Re-Os isotope systematics and fractionation of siderophile elements in metal phases from CBa chondrites     

Nao Nakanishi  Tetsuya Yokoyama  Satoki Okabayashi  Tomohiro Usui  Hikaru Iwamori 《Meteoritics & planetary science》2018,53(5):1051-1065

We report Os isotope compositions of metal grains in two CB_a chondrites (Bencubbin and Gujba) determined using a micromilling sampling coupled with thermal ionization mass spectrometry, together with the abundances of major and trace siderophile elements obtained by electron probe microanalysis and femtosecond laser ablation inductively coupled plasma–mass spectrometry. The CB_a metal grains presented ¹⁸⁷Os/¹⁸⁸Os ratios akin to carbonaceous chondrites with limited variations (0.1257–0.1270). Most of the CB_a metal grains were scattered along a ¹⁸⁷Re-¹⁸⁷Os reference isochron of IIIAB iron meteorites, indicating that the CB_a metals experienced limited Re-Os fractionation at the time of their formation. The Re/Os ratios of sampling spots for the CB_a metals, recast from the observed ¹⁸⁷Os/¹⁸⁸Os ratios, had a positive correlation with their Os/Ir ratios. In addition, the metal grains showed a positive correlation in a Pd/Fe versus Ni/Fe diagram. These correlations suggest that the CB_a metal grains have formed via equilibrium condensation or evaporation from a gaseous reservoir at ~10⁻⁴ bar with enhanced metal abundances. Compared to the Bencubbin metals, the Gujba metals are characterized by having systematically lower Pd/Fe and Ni/Fe ratios that span subchondritic values. Such a difference was most likely induced by the compositionally heterogeneous impact plume from which the metals were condensed.  相似文献   

An interactive system to assist mineral identification in ore microscopy     

Tetsuya Shoji  Hiroaki Kaneda 《Mathematical Geology》1994,26(8):961-972

An interactive computer system has been developed to assist the mineral identification in ore microscopy. The reference file of the system consists of optical, mechanical, and chemical properties of about 130 ore minerals. The properties are name, chemical formula, color, bireflectance, anisotropism, internal reflection, reflectance at wavelengths of 470, 546, 589, and 650 nm, and polishing hardness and micro-indentation hardness. All the properties except reflectance and microindentation hardness are qualitative or semi-qualitative. Most of the properties are given as characters relative to the more common minerals. This implies that most of the identification processes advance on the basis of the comparison between a subject mineral and coexisting minerals. For this reason, the system asks a user at first to input already identified mineral names. This is quite different from the mineral identification procedures used in petrographic microscopy. To reduce the number of possible minerals, the system presents a series of questions to a user, and the user selects any of the prepared answers according to his observation. The user can also choose any desired question independently of the sequence. The user is expected to be able to recognize some common minerals, such as pyrite, chalcopyrite, galena, and hematite, without the assistance of the system.  相似文献   

Crustal structure in and around the region of the 1995 Kobe Earthquake deduced from a wide-angle and refraction seismic exploration     

Takeshi Ohmura  Takeo Moriya  Chengshi Piao  Takaya Iwasaki  Toshikastu Yoshi  Shin'ichi Sakai  Tetsuya Takeda  Kaoru Miyashita  Humihito Yamazaki  Kiyoshi Ito  Akira Yamazaki  Yoji Shimada  Katsuya Tashiro  Hiroki Miyamachi 《Island Arc》2001,10(3-4):215-227

Abstract The 1995 Kobe (Hyogo-ken Nanbu) earthquake (M_JMA 7.2, M_w 6.9) occurred on Jan. 17, 1995, at a depth of 17 km, beneath the areas of southern part of Hyogo prefecture and Awaji Island. To investigate P-wave velocity distribution and seismological characteristics in the aftershock area of this great earthquake, a wide-angle and refraction seismic exploration was carried out by the Research Group for Explosion Seismology (RGES) . The profile including 6 shot points and 205 observations was 135 km in length, extending from Keihoku, Northern Kyoto prefecture, through Kobe, to Seidan on Awaji Island. The charge of each shot was 350–700 kg. The P-wave velocity structure model showed a complicated sedimentary layer which is shallower than 2.5 km, a 2.5 km-thick basement layer whose velocity is 5.5 km/s, overlying the crystalline upper crust, and the boundary between the upper and lower crust.
Almost all aftershock hypocenters were located in the upper crust. However, the structure model suggests that the hypocenters of the main shock and some aftershock clusters were situated deeper than the boundary between the upper and lower crust. We found that the P-velocity in the upper crust beneath the northern part of Awaji Island is 5.64 km/s which is 3% lower than that of the surrounding area. The low-velocity zone coincides with the region where the high stress moment release was observed.  相似文献   

