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Compressional and shear wave velocities of topaz have been measured by ultrasonic interferometry in a multi-anvil apparatus up to 13 GPa at room temperature. By fitting the measured velocities under pressure to finite strain equations, the elastic moduli of topaz and their pressure derivatives were obtained, yielding K_S0 = 165.5 (25) GPa, K_S' = 2.9 (1), G₀ = 116.5 (17) GPa, and G' = 1.0 (1). Modeling of the velocity profiles of subducted sediments suggests that at 8 GPa (~240 km depth) the P- and S- wave velocities of the subducted sediments exhibit a first order increase of 10% andmore » 11%, respectively. Furthermore, the comparison between seismic observations and velocity contrasts of sediment + MORB model at 240 km shows dehydration of a 1.5–3.9 km thick sediment layer can potentially contribute to the seismically observed Lehmann discontinuity in Tonga, Japan, Philippine Sea, South America, Indonesia, and South Shetland subduction zones.« less

Abstract Phase A (Mg ₇ Si ₂ O ₈ (OH) ₆ ) is one of the important dense hydrous magnesium silicates in subducting slab, because it forms after the breakdown of antigorite serpentine and could be the dominant hydrous phase in the upper‐mantle deep slab for the water transportation into deep Earth. In this study, the compressional ( P ) and shear ( S ) wave velocities of phase A were measured at simultaneous pressure and temperature conditions up to 11 GPa and 1073 K. Combined with elastic properties of olivine and pyroxenes, we calculate the hydration effect on the velocities ofmore » harzburgite lithology in cold subduction zones throughout the depth ranges where phase A is thermodynamically stable. Our calculations suggest that the hydration increases both P ‐ and S ‐wave velocities of harzburgite; at ∼5 wt% hydration, its seismic detectability is enhanced by 1%–1.5% in velocity contrasts relative to its anhydrous counterpart.« less

Inmore » this work, the compressional (P) and shear wave velocities (S) and unit cell volumes (densities) of polycrystalline tungsten (W) have been measured simultaneously up to 10.5 GPa and 1073 K using ultrasonic interferometry in conjunction with x-ray diffraction and x-radiography techniques. Thermoelastic properties of W were derived using different methods. We obtained the isothermal bulk modulus K_T0 = 310.3(1.5) GPa, its pressure derivative K'_T0 = 4.4(3), its temperature derivative at constant pressure ${\left(\mathrm{\partial }{K}_T/\mathrm{\partial }T\right)}_P=–0.0138\left(1\right)\mathrm{GPa}{\mathrm{K}}^{–1}$ and at constant volume ${\left(\mathrm{\partial }{K}_T/\mathrm{\partial }T\right)}_V=–0.0050\mathrm{GPa}{\mathrm{K}}^{–1}$, the thermal expansion α(0, T) = 1.02(27) × 10^–5 + 7.39(3.2) × 10^–9 T (K^–1), as well as the pressure derivative of thermal expansion ${(\mathrm{\partial }\alpha /\mathrm{\partial }P)}_T=–1.44\left(1\right)\times {10}^{–7}{\mathrm{K}}^{–1}\mathrm{GP}{\mathrm{a}}^{–1}$ based on the high-temperature Birch–Murnaghan equation of state (EOS), the Vinet EOS, and thermal pressure approach. Finite strain analysis allowed us to derive the elastic properties and their pressure/temperature derivatives independent of the choice of pressure scale. A least-squares fitting yielded K_S0 = 314.5(2.5) GPa, K_S0' = 4.45(9), (∂K_S/∂T)_P = – 0.0076(6) GPa K^–1, G₀ = 162.4(9) GPa, G₀' = 1.8(1), (∂G/∂T)_P = – 0.0175(9) GPa K^–1, and ${\alpha }_{298K}=1.23\times {10}^{–5}{\mathrm{K}}^{–1}$. Fitting current data to the Mie–Grüneisen–Debye EOS with derived ${\theta }_0=383.4\mathrm{K}$ yielded ${\gamma }_0=1.81\left(6\right)\mathrm{and}q=0.3$. The thermoelastic parameters obtained from various approaches are consistent with one another and comparable with previous results within uncertainties. Our current study provides a complete and self-consistent dataset for the thermoelastic properties of tungsten at high P–T conditions, which is important to improve the theoretical modeling of these materials under dynamic conditions.« less

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Elastic properties of antigorite are important for interpretation of seismic mapping of serpentinization in the mantle wedge above subducting slabs. The compressional (V_P) and shear (V_S) wave velocities in pure antigorite aggregates were measured simultaneously up to 8.4 GPa by ultrasonic interferometry. We found that V_P increases monotonically with pressure while V_S increases with pressure up to about 3 GPa but undergoes a negative pressure dependence above 4 GPa. Compared to other mantle minerals, antigorite exhibits significantly lower P and S wave velocities as well as a higher V_P/V_S ratio at upper mantle pressures. We modeled velocity reductions manifesting throughmore » the formation of antigorite in mantle peridotite and provide compelling evidence that seismic anomalies with low-velocity and high V_P/V_S ratios is caused by varying degrees of serpentinization in subduction zones.« less

