Chemistry of the Earth's Deep Mantle and Core

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AbstractEAR-0126009Hemley and MaoCarnegie Institution of Washington, Geophysical LaboratoryThe goal of this project is to determine the chemical properties of lower mantle and core materials at relevant deep Earth conditions in order to obtain direct experimental constraints on the chemical composition, formation, and evolution of the planet's interior. The research takes advantage of numerous new developments in situ high-pressure techniques, including synchrotron x-ray diffraction and spectroscopy, infrared and optical techniques, neutron diffraction, and new high diamond-cell methods. The project will start by improving both pressure and temperature calibration at deep mantle and core conditions. With this improved accuracy, in-situ x-ray diffraction studies will be performed to resolve current questions about the post-spinel phase boundary as a function of pressure-temperature and composition (P-T-X). The defect structure and concentration of iron and aluminum-bearing magnesium silicate perovskites will be characterized by detailed compositional studies and by direct site-occupancy measurements with neutron powder diffraction. A series of complementary synchrotron x-ray spectroscopic techniques used to characterize the spin and oxidation state of iron in these phases throughout the P-T range of the lower mantle. The question of additional, very high P-T phases of Fe and Fe-Ni alloys will be investigated using diamond gasket double-sided laser heating/synchrotron x-ray diffraction techniques. High-resolution x-ray emission, nuclear resonant forward scattering, and optical Raman spectroscopies will be used to identify possible pressure-induced changes in electronic, magnetic, and vibrational properties of iron alloys to core pressures. High P-T x-ray diffraction measurements in the lower pressure range will also allow investigations of structural changes in the liquid state of Fe. The problem of the light element in the core will be examined in a few pseudo-binary systems with Fe-Ni, starting with oxygen and then moving to sulfur and hydrogen using the same battery of diffraction and spectroscopic techniques.