EVo can be set up using either melt volatile contents, or for a set amount of atomic volatile which is preferable for conducting experiments over a wide range of fO2 values.

Note: In very rare cases, this version of EVo may result in a run failure if low pressure conditions are being used. If these low pressure runs are needed, an alternative EVo version which contains a multipoint precision module (GMPY2) is available upon emailing me at [email protected]. However, for the vast majority of scenarios, this version is preferable, as it runs faster.

This programme requires Python 3 to run.

If you use python virtual environments, or Anaconda, requirements files (requirements.txt and environment.yml for virtualenv and conda, respectively) can be found in the Data file.

Installation/Usage:

To install locally, EVo must be downloaded from GitHub using

git clone [email protected]:pipliggins/EVo.git

into the project directory where you wish to use EVo. EVo must then be locally pip-installed:

cd EVO
python -m pip install -e evo/

From this point, EVo can either be imported into your python scripts as a regular module using install evo

and run using evo.main('chem_file', 'env_file', 'output_options_file')

Or EVo can be run directly from the terminal from inside the evo directory:

cd EVO/evo
python dgs.py input/chem.yaml input/env.yaml --output input/output.yaml

The model should run and produce an output file Outputs/dgs_output_*.csv, and a set of graphs in the Output folder, if a decompression run has been selected.

The different run types, model parameters and input values are all set in the env.yaml file. Run types are toggled on or off using True/False, as are the various requirements. You will be warned in the terminal window if the run type you have chosen, and the input parameters selected, do not match. A summary of which parameters are required for which run type will also be given below.

There are multiple run types which can be selected within EVo. At the highest level, a run can either be (1). single pressure, where equilibration between the gas and the melt only occurs at 1 pressure step set using P_START, or (2) a decompression run, where calculations start at P_START and run through pressure steps (the max and min size of which can be set using DP_MAX and DP_MIN respectively) until P_STOP is reached. These two high-level un options can be toggled between using SINGLE_STEP, where True sets up EVo to do a single pressure run, and False asks for decompression.

Within these two high-level run types, 3 options for selecting starting conditions are available:

• Standard: pick a pressure (P_START), a starting gas weight fraction (WgT) and some combination of either current melt volatile contents, or gas fugacities. EVo will calculate the missing variables and either stop at that point for a single pressure run, or continue on in decompression mode. This is the default option, and will be used if both FIND_SATURATION and ATOMIC_MASS_SET are False.
• Volatile saturation: Chosen by switching FIND_SATURATION to True, given only the melt volatile contents and magma fO2, EVo will calculate the volatile saturation pressure and start a run from there. Any values given in P_START and WgT will be ignored; WgT will be set to 1e-8 at the volatile saturation point.
• Atomic set: Chosen by switching ATOMIC_MASS_SET to True (and FIND_SATURATION to False). Given the melt fO2 and the atomic weight fractions of each of the other volatile species (H, +/- C, S & N, set using ATOMIC_H etc.), Evo will calculate both the appropriate distribution of each element across the different species considered, and the volatile saturation point of that composition. Particularly useful for studies where fO2 is varied but the amount of other elements should be held constant. Again, P_START and WgT will be ignored, WgT will be set to 1e-8 at the volatile saturation point.

Listed below is a table of all the options available in the env.yaml file, with a brief explanation of their function.

The various combinations of initial conditions available for each run type is tabulated below. In all cases unless stated otherwise, the starting fO2 must be set by selecting one from 'FO2_START' (use absolute fO2 value) or 'FO2_BUFFER_START' (use fO2 relative to buffer).

This repository is still in development, and as such warnings about actions which are currently unsupported may not exist.

The following HAVE NOT been implemented yet and so will not work, even if no error is generated and the code appears to run - it's not doing what you think it's doing!

• Gas-only chemistry

This table summarises the headers and meanings in the output CSV file.