The elastic properties of praseodymium (Pr) were investigated at pressures up to 12 GPa at room temperature using ultrasonic interferometry technique. Softening and discontinuities in compressional (P) and shear (S) wave velocities were observed at around 2.5, 6.5 and 10.5 GPa, which are interpreted as indications of the phase transitions from Pr-I (dhcp) to Pr-II (fcc), Pr-II (fcc) to Pr-III (d-fcc) and Pr-III (d-fcc) to Pr-VII (monoclinic or orthorhombic), respectively. Very small discontinuities in compressibility have been observed across the phase transitions of I-II and II-III of Pr, which are unlikely visible in the X-ray diffraction studies. Finally, a comparisonmore » with the elastic behaviors of other lanthanide elements (e.g., Ce and La) suggests that the elastic anomalies associated with these phase transitions are likely to be caused by the 6s-5d electron transfer and the softening of acoustic phonon mode facilitated by decreased atomic distances under pressure.« less

Compressional (V_P) and shear wave (V_S) velocities of polycrystalline tungsten have been measured up to ~13 GPa at room temperature using ultrasonic interferometry in a multi-anvil apparatus. Using finite strain equation of state approaches, the elastic bulk and shear moduli and their pressure dependences are derived yielding $$K_{S0}$$= 325.9 ± 4.8 GPa, $$G_0$$ =164.1±2.5 GPa, $$K^{'}_{S0}$$ =3.65 ± 0.05 and $$G^{'}_0$$ =1.28 ± 0.02. On the basis of the current experimental data, the high-pressure behavior of Young’s modulus, Poisson’s ratio and ductility/brittleness for tungsten are also investigated. Complementary to the experimental data, the single crystal elastic constants, as well asmore » the elastic anisotropy of tungsten are computed using density functional theory (DFT). The Voigt-Reuss-Hill average of the bulk and shear moduli calculated using the single crystal elastic constants from DFT are found comparable to the current experimental results within about 5%. Here, the present study offers a dataset for the elasticity of polycrystalline bcc tungsten to a maximum pressure more than 25-fold higher than other previous ultrasonic studies, which can further our understanding about the elastic, mechanical and electronic properties of tungsten under extreme conditions as well as thermodynamic modelling of its alloys.« less

We report the compressional and shear wave velocities for coesite have been measured simultaneously up to 5.8 GPa and 1073 K by ultrasonic interferometry for the first time. The shear wave velocity decreases with pressure along all isotherms. The resulting contrasts between coesite and stishovite reach ~34% and ~45% for P and S wave velocities, respectively, and ~64% and ~75% for their impedance at mantle conditions. The large velocity and impedance contrasts across coesite-stishovite transition imply that to generate the velocity and impedance contrasts observed at the X-discontinuity, only a small amount of silica would be required. The velocity jumpmore » dependences on silica, d(lnV_P)/d(SiO₂) = 0.38 (wt %)^-1 and d(lnV_S)/d(SiO₂) = 0.52 (wt %)^-1, are utilized to place constraints on the amount of silica in the upper mantle and provide a geophysical approach to track mantle eclogite materials and ancient subducted oceanic slabs.« less

Compressional and shear wave velocities of the a phase of hafnium have been measured up to 10.4GPa at room temperature using ultrasonic interferometry in a multi-anvil apparatus. A finite strain equation of state analysis yielded Ks0 ¼ 110:4 ð5Þ GPa; G0 ¼ 54:7ð5Þ GPa; K0 s0 ¼ 3:7; andG0 0 ¼ 0:6 for the elastic bulk and shear moduli and their pressure derivatives at ambient conditions.Complementary to the experimental data, the single crystal elastic constants, the elastic anisotropy, and the unit cell axial ratio c/a of a-hafnium at high pressures were investigated by Density Functional Theory (DFT) based first principlesmore » calculations. A c/a value of 1.605 is predicted for a-Hf at 40GPa, which is in excellent agreement with previous experimental results. The low-pressure derivative of the shear modulus observed in our experimental data up to 10 GPa was found to originate from the elastic constant C44, which exhibits negligible pressure dependence within the current experimental pressure range. At higher pressures (>10GPa), C44 was predicted to soften and the shear wave velocity S trended to decrease with pressure, which can be interpreted as a precursor to the a-x transition similar to that observed in other group IV elements (titanium and zirconium). The acoustic velocities, the bulk and shear moduli, and the acoustic Debye temperature (240.1K) determined from the current experiments were all compared well with those predicted by our theoretical DFT calculations.« less