Ram-pressure stripping of halo gas in disc galaxies: implications for galactic star formation in different environments     

Kenji Bekki 《Monthly notices of the Royal Astronomical Society》2009,399(4):2221-2230

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Lost primordial continents   总被引：7，自引：2，他引：5  

Kenji Kawai  Taku Tsuchiya  Jun Tsuchiya  Shigenori Maruyama 《Gondwana Research》2009,16(3-4):581-586

We investigate the bulk density variations of some representative compositions for the lower mantle based on the pressure–volume–temperature equation of state of the constituent mineral phases. The density variations of pyrolite, harzburgite, mid-ocean ridge basalt (MORB), tonalite–trondhjemite–granodiorite (TTG), and anorthosite are studied at a temperature of 300 K and at lower mantle pressures. The density of MORB is greater than that of pyrolite throughout the lower mantle, while the density of harzburgite is slightly lower than that of pyrolite. The density of anorthosite is comparable to that of pyrolite in the lower mantle in general, and greater in the lowermost mantle, while the density of TTG is lower than pyrolite throughout the lower mantle. The above results have important implications for the fate of primordial continents, TTG and anorthosite crust. While subducted TTG might be stagnant in the mantle transition zone, dense subducted anorthositic crust could be expected to sink to the core–mantle boundary (CMB) and thus might be a major component of the D" layer immediately above the CMB. Thus, we propose that significant bodies of continental material could be present in the mantle in the transition zone and immediately above the CMB, in addition to the continents on the Earth's surface.  相似文献   

Uranium-series chronology for sediments of Lake Hovsgol, Mongolia, and the 1-Ma records of uranium and thorium isotopes from the HDP-04 drill core     

Aya Sakaguchi  Masayoshi Yamamoto  Junpei Tomita  Kenta Mino  Keiichi Sasaki  Kenji Kashiwaya  Takayoshi Kawai 《Quaternary International》2009,205(1-2):65

Uranium and thorium isotopes in an 81-m long sediment core (HDP-04) of Lake Hovsgol, Mongolia, were measured to investigate their downcore distributions and to explore potential linkage to paleoenvironmental changes. Three-dimensional isochron techniques using isotope-ratio diagrams in ²³⁸U–²³⁴U–²³⁰Th–²³²Th system presented by Ludwig and Titterington were applied to age date the lake sediments at the depths of 11.42, 14.71 and 14.83 m in the HDP-04 section, the estimated ages of these horizons are 66 ± 8, 122 ± 11 and 128 ± 22 ka, respectively. The ²³⁸U concentration throughout the entire section fluctuated by a factor of 12, ranging from 19.9 to 232.1 mBq/g with anomalously high ²³⁸U peak at 23.8 m in depth, while the ²³²Th concentration varied only by a factor of about two between 24.3 and 54.0 mBq/g. The discrimination of the bulk ²³⁸U into authigenic and terrigenous ²³⁸U fractions was attempted, based on the measured ²³²Th as a correction index for terrigenous materials. In the upper 24 m corresponding to the last 250 ka, the authigenic ²³⁸U was higher in interglacials and lower in glacials. This depth profile of authigenic ²³⁸U contents was almost identical pattern with that found in a sediment core (VER98-1-6) from the Academician Ridge, Lake Baikal. Further, this profile can be correlated well with that of photosynthetic pigment contents, one of proxies of paleoproductivity, suggesting that the variation of authigenic ²³⁸U contents were associated with the environmental change around Lake Hovsgol.  相似文献   

Reply to the comment on “Arsenic release from biotite into a Holocene groundwater aquifer in Bangladesh” by Hossain M. Anawar and Martin Mihaljevič     

Ashraf Ali Seddique  Harue Masuda  Muneki Mitamura  Keiji Shinoda  Takamoto Okudaira  Toshiro Yamanaka  Takaaki Itai  Teruyuki Maruoka  Kenji Uesugi  Kazi Matin Ahmed 《Applied Geochemistry》2009

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Persistent multi-decadal Greenland temperature fluctuation through the last millennium     

Takuro Kobashi  Jeffrey P. Severinghaus  Jean-Marc Barnola  Kenji Kawamura  Tara Carter  Tosiyuki Nakaegawa 《Climatic change》2010,100(3-4):733-756

Future Greenland temperature evolution will affect melting of the ice sheet and associated global sea-level change. Therefore, understanding Greenland temperature variability and its relation to global trends is critical. Here, we reconstruct the last 1,000 years of central Greenland surface temperature from isotopes of N₂ and Ar in air bubbles in an ice core. This technique provides constraints on decadal to centennial temperature fluctuations. We found that northern hemisphere temperature and Greenland temperature changed synchronously at periods of ~20 years and 40–100 years. This quasi-periodic multi-decadal temperature fluctuation persisted throughout the last millennium, and is likely to continue into the future.  相似文献   

Influence of pressure and temperature on the electrical conductivity of dolomite     

Shigeaki Ono  Kenji Mibe 《Physics and Chemistry of Minerals》2015,42(9):773-779

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Identification of magnetite in lunar regolith breccia 60016: Evidence for oxidized conditions at the lunar surface     

