Experimental Studies on the Thermodynamics and Kinetics of Coexisting Olivine, Silicate Melt, and Vapor

Citation

Saper, Lee Michael (2022) Experimental Studies on the Thermodynamics and Kinetics of Coexisting Olivine, Silicate Melt, and Vapor. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/f8qb-3g41. https://resolver.caltech.edu/CaltechTHESIS:08242021-041734202

Abstract

This thesis focuses on experiments run in 1 atm gas-mixing furnaces exploring the thermodynamics and kinetics of coexisting olivine, silicate melt, and vapor. Chapter 1 provides a high-level introduction and summary of the results for each of the following chapters. Chapter 2 and Chapter 3 both involve experiments run on natural olivines containing melt inclusions. Chapter 2 describes a set of homogenization and cooling rate experiments designed to characterize chemical zonation that develops across melt inclusions during cooling. A diffusion model for MgO in the inclusion liquid was calibrated based on these experiments and then used to calculate the syneruptive cooling rates of lavas on Earth and on Mars based on comparison of the model to experimental and natural diffusion profiles in melt inclusions. Chapter 3 presents the first co-determined measurements of S and Fe oxidation state in experimental silicate melts that were equilibrated with the oxygen fugacity of a gas-mixing furnace. The use of melt inclusions as sulfur-bearing experimental vessels is explored, as are implications for interpreting room temperature measurements of the oxidation state of multivalent elements. A set of natural melt inclusions are used as a case study to demonstrate that the temperature-dependence of sulfur-iron electron exchange in basaltic liquids is either weak or leads to the conversion of ferric iron to ferrous iron during cooling. Chapter 4 presents a new parameterization of the composition-dependence of the olivine-liquid Fe-Mg exchange coefficient, Kᴅ^ol/liq_,Fe2+-Mg, based on experiments at low oxygen fugacity where corrections for Fe³⁺ are minor. A quantitative thermodynamic model is fit to the data, showing that the Kᴅ is a function of the Si, Al, Ti, Na+K contents of the liquid as well as olivine composition. Models of Kᴅ^ol/liq_,Fe2+-Mg that do not incorporate liquid compositional variables cannot account for the variability of Kᴅ (~0.22-0.38) observed at low oxygen fugacity in a compilation of high-quality literature experiments. Lastly, in Appendix 1, the published version of Richter, Saper, et al. (2021), GCA 295 is included. For this chapter, I contributed MELTS calculations (Ghiorso and Sack 1995; Smith and Asimow 2005) which were used to model crystallization processes and to set boundary conditions for models elemental and isotopic diffusion of Mg and Li in lunar olivines and martian olivines and augites. The combined elemental and isotopic diffusion profiles were used to discriminate between zoning formed due to crystallization from that due to diffusion.

Thesis Files