Unquenchable high-pressure perovskite polymorphs of MnSnO3 and FeTiO3     

Kurt Leinenweber  Wataru Utsumi  Yoshihiko Tsuchida  Takehiko Yagi  Kei Kurita 《Physics and Chemistry of Minerals》1991,18(4):244-250

New high-pressure orthorhombic (GdFeO₃-type) perovskite polymorphs of MnSnO₃ and FeTiO₃ have been observed using in situ powder X-ray diffraction in a diamond-anvil cell with synchrotron radiation. The materials are produced by the compression of the lithium niobate polymorphs of MnSnO₃ and FeTiO₃ at room temperature. The lithium niobate to perovskite transition occurs reversibly at 7 GPa in MnSnO₃, with a volume change of -1.5%, and at 16 GPa in FeTiO₃, with a volume change of -2.8%. Both transitions show hysteresis at room temperature. For MnSnO₃ perovskite at 7.35 (8) GPa, the orthorhombic cell parameters are a=5.301 (2) A, b=5.445 (2) Å, c=7.690 (8) Å and V= 221.99 (15) ų. Volume compression data were collected between 7 and 20 GPa. The bulk modulus calculated from the compression data is 257 (18) GPa in this pressure region. For FeTiO₃ perovskite at 18.0 (5) GPa, cell parameters are a=5.022 (6) Å, b=5.169 (5) Å, c=7.239 (9) Å and V= 187.94 (36) ų. Based on published data on the quench phases, the FeTiO₃ perovskite breaks down to a rocksalt + baddelyite mixture of FeO and TiO₂ at 23 GPa. This is the first experimental verification of the pressure-induced breakdown of a perovskite to simple oxides.  相似文献   

Chemical and mineralogical compositions of two grains recovered from asteroid Itokawa          下载免费PDF全文

M. Ebihara  N. Shirai  S. Sekimoto  T. Nakamura  A. Tsuchiyama  J. Matsuno  T. Matsumoto  M. Tanaka  M. Abe  A. Fujimura  Y. Ishibashi  Y. Karouji  T. Mukai  T. Okada  M. Uesugi  T. Yada 《Meteoritics & planetary science》2015,50(2):243-254

Two silicate grains (RB‐QD04‐0049 and RA‐QD02‐0064, whose estimated masses are 0.050 μg and 0.048 μg, respectively) recovered from the asteroid Itokawa by the Hayabusa spacecraft were studied for their mineralogical characteristics by synchrotron X‐ray diffraction and synchrotron X‐ray microtomography and further analyzed for their bulk chemical compositions by instrumental neutron activation analysis (INAA). According to X‐ray tomography, RB‐QD004‐0049 is composed of olivine, high‐Ca pyroxene, plagioclase, Ca‐phosphate, and troilite, whereas RA‐QD002‐0064 entirely consists of olivine. INAA data are consistent with these mineral compositions except for rare earth elements (REEs). Although the grain RB‐QD004‐0049 contains measurable REEs, which seems to be consistent with the presence of Ca‐phosphate, their abundances are anomalously high. Very low abundance of Co implies less than 0.1 mass% of metals in these two grains by calculation, which is in contrast to the result for the previously analyzed grain RA‐QD02‐0049 (Ebihara et al., 2011). FeO/Sc ratios of the grains fall within the range of those for ordinary chondrite olivines, implying that these grains are extraterrestrial in origin. FeO/MnO ratios also confirm this conclusion and further suggest that the Hayabusa grains analyzed in this study are similar to material found in LL chondrites rather than CK chondrites although olivines from LL and CK chondrites have similar Fa# (molar% of Fe relative to [Fe+Mg] in olivine) (~30) to those of the Hayabusa grains including the two grains analyzed in this study.  相似文献   

BSRs and Associated Reflections as an Indicator of Gas Hydrate and Free Gas Accumulation: An Example of Accretionary Prism and Forearc Basin System along the Nankai Trough, off Central Japan   总被引：1，自引：0，他引：1  

