Determination of water partition coefficients between upper mantle minerals and melts as a function of pressure, temperature, and CO2 content using a rapid quench cell in multi-anvil experiments

• Applicant: Professor Dr. Tomoo Katsura
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 402695659

It is commonly accepted that the Earth’s mantle contains trace amounts of water varying from 10^(1) to 10^(3) wt. ppm in different regions. However, the question about how water is distributed and cycled in the earth interior remains. Although the behaviors of water in the shallow part of upper mantle are already well constrained by natural sampling, those in the deep asthenosphere are still under debate due to the lack of natural samples. Knowledge about water partitioning between minerals and basaltic melts under asthenosphere conditions is the key for understanding the water behavior in the mantle. In spite of that a series of experimental studies about water partition coefficients between the major upper mantle minerals (olivine and pyroxene) and melts have been reported, all of those data are based on experiments performed at pressures below 4 GPa, corresponding to lithosphere or topmost asthenosphere conditions. The water partitioning in the deep asthenosphere (up to 13 GPa) is unknown since it should be pressure-dependent inferred from the significant pressure dependence of water solubility in olivine. The reason for the limited pressure condition is that basaltic melts cannot be quenched to glass in a typical multi-anvil or piston-cylinder experiment at higher than 4 GPa, and therefore impossible to directly measure the water contents in melts, sequentially, unable to determine the water partition coefficients between minerals and melts.In order to investigate the water partitioning between upper mantle minerals and basaltic melts at high pressures corresponding to those in the deep asthenosphere, in this study, we will design a multi-anvil cell assembly with much faster quenching rate (here called “rapid quench cell”) than typical multi-anvil experiments to quench the basaltic melts to glass at high pressures. By directly measuring the water contents in the glass and coexisted forsterite and enstatite, their water partition coefficients will be obtained as a function of pressure from 1 to 13 GPa, temperature from 1300 to 1900 K. The preliminary experiments demonstrated that melt coexisting with olivine can be quenched from 1870 K at a pressure of 8 GPa, and implied a possibility that the previous study might misinterpreted the pressure and/or temperature dependence of the partition coefficients. Additionally, since CO2 content in melts may significantly affect the water partitioning, the CO2-content dependence of water partition coefficients will also be investigated.

• DFG Programme: Research Grants