Experimental Tests of the Effects of Order-Disorder on Stability and Elasticity of Minerals at High Pressures and Temperatures

Suny At Stony Brook, Stony Brook NY

Investigators

Abstract

Parise and Chen EAR-0125094 This proposal plans a focused study on three systems of direct relevance to the Earth's lower crust and mantle and for which considerable data exist: dolomite, selected oxide spinels such as magnesioferrite (MgFe2O4) and qandilite (Mg2TiO4), and orthopyroxene (opx, En50Fs50). The goal is to determine the state of order in these materials as a function of both temperature and pressure using Rietveld refinement, confirm the breakdown curve proposed by Luth from his quench experiments on dolomite, and determine the relationship between order (X) and P- and S-wave velocities at high PT. It is recognized that quench experiments followed by single crystal structure determination can be useful, and that measurements at high pressure or high temperature alone are valuable. However, an opportunity exists now to couple crystallographic measurements with the estimation of ultrasonic travel times at simultaneously maintained high pressure and temperature for the first time, and thereby more closely approach measurements directly relevant to the Earth's lower crust and upper-mantle. These simultaneous measurements are ideally suited to the problem of order-disorder and its effects on stability and elasticity. X-Ray diffraction provides a record of X and of the thermal EoS while the new set up for ultrasonic work provides simultaneous determinations of P and S-wave velocities. The latter measurements are crucial since there is no longer a need to change samples to perform separate measurements for P- and S-waves; several groups report that while in some materials (orthopyroxene for example) P-waves appear unaffected by cation substitution, the S-wave velocities do vary. Some technical development will accompany the project and it is hoped this will find application in the research of other groups interested in simultaneous real-time determination of structure and elasticity, and in correlating atomic structure with physical properties.