Junji Koyama  Feng Deyi  Yao Jialiu 《地震学报(英文版)》1996,9(1):179

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Rèsumè on new monograph “Advance in Mathematical Seismology” edited by Junji Koyama & Feng Deyi     

Junji Koyama  Feng Deyi  Yao Jialiu 《地震科学（英文版）》1996,9(1):179-179

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Calorimetric study of the stability of high pressure phases in the systems CoOSiO₂ and “FeO”SiO₂, and calculation of phase diagrams in MOSiO₂ systems     

Alexandra Navrotsky  Faivel S. Pintchovski  Syun-Iti Akimoto 《Physics of the Earth and Planetary Interiors》1979,19(4):275-292

High temperature calorimetric measurements of the enthalpies of solution in molten if2 PbO · B₂O₃ of α- and γ-Fe₂SiO₄ and α-, β-, and γ-Co₂SiO₄ permit the calculation of phase relations at high pressure and temperature. The reported triple point involving α-, β-, and γ-Co₂SiO₄ is confirmed to represent stable equilibrium. The curvature in the α?β phase boundary in Co₂SiO₄ and of an α?γ boundary in Fe₂SiO₄ at high temperature is explained in part by the effects of compressibility and thermal expansion, but better agreement with the observed phase diagram is obtained when one considers the effect of small amounts of cation disorder in the spinel and/or modified spinel phases. The calculated ΔH⁰ and ΔS⁰ values for the α?β, α?γ, and β?γ transitions show that enthalpy and en changes both vary strongly in the series Mg, Fe, Co, and Ni, and are of equal importance in determining the stability relations. The disproportionation of Fe₂SiO₄ and Co₂SiO₄ spinel to rocksalt plus stishovite is calculated to occur in the 170–190 kbar region; cation disorder and/or changes in wüstite stoichiometry can affect the P?T slope. The calorimetric data for CoSiO₃ and FeSiO₃ are in good agreement with the observed phase boundary for pyroxene formation from olivine and quartz. The decomposition of pyroxene to spinel and stishovite at pressures near the coesite-stishovite transition is predicted in both iron and cobalt systems. The use of calorimetric data, obtained from small samples of high pressure phases, is very useful in predicting equilibrium phase diagrams in the 50–300 kbar range.  相似文献   

Growth of quartz crystals twinned after Japan Law     

Ichiro Sunagawa  Junji Takahashi  Kazutoshi Aonuma  Minoru Takahashi 《Physics and Chemistry of Minerals》1979,5(1):53-63

The flattened or elongated morphology often observed in contact twinned crystals has been referred to the so-called re-entrant corner effect at twin junctions. To re-investigate the validity of this mechanism, natural quartz crystals twinned after Japan Law have been subjected to re-growth in a commercial synthetic quartz autoclave, and the change in their morphology and surface microtopography by re-growth studied. It is found that although twin re-entrant corners may play a role of preferential growth sites, this role can be weakened considerably and in fact can become almost negligible when crystals grow under high supersaturation condition. Preferential growth at the re-entrant corner of a twin junction is probably due to clusters of dislocations concentrated in the composition plane, and not due to the so-called re-entrant corner effect in its original sense.  相似文献   

Pyroxene-garnet solid-solution equilibria in the systems Mg₄Si₄O₁₂Mg₃Al₂Si₃O₁₂ and Fe₄Si₄O₁₂Fe₃Al₂Si₃O₁₂ at high pressures and temperatures     

