In-Situ Study of Pressure Effect on Cation Order-Disorder Phenomenon in Mantle Minerals

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Chen and WeidnerEAR-9909413Order-disorder phenomena play a key role in the energetics and crystal chemistry of minerals. Variation of the cation order-disorder distribution in minerals results in changes in their free energy, and, therefore phase stability and physical properties, such as strength, elastic moduli, and thermal conductivity. The goal of this proposal is to study the cation order-disorder phenomena in mantle minerals at high pressure and temperature in order to understand accurately the physical properties of the minerals in the Earth interior. The project will take advantage of new developments of the state-of-art in-situ x-ray diffraction system with a multi-anvil large volume press and monochromatic synchrotron radiation at the X17B beamline of the NSLS. Crystal structure refinement based on the in-situ diffraction data is the major analytical tool. The minerals to be studied include olivine, wadsleyite, orthopyroxene and spinel. In this proposal we focus on the order-disorder distribution between Fe (or Ni) and Mg (or Al) cations in these minerals. The proposed studies will significantly improve the detail in information of the physical properties of the minerals at the mantle conditions and increase the accuracy of critical physical parameters for mantle modeling.