You Qing Fei

Experimentally determined postspinel transformation boundary in Mg2SiO4 using MgO as an internal pressure standard and its geophysical implications

[1]xa0We have determined the postspinel transformation boundary in Mg2SiO4 by combining quench technique with in situ pressure measurements, using multiple internal pressure standards including Au, MgO, and Pt. The experimentally determined boundary is in general agreement with previous in situ measurements in which the Au scale of Anderson et al. [1989] was used to calculate pressure: Using this pressure scale, it occurs at significantly lower pressures compared to that corresponding to the 660-km seismic discontinuity. In this study, we also report new experimental data on the transformation boundary determined using MgO as an internal standard. The results show that the transition boundary is located at pressures close to the 660-km discontinuity using the MgO pressure scale of Speziale et al. [2001] and can be represented by a linear equation, P(GPa) = 25.12 − 0.0013T(°C). The Clapeyron slope for the postspinel transition boundary is precisely determined and is significantly less negative than previous estimates. Our results, based on the MgO pressure scale, support the conventional hypothesis that the postspinel transformation is responsible for the observed 660-km seismic discontinuity.

Effect of pressure, temperature, and composition on lattice parameters and density of (Fe,Mg)SiO3‐perovskites to 30 GPa

High-pressure, high-temperature properties of MgSiO3, (Fe0.1Mg0.9)SiO3, and (Fe0.2Mg0.8)SiO3 perovskites have been investigated using a newly developed X ray diffraction technique involving monochromatic synchrotron radiation. The first direct measurements of unit cell distortions and equation-of-state parameters of the orthorhombic perovskite as functions of composition and simultaneous high pressure and high temperature were obtained. The experiments were conducted under hydrostatic pressure up to 30 GPa, into the stability field of the perovskite. The results demonstrate that the perovskite is elastically anisotropic, with the lattice parameter b being 25% less compressible than a and c. Under increasing pressures the orthorhombic perovskite is distorted further away from the ideal cubic structure in agreement with theoretical predictions. The 298-K isothermal equations of state of the three perovskites are indistinguishable within the uncertainty limits of the experiment. The zero-pressure bulk modulus KT0 = 261 (±4) GPa with its pressure derivative KT0′ = 4 is close to that determined in previous static high pressure measurements. The thermal expansion obtained from the high P - T experiments are consistent with previous measurements carried out at zero pressure but shows a strong volume dependence. The temperature derivative of the isothermal bulk modulus at constant pressure (∂KT/∂T)p is −6.3(±0.5)×10−2 GPa/K. Analyses of the high-temperature data give a value for the Anderson-Gruneisen parameter δT of 6.5–7.5, which is significantly higher than that used in recent lower mantle models.

Erratum to: Polymorphic phase transition in Superhydrous Phase B

the original publication of the article reported polarized FtIr spectra taken on oriented superhydrous phase B crystals. unfortunately, the authors mixed up the crystallographic cand a-axes during their measurement. the atomic coordinates for hydrogen H2 should be x = 0.45; y = 0.18; z = 0.27. thus, spectra in Fig. 10a are taken on the (001) plane with E parallel b (0°) and spectra in Fig. 10b are taken on the (010) plane with E parallel c (0°).