Phase relations of iron and iron–nickel alloys up to 300 GPa: Implications for composition and structure of the Earth's inner core     

Yasuhiro Kuwayama  Kei Hirose  Nagayoshi Sata  Yasuo Ohishi 《Earth and Planetary Science Letters》2008,273(3-4):379-385

We have investigated the phase relations of iron and iron–nickel alloys with 18 to 50 wt.% Ni up to over 300 GPa using a laser-heated diamond-anvil cell. The synchrotron X-ray diffraction measurements show the wide stability of hcp-iron up to 301 GPa and 2000 K and 319 GPa and 300 K without phase transition to dhcp, orthorhombic, or bcc phases. On the other hand, the incorporation of nickel has a remarkable effect on expanding the stability field of fcc phase. The geometry of the temperature–composition phase diagram of iron–nickel alloys suggests that the hcp–fcc–liquid triple point is located at 10 to 20 wt.% Ni at the pressure of the inner core boundary. The fcc phase could crystallize depending on the nickel and silicon contents in the Earth's core, both of which are fcc stabilizer.  相似文献   

Physically based maximum precipitation estimation under future climate change conditions          下载免费PDF全文

Kei Ishida  M. Levent Kavvas  Z. Q. Richard Chen  Alain Dib  Andres J. Diaz  Michael L. Anderson  Toan Trinh 《水文研究》2018,32(20):3188-3201

Estimation of the extreme precipitation over a target watershed under a changing climate would be necessary to design safe large hydraulic structures. For this purpose, the maximum precipitation (MP) estimation approach was applied to the American River Watershed (ARW) in Northern California under several future climate conditions over 90 water years (2010–2099). These future climate conditions were obtained using 13 future climate projections from two general circulation models (ECHAM5 and CCSM3) based on four future climate scenarios (Special Report on Emissions Scenarios: A1B, A1FI, A2, and B1). A total of 1,170 future projected severe storm events (90 years × 13 projections) were selected with respect to the 72‐hr basin‐average precipitation over the ARW. The 72‐hr basin‐average precipitation for each of the selected severe storm events was maximized over the ARW by horizontally shifting the atmospheric boundary conditions of a regional atmospheric model in order to optimize the path of the storm system that corresponded to the particular event. After maximization, the MP estimates, which are the largest precipitation depths among the maximized results, were obtained as 836.7 mm for the early half‐century period (2010–2054) and 1,056.5 mm for the late half‐century period (2055–2099).  相似文献   

Mineralogy of interstitial rim materials of the Y74123 and Y790981 ureilites and their origin     

Hiromi Ogata    Hiroshi Takeda 《Meteoritics & planetary science》1991,26(3):195-201

Abstract— Y74123 is an olivine-rich, relatively unshocked ureilite and contains more interstitial pigeonitic materials than do ureilites which have been reported previously. Thus, Y74123 is especially suited for detailed study of the interstitial materials. We have studied these materials by optical microscope, electron microprobe, scanning electron microscope, high resolution transmission electron microscope (TEM) and analytical TEM to gain a better understanding of their nature and origin. Y790981, with shock partial melts, has also been examined by the same techniques. Bulk chemical compositions of the interstitial materials in Y74123 are pyroxene-like and have higher CaO and Al₂O₃ contents than the large pigeonite and olivine core. Interstitial materials at olivine-pigeonite grain boundaries are richer in CaO and Al₂O₃ than those at olivine-olivine grain boundaries. TEM observations of the interstitial material of Y74123 show that it consists of alternating pigeonite-augite lamellae more than 3.5 μm thick on (001). This texture suggests that the rim material had already crystallized before the parent body breakup. The shock-produced glassy veins in Y790981 cut through the rim materials. These observations are consistent with the idea that the interstitial materials in this ureilite are a mixture of residual liquids of high Ca melts and shock-produced partial melts of olivine and pigeonite. This mixture accumulated along the grain boundaries and some of it is trapped within grains.  相似文献   

High-pressure and ultrahigh-temperature metamorphism at Komateri, northern Madurai Block, southern India   总被引：1，自引：0，他引：1  

Toshiaki Tsunogae  M. Santosh  Hiroyuki Ohyama  Kei Sato 《Journal of Asian Earth Sciences》2008,33(5-6):395-413