M. Akaogi  S. Akimoto 《Physics of the Earth and Planetary Interiors》1977,15(1):90-106

Pyroxene-garnet solid-solution equilibria have been studied in the pressure range 41–200 kbar and over the temperature range 850–1,450°C for the system Mg₄Si₄O₁₂Mg₃Al₂Si₃O₁₂, and in the pressure range 30–105 kbar and over the temperature range 1,000–1,300°C for the system Fe₄Si₄O₁₂Fe₃Al₂Si₃O₁₂. At 1,000°C, the solid solubility of enstatite (MgSiO₃) in pyrope (Mg₃Al₂Si₃O₁₂) increases gradually to 140 kbar and then increases suddenly in the pressure range 140–175 kbar, resulting in the formation of a homogeneous garnet with composition Mg₃(Al_0.8Mg_0.6Si_0.6)Si₃O₁₂. In the MgSiO₃-rich field, the three-phase assemblage of β- or γ-Mg₂SiO₄, stishovite and a garnet solid solution is stable at pressures above 175 kbar at 1,000°C. The system Fe₄Si₄O₁₂Fe₃Al₂Si₃O₁₂ shows a similar trend of high-pressure transformations: the maximum solubility of ferrosilite (FeSiO₃) in almandine (Fe₃Al₂Si₃O₁₂) forming a homogeneous garnet solid solution is 40 mol% at 93 kbar and 1,000°C.If a pyrolite mantle is assumed, from the present results, the following transformation scheme is suggested for the pyroxene-garnet assemblage in the mantle. Pyroxenes begin to react with the already present pyrope-rich garnet at depths around 150 km. Although the pyroxene-garnet transformation is spread over more than 400 km in depth, the most effective transition to a complex garnet solid solution takes place at depths between 450 and 540 km. The complex garnet solid solution is expected to be stable at depths between 540 and 590 km. At greater depths, it will decompose to a mixture of modified spinel or spinel, stishovite and garnet solid solutions with smaller amounts of a pyroxene component in solution.  相似文献   

Electrical conductivity jump produced by the α-β-δ transformation in Mn₂GeO₄     

Takehiko Yagi  Syun-Iti Akimoto 《Physics of the Earth and Planetary Interiors》1974,8(3):235-240

The electrical conductivity of three polymorphs of Mn₂GeO₄ was measured under high pressures in the temperature range of 300–1200 K. It was found that the electrical conductivity increases discontinuously due to the transformation both from olivine structure (α) to modified spinel structure (β) and from β to strontium plumbate structure (δ). The amount of discontinuous change is about one half order of magnitude from α to β and one third order of magnitude from β to δ at 1200 K. In order to see the effect of the presence of iron ions, the electrical conductivity of the solid solution of (Mn_0.9Fe_0.1)₂GeO₄ was also measured. It was found that at low temperatures, where impurity conduction may be dominant, the solid solution is more conductive than the pure Mn₂GeO₄, but at high temperature no significant differences were observed between the solid solution and pure Mn₂GeO₄ in all polymorphs.A phase transformation from modified spinel structure to strontium plumbate structure is considered to be one of the plausible transformations occurring at a depth around 650 km in the earth's mantle. These experiments suggest that if this kind of transformation occurs in the mantle, some degrees of discontinuous change in electrical conductivity may be expected around 650 km.  相似文献   

Editorial     

Briad Ridley  Dieter Ehhalt  Hajime Akimoto 《Journal of Atmospheric Chemistry》2001,38(1):1-1

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Solubility controlled noble gas fractionation during magmatic degassing: Implications for noble gas compositions of primary melts of OIB and MORB     

Junji Yamamoto  Pete G. Burnard 《Geochimica et cosmochimica acta》2005,69(3):727-734