Electric conductivity of Fe2SiO4–Fe3O4 spinel solid solutions     

T. Yamanaka  H. Shimazu  K. Ota 《Physics and Chemistry of Minerals》2001,28(2):110-118

 The spinel solid solution was found to exist in the whole range between Fe₃O₄ and γ-Fe₂SiO₄ at over 10 GPa. The resistivity of Fe_{3− x} Si _x O₄ (0.0<x<0.288) was measured in the temperature range of 80∼300 K by the AC impedance method. Electron hopping between Fe³⁺ and Fe²⁺ in the octahedral site of iron-rich phases gives a large electric conductivity at room temperature. The activation energy of the electron hopping becomes larger with increasing γ-Fe₂SiO₄ component. A nonlinear change in electric conductivity is not simply caused by the statistical probability of Fe³⁺–Fe²⁺ electron hopping with increasing the total Si content. This is probably because a large number of Si⁴⁺ ions occupies the octahedral site and the adjacent Fe²⁺ keeping the local electric neutrality around Si⁴⁺ makes a cluster, which generates a local deformation by Si substitution. The temperature dependence of the conductivity of solid solutions indicates the Verwey transition temperature, which decreases from 124(±2) K at x=0 (Fe₃O₄) to 102(±5) K at x=0.288, and the electric conductivity gap at the transition temperature decreases with Si⁴⁺ substitution. Received: 15 March 2000 / Accepted: 4 September 2000  相似文献   

Physical and physico - chemical theory of generation,upward transfer,differentiation, and explosion of magmas     

Shimazu  Yasuo 《Bulletin of Volcanology》1963,26(1):237-246

Bulletin of Volcanology -  相似文献   

A sensitivity of squall-line intensity to environmental static stability under various shear and moisture conditions   总被引：2，自引：0，他引：2  

Tetsuya Takemi   《Atmospheric Research》2007,84(4):374-389

Squall lines develop in various climate regions having diverse environmental profiles of wind shear, moisture, and temperature. In order to explore the sensitivity of squall lines to these environmental profiles, we have performed an extensive set of numerical simulations under various shear and moisture conditions in midlatitude-continental and tropical–oceanic temperature environments. From the results of the sensitivity simulations and the analyses of the environmental parameters, it is found that the static stability in a convectively unstable layer is of primary importance in determining the strength of squall lines. Under temperature environments having the same static stability, convective available potential energy (CAPE) and precipitable water content (PWC) well describe the squall-line intensity. Vertical shear also plays an important role in determining the squall-line structure as well as the intensity through the interaction with surface cold pool. The combination of the static stability in a convectively unstable layer, CAPE, and PWC should be examined in diagnosing the intensity of squall lines that develop with an optimal shear for their environment.  相似文献   

Antarctic saline lakes—stable isotopic ratios,chemical compositions and evolution     

Osamu Matsubaya  Hitoshi Sakai  Tetsuya Torii  Harry Burton  Knowles Kerry 《Geochimica et cosmochimica acta》1979,43(1):7-25

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Meteorological assessment of the surface temperatures on Titan: constraints on the surface type     

Tetsuya Tokano 《Icarus》2005,173(1):222-242

The latitudinal profile of near-surface air temperature on Titan retrieved by Voyager 1 has been difficult to understand and raised several speculations about possible exotic processes that might be occurring near Titan's surface, while the thermal properties of the surface itself are unknown. This study systematically investigates the seasonal and spatial variation of the surface temperature and air temperature in the lower troposphere by a 3-dimensional general circulation model for different putative surface types (porous icy regolith, rock-ice mixture, hydrocarbon lakes). For any viable surface type the surface temperature is unlikely to be constant through the year and should more or less vary seasonally and even diurnally, most likely by a few K. Recent observations of tropospheric clouds may be evidence of seasonal variation of the surface temperature and the model predicts in the case of solid surface the development of a convective layer with superadiabatic lapse rates near the surface exactly at those latitudes and seasons where clouds have been identified. The latitudinal profile of the surface temperature retrieved from Voyager 1 infrared spectra can be explained without invoking exotic effects, provided the thermal inertia of the surface is relatively small and/or the surface albedo is low. A dominance of water ice (high thermal inertia and high albedo) at the surface is unfavorable to reproduce the observation. The latitudinal gradient of the surface temperature is particularly large at the hydrocarbon lake surface due to low albedo and small surface drag. Local anomalies of the surface albedo or surface thermal inertia are likely to cause substantial inhomogeneities of the surface temperature. Quasi-permanent accumulation of stratospheric haze at both poles would create a perennial equator-to-pole contrast of the surface temperature, but also a substantially lower global-mean surface temperature due to an enhanced anti-greenhouse effect in summer. The air temperature in the lower troposphere exhibits a tiny latitudinal gradient and a pole-to-pole gradient due to the presence of a pole-to-pole Hadley circulation, indicating that the temperature within the planetary boundary layer may exhibit a vertical profile characteristic of season, location and scenario. There may be a shallow near-surface inversion layer in cold seasons and a shallow convective layer in warm seasons.  相似文献   

