Elasticity of Selected Deep Earth Phases Under Simultaneous High P-T Conditions Using Nuclear Resonant Inelastic X-ray Scattering

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Recently observed seismic complexities require new and more accurate measurements of candidate lower mantle materials. The effort to understand the origin of these seismic complexities is an active area of modern cross-disciplinary research. Typically, models of the deep Earth have been made by extrapolating mineral properties to relevant pressure-temperature (P-T) conditions and comparing them with seismological determined compressional- and shear-wave velocities and density. However, the behavior of the shear properties of deep mantle materials is widely unknown. As a result, many extrapolations use either low P-T data, analogue materials, and/or infer that the chemically complex minerals behave the same as their end-member compositions. Even though ferropericlase (Mg,Fe)O and aluminous (Mg,Fe)SiO3 perovskite together make up more than 75% by volume of Earth's lower mantle, they are mostly optically opaque, making them difficult or impossible to study using optical scattering methods. In an effort to overcome these challenges, the use of established synchrotron methods of micro x-ray diffraction (Xrd) and nuclear resonant inelastic x-ray scattering (Nrixs) is engaged with diamond anvil cell and laser heating technology to obtain equations of state for chemically complex deep Earth materials under appropriate, yet uncharted, high-P-T conditions. With knowledge of the density determined from Xrd for these materials, the aggregate compressional and shear wave velocities, as well as the adiabatic bulk and shear moduli, is determined from the measured partial phonon density of states determined from Nrixs. These data permit the evaluation of the effects of iron and aluminum on the sound velocities and elasticity of deep Earth materials in a previously unexplored P-T sector. The results are expected to provide constraints on the correlation between seismological lateral variations and chemical composition.