Katherine H. Joy  Channon Visscher  Michael E. Zolensky  Takashi Mikouchi  Kenji Hagiya  Kazumasa Ohsumi  David A. Kring 《Meteoritics & planetary science》2015,50(7):1157-1172

Lunar regolith breccias are temporal archives of magmatic and impact bombardment processes on the Moon. Apollo 16 sample 60016 is an “ancient” feldspathic regolith breccia that was converted from a soil to a rock at ~3.8 Ga. The breccia contains a small (70 × 50 μm) rock fragment composed dominantly of an Fe‐oxide phase with disseminated domains of troilite. Fragments of plagioclase (An_95‐97), pyroxene (En_74‐75, Fs_21‐22,Wo_3‐4), and olivine (Fo_66‐67) are distributed in and adjacent to the Fe‐oxide. The silicate minerals have lunar compositions that are similar to anorthosites. Mineral chemistry, synchrotron X‐ray absorption near edge spectroscopy (XANES) and X‐ray diffraction (XRD) studies demonstrate that the oxide phase is magnetite with an estimated Fe³⁺/ΣFe ratio of ~0.45. The presence of magnetite in 60016 indicates that oxygen fugacity during formation was equilibrated at, or above, the Fe‐magnetite or wüstite–magnetite oxygen buffer. This discovery provides direct evidence for oxidized conditions on the Moon. Thermodynamic modeling shows that magnetite could have been formed from oxidization‐driven mineral replacement of Fe‐metal or desulphurisation from Fe‐sulfides (troilite) at low temperatures (<570 °C) in equilibrium with H₂O steam/liquid or CO₂ gas. Oxidizing conditions may have arisen from vapor transport during degassing of a magmatic source region, or from a hybrid endogenic–exogenic process when gases were released during an impacting asteroid or comet impact.  相似文献   

Tree ring information and rainfall characteristic for landslide in the Kobe District,Japan     

Kenji Kashiwaya  Takashi Okimura And  Takeshi Kawatani 《地球表面变化过程与地形》1989,14(1):63-71

Heavy rainfall on the south side of the Rokko Mountains has often caused severe landslides and debris flows. Analysis of the annual summation of rainfall in excess of 100 mm/day shows that the rainfall in this area has dominant periodicities of about 25–30, 10–13, and 5–7 years. The period of about 25–30 years corresponds to that of occurrence of the natural disasters produced by heavy rainfall; years when the maximum rainfall correspond to years when there have been severe landslides and debris flows in the area. Temporal change in this rainfall may provide a first approximation for erosional force. Analyses of tree ring width from these mountains indicate that the sequences have a dominant periodicity of about 25–30 years. Cross-spectral analyses for rainfall and ring width in this area show high coherency for the periods of about 25–30 years; evidence that variations in the ring width may be used as proxy data for erosional force.  相似文献   

Quartz microtextures of the Sambagawa schists and their implications in convergent margin processes   总被引：1，自引：0，他引：1  

Nobuo  Sakakibara  Ikuo  Hara  Kenji  Kanai  Kenji  Kaikiri  Tugio  Shiota  Kei  Hide Peter  Paulitsch 《Island Arc》1992,1(1):186-197

Abstract Quartz c-axis fabrics of the Sambagawa schists produced along a late Mesozoic convergent plate margin were analysed so that their tectono-metamorphic history could be clarified. It has been noted by many authors that quartz fabrics produced by earlier phase deformation are easily modified by strain increment during later phase deformation. This paper attempts to elucidate the high-temperature phases of prograde metamorphism (Sim-Bim phase) and of retrograde metamorphism (Sb₁ phase and Sb₂₋₁ phase) from quartz grains included in garnet and plagioclase porphyroblasts. Quartz c-axis fabrics for all these phases are explained in terms of a type I crossed girdle, without (only rarely with) higher concentration in the principal axis of strain Y (X>Y>Z), that must have been produced by the activity of a dominant slip system such as rhomb and basal. As a result, the plastic deformation of quartz, which was responsible for the formation of the type I crossed girdle, occurred even under temperatures greater than 500°C and pressures a little greater than 10–11 kb, which correspond to the physical condition of the Sim-Bim phase. It has been assumed that a high strain rate (and/or low H₂O content) caused rhomb and basal to be active as dominant slip systems in the subduction zone related to the formation of the Sambagawa schists even under high temperatures (> 500°C).  相似文献   

Geoengineering techniques used in the construction of underground openings in jointed rocks     

Kenji Aoki  Yukihiro Shiogama 《Engineering Geology》1993,35(3-4):167-173

Aoki, K. and Shiogama, Y., 1993. Geoengineering techniques used in the construction of underground openings in jointed rocks. In: M. Langer, K. Hoshino and K. Aoki (Editors), Engineering Geology in the Utilization of Underground Space.Eng. Geol., 35: 167–173.

Examples of underground openings used for pumped storage hydroelectric power stations and storage facilities for crude oil in Japan are described. In these examples the observational construction technique is important to compensate for missing data in the preliminary surveys. Some new drilling and assessment techniques that have been developed are also introduced.  相似文献