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Hydrogen Effect on the Sound Velocities of Upper Mantle Omphacite

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Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA
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Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131, USA
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Department of Geological Sciences, University of Colorado, Boulder, CO 80309, USA
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GeoSoiEnviroCARS, University of Chicago, Argonne National Laboratory, Argonne, IL 60439, USA
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Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI 96822 USA
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Department of Geosciences, Princeton University, Princeton, NJ 08544, USA
*
Authors to whom correspondence should be addressed.
Minerals 2019, 9(11), 690; https://doi.org/10.3390/min9110690
Received: 7 October 2019 / Revised: 5 November 2019 / Accepted: 6 November 2019 / Published: 8 November 2019
(This article belongs to the Special Issue Mineral Physics—In Memory of Orson Anderson)
Clinopyroxene (Cpx) is commonly believed to be the best structural water (hydrogen) carrier among all major upper mantle nominally anhydrous minerals (NAMs). In this study, we have measured the single-crystal elastic properties of a Cpx, a natural omphacite with ~710 ppm water at ambient pressure (P) and temperature (T) conditions. Utilizing the single-crystal X-ray diffraction (XRD) and electron microprobe data, the unit cell parameters and density were determined as a = 9.603(9) Å, b = 8.774(3) Å, c = 5.250(2) Å, β = 106.76(5)o, V = 255.1(4) Å3, and ρ = 3.340(6) g/cm3. We performed Brillouin spectroscopy experiments on four single crystals along a total of 52 different crystallographic directions. The best-fit single-crystal elastic moduli (Cijs), bulk and shear moduli were determined as: C11 = 245(1) GPa, C22 = 210(2) GPa, C33 = 249.6(9) GPa, C44 = 75.7(9) GPa, C55 = 71.2(5) GPa, C66 = 76(1) GPa, C12 = 85(2) GPa, C13 = 70(1) GPa, C23 = 66(2) GPa, C15 = 8.0(6) GPa, C25 = 6(1) GPa, C35 = 34.7(6) GPa, and C46 = 8.7(7) GPa, KS0 = 125(3) GPa, and G0 = 75(2) GPa, respectively. Compared with the anticipated elastic properties of an anhydrous omphacite with the same chemical composition, our results indicate that the incorporation of ~710 ppm structural water has no resolvable effect on the aggregate elastic properties of omphacite, although small differences (up to ~9 GPa) were observed in C13, C25, C44, and C66. View Full-Text
Keywords: elasticity; omphacite; clinopyroxene; eclogite; structural water; nominally hydrous minerals; seismic velocities elasticity; omphacite; clinopyroxene; eclogite; structural water; nominally hydrous minerals; seismic velocities
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Mans, W.; Zhang, J.S.; Hao, M.; Smyth, J.R.; Zhang, D.; Finkelstein, G.J.; Dera, P. Hydrogen Effect on the Sound Velocities of Upper Mantle Omphacite. Minerals 2019, 9, 690.

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