Equations of State, Elasticity, and Rheology of Earth Materials at High Pressures and Temperatures

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Mao 0001173 A series of high-pressure experimental studies of the elasticity and equations of state of mantle and core materials needed to address major problems concerning the structure, dynamics, and evolution of the Earth's deep interior is proposed. The project takes advantage of numerous recent developments in diamond-anvil cell techniques, including cell design, high-temperature methods, synchrotron single-crystal and polycrystalline x-ray diffraction, synchrotron x-ray spectroscopy, and Brillouin scattering spectroscopy. The following experiments will be performed. (1) P-V-T equations of state of iron, iron alloys, and iron compounds will be studied to core pressures using polycrystalline x-ray diffraction with monochromatic x-radiation, hydrostatic pressure media, and an improved pressure calibration. (2) The shear modulus and elasticity tensor of core materials (initially e-Fe) will be determined up to 50 GPa and temperatures up to 1500 K using radial x-ray diffraction methods with monochromatic synchrotron radiation. (3) The technique will be further applied to study the rheological properties of these materials (including Fe, Fe-Ni, FeO, and FeS2) with accurate measurements of the intensities of reflections as a function of temperature and time. (4) The phonon densities of states of iron-bearing materials will be determined to core pressures using nuclear resonant inelastic x-ray scattering, as recently done for Fe to 153 GPa. Combined with theoretical calculations, the technique will be extended in later stages of the project to simultaneous high pressures and temperatures. (5) The P-V-T equations of state of principal deep mantle oxide and silicate phases will be determined using polycrystalline x-ray diffraction in hydrostatic media over the entire geotherm of the lower mantle. (6) This will be complemented by single-crystal x-ray diffraction of select phases for complete structure refinements to 100 GPa using a new combined energy dispersive/angle dispersive technique. (7) Brillouin scattering measurements of deep mantle phases [initially stishovite and (Mg,Fe)SiO3 perovskite] will be carried out to pressures above 50 GPa, and in the later stages of the project their temperature derivatives will be determined with resistive heating techniques. These results will provide an essential baseline for interpreting seismic velocity distributions and anisotropy of the lower mantle. (8) Finally, the calibration of pressure will be extended to high pressures and temperatures (800 K and 50 GPa) using the integrated Brillouin/x-ray diffraction approach recently applied to MgO at room temperature.