High temperature resonance ultrasound spectroscopy studies of single crystal minerals

Elasticity of mineral phases at temperature and pressure conditions relevant to earth interior is essential for constraining the composition and the dynamics of the deep Earth. To constrain the temperature dependence of elasticity of hydrous minerals relevant to the earth’s subduction zones, we used high temperature Resonance Ultrasound Spectroscopy (RUS). We explored the temperature dependence of the full elastic moduli tensor, speed of sound, attenuation, and anisotropy of naturally occurring single crystal topaz (Al2SiO4F1.42(OH)0.58) [1] with a rectangular parallelepiped geometry. The RUS spectra are influenced by the geometry, density, and the full elastic moduli tensor [2]. We determined the crystal symmetry and crystallographic alignment of the crystals using X-ray diffraction. The geometry and density are well constrained from previous results on thermal expansion. The elasticity results on topaz are in good agreement with previous studies. We combine the high temperature elasticity of natural topaz with the results from the first principles on end member hydrous topaz and shed insight into how pressure temperature and composition, i.e., the fluorine and hydrogen content could influence elasticity of minerals in the Earth’s interior, in particular in subduction zone settings. [Work supported by U.S. NSF Award Nos. EAR-1634422 and EAR-1753125.] References: [1] Tennakoon et al., Sci. Rep., 8, 1372 (2018). [2] A. Migliori and J. D. Maynard, Rev. Sci. Instrum. 76, 121301 (2005).