Geochemical mapping in Aichi prefecture,Japan: Its significance as a useful dataset for geological mapping     

Koshi Yamamoto  Tsuyoshi Tanaka  Masayo Minami  Koichi Mimura  Yoshihiro Asahara  Hidekazu Yoshida  Setsuo Yogo  Makoto Takeuchi  Masami Inayoshi 《Applied Geochemistry》2007

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Petrogenesis and geochronology of Mishao peraluminous I-type granites,Shalair valley area,NE Iraq     

Imad Kadhim Abdulzahra  Ayten Hadi  Yoshihiro Asahara  Hossein Azizi  Koshi Yamamoto 《Chemie der Erde / Geochemistry》2018,78(2):215-227

The Shalair area, which is located in northeastern Iraq, is considered to be part of the northern Sanandaj-Sirjan Zone (SaSZ) and contains several granitoid bodies. One of these bodies, the Mishao porphyritic-granite (MG), was crystallized at 111.6?±?2.4 Ma, based on its zircon U-Pb age. Its geochemical characteristics suggest that the MG rocks are calc-alkaline, peraluminous, I-type granites with microgranular mafic enclaves. They are enriched in SiO₂, Na₂O, Al₂O₃ and Zr and depleted in MgO, Fe₂O₃, Nb and Ti; in contrast, the enclave sample records lower SiO₂ content and higher contents of MgO and Fe₂O₃. These rocks show an enrichment of LREE relative to HREE, and pronounced negative Eu anomalies implying feldspar fractionation. The isotopic and geochemical characteristics of the MG samples suggest that these rocks are evolved through fractional crystallization. In the La/Nb-Nb diagram and Sm/Nd ratios, the MG rocks and the enclave samples exhibit strong evidence for crustal contamination. The MG rocks record high initial ⁸⁷Sr/⁸⁶Sr (0.70625–0.70740) and low ¹⁴³Nd/¹⁴⁴Nd(i) (0.51235–0.51274) ratios. These Sr-Nd isotopic data, combined with the presence of high Th/U and Rb/Sr ratios and significant depletions of Nb, Ta and Ti, show a relation of these bodies to an active continental margin regime. Based on the age and geochemical data of the MG, this study presents new information about the occurrence of Middle Cretaceous magmatic activities, which are related to the active continental margins in the SaSZ that run parallel to the Zagros Fold-Thrust Belt.  相似文献   

Prediction of monthly mean chlorophylla concentration in Mikawa Bay using GMDH     

Michio J. Kishi  Akihiko Yagi 《Journal of Oceanography》1983,39(6):289-294

Data on organic and inorganic nitrogen and phosphorus, and meteorological conditions observed a few times a month at a buoy station in Mikawa Bay (Japan) are averaged on a monthly basis, and monthly transitions of chlorophylla at the station are predicted by GMDH (Group Method of Data Handling, one of the methods of nonlinear system identification) using these monthly mean data. The prediction is successful. GMDH is useful in describing the ecosystem and in predicting transitions within the bay.  相似文献   

A Numerical Study of Turbulence Statistics and the Structure of a Spatially-Developing Boundary Layer Over a Realistic Urban Geometry     

Atsushi Inagaki  Manabu Kanda  Nurul Huda Ahmad  Ayako Yagi  Naoyuki Onodera  Takayuki Aoki 《Boundary-Layer Meteorology》2017,163(2):161-177

Sonic anemometer measurements are analyzed from two primary field programs and 12 supplementary sites to examine the behaviour of the turbulent heat flux near the surface with high wind speeds in the nocturnal boundary layer. On average, large downward heat flux is found for high wind speeds for most of the sites where some stratification is maintained in spite of relatively intense vertical mixing. The stratification for high wind speeds is found to be dependent on wind direction, suggesting the importance of warm-air advection, even for locally homogenous sites. Warm-air advection is also inferred from a large imbalance of the heat budget of the air for strong winds. Shortcomings of our study are noted.  相似文献   

Preferential dissolution of SiO<Subscript>2</Subscript> from enstatite to H<Subscript>2</Subscript> fluid under high pressure and temperature     

Ayako Shinozaki  Hiroyuki Kagi  Hisako Hirai  Hiroaki Ohfuji  Taku Okada  Satoshi Nakano  Takehiko Yagi 《Physics and Chemistry of Minerals》2016,43(4):277-285