Evaluation of the Residual Mass Fractionation in High-Precision Cr Isotopic Analysis with TIMS     

Tetsuya Yokoyama  Yusuke Ohkuma  Keiji Nishikawa  Koki Sumiya  Ikshu Gautam 《Geostandards and Geoanalytical Research》2023,47(2):415-435

The Cr isotope ratios of terrestrial and extra-terrestrial materials are emerging as one of the most important tracers in geosciences. Previous studies on Cr isotopic measurements using TIMS have found that there is residual Cr isotopic fractionation between the mass-fractionation-corrected ⁵³Cr/⁵²Cr and ⁵⁴Cr/⁵²Cr ratios, which may cause an offset of obtained ratios from the reference values. The residual fractionation was thought to be caused by the evaporation of Cr-oxide species during thermal ionisation, but the mechanism by which this residual fractionation could be reduced remained unclear. Here we revisit the issue of residual fractionation and propose that this problem can be alleviated by utilising W filaments instead of conventionally used Re filaments for Cr ionisation. Using W filaments, the formation of CrO⁺ was suppressed during heating as the filament temperature was ~ 100 °C lower than when Re filaments were used. In repeated measurement of a carbonaceous chondrite, the intermediate precisions of ⁵³Cr/⁵²Cr and ⁵⁴Cr/⁵²Cr ratios in the W filament runs were two to three times better than those of the Re filament runs. Therefore, the new finding of this study will be of key importance for future studies of Cr isotopes for terrestrial and extra-terrestrial materials.  相似文献   

Hydrometeorological behaviour of pine and larch forests in eastern Siberia     

Shuko Hamada  Takeshi Ohta  Tetsuya Hiyama  Takashi Kuwada  Atsuhiro Takahashi  Trofim C. Maximov 《水文研究》2004,18(1):23-39

Seasonal changes in the water and energy exchanges over a pine forest in eastern Siberia were investigated and compared with published data from a nearby larch forest. Continuous observations (April to August 2000) were made of the eddy‐correlation sensible heat flux and latent heat flux above the canopy. The energy balance was almost closed, although the sum of the turbulent fluxes sometimes exceeded the available energy flux (R_n ? G) when the latent heat flux was large; this was related to the wind direction. We examined the seasonal variation in energy balance components at this site. The seasonal variation and magnitude of the sensible heat flux (H) was similar to that of the latent heat flux (λE), with maximum values occurring in mid‐June. Consequently, the Bowen ratio was around 1·0 on many days during the study period. On some clear days just after rainfall, λE was very large and the sum of H and λE exceeded R_n ? G. The evapotranspiration rate above the dry canopy from May to August was 2·2 mm day^?1. The contributions of understory evapotranspiration (E_u) and overstory transpiration (E_o) to the evapotranspiration of the entire ecosystem (E_t) were both from 25 to 50% throughout the period analysed. These results suggest that E_u plays a very important role in the water cycle at this site. From snowmelt through the tree growth season (23 April to 19 August 2000), the total incoming water, comprised of the sum of precipitation and the water equivalent of the snow at the beginning of the melt season, was 228 mm. Total evapotranspiration from the forest, including interception loss and evaporation from the soil when the canopy was wet, was 208–254 mm. The difference between the incoming and outgoing amounts in the water balance was from +20 to ?26 mm. The water and energy exchanges of the pine and larch forest differed in that λE and H increased slowly in the pine forest, whereas λE increased rapidly in the larch forest and H decreased sharply after the melting season. Consequently, the shape of the Bowen ratio curves at the two sites differed over the period analysed, as a result of the differences in the species in each forest and in soil thawing. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献