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Highlights: [•] Velocities of grossular garnet to 10GPa and 1000K. [•] Ultrasonic interferometry in conjunction with synchrotron X-radiation. [•] Garnet elasticity not sensitive to Ca content except for shear modulus. [Copyright &y& Elsevier]

Abstract: Data are presented on the elastic properties of β-(Mg0.92Fe0.08)2SiO4 (iron-bearing wadsleyite) from 295K to 640K at ambient pressure. Elasticity measurements were made on hot-pressed polycrystals using resonant ultrasound spectroscopy (RUS). Multiple temperature excursions were done with data retrieved during both heating and cooling cycles. Room temperature (RT) values for the adiabatic bulk (K S ) and shear (G) moduli are 170.8(1.2)GPa and 108.9(0.4)GPa, respectively. The average derivatives over the temperature (T) range studied are (∂K S /∂T) P =−1.75(0.07)×10−2 GPaK−1 and (∂G/∂T) P =−1.55(0.06)×10−2 GPaK−1. Comparison of these results with those from our recent study of Mg-endmember wadsleyite shows no measurable difference in the average (∂K S /∂T) P or (∂G/∂T) P from RT to 640K due to Fe content. Slight nonlinearity in the temperature dependences of both K S and G are observed, such that second order fits for both K S (T) and G(T) are statistically justified. Whereas, the current nonlinearity in G(T) for β-(Mg0.92Fe0.08)2SiO4 is similar to that observed for β-Mg2SiO4, second order effects in K S (T) were not observed previously for wadsleyite. [ABSTRACT FROM AUTHOR]

Abstract: Compressional (P) and shear (S) wave velocities have been measured for two synthetic polycrystalline specimens of pyrope–majorite garnets [Py60Mj40 and Py50Mj50] by ultrasonic interferometry to 8GPa and 1000K, in a DIA-type cubic anvil high pressure apparatus (SAM-85) interfaced with synchrotron X-radiation and X-ray imaging. Elastic bulk (K S) and shear (G) moduli data obtained at the end of the cooling cycles were fitted to functions of Eulerian strain to third order yielding pressure derivatives of the elastic moduli (∂K S/∂P) T =4.3 (3); (∂G/∂P) T =1.5 (1) for Py60Mj40 garnet and (∂K S/∂P) T =4.4 (1); (∂G/∂P) T =1.3 (1) for Py50Mj40 garnet. Both (∂K S/∂P) T and (∂G/∂P) T are identical for the two garnet compositions and are also consistent with Brillouin scattering data for polycrystalline Py50Mj50. Moreover, the new pressure derivatives of the elastic moduli are equal within experimental uncertainties to those of end-member pyrope garnet from ultrasonic studies [Gwanmesia, G.D., Zhang. J, Darling, K., Kung, J., Li, B., Wang, L., Neuville, D., Liebermann, R.C., 2006. Elasticity of polycrystalline pyrope (Mg3Al2Si3O12) to 9GPa and 1000°C. Phys. Earth Planet. Inter. 155, 179–190] and from Brillouin spectroscopic studies [Sinogeikin, S.V., Bass, J.D., 2002a. Elasticity of majorite and majorite–pyrope solid solution to high pressure: implications for the transition zone. Geophys. Res. 9(2), 1017], thereby demonstrating that the pressure derivatives of the elastic moduli are independent of the physical acoustics technique employed and unaffected by substitution of Si for Mg and Al within the Py–Mj solid solution in the range (Py100–Py50) of the present measurements. Temperature dependence of the elastic obtained from linear regression of entire P–T–K and P–T–G data are (∂K S/∂T) P =−14.6 (4)MPa/K; (∂G/∂T) P =−9.4 (4)MPa/K for Py60Mj40 garnet, and (∂K S/∂T) P =−14.6 (4)MPa/K; (∂G/∂T) P =−9.33 (2)MPa/K for Py50Mj50 garnet. These values are essentially identical for the two compositions and are also in excellent agreement with the Brillouin scattering data of [Sinogeikin, S.V., Bass, J.D., 2002b. Elasticity of pyrope and majorite–pyrope solid solutions to high temperatures. Phys. Earth Planet. Inter. 203, 549–555] for Py50Mj50 garnet; however, they are higher than those for pyrope by about 23% for (∂K S/∂T) P and 11% for (∂G/∂T) P [Gwanmesia, G.D., Zhang. J, Darling, K., Kung, J., Li, B., Wang, L., Neuville, D., Liebermann, R.C., 2006. Elasticity of polycrystalline pyrope (Mg3Al2Si3O12) to 9GPa and 1000°C. Phys. Earth Planet. Inter. 155, 179–190]. [Copyright &y& Elsevier]