Stability and phase relations of coexisting enstatite and H₂ fluid were investigated in the pressure and temperature regions of 3.1–13.9 GPa and 1500–2000 K using laser-heated diamond-anvil cells. XRD measurements showed decomposition of enstatite upon heating to form forsterite, periclase, and coesite/stishovite. In the recovered samples, SiO₂ grains were found at the margin of the heating hot spot, suggesting that the SiO₂ component dissolved in the H₂ fluid during heating, then precipitated when its solubility decreased with decreasing temperature. Raman and infrared spectra of the coexisting fluid phase revealed that SiH₄ and H₂O molecules formed through the reaction between dissolved SiO₂ and H₂. In contrast, forsterite and periclase crystals were found within the hot spot, which were assumed to have replaced the initial orthoenstatite crystals without dissolution. Preferential dissolution of SiO₂ components of enstatite in H₂ fluid, as well as that observed in the forsterite H₂ system and the quartz H₂ system, implies that H₂-rich fluid enhances Mg/Si fractionation between the fluid and solid phases of mantle minerals.  相似文献   

Intergranular trace elements in mantle xenoliths from Russian Far East: Example for mantle metasomatism by hydrous melt     

Junji  Yamamoto  Shun'ichi  Nakai  Koshi  Nishimura  Ichiro  Kaneoka  Hiroyuki  Kagi  Keiko  Sato  Tasuku  Okumura  Vladimir S.  Prikhod'ko  Shoji  Arai 《Island Arc》2009,18(1):225-241

Based on both major and trace element chemistry, the occurrence of the intergranular component in mantle-derived xenoliths from far eastern Russia has been constrained. Whole-rock trace element measurements of one xenolith show apparent negative anomalies in Ce, Th, and high field strength elements on normalized trace element patterns. The trace element pattern of the whole rock differs from those of constituent minerals, indicating that the anomalies in the whole rock are attributable to the presence of an intergranular component. That assumption was confirmed using in situ analysis of trace elements in the intergranular substance and melt inclusion using laser ablation inductively coupled plasma–mass spectrometry. Both the intergranular component and the melt inclusions have identical trace element patterns, which mean that these materials are a cognate metasomatizing agent. The anomalies are regarded as mantle metasomatism related to an aqueous fluid. Hydrous minerals were observed on the wall of the melt inclusions using micro-Raman spectroscopy, indicating that the melt inclusions contained a large amount of water. Thus, this study reveals a trace element composition of a hydrous metasomatizing agent in the mantle.  相似文献   

Probing the evolution of early-type galaxies using multicolour number counts and redshift distributions     

Fumiaki Nakata  Kazuhiro Shimasaku  Mamoru Doi  Nobunari Kashikawa  Wataru Kawasaki  Yutaka Komiyama  Sadanori Okamura  Maki Sekiguchi  Masafumi Yagi  Naoki Yasuda 《Monthly notices of the Royal Astronomical Society》1999,309(4):L25-L29

We investigate pure luminosity evolution models for early-type (elliptical and S0) galaxies (i.e. no number density change or morphological transition), and examine whether these models are consistent with observed number counts in the B , I and K bands, and redshift distributions of two samples of faint galaxies selected in the I and K bands. The models are characterized by the star formation time-scale τ _SF and the time t _gw when the galactic wind starts to blow, in addition to several other conventional parameters. We find that the single-burst model ( τ _SF=0.1 Gyr and t _gw=0.353 Gyr), which is known to reproduce the photometric properties of early-type galaxies in clusters, is inconsistent with the redshift distributions of early-type galaxies in the field environment, owing to overpredictions of the number of galaxies at z ≳1.4 even with strong extinction which is at work until t _gw. In order for dust extinction to be more effective, we treat τ _SF and t _gw as free parameters, and find that models with τ _SF≳0.5 Gyr and t _gw>1.0 Gyr can be made consistent with both the observed redshift distributions and the number counts, if we introduce strong extinction [ E ( B − V )≥1 as a peak value]. These results suggest that early-type galaxies in the field environment do not have the same evolutionary history as described by the single-burst model.  相似文献   

Depositional ages and characteristics of Middle–Upper Jurassic and Lower Cretaceous lacustrine deposits in southeastern Mongolia          下载免费PDF全文

Hitoshi Hasegawa  Hisao Ando  Noriko Hasebe  Niiden Ichinnorov  Tohru Ohta  Takashi Hasegawa  Masanobu Yamamoto  Gang Li  Bat‐Orshikh Erdenetsogt  Ulrich Heimhofer  Takayuki Murata  Hironori Shinya  G. Enerel  G. Oyunjargal  O. Munkhtsetseg  Noriyuki Suzuki  Tomohisa Irino  Koshi Yamamoto 《Island Arc》2018,27(3)

