Determination of elastic constants of single-crystal chromian spinel by resonant ultrasound spectroscopy and implications for fluid inclusion geobarometry
We determined elastic constants of a single-crystal chromian spinel at temperatures from −15 to 45 °C through the Rectangular Parallelepiped Resonance method. The sample is a natural chromian spinel, which was separated from a mantle xenolith. Elastic constants at an ambient temperature (T = 24.0 °C) are C 11 = 264.8(1.7) GPa, C 12 = 154.5(1.8) GPa and C 44 = 142.6(0.3) GPa. All the elastic constants decrease linearly with increasing temperature. The temperature derivatives are dC 11/dT = −0.049(2) GPa/°K, dC 12/dT = −0.019(1) GPa/°K and dC 44/dT = −0.020(1) GPa/°K. As an implication of the elastic constants, we applied them to the correction of a fluid inclusion geobarometry, which utilizes residual pressure of fluid inclusion as a depth scale. Before entrainment by a magma, the fluid inclusions must have the identical fluid density in constituent minerals of a xenolith. It has been, however, pointed out that fluid density of fluid inclusions significantly varies with host mineral species. The present study elucidates that elastic constants and thermal expansion coefficients cannot explain the difference in fluid density among mineral species. The density difference would reflect the difference in the degree of plastic deformation in the minerals.
KeywordsChromian spinel Elastic constants Resonance method Fluid inclusion Mantle xenolith Geobarometry
We thank T. Okuchi, D. Yamazaki and T. Yoshino for their help in analyzing our sample. This study was supported from the Institute for Study of the Earth’s Interior, Okayama University for long-term Joint-Use Research.
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