The open-source software package pyUserCalc provides a process-based, forward model for calculating the geochemical compositions of mantle-derived partial melts. The package, first developed by Elkins and Spiegelman (2021), determines the degree of chemical and isotopic equilibration achieved during one-dimensional decompression melting and dynamic magma transport via two-phase flow, using Darcy’s Law for differential fluid transport rates, and the Damköhler (Da) number of the system, which is the ratio of the chemical reaction rate relative to the physical decompression rate. Model inputs include variable melt fractions, permeability, and rock/liquid partition coefficients with depth (which rely on prior determination of melting rates, mineral modes, and preferred trace element partitioning values), the solid mantle upwelling rate, the maximum liquid-filled porosity fraction, the Da number, and initial concentrations. The model then solves for all isotopic concentrations in the liquid as an initial value problem. Additional tools compute trace element concentrations and the effects of two-dimensional integration over a triangular decompressing melt regime for various liquid transport rates.

Ongoing effort is focused on new code to calculate the outcomes of partial melting under increasingly sophisticated conditions, to build more realistic and useful tools for further applied research in geochemical modeling. In addition to producing an updated and streamlined overall package, we have recently developed a preliminary method that incorporates rate-dependent diffusion effects for individual elements over the melting regime. New python scripts are in progress that reproduce the simultaneous two-lithology melting calculations of Melt-PX (Lambart et al., 2016), as well as a workflow that computes accompanying mineral modes for compositions and conditions of interest with pMELTS (Ghiorso et al., 2002). We are also developing code to calculate outcomes for two-porosity regimes, which simulate rapid extraction of liquid from high-porosity channelized zones embedded within a low-porosity decompressing matrix. As these tools are developed, debugged, and tested, they will be shared to the pyUserCalc open repository at https://gitlab.com/ENKI-portal/pyUsercalc, and shared with model tutorial content at the NAGT sponsored program, https://magmagenesis.org.

References

Elkins, L.J. and Spiegelman, M., 2021, Earth and Space Science, v.8, e2020EA001619, https://doi.org/10.1029/2020EA001619.

Ghiorso, M.S., Hirschmann, M.M., Reiners, P.W., & Kress III, V.C., 2002, Geochemistry, Geophysics, Geosystems, v.3(5), 1-35.

Lambart, S., Baker, M.B., & Stolper, E.M., 2016, JGR: Solid Earth, v.121(8), 5708-5735.