Re-Os isotope systematics and fractionation of siderophile elements in metal phases from CBa chondrites          下载免费PDF全文

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   

Mercury distribution in seawater in Minamata Bay and the origin of particulate mercury     

Mikio Kumagai  Hajime Nishimura 《Journal of Oceanography》1978,34(2):50-56

Horizontal and vertical distributions of mercury were determined in seawater in Minamata Bay and Yatsushiro Sea. The concentrations of total and particulate mercury respectively ranged from 56–285 ng l^–1 and 2.1–506 ng l^–1. They were both highest in the inner most part of Minamata Bay where the sediment was most heavily polluted, and decreased with increasing distance from there. Vertically, an evident increase in concentration was observed near the bottom. A good agreement was found between the mercury content in suspended matter and that in fine sediment particles.These facts show that the particulate mercury is supplied mostly from the bottom sediment, and that it is spreading offshore with dispersing in seawater. This process would eventually result in the pollution of sediment in Yatsushiro Sea.  相似文献   

Gold Mineralization and Occurrence of Sinter in the Hoshino Area, Fukuoka Prefecture, Japan     

Ahmed Belhadi    Tetsuya Nakanishi  Koichiro Watanabe  Eiji Izawa 《Resource Geology》2002,52(4):371-380

Abstract. Several epithermal gold deposits occur in the Hoshino area, which is located in the western end of the late Cenozoic Hohi volcanic zone, north‐central Kyushu, Japan. The area is characterized by intermediate to felsic extrusive rocks of Pliocene age. In the Hoshino area, the shallow manifestation of the hydrothermal activity is exposed on the surface. Several outcrops of sinter are still preserved on the top of hydro thermally altered volcanic rocks, and high‐grade gold‐bearing quartz veins occur on the surface at lower levels. The hydrothermal alteration resulted into well‐developed alteration zones. The zonal alteration pattern, primarily of near‐neutral pH type, is characterized by the outer smectite zone of a lower temperature, and the inner mixed layer minerals zone of a higher temperature. Quartz vein‐related or fracture‐controlled alteration, is represented by the occurrence of interstratified illite/smectite and K‐feldspar, suggesting a potassium‐enriched alteration. The mineralization in the Hoshino area is recognized on the surface by the occurrence of gold‐bearing quartz veins distributed mainly in the mixed layer minerals zone. The fracture system related to the gold mineralization is mainly characterized by NW‐SE trend. The alteration pattern and the mineralogical composition of the veins suggest that the mineralizing fluids had near‐neutral pH and the mineralization is of low‐sulfidation‐type. Fluid inclusion data and textures observed in quartz veins indicate that gold precipitated during boiling. The chemical composition of quartz veins shows that high‐grade gold‐bearing quartz veins are characterized by higher content of Al₂O₃, K₂O and Rb. Several outcrops of silica‐sinters are distributed on the top of the mixed layer minerals zone. Although their structures are not very well preserved, because of later silicification, the Hoshino sinters still show characteristic textures identical to those observed in modern sinters, such as the presence of plant fossil incorporated into the sinters, the strongly developed depositional laminations and the columnar structures perpendicular to the depositional surfaces. Quartz is the only silica mineral constituting the Hoshino sinters presently. The conversion of amorphous silica into quartz was probably governed by higher temperatures resulting from later hydrothermal activity. This later hydrothermal activity is reflected by the intense silicification affecting mainly the lower parts of the sinters and also by the presence of quartz veins cutting the sinters. The distribution of sinters in the Hoshino area is very significant. The presence beneath the sinters of concealed high‐grade gold‐bearing quartz veins should be highly considered and exploration work is strongly suggested.  相似文献   

Factors controlling typhoons and storm rain on the Korean Peninsula during the Little Ice Age   总被引：1，自引：0，他引：1  

Kota Katsuki  Dong-Yoon Yang  Koji Seto  Moriaki Yasuhara  Hiroyuki Takata  Masashi Otsuka  Toshimichi Nakanishi  Yoonyeol Yoon  In-Kwon Um  Richard C. W. Cheung  Boo-Keun Khim  Kaoru Kashima 《Journal of Paleolimnology》2016,55(1):35-48

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A laboratory experiment on the role of grass for infiltration and runoff processes   总被引：1，自引：0，他引：1  

Mikio Hino  Koichi Fujita  Hideharu Shutto   《Journal of Hydrology》1987,90(3-4):303-325

Two lysimeters with the same dimensions were provided, and filled with the same loam clay. On the soil surface of one lysimeter, grass was planted to compare the hydrologic response of the grassed lysimeter with that of the other bare soil lysimeter.

About half of the runoff from the bare soil lysimeter occurred as overland flow, the rest being groundwater flow. Overland flow scarcely occurred from the grassed lysimeter. Grass roots that developed deep into the soil layer play an important role in increasing the infiltration rate as well as in drying the soil uniformly throughout the soil layer by evapotranspiration, preparing for high infiltration and large rainwater storage for the subsequent rainfall event. Accordingly, the total loss by evapotranspiration from the grassed soil amounts to almost twice that from the bare soil.

For an evaporation- and evapotranspiration-prohibited experiment, the recession characteristics from a saturation state showed similar features for the bare and grassed soils, indicating the same microstructure of high moisture reservability for both soils.

The well-developed grass root system reformed the soil structure considerably to produce the seemingly contradicting characteristics of high moisture conductivity and high moisture reservability; i.e. a high infiltration rate and prolonged groundwater discharge.