Kei Baba  Yasuhiro Yamada 《Resource Geology》2004,54(1):11-24

Abstract. Multi-channel seismic data obtained from the Nankai accretionary prism and forearc basin system has been studied to elucidate the migration and accumulation process of gas to the BGHS and examine the distribution pattern of BSRs and characteristic reflections associated with them.
BSRs are distributed widely in the Nankai accretionary prism and associated forearc basins (33,000 km²) and 90 % of them have migration and recycling origins. The widest distribution of the BSRs can be seen at the prism. A correlation between the BSR distributions and prism size shows that the BSRs tend to be more well-developed in a prism of large size. This suggests that a large prism may produce much amount of gas-bearing fluids that migrate to the BGHS and form the BSRs (tectonic control), hi the forearc basins, the BSRs are identified at topographic highs, anticlines and basin margins (structural control).
The upward migration of gas-bearing fluids is carried out through permeable sand layers and as a result, the distribution of BSRs is confined to alternating beds of sand and mud facies (sedimentary control). However, if there is enough time for upward migration and accumulation of gas to the BGHS, the BSRs can be generated widely in low-permeable mud facies (time control).
Those results imply that structural, tectonic, sedimentary and time controls are primary factors to decide the distribution of BSRs in the Nankai Trough area.  相似文献   

Experimental Study of Fe-Mg Exchange Reaction Between Orthopyroxene and Sapphirine and its Calibration as a Geothermometer     

Toshisuke Kawasaki  Kei Sato 《Gondwana Research》2002,5(4):741-747

The exchange of Fe²⁺ and Mg²⁺ between orthopyroxene and sapphirine has been investigated at pressures 7-16 kbar and temperatures 850-1300°C using a piston cylinder apparatus for the synthetic and natural systems. This reaction is temperature-dependent and would be a good geothermometer. The equilibration temperature T is approximately expressed by the distribution coefficient as follows: T(°C)=1515/(ln K_D+0.943)-273.

This empirical equation was applied to some Antarctic granulites and associated rocks. The new orthopyroxene-sapphirine geothermometer gives consistent results with those estimated from the Fe-Mg orthopyroxene-garnet geothermometer.  相似文献   

Energy balance above a boreal coniferous forest: a difference in turbulent fluxes between snow‐covered and snow‐free canopies     

Yuichiro Nakai  Tomoki Sakamoto  Tomomi Terajima  Kenzo Kitamura  Tomoki Shirai 《水文研究》1999,13(4):515-529

To evaluate the interactive effects of snow and forest on turbulent fluxes between the forest surface and the atmosphere, the surface energy balance above a forest was measured by the eddy correlation method during the winter of 1995–1996. The forest was a young coniferous plantation comprised of spruce and fir. The study site, in Sapporo, northern Japan, had heavy and frequent snowfalls and the canopy was frequently covered with snow during the study period. A comparison of the observed energy balance above the forest for periods with and without a snow‐covered canopy and an analysis using a single‐source model gave the following results: during daytime when the canopy was covered with snow, the upward latent heat flux was large, about 80% of the net radiation, and the sensible heat flux was positive but small. On the other hand, during daytime when the canopy was dry and free from snow, the sensible heat flux was dominant and the latent heat flux was minor, about 10% of the net radiation. To explain this difference of energy partition between snow‐covered and snow‐free conditions, not only differences in temperature but also differences in the bulk transfer coefficients for latent heat flux were necessary in the model. Therefore, the high evaporation rate from the snow‐covered canopy can be attributed largely to the high moisture availability of the canopy surface. Evaporation from the forest during a 60‐day period in midwinter was estimated on a daily basis as net radiation minus sensible heat flux. The overall average evaporation during the 60‐day period was 0·6 mm day⁻¹, which is larger than that from open snow fields. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Siderophile element characteristics of acapulcoite–lodranites and winonaites: Implications for the early differentiation processes of their parent bodies     

Yoshihiro Hidaka  Naoki Shirai  Akira Yamaguchi  Mitsuru Ebihara 《Meteoritics & planetary science》2019,54(5):1153-1166

We have studied magnetic fractions of five acapulcoites, three lodranites, and two winonaites to investigate chemical compositions of their precursor materials and metallic partial melting processes occurring on their parent bodies. One winonaite metal is similar in composition to low Au, low Ni IAB iron subgroup, indicating genetic relationship between them. Magnetic fractions of chondrule‐bearing acapulcoite and winonaite have intermediate chemical compositions of metals between H chondrites and EL chondrites. This fact indicates that the precursor materials of acapulcoite–lodranites and winonaites were similar to H and/or EL chondrites in chemical compositions. Magnetic fractions in acapulcoite–lodranites have a large variety of chemical compositions. Most of them show enrichments of W, Re, Ir, Pt, Mo, and Rh, and one of them shows clear depletion in Re and Ir relative to those of chondrule‐bearing acapulcoite. Chemical compositional variations among acapulcoite–lodranite metals cannot be explained by a single Fe‐Ni‐S partial melting event, but a two‐step partial melting model can explain it.  相似文献   

