Increasingly sophisticated Earth models are being developed that show how processes in Earth's interior affect conditions near the surface. These models, however, must be constrained by accurate and precise laboratory data. The elastic properties of high-pressure mineral phases in Earth's interior, and how these properties are affected by changes in temperature, pressure, and mineral structure and composition, are data of special interest and importance. This project represents a collaboration to investigate the elastic behavior of polycrystalline specimens of several mineral phases in Earth's transition zone.
The collaboration will draw on individual expertise in two areas of research. Gabriel Gwanmesia (Delaware State University) will assume responsibility for synthesizing polycrystalline specimens of high-pressure phases. Donald Isaak (University of California at Los Angeles) will be responsible for measuring the elastic properties of these specimens at room temperature and elevated temperature using the resonant ultrasound spectroscopy (RUS) technique.
Previous attempts to study temperature effects on elasticity of high-pressure phases using special techniques such as RUS have been hindered by the lack of quality single-crystals. These limitations can be avoided through use of polycrystalline specimens synthesized by specialists at facilities developed over many years through NSF funding. A specific goal of this project, therefore, is to investigate how temperature effects of elasticity of polycrystalline specimens vary with Mg/Fe and water concentrations in the olivine/wadsleyite/ringwoodite system and with Ca concentration in the clinopyroxene/majorite/garnet system. When used with data on pressure effects of elasticity and seismic tomography, results from this study will better constrain geochemical and geodynamical models of whole-Earth tectonics and help elucidate the role of the transition zone in dynamic and thermal processes from Earth's core to surface.
This project will also address a primary goal of the Elasticity Grand Challenge of the NSF-sponsored COMPRES consortium which is to reconcile elasticity data reported from a variety of measuring techniques. Specifically, the project represents an attempt to use an existing elasticity measurement technique (RUS) to provide significant new cross checks on reports of elasticity measurements done with other techniques, and to help discriminate, in some cases, between data that are in serious conflict regarding composition and temperature effects on elasticity for high-pressure phases.
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