Abstract: Brillouin scattering measurements on single-crystal stishovite, a high-pressure polymorph of SiO2, were carried out to 22GPa. Acoustic velocities in three 30-μm thick crystal platelets of synthetic stishovite were measured in a forward symmetric scattering geometry, and the full set of elastic constants were retrieved to 12GPa. The measured velocity data were fit to Christoffel’s equation, yielding ambient-pressure elastic constants of C 11 =455(1)GPa, C 33 =762(2)GPa, C 12 =199(2)GPa, C 13 =192(2)GPa, C 44 =258(1)GPa, and C 66 =321(1)GPa. The elastic modulus (C 11 − C 12)/2 was observed to decrease with pressure, indicating acoustic mode softening, consistent with theoretical predications for the behavior of stishovite as it approaches the transition to the CaCl2-type phase. The bounds on the aggregate adiabatic bulk and shear moduli are K S0 =315(1)GPa, G 0 =240(1)GPa for the Voigt bound, K S0 =301(1)GPa, G 0 =216(1)GPa for the Reuss bound. Pressure derivatives of aggregate bulk and shear moduli were constrained to be (∂K S/∂P)T0 =4.34(16) and (∂G/∂P)0 =0.7(1) for the Reuss bound, and (∂K S/∂P)T0 =4.0(1) and (∂G/∂P)0 =1.1(1) for the Voigt–Reuss–Hill (VRH) average, respectively, by fitting the data to Eulerian finite strain equations. The volume compression curve obtained from our Brillouin measurement is in very good agreement with previous compression studies up to 50GPa. [Copyright &y& Elsevier]

Abstract: New, high quality data are presented on the elastic properties of β-Mg2SiO4 (wadsleyite) from 295 to 660K at ambient pressure. Elasticity measurements were carried out on a sintered polycrystal using resonant ultrasound spectroscopy (RUS). Room temperature values for the adiabatic bulk (K S) and shear (G) moduli are 170.2(1.9) and 113.9(0.7)GPa, respectively. The K S data exhibit linear dependence on temperature (T) with (∂K S/∂T) P =−1.71(5)×10−2 GPaK−1. Our result for (∂K S/∂T) P is consistent with a relatively high magnitude for this derivative which contrasts with −1.20×10−2 to −1.30×10−2 GPaK−1 reported in some earlier studies. The average (∂G/∂T) P =−1.57(3)×10−2 GPaK−1 over the temperature range studied. This result is consistent with most earlier measurements of (∂G/∂T) P for wadsleyite. The (∂K S/∂T) P and average (∂G/∂T) P for wadsleyite over 295–660K are not measurably affected by the presence of iron as seen from comparing our results with those from a RUS study on β-(Mg0.91Fe0.09)2SiO4. Further, our results for (∂K S/∂T) P and average (∂G/∂T) P are consistent with olivine content of 44–54% at 410-km depth in Earth, given other assumptions made in recent studies about properties of the α- and β-olivine phases for P, T conditions at that depth. Our G(T) data appear to exhibit small, but persistent, nonlinear behavior; the magnitude of (∂G/∂T) P increases with T. We discuss the important implications on upper mantle mineralogy if this nonlinear effect is confirmed and is demonstrated to apply when extrapolating beyond the temperature range of 295–660K. [Copyright &y& Elsevier]

Abstract: Acoustic wave velocities for synthetic polycrystalline pyrope (Mg3Al2Si3O12) were measured to 9GPa and temperatures up to 1000°C by ultrasonic interferometry combined with energy-dispersive synchrotron X-ray diffraction in a cubic-anvil DIA-type apparatus (SAM-85). Specimen lengths at high pressures (P) and temperatures (T) are directly measured by X-radiographic methods. Elastic wave travel times and X-ray diffraction data were collected after heating and cooling at high pressures to minimize effect of non-hydrostatic stress on the measurements. A linear fit to the high P and T data set yields the elastic bulk and shear moduli [K S =175 (2)GPa; G =91 (1)GPa] and their pressure and temperature derivatives [; G′=1.7±0.2 and (∂K S /∂T) P =−18 (2) MPa/K; (∂G/∂T) P =−10 (1) MPa/K]. In a separate analysis, the pressure–volume–temperature data collected during these acoustic experiments were fit to a high temperature Birch–Murnaghan (HTBM) equation [with K′ fixed at 3.9] and to each isothermal P–V–T data yielding (∂K T /∂T) P =−22 (2) MPa/K and (∂K T /∂T) P =−20 (5) MPa/K, respectively. Comparison of Py100 data with those other Py–Mj compositions indicates that the thermo elastic properties are insensitive to majorite content in the garnet along the pyrope–majorite join. [Copyright &y& Elsevier]

Sound velocities in polycrystalline San Carlos olivine have been measured to pressures of 7 GPa at room temperature in a 1000 t uniaxial, split-cylinder apparatus (USCA-1000) of the Kawai multi-anvil type. These velocities and elastic moduli are in good agreement with those calculated from single-crystal moduli determined by previous investigators. In preliminary experiments in a DIA-type, cubic anvil apparatus (SAM-85), ultrasonic interferometric techniques were used in conjunction with synchrotron X-radiation to determine the elastic properties of San Carlos olivine under simultaneous high pressures and temperatures. We demonstrate the feasibility of such experiments even in specimens which have undergone plastic deformation at elevated pressures and temperatures. [Copyright &y& Elsevier]