The role of the grain boundary at chemical and isotopic fronts in marble during contact metamorphism     

Hideki Wada  Takamaru Ando  Masayuki Suzuki 《Contributions to Mineralogy and Petrology》1998,132(4):309-320

Carbon and oxygen isotopic profiles around a low pressure metasomatic wollastonite reaction front in a marble of the Hida metamorphic terrain, central Japan, display typical metamorphic fluid-enhanced isotopic zonations. Isotopic profiles obtained from detailed microscale analyses perpendicular to the chemical reaction front in calcite marble show that diffusion-enhanced isotopic exchange may control these profiles. Carbon and oxygen isotopic behaviour in grain boundaries is remarkably different. Oxygen isotopic troughs (¹⁸O depleted rims) around the calcite-grain boundaries are widely observed in this contact aureole, demonstrating that diffusion of oxygen in calcite grain boundary dominates over lattice diffusion in calcite. In contrast, no difference is observed in carbon isotopic profiles obtained from grain cores and rims. There is thus no specific role of the grain boundary for diffusion of carbonic species in the metamorphic fluid during transportation. Carbon chemical species such as CO₂ and CO₃ ions in metamorphic fluid migrate mainly through lattice diffusion. The carbon and oxygen isotope profiles may be modelled by diffusion into a semi-infinite medium. Empirically lattice diffusion of oxygen isotopes is almost six times faster than that of carbon isotopes, and oxygen grain-boundary diffusion is ten times faster than oxygen lattice diffusion. Oxygen isotopic results around the wollastonite vein indicate that migration of the metamorphic fluid into calcite marble was small and was parallel to the aquifer. From the stability of wollastonite and the attainment of