We report for the first time the evidence for prograde high-pressure (HP) metamorphism preceding a peak ultrahigh-temperature (UHT) event in the northernmost part of the Madurai Block in southern India. Mg–Al-rich Grt–Ged rocks from Komateri in Karur district contain poikiloblastic garnet with numerous multi-phase inclusions. Although most of the inclusion assemblages are composed of gedrite, quartz, and secondary biotite, rare staurolite + sapphirine and spinel + quartz are also present. The X_Mg (=Mg/[Fe+Mg]) of staurolite (0.45–0.49) is almost consistent with that reported previously from Namakkal district in the Palghat–Cauvery Shear Zone system (X_Mg = 0.51–0.52), north of the Madurai Block. The HP event was followed by peak UHT metamorphism at T = 880–1040 °C and P = 9.8–12.5 kbar as indicated by thermobarometric computations in the Grt–Ged rock and associated mafic granulite. Symplectic intergrowth of spinel (X_Mg = 0.50–0.59, ZnO < 1.7 wt.%) and quartz, a diagnostic indicator of UHT metamorphism, probably formed by decompression at UHT conditions. The rocks subsequently underwent retrograde metamorphism at T = 720–760 °C and P = 4.2–5.1 kbar. The P–T conditions and clockwise exhumation trajectory of the Komateri rocks, comparable to similar features recorded from the Palghat–Cauvery Shear Zone system, suggest that the Madurai Block and the Palghat–Cauvery Shear Zone system underwent similar HP and UHT metamorphic history probably related to the continent–continent collision during the final stage of amalgamation of Gondwana supercontinent.  相似文献   

Spatio-temporal evolution of Coulomb stress in the Pacific slab inverted from the seismicity rate change and its tectonic interpretation in Hokkaido, Northern Japan     

Subesh Ghimire  Kei Katsumata  Minoru Kasahara 《Tectonophysics》2008,455(1-4):25-42

We estimated spatio-temporal evolution of Coulomb stress within the subducted Pacific slab in Hokkaido from the analysis of seismicity rate change. For this purpose we used earthquake catalog from the Institute of Seismology and Volcanology (ISV), Hokkaido University for the period 1993/4/1–2006/12/31 after relocating to compensate location errors due to the heterogeneous P- and S-wave structure beneath Hokkaido. We found that spatial pattern of Coulomb stress change inverted from the seismicity rate change is comparable with static change in Coulomb stress estimated from dislocation models. Our results and analyses reveal important insights on spatio-temporal pattern of deformation of the subducted Pacific slab in terms of Coulomb stress change. We found that the 2003 Tokachi Oki earthquake (Mw = 8.0) pervasively perturbed Coulomb stress in a regional scale with a significant impact to trigger the 2004 Kushiro Oki earthquake. The 2004 Kushiro Oki earthquake (Mw = 7.0) is another significant stressing event that changed the pattern of Coulomb stress in the area. We found that stressing events with magnitude smaller than 7.0 has minimal impact on Coulomb stress change in the Pacific slab. Similarly, comparatively deep focused large earthquakes could not change Coulomb stress significantly. Further the pattern of Coulomb stress change after the 2003 Tokachi Oki earthquake correlates the pattern of afterslip distribution in Hokkaido.  相似文献   

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   

Three-dimensional simulations of molecular cloud fragmentation regulated by magnetic fields and ambipolar diffusion     

Takahiro Kudoh  Shantanu Basu  Youichi Ogata  Takashi Yabe 《Monthly notices of the Royal Astronomical Society》2007,380(2):499-505

We employ the first fully three-dimensional simulation to study the role of magnetic fields and ion–neutral friction in regulating gravitationally driven fragmentation of molecular clouds. The cores in an initially subcritical cloud develop gradually over an ambipolar diffusion time while the cores in an initially supercritical cloud develop in a dynamical time. The infalling speeds on to cores are subsonic in the case of an initially subcritical cloud, while an extended (≳0.1 pc) region of supersonic infall exists in the case of an initially supercritical cloud. These results are consistent with previous two-dimensional simulations. We also found that a snapshot of the relation between density (ρ) and the strength of the magnetic field ( B ) at different spatial points of the cloud coincides with the evolutionary track of an individual core. When the density becomes large, both the relations tend to   B ∝ρ^0.5  .  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   

Variations in trace elements,isotopes, and organic geochemistry during the Hangenberg Crisis,Devonian–Carboniferous transition,northeastern Vietnam     

Atena Shizuya  Masahiro Oba  Takuto Ando  Yukari Ogata  Reishi Takashima  Hiroshi Nishi  Toshifumi Komatsu  Phong D. Nguyen 《Island Arc》2020,29(1)

The Hangenberg Crisis at the Devonian–Carboniferous boundary is known as a polyphase extinction event that affected more than 45 % of marine and terrestrial genera. As the cause of this event is still debated, analyses were carried out on sedimentary samples from the Devonian–Carboniferous Pho Han Formation in northeastern Vietnam to reconstruct the paleoenvironment around the time of this event using stable carbon isotopes; total sulfur; manganese; vanadium; molybdenum; and sedimentary organic matter, such as dibenzothiophenes, cadalene, and regular steranes. These geochemical signatures provide a high‐resolution redox history for this section and show that transgression‐driven high primary productivity, possibly enhanced by terrestrial input, caused severe oxygen depletion along the continental margin of the South China block during the Hangenberg Crisis.  相似文献