Sound Velocities and Elastic Moduli of Minerals Mantle Pressures and Temperatures with Laser Heating

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BassEAR-0003383The focus of this project is laboratory measurements of sound velocities and elastic moduli of oxide minerals under the actual pressure and temperature (P and T) conditions of the Earth's deep interior. This project involves several related activities: 1) The development of an apparatus to measure sound velocities at ultra-high P-T conditions. The apparatus will be based on CO2 laser heating of samples while they are pressurized in a diamond anvil cell. Sound velocities will be measured by Brillouin scattering. Our goal is to measure the velocities of minerals up to T=2500 K and P=50 GPa, which spans the P-T conditions to a depth of ~1300 km. 2) Velocity measurements at high pressure only, at high temperature only, and at simultaneous P-T conditions using a resistively-heated diamond-anvil cell (where the temperature is moderate but accurately known). This will identify the separate effects of P and T on velocities, and help characterize conditions under laser heating. 3) Thermal expansion measurements using synchrotron x-radiation. Initial experiments will involve MgO, a lower mantle constituent. We will assess the precision and accuracy of the measurements, thermal stresses, and deviatoric stresses in the pressure medium. We will then study likely constituents of the Earth's mantle, chosen from: olivine and its high pressure polymorphs beta- and gamma-(Mg,Fe)2SiO4, majorite-garnet solid solutions, pyroxenes, magnesium-silicate perovskites, and hydrous phases. Comparisons of our results with seismologically-determined velocities for the Earth will be used to improve our understanding of the chemical and thermal state of the Earth's interior.