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   

A concordance model of the Lyman α forest at z= 1.95     

Tridivesh Jena  Michael L. Norman  David Tytler  David Kirkman  Nao Suzuki  Angela Chapman  Carl Melis  Pascal Paschos  Brian O'Shea  Geoffrey So  Dan Lubin  Wen-Ching Lin  Dieter Reimers  Eckardt Janknecht  Cora Fechner 《Monthly notices of the Royal Astronomical Society》2005,361(1):70-96

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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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大兴安岭中段龙江盆地热河生物群化石组合及生存时限——来自生物地层、年代地层新证据     

张渝金  杨雅军  蔡闹  吴新伟  张超  郭威 《地质学报》2018,92(2):197-214

龙江盆地光华组层型剖面出露完整,沉积连续,含丰富的热河生物群化石,是大兴安岭中段研究热河生物群起源、演化及辐射的重点剖面之一。本文对光华组层型剖面进行了重新精细测制,认为光华组整合于龙江组安山质角砾熔结凝灰岩之上,被甘河组玄武岩局部不整合覆盖,自下而上可识别出下、中、上3个岩性段;对该组所产动植物化石进行了系统的采集和鉴定,丰富了大兴安岭中段热河生物群的生物类别,并依据新采集化石和前人资料,尝试建立了叶肢介、介形虫、植物化石、昆虫等组合,探讨了各生物组合特征。根据对光华组剖面中段顶底岩层进行了LA-ICP-MS U-Pb锆石年代学研究,揭示龙江盆地热河生物生存的时代为125.4±1.4Ma至120.1±1.1Ma,大致跨越500万年,反映龙江盆地热河生物群繁盛于从阿普特期早期至阿普特期中期。结合古生物特点和笔者前期研究成果,认为龙江盆地热河生物群生存的古环境可能是间歇性或季节性的湖泊;古气候应处于温暖湿润的季节性变化的暖温带,并伴有短暂的半干旱气候。  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   

Attenuation of multiple ScS waves beneath the Japanese Arc     

Ichiro Nakanishi 《Physics of the Earth and Planetary Interiors》1979,19(4):337-347

36 pairs of multiply-reflected ScS waves from deep earthquakes around Japan are analyzed to investigate the anelastic properties of the mantle on the continental and oceanic sides of the dipping slab. The average Q-value for shear waves passing through the mantle on the oceanic side is found to be 226 in the frequency range 10–40 mHz. This Q-value is in good agreement with the Q models SL8 (Anderson and Hart, 1978) and QBS (Sailor and Dziewonski, 1978) which have been derived from free oscillation data. Assuming that the Q-value for the mantle deeper than 400 km on the continental side of the Japanese Arc is the same as that for the model SL8, we obtain a value of Q = 53 in the upper mantle above the dipping slab beneath the Sea of Japan. Higher Q-values are obtained for the mantle behind the northern Izu-Bonin arc.  相似文献   

Reflections of P'P' from upper mantle discontinuities beneath the Mid-Atlantic Ridge     

Ichiro Nakanishi 《Geophysical Journal International》1988,93(2):335-346

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Dense gas in normal and active galaxies     

Kotaro Kohno  Koichiro Nakanishi  Tomoka Tosaki  Kazuyuki Muraoka  Rie Miura  Hajime Ezawa  Ryohei Kawabe 《Astrophysics and Space Science》2008,313(1-3):279-285

Dense molecular medium plays essential roles in galaxies. As demonstrated by the tight and linear correlation between HCN(1–0) and FIR luminosities among star-forming galaxies, from very nearby to high-z ones, the observation of a dense molecular component is indispensable to understand the star formation laws in galaxies. In order to obtain a general picture of the global distributions of dense molecular medium in normal star-forming galaxies, we have conducted an extragalactic CO(3–2) imaging survey of nearby spiral galaxies using the Atacama Submillimeter Telescope Experiment (ASTE). From the survey (ADIoS; ASTE Dense gas Imaging of Star-forming galaxies), CO(3–2) images of M 83 and NGC 986 are presented. Emphasis is placed on the correlation between the CO(3–2)/CO(1–0) ratio and the star formation efficiency in galaxies. In the central regions of some active galaxies, on the other hand, we often find enhanced or overluminous HCN(1–0) emission. The HCN(1–0)/CO(1–0) and HCN(1–0)/HCO⁺(1–0) intensities are often enhanced up to ∼0.2–0.3 and ∼2–3, respectively. Such elevated ratios have never been observed in the nuclear starburst regions. One possible explanation for these high HCN(1–0)/CO(1–0) and HCN(1–0)/HCO⁺(1–0) ratios is X-ray induced chemistry in X-ray dominated regions (XDRs), i.e., the overabundance of the HCN molecule in the X-ray irradiated dense molecular tori. If this view is true, the known tight correlation between HCN(1–0) and the star-formation rate breaks in the vicinity of active nuclei. Although the interpretation of these ratios is still an open question, these ratios have a great potential for a new diagnostic tool for the energy sources of dusty galaxies in the ALMA era because these molecular lines are free from dust extinction.  相似文献