Sulfur Partitioning between Solid and Liquid Iron at High Pressure

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Sulfur Partitioning between Solid and Liquid Iron at High PressureIntellectual Merit. The Fe-FeS system, with eutectic melting behavior and preferential S partitioning to liquid iron, has been used as a model system to explain the basic observations of the Earth?s core system, including the liquid outer core and solid inner core configuration and the large density jump at the inner core boundary (ICB). In order to evaluate the role of S during the core formation and evolution of the core, full knowledge of the phase relations in the Fe-FeS system as a function of pressure up to core pressures is needed. It is proposed to determine the melting relations in the Fe-FeS system up to 30 GPa in the multi-anvil apparatus and to extend the measurements up to at least 140 GPa in high-temperature diamond-anvil cell using combination of in-situ observations and ex-situ characterization with FIB/SEM crossbeam. A thermodynamic model will be developed to reproduce the experimental data, and used to extrapolate the experimentally determined phase relations in the Fe-FeS system to ICB conditions. Emphasis is placed on obtaining reliable, high-quality data through innovative experimental design and development of quantitative analysis with high spatial resolution. Although designed for proposed work on the Fe-FeS binary system, the techniques developed here will open a new class of experiments that can be applied to other systems in the future (e.g., to investigate the roles of other light elements, such as Si and O, in the Earth?s core). The thermodynamic model will be used to evaluate the S contribution to the density jump at the ICB by calculating the S partitioning between solid and liquid iron and its effect on the density change. The calculated melting temperature as a function of the S content will serve as a reference point for other multi-component Earth?s core models.Broad Impacts. The proposed research will open new research directions in experimental petrology. It addresses a broad issue in deep Earth study at the interface of petrology, mineral physics, geochemistry, and geophysics. The experimental techniques and procedures developed through this research will be available to the community. The PI will continue to involve and train graduate students and postdoctoral associates in the proposed research and provide them with broad, competitive research experience. Research results will be disseminated primarily through publications in scientific journals, participation at scientific conferences, and occasionally through public news media. The proposed projects will produce high-quality data that are necessary for understanding the interior of the Earth and developing new frontiers for cutting-edge research. The expected results will have broad impact in many different fields including experimental petrology, geochemistry, geophysics, mineral physics, and geodynamics.