Origin of iron-rich olivine in the matrices of type 3 ordinary chondrites: an experimental study     

Hiroko Nagahara  Ikuo Kushiro 《Earth and Planetary Science Letters》1987,85(4)

In order to understand the origin of iron-rich olivine in the matrices of type 3 ordinary chondrites, the reaction of metallic iron and enstatite, with and without forsterite and SiO₂, has been experimentally reproduced at temperatures between 1150° and 800°C and P_O2 between 10⁻¹¹ and 10⁻¹⁶ atm (between the IQF and MW buffers). The olivine produced ranges from Fo₅₈ to Fo₃₄ and this composition does not change significantly with temperature and time of the runs. The magnesian olivine which forms does become more magnesian with increasing forsterite/enstatite ratio of the starting materials. Iron-rich olivine (Fo< 35) cannot be formed by the reaction of enstatite and metallic iron, with or without forsterite as starting materials but it can be formed in the presence of free silica. The composition of olivine becomes more iron-rich with increasing silica/enstatite ratio. The compositional range of olivine formed from each mixture is 25–30 mole% Fo regardless of the temperature, composition, mineral assemblage, and run duration.From these experimental results, two possibilities suggested for the origin of the iron-rich olivine in the matrices of type 3 ordinary chondrites: (1) free silica must have been present if the iron-rich olivine was formed by solid-state reactions under oxidizing condition in the solar nebula; (2) reaction of silicon-rich gas with metallic iron took place under oxidizing condition in the solar nebula. Though it is difficult to define which alternative was dominant, the formation of free silica or silicon-rich gas may be a result of fractional condensation. This is possible if there is a reaction relation between forsterite and gas to produce enstatite. The suggested fractional condensation is supported by the fact that the compositions of the fine-grained matrices of type 3 ordinary chondrites are more silica-rich than the bulk compositions of the chondrites. Though it is not known whether such conditions were established all over the nebula or locally in the nebula, both fractionation and more oxidizing conditions than the average solar nebula are required for the formation of matrix olivine.  相似文献   

Insight into nitrous oxide production processes in the western North Pacific based on a marine ecosystem isotopomer model   总被引：2，自引：0，他引：2  

Chisato Yoshikawa  Hitomi Abe  Maki N. Aita  Florian Breider  Keichi Kuzunuki  Sakae Toyoda  Nanako O. Ogawa  Hisami Suga  Naohiko Ohkouchi  Sebastian O. Danielache  Masahide Wakita  Makio C. Honda  Naohiro Yoshida 《Journal of Oceanography》2016,72(3):491-508

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Site-specific ground response analysis and liquefaction assessment of Vijayawada city (India)     

Neelima D. Satyam  Ikuo Towhata 《Natural Hazards》2016,81(2):705-724

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A generic formulation for microtremor exploration methods using three-component records from a circular array   总被引：1，自引：0，他引：1  

Ikuo Cho  Taku Tada  Yuzo Shinozaki 《Geophysical Journal International》2006,165(1):236-258

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Water content in natural eclogite and implication for water transport into the deep upper mantle   总被引：14，自引：0，他引：14  

Ikuo Katayama  Satoru Nakashima  Hisayoshi Yurimoto 《Lithos》2006,86(3-4):245-259

Infrared spectroscopy and ion micro-probe measurements showed that the major constituent minerals of eclogites from the Kokchetav massif, which have been subducted to 180 km depths, contain significant amounts of water up to 870 ppm H₂O (by weight) in omphacite, 130 ppm H₂O in garnet and 740 ppm H₂O in rutile. Omphacite shows three hydroxyl absorption bands at 3440–3460, 3500–3530 and 3600–3625 cm^− 1, garnet has a single band at 3580–3630 cm^− 1 and rutile has a single sharp band at 3280 cm^− 1. The hydroxyl absorbance at these wavenumbers changes with the crystal orientation in polarized infrared radiation, indicating that the water is structurally incorporated in these minerals. The water contents in omphacite and garnet increase systematically with the metamorphic pressure of the host eclogites. The partitioning coefficient of the water content between coexisting garnet and omphacite is similar in different eclogites, D^Grt/Omp0.1–0.2, but decreases slightly at high pressure. Based on the mineral proportions of the eclogites, we estimate bulk-rock water content in the eclogites ranging from 3070 to 300 ppm H₂O (by weight). Although hydrous minerals are absent in the diamond-grade eclogite (60 kbar and 1000 °C), trace amounts of water are incorporated in the nominally anhydrous minerals such as omphacite and garnet. The presence of significant water in these minerals implies that the subducting oceanic crust can transport considerable amounts of water into the deep upper mantle beyond the stability of hydrous minerals. Such water may be stored in the deep upper mantle and have an important influence on dynamics in the Earth's interior.  相似文献   