Trace metals in Japanese eel Anguilla japonica in relation to ecological migratory types and growth stages     

Dung Quang Le  Naoko Chino  Kotaro Shirai  Takaomi Arai 《Estuarine, Coastal and Shelf Science》2010

In order to understand the metal concentrations in Japanese eel Anguilla japonica, nine elements were analyzed in the livers of different migratory types of eels collected from Tokushima region (south Japan). Migratory types were defined by examining the Sr:Ca ratio in otoliths. The results showed that there were significant differences in V, Cr, Cd, and Pb concentrations among the migratory types. Mature-sea-eels show a higher risk of metal accumulation than other migratory types of eels, and the concentrations of Mn, Cu, and Zn in mature eels were significantly higher than those in immature eels. The study suggests that the eel liver is a valuable bioindicator for trace metals; however, when using the eel as a bioindicator to reveal the pollutants in aquatic systems, life history analysis should be carried out for accurate interpretation of the results.  相似文献   

Phase transition in CaSiO₃ perovskite     

Tetsuya Komabayashi  Kei Hirose  Nagayoshi Sata  Yasuo Ohishi  Leonid S. Dubrovinsky 《Earth and Planetary Science Letters》2007,260(3-4):564-569

A phase transition in pure CaSiO₃ perovskite was investigated at 27 to 72 GPa and 300 to 819 K by in-situ X-ray diffraction experiments in an externally-heated diamond-anvil cell. The results show that CaSiO₃ perovskite takes a tetragonal form at 300 K and undergoes phase transition to a cubic structure above 490–580 K in a pressure range studied here. The transition boundary is strongly temperature-dependent with a slightly positive dT / dP slope of 1.1 (± 1.3) K/GPa. It is known that the transition temperature depends on Al₂O₃ content dissolved in CaSiO₃ perovskite [Kurashina et al., Phys. Earth Planet. Inter. 145 (2004) 67–74]. The phase transition in CaSiO₃(+ 3 wt.% Al₂O₃) perovskite therefore could occur in a cold subducted mid-oceanic ridge basalt (MORB) crust at about 1200 K in the upper- to mid-lower mantle. This phase transition is possibly ferroelastic-type and may cause large seismic anomalies in a wide depth range.  相似文献   

High-pressure behavior of MnGeO3 and CdGeO3 perovskites and the post-perovskite phase transition     

Shigehiko Tateno  Kei Hirose  Nagayoshi Sata  Yasuo Ohishi 《Physics and Chemistry of Minerals》2006,32(10):721-725

The stability and high-pressure behavior of perovskite structure in MnGeO₃ and CdGeO₃ were examined on the basis of in situ synchrotron X-ray diffraction measurements at high pressure and temperature in a laser-heated diamond-anvil cell. Results demonstrate that the structural distortion of orthorhombic MnGeO₃ perovskite is enhanced with increasing pressure and it undergoes phase transition to a CaIrO₃-type post-perovskite structure above 60 GPa at 1,800 K. A molar volume of the post-perovskite phase is smaller by 1.6% than that of perovskite at equivalent pressure. In contrast, the structure of CdGeO₃ perovskite becomes less distorted from the ideal cubic perovskite structure with increasing pressure, and it is stable even at 110 GPa and 2,000 K. These results suggest that the phase transition to post-perovskite is induced by a large distortion of perovskite structure with increasing pressure.  相似文献   

Numerical Simulation of Accretion Discs in Close Binary Systems andDiscovery of Spiral Shocks     

Takuya Matsuda  Makoto Makita  Hidekazu Fujiwara  Takizo Nagae  Kei Haraguchi  Eiji Hayashi  H.M.J. Boffin 《Astrophysics and Space Science》2000,274(1-2):259-273

The history of hydrodynamic numerical simulations for accretion disks in close binary systems is reviewed, in which emphasis is placed, in particular, on the facts that spiral shock waves were numerically found in 1986 by researchers including one of the present authors and that spiral structure was discovered in IP Pegasi in 1997 by Steeghs et al. The results of our two and three-dimensional numerical simulations in recent years are then summarized, with comparison being made with observations. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献