Noble gas abundances in basaltic glasses from ocean islands (OIBs) are generally lower than those of mid-oceanic ridge basalts (MORBs), contrary to most geodynamic models which usually require that the source of OIBs is less degassed (resulting in higher primordial noble gas abundances) and more trace element enriched (resulting in higher radiogenic noble gas abundances) than the MORB source. Therefore, noble gas abundances in OIBs are often thought to have been reduced by extensive gas loss from the magma before eruption.The extent of magmatic degassing can be tested as it will cause characteristic changes in the composition of the volatiles; notably the ⁴He/⁴⁰Ar* ratio (where ⁴⁰Ar* is ⁴⁰Ar corrected for atmospheric contamination) will increase in residual volatiles due to the higher solubility of He relative to Ar. The degree of He-Ar fractionation for a given fraction of gas loss depends on the ratio of the solubilities, S_He/S_Ar, which is sensitive to (among other things) the CO₂ and H₂O content of the basalt at the time of degassing.From a global database of OIB and MORB glasses, we show that ⁴He/⁴⁰Ar* ratios of MORB glasses are broadly consistent with degassing of a magma with an initial ⁴⁰Ar of ≈1.5 × 10⁻⁵ ccSTP/g, i.e., similar to that of the “popping rock.” However, OIB glasses generally have lower ⁴⁰Ar* concentration for a given ⁴He/⁴⁰Ar*. While this would appear to require lower ⁴⁰Ar* abundances in the undegassed OIB magmas, the higher volatile contents of OIBs will reduce S_He/S_Ar (relative to MORBs) during degassing. By modeling S_He/S_Ar in OIBs, it is possible to show that extensive degassing of OIBs can occur without dramatically increasing the ⁴He/⁴⁰Ar* ratio. We show that undegassed ⁴⁰Ar concentrations of OIB magmas were probably similar to those of MORBs.  相似文献   

汾渭平原典型城乡PM_2.5中多环芳烃特征与健康风险     

蔡瑞婷  肖舜  董治宝  曹军骥  张宁宁  刘随心  沈振兴  徐红梅  陶燕  李星敏  王鑫  王雨萌 《地理学报》2021,76(3):740-752

为查明汾渭平原典型城乡地区重度污染天气PM_2.5中多环芳烃（PAHs）污染特征及其人群健康效应,本文于2018—2019年冬季分别选取西安和陇县作为城乡对比参照点,采集了重度污染天气PM_2.5颗粒态气溶胶样品。利用气相色谱—质谱联用仪（GC-MS）检测样品中具有“三致效应”的15种PAHs含量及组分特征,使用特征比值法及主成分法进行PAHs源解析,并分析了气象因素对PAHs质量浓度的可能影响,通过对苯并芘（BaP）等效毒性浓度和终生超额致癌风险度（ILCR）的计算,对人群健康风险进行评估。结果表明：西安与陇县在重度污染天气条件下PM_2.5中15种PAHs总平均质量浓度分别为243.78 ng/m³、609.39 ng/m³,其中4~6环PAHs占比最高;且PAHs浓度与气温、气压及风速呈显著负相关,与相对湿度则无明显相关性。西安PAHs污染主要来自燃烧源与交通排放源,而煤炭及生物质燃烧是造成陇县PAHs质量浓度偏高的主要原因。健康风险评估结果显示,重污染天气下陇县人群通过呼吸引发的致癌风险要高于西安,女性致癌风险高于男性,成人致癌风险高于儿童,且两地区成人ILCR值均超过风险阈值,存在潜在致癌风险,儿童则无明显致癌风险。  相似文献   

The system iron-enstatite-water at high pressures and temperatures—formation of iron hydride and some geophysical implications     

Toshihiro Suzuki  Syun-iti Akimoto  Yuh Fukai 《Physics of the Earth and Planetary Interiors》1984,36(2):135-144

The system iron-enstatite-water was investigated at pressures around 5 GPa and at temperatures ranging from 1000 to 1200°C, using several different kinds of starting materials. Quenched samples showed the coexistence of iron, olivine and pyroxene. Synthesis of the Fe-containing olivine in the run products proves that a series of reactions, Fe + H₂O → FeH_x + FeO and FeO + MgSiO₃ → (Mg, Fe)₂SiO₄, have taken place. Spherical “balls of iron” were observed in the 1200°C run. This strongly indicates that the melting temperature of iron decreased by ～ 500 K by the possible dissolution of hydrogen. Following geophysical implications are derived from these experimental results. If water was retained in the hydrous minerals in the primordial material, the iron-water reaction is expected to occur throughout the core-formation process. The reaction product FeH_x will melt and then sink to form a proto-core and iron oxide will be dissolved in the Earth's mantle. The dissolution of hydrogen in the Earth's core is a natural consequence of the core-formation process.  相似文献