Lower Cretaceous lacustrine oil shales are widely distributed in southeastern Mongolia. Due to the high organic carbon content of oil shale, many geochemical studies and petroleum exploration have been conducted. Although most of the oil shales are considered to be Early Cretaceous in age, a recent study reveals that some were deposited in the Middle Jurassic. The present study aims at establishing depositional ages and characteristics of the Jurassic and Cretaceous lacustrine deposits in Mongolia. The Lower Cretaceous Shinekhudag Formation is about 250 m thick and composed of alternating beds of shale and dolomite. The Middle Jurassic Eedemt Formation is about 150 m thick and composed of alternating beds of shale, dolomitic marl, and siltstone. The alternations of shale and dolomite in both formations were formed by lake level changes, reflecting precipitation changes. Shales were deposited in the center of a deep lake during highstand, while dolomites were formed by primary precipitation during lowstand. Based on the radiometric age dating, the Shinekhudag Formation was deposited between 123.8 ±2.0 Ma and 118.5 ±0.9 Ma of the early Aptian. The Eedemt Formation was deposited at around 165–158 Ma of Callovian–Oxfordian. The calculated sedimentation rate of the Shinekhudag Formation is between 4.7 ±2.6 cm/ky and 10.0 ±7.6 cm/ky. Shales in the Shinekhudag Formation show micrometer‐scale lamination, consisting of algal organic matter and detrital clay mineral couplets. Given the average thickness of micro‐laminae and calculated sedimentation rate, the micro‐lamination is most likely of varve origin. Both Middle–Upper Jurassic and Lower Cretaceous lacustrine oil shales were deposited in intracontinental basins in the paleo‐Asian continent. Tectonic processes and basin evolution basically controlled the deposition of these oil shales. In addition, enhanced precipitation under humid climate during the early Aptian and the Callovian–Oxfordian was another key factor inducing the widespread oil shale deposition in Mongolia.  相似文献   

A mathematical model of trace element and isotopic behavior during simultaneous assimilation and imperfect fractional crystallization     

Koshi Nishimura 《Contributions to Mineralogy and Petrology》2012,164(3):427-440

The process of coupled assimilation and fractional crystallization (AFC) is one of the most popular petrogenetic concepts that explains magmatic differentiation. Conventional geochemical models for this process assume that crystals are removed instantaneously from the magma body as they are produced; however, recent advances in isotopic microanalysis have clarified that the crystals are suspended within the magma body for a certain period, affecting the whole-rock composition in response to the intra-grain isotopic zoning. This study develops a mass balance model for simultaneous assimilation and imperfect fractional crystallization (AIFC) to describe the effects of suspended crystals on the path of magma evolution. The mass balance differential equations for the liquid and suspended crystals are solved simultaneously. The analytical solution of the AIFC equations gives a quantitative account of the evolution paths of trace elements and isotopes within bulk crystals, liquid, and magma (crystals plus liquid). The chemical path of the magma differs markedly from that predicted by the conventional AFC model.  相似文献   

Geological setting of basaltic rocks in an accretionary complex,Khangai–Khentei Belt,Mongolia     

Kazuhiro Tsukada  Yuki Nakane  Koshi Yamamoto  Toshiyuki Kurihara  Shigeru Otoh  Kenji Kashiwagi  Minjin Chuluun  Sersmaa Gonchigdorj  Manchuk Nuramkhaan  Masakazu Niwa  Tetsuya Tokiwa 《Island Arc》2013,22(2):227-241

We describe the mode of occurrence and geochemical characteristics of basalts, in the Khangai–Khentei belt in Mongolia, overlain by Middle Paleozoic radiolarian chert in an extensive accretionary complex. These basalts are greatly enriched in K, Ti, Fe, P, Rb, Ba, Th, and Nb in comparison to the composition of the mid‐ocean ridge basalts, indicative of within‐plate alkaline type. Ti/Y vs Nb/Y and MnO/TiO₂/P₂O₅ ratios of the basalts also suggest within‐plate affinities. Considering the geochemical characteristics as well as the conformable relationship with the overlying radiolarian chert, the alkaline basalts were clearly not continental but formed a pelagic oceanic island. The mode of occurrence and geochemistry of the basalts show that the alkaline basaltic volcanic activity had taken place to form an oceanic island in the Paleozoic pelagic region sufficiently far from continents to allow radiolarian ooze accumulation.  相似文献