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Susannah Dorfman Colloquium Abstract (Mar 28, 2018)

The Mineral Physics Test Kitchen: Recipes for Earth's Mantle and Core

The interiors of Earth and other planets were "cooked" by processes of accretion and differentiation and can be "tasted" by geochemical sampling at the surface and remote geophysical observations of physical properties at depth. Mineral physics experiments and simulations seek to reverse-engineer the recipes that generate the features we detect in the deep Earth today. Because Earth and other planets are almost entirely composed of materials at high pressures and temperatures, the key to translating geophysical observations to structure and composition is the dependence of mineral stability and physical properties such as density, elasticity, and transport properties on composition and thermodynamic conditions. I will discuss recent observations of chemical reactions and properties of minerals relevant to Earth's mantle and core, and implications of these experiments for the compositions of layers and regions in the deep Earth.

Technical Talk: Control and Measurement of Stress in Experiments Up to Mbar Pressures

The physical properties of materials at extreme pressures are important to the structures and compositions of planetary interiors, discovery of potentially useful new compounds, and testing theoretical predictions of effects of compression on electronic structure and bonding. In order to measure these properties in the laboratory, the only tool that can generate static pressures in the Mbar regime relevant to Earth’s deep mantle and core is the diamond anvil cell (DAC). However, stress conditions in the DAC are both difficult to control and to measure: uniaxial loading generates deviatoric stresses, and stress conditions must be determined using calibrated pressure internal standards. The resulting uncertainty in pressure, up to ~10% at Mbar conditions, substantially limits constraints on composition of the mantle, geothermal temperature gradients, and interpretation of seismic discontinuities. In this talk, I will highlight recent results on improving accuracy in pressure and outlook for controlling deviatoric stresses in DAC experiments, including both minimizing deviatoric stresses through the use of quasi-hydrostatic media, and tuning deviatoric stress via thin film technology. Applications of these experiments to strength, phase transitions, and properties of Earth materials will also be presented.