An Algorithm for Thermodynamic Parameter Optimization: Application to the Martian Mantle. (11th May 2021)

• Record Type: Journal Article
• Authors: Khan, D.; Liebske, C.; Connolly, J. A. D.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 22:Number 5(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-05-11
• Subjects: Mars -- optimization -- thermodynamics; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2020GC009399
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: The compilation of thermodynamic models for geophysical applications is such a tedious and complex process that it is generally impractical for researchers to refit parameters in existing models in light of new constraints. To mitigate this difficulty, we develop a Bayesian algorithm that permits the modification of a thermodynamic model to account for additional observational constraints. This algorithm can be applied to any thermodynamic dataset and can utilize a wide variety of experimental constraints. To demonstrate the applicability of the algorithm it is used to revise the Stixrude and Lithgow‐Bertelloni (2011, https://doi.org/10.1111/j.1365‐246x.2010.04890.x ), whole‐mantle terrestrial thermodynamic model, using phase equilibrium constraints provided by Bertka and Fei (1997, https://doi.org/10.1029/96jb03270 ), for the more iron‐rich compositions that are thought to be relevant to the Martian mantle. The revised thermodynamic model provides a more reliable prediction of phase equilibria in the Martian mantle. Seismic properties are calculated in an internally self‐consistent manner along hot and cold areotherms to constrain the upper and lower bounds of these properties for different bulk silicate Mars compositional models. Plain Language Summary: Thermodynamic models capable of predicting geophysical properties, such as seismic wave velocities and density are useful in determining the structure of planetary interiors. We have developed an algorithm capable of refining parameters in thermodynamic models in light of new experimentally determined constraints. This algorithm is applied to the widely used Stixrude and Lithgow‐Bertelloni (2011, https://doi.org/10.1111/j.1365‐246x.2010.04890.x ), thermodynamic model with data for a Mars‐like composition and pressure‐temperature conditions. Our results show that small changes to the thermodynamic dataset can result in a marked improvement in the agreement between the predicted and experimental results, providing estimates for geophysical properties that are consistent with experimental data. This will enable us to more reliably constrain the composition of the Martian mantle from the seismic data provided by NASA's InSight mission. Key Points: Bayesian algorithm capable of optimizing existing thermodynamic models to account for new observational constraints Experimentally determined phase equilibria are reproduced with minor refinements to existing thermodynamic model Revised bounds for seismic velocity and density profiles in the Martian mantle