Finally, the importance of the initial soil moisture in the rainfall-runoff process, rainfall loss and runoff ratio is stressed.  相似文献   

The formation of large mudwaves by turbidity currents on the levees of the Toyama deep-sea channel, Japan Sea   总被引：5，自引：0，他引：5  

Takeshi Nakajima  & Mikio Satoh 《Sedimentology》2001,48(2):435-463

The development of mudwaves on the levees of the modern Toyama deep‐sea channel has been studied using gravity core samples combined with 3·5‐kHz echosounder data and airgun seismic reflection profiles. The mudwaves have developed on the overbank flanks of a clockwise bend of the channel in the Yamato Basin, Japan Sea, and the mudwave field covers an area of 4000 km². Mudwave lengths range from 0·2 to 3·6 km and heights vary from 2 to 44 m, and the pattern of mudwave aggradation indicates an upslope migration direction. Sediment cores show that the mudwaves consist of an alternation of fine‐grained turbidites and hemipelagites whereas contourites are absent. Core samples demonstrate that the sedimentation rate ranged from 10 to 14 cm ka^?1 on the lee sides to 17–40 cm ka^?1 on the stoss sides. A layer‐by‐layer correlation of the deposits across the mudwaves shows that the individual turbidite beds are up to 20 times thicker on the stoss side than on the lee side, whereas hemipelagite thicknesses are uniform. This differential accretion of turbidites is thought to have resulted in the pattern of upcurrent climbing mudwave crests, which supports the notion that the mudwaves have been formed by spillover turbidity currents. The mudwaves are interpreted to have been instigated by pre‐existing large sand dunes that are up to 30 m thick and were created by high‐velocity (10°ms^?1), thick (c. 500 m) turbidity currents spilling over the channel banks at the time of the maximum uplift of the Northern Japan Alps during the latest Pliocene to Early Pleistocene. Draping of the dunes by the subsequent, lower‐velocity (10^?1ms^?1), mud‐laden turbidity currents is thought to have resulted in the formation of the accretionary mudwaves and the pattern of upflow climbing. The dune stoss slopes are argued to have acted as obstacles to the flow, causing localized loss of flow strength and leading to differential draping by the muddy turbidites, with greater accretion occurring on the stoss side than on the lee slope. The two overbank flanks of the clockwise channel bend show some interesting differences in mudwave development. The mudwaves have a mean height of 9·8 m on the outer‐bank levee and 6·2 m on the inner bank. The turbidites accreted on the stoss sides of the mudwaves are 4–6 times thicker on the outer‐bank levee than their counterparts on the inner‐bank levee. These differences are attributed to the greater flow volume (thickness) and sediment flux of the outer‐bank spillover flow due to the more intense stripping of the turbidity currents at the outer bank of the channel bend. Differential development of mudwave fields may therefore be a useful indicator in the reconstruction of deep‐sea channels and their flow hydraulics.  相似文献   

Strong interaction between the ring system and the ionosphere of saturn     

Mikio Shimizu 《Earth, Moon, and Planets》1980,22(4):521-522

An abnormally low electron density in the Saturnian ionosphere observed by the radio occultation experiment of the Pioneer 11 may be explained in terms of the contamination of water in the Saturnian upper atmosphere from its ring system.  相似文献   

The structure of cometary atmospheres     

Mikio Shimizu 《Astrophysics and Space Science》1976,40(1):149-155

The temperature distributions in cometary atmospheres at various heliocentric distances for comets of Bennett and Encke types have been calculated by taking into account heating due to the absorption of solar ultraviolet radiation, cooling by H₂O far infrared emission, and various dynamical processes (expansion, advection, and thermal conduction). The agreement of the results with the observations is in general satisfactory. The conversion of CH₄ and NH₃ to CO and N₂ through thermochemical reaction with H₂O is concluded to be impossible, since the temperature is too low at a heliocentric distance 1.5 AU where CO⁺ ions begin to be observable.  相似文献   

Generation of complete theoretical seismograms for SH—     

Keith Nakanishi  Fred Schwab  Leon Knopoff 《Geophysical Journal International》1977,48(3):525-530

Summary. We report the initial results of our attempts to obtain theoretical seismograms for direct comparison with the experimental time series obtained with the long-period instruments of the WWSSN. The entire theoretical seismogram, including both body waves and surface waves, can be generated for a spherical, anelastic earth by simple inverse Fourier transformation of the sum of the propagating fundamental and higher-mode surface waves. The key to success in reproducing the WWSSN records involves the number of modes, and the minimum period used in these computations; here we use eight modes and a minimum period of 2 s. Efficient computational algorithms make it possible to handle up to 2000 frequency points for each mode; approximately 200 layers are used to model the radial heterogeneity of the earth; attenuation is treated exactly. Examples are given of the SH theoretical seismograms resulting from dislocation sources buried at various depths in the Earth.  相似文献   

An Improved Mellor–Yamada Level-3 Model: Its Numerical Stability and Application to a Regional Prediction of Advection Fog     

Mikio Nakanishi  Hiroshi Niino 《Boundary-Layer Meteorology》2006,119(2):397-407

This note describes a numerically stable version of the improved Mellor–Yamada (M–Y) Level-3 model proposed by Nakanishi and Niino [Nakanishi, M. and Niino, H.: 2004, Boundary-Layer Meteorol. 112, 1–31] and demonstrates its application to a regional prediction of advection fog. In order to ensure the realizability for the improved M–Y Level-3 model and its numerical stability, restrictions are imposed on computing stability functions, on L/q, the temperature and water-content variances, and their covariance, where L is the master length scale and q ²/2 the turbulent kinetic energy per unit mass. The model with these restrictions predicts vertical profiles of mean quantities such as temperature that are in good agreement with those obtained from large-eddy simulation of a radiation fog. In a regional prediction, it also reasonably reproduces the satellite-observed horizontal distribution of an advection fog.  相似文献