High Temperature Elasticity of Pyroxenes

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Isaak 0073989 Understanding the mineralogy of Earth's upper mantle requires that the elastic properties of all candidate minerals are known. There are, however, virtual gaps in the elasticity database at elevated pressure and temperature for orthopyroxene and especially clinopyroxene. The primary objective of this work is to measure the temperature dependencies of the elastic moduli of single-crystal clinopyroxene using resonant ultrasound spectroscopy (RUS). This objective requires completing the following intermediate goals: 1) developing the RUS theory and computer code appropriate for monoclinic crystal symmetry; 2) making mode identification when comparing calculated and measured spectra at room temperature; 3) obtaining resonance spectra at high temperature for three clinopyroxenes of varying Mg, Fe, Ca compositions; and 4) reducing the clinopyroxene resonance data at elevated temperature to appropriate Cij vs. T. The secondary objective of this work is to measure the high temperature elasticity of two orthopyroxene minerals using the orthorhombic RUS scheme that was developed earlier and applied to olivine elasticity measurements. Successful completion of these objective will provide needed data on pyroxenes at high temperature, new constraints for the mineralogy of Earth's upper mantle, and new applications of RUS for measuring elasticity of low symmetry monoclinic crystals.