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51.
T. Sanehira T. Irifune T. Shinmei F. Brunet K. Funakoshi A. Nozawa 《Physics and Chemistry of Minerals》2006,33(1):28-34
In situ X-ray diffraction study was conducted to identify the crystal structure of the “Al-phase”, which was previously reported
to form in basaltic compositions at pressures and temperatures of the uppermost part of the lower mantle. Le Bail whole-pattern
fitting method was adopted to investigate the structure of the Al-phase under high pressure and temperature as well as ambient
conditions. Observed patterns were satisfactorily fitted using the “hexagonal phase” with space group P63/m (plus minor amount of garnet) under both of these conditions. On the other hand, the calcium ferrite structure model proposed
in some earlier studies based on quench experiments yielded profile-fitting results at significantly lower confidence levels,
particularly at simultaneous high pressure and high temperature conditions, suggesting that this phase may not form in oceanic
crust materials subducted in the uppermost lower mantle. The difference in densities of hexagonal and calcium ferrite phases,
however, is only ~1% under pressures and temperatures of the uppermost part of the lower mantle conditions, which yields a
negligible effect on the bulk density of the subducted oceanic crust. 相似文献
52.
In Japan, the crust and uppermost mantle seismic character is yet unimaged although many refraction surveys have been recorded. The longest seismic profiles are analyzed. A remarkable feature, a long-duration coda wave after the PmP wave (reflected wave at the Moho boundary), is observed on the record sections. Several possible models are considered to explain the long-duration coda wave. The model with many scatterers located in the uppermost mantle explains the observed data well while the undulating Moho and continuous layering models do not account for some aspects of the observed data. The scatterer distributed uppermost mantle is not consistent with that of continental region which is often characterized as transparent. We estimate the scattering coefficient of the uppermost mantle and crust using simulations. The scattering coefficients obtained for upper crust, lower crust, and uppermost mantle are 0.01, 0.02, and 0.025, respectively. The scattering coefficient of the uppermost mantle is slightly larger than that of lower crust, which is characterized as being reflective. The many scatterers in the uppermost mantle might be related to magmatism in Japan. This will be one of the important observations for understanding formation processes of the Moho boundary and uppermost mantle in the island-arc environment. 相似文献
53.
Lin Li Takaya Nagai Tomoki Ishido Satoko Motai Kiyoshi Fujino Shoichi Itoh 《Physics and Chemistry of Minerals》2014,41(6):431-437
Experiments using laser-heated diamond anvil cells combined with synchrotron X-ray diffraction and SEM–EDS chemical analyses have confirmed the existence of a complete solid solution in the MgSiO3–MnSiO3 perovskite system at high pressure and high temperature. The (Mg, Mn)SiO3 perovskite produced is orthorhombic, and a linear relationship between the unit cell parameters of this perovskite and the proportion of MnSiO3 components incorporated seems to obey Vegard’s rule at about 50 GPa. The orthorhombic distortion, judged from the axial ratios of a/b and \( \sqrt{2}\,a/c, \) monotonically decreases from MgSiO3 to MnSiO3 perovskite at about 50 GPa. The orthorhombic distortion in (Mg0.5, Mn0.5)SiO3 perovskite is almost unchanged with increasing pressure from 30 to 50 GPa. On the other hand, that distortion in (Mg0.9, Mn0.1)SiO3 perovskite increases with pressure. (Mg, Mn)SiO3 perovskite incorporating less than 10 mol% of MnSiO3 component is quenchable. A value of the bulk modulus of 256(2) GPa with a fixed first pressure derivative of four is obtained for (Mg0.9, Mn0.1)SiO3. MnSiO3 is the first chemical component confirmed to form a complete solid solution with MgSiO3 perovskite at the P–T conditions present in the lower mantle. 相似文献