地球物理学方法在区分多年冻土区咸水层和淡水融化层中的应用     

Kenji Yoshikawa  Vladimir Romanovsky  Nataria Duxbury  Jerry Brown  Alexandre Tsapin 《冰川冻土》2004,26(Z1):301-309

Direct current resistivity and ground penetrating radar surveys were employed to obtain the value of the resistivity and dielectric constant in the brine near the Barrow, Alaska. The geophysical surveys were undertaken together with the permafrost drilling program for the measuring of the ground temperature regime and for the core sampling. The sampled cores were measured for their physical and chemical properties in the laboratory under different temperature conditions (-60 to 20 ℃). Laboratory results support field observations and led to the development of a technique for distinguishing freshwater taliks and brine layers in permafrost. These methods were also employed in freshwater taliks near Council,Alaska. The electrical resistivity is a powerful and sensitive parameter for brine detection. However, the resistivity is a less sensitive indicator of the soil type or water content under highly saline conditions.High frequency dielectric constant is an ideal second parameter for the indication of the soil type, liquid water content and other physical properties. The imaginary part of the dielectric constant and resistivity have a significant dependence upon salinity, i.e. upon freezing temperature. The ground temperature regime and the freezing point of the brine layer are important parameters for studying the electric properties of permafrost terrain.  相似文献   

Prediction of volcanic eruption Aso and Sakurazima and some related geophysical problems     

Akira Kubotera  Keizo Yoshikawa 《Bulletin of Volcanology》1963,26(1):297-317

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Phytoplankton photosynthetic parameters and primary production in Japan Sea and the East China Sea: Toward improving primary production models     

Takashi Yoshikawa  Ken Furuya 《Continental Shelf Research》2008

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A complete introduction to the SCJ proposal and its commentary on the development of seismically resilient cities     

Akira Wada  Ikuo Towhata  Kazuo Tamura  Qu Zhe 《地震工程与工程振动(英文版)》2018,17(4):677-691

In modern society, the population, wealth and social functions are increasingly concentrated in a few large cities. Such concentration brings about efficiency while at the same time it increases the vulnerability of the society. To address this issue, the Science Council of Japan (SCJ) published a proposal entitled “Shape Cities and Societies Safer against Severe Earthquakes”. It makes a variety of suggestions for enhancing the seismic resilience of large cities, including: (1) comprehensive thinking based on the latest scientific knowledge and rich imagination; (2) selection of sites suitable for residence and social activities; (3) introducing the urban seismic coefficient; (4) promoting the enhancement of the seismic performance of buildings and civil structures; (5) easing the concentration of population and functions; (6) building communities that enable shelter and escape; (7) resilient technology of information and communication system and its effective utilization; (8) preparation and implementation of emergency response after earthquakes; (9) development and application of new structural seismic technology; (10) learning from domestic and foreign earthquake disasters and launching of international cooperation and knowledge sharing and (11) taking actions from a multidisciplinary perspective. The proposal is introduced in this paper.  相似文献   

Development of a thin diatom layer observed in a stratified embayment in Japan     

Goh Onitsuka  Yutaka Yoshikawa  Tomoyuki Shikata  Kei Yufu  Kazuo Abe  Takahisa Tokunaga  Katsunori Kimoto  Takeshi Matsuno 《Journal of Oceanography》2018,74(4):351-365

The temporal evolution of a thin phytoplankton layer was observed by field measurements using a research vessel and mooring instruments in the Yatsushiro Sea, a semi-enclosed narrow embayment in Japan, in early August 2013. The subsurface chlorophyll maximum developed into a thin layer within 2 days just below the pycnocline at around 10-m depth, where turbulent mixing (the dissipation rate of turbulent kinetic energy) was weak (low). The layer persisted for 1.5 to 2 days and declined after irradiance drastically decreased at the sea surface. At the peak period, the layer thickness, which is defined as the full-width at half-maximum of the peak in chlorophyll a concentration, ranged from 0.6 to 1.4 m, and the maximum concentration reached 42.3 mg m^?3. The horizontal extent of the layer was approximately 10 km along the longitudinal axis of the bay. The phytoplankton population characterized by the layer was dominated by a chain-forming centric diatom, Chaetoceros spp. The formation mechanisms of the thin diatom layer were investigated using the observed data and a vertical one-dimensional model that includes physical and biological processes. The results suggest that the development of the thin layer was caused by in situ growth and aggregation due to nutrient-dependent sinking of the species under weak turbulence. The study highlights that continuous multidisciplinary observations and understanding species-specific physiological responses to environmental variations are necessary to elucidate drastically fluctuating phytoplankton dynamics in a coastal water.  相似文献