High-Pressure Elasticity of Mantle Minerals

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Seismological studies are producing new and detailed images of the three-dimensional structure of the Earth's lithosphere and mantle. These advances offer the possibility to map variations in temperature and chemistry of the planet's deep interior in unprecedented detail. A key component for such studies is knowledge of the elastic properties of mantle minerals, and how these respond to changes in structure, composition, pressure, and temperature. For many mantle minerals, current knowledge of high-pressure elastic properties is fragmentary at best. In this project, the elastic tensors of a number of important mantle minerals will be measured at high pressures using Brillouin scattering in a diamond anvil cell. A primary focus will be on hydrous phases that are relevant to understanding the effect on seismic wavespeeds of metamorphic processes operating in subduction zones. Brillouin scattering will also be used to study the high-pressure elasticity of natural orthopyroxenes with variable iron content. These results are needed to understand how pressure and composition simultaneously affect elastic properties in this major upper mantle constituent. This research program will provide fundamental new knowledge about the physics of materials at high pressures and the structure and composition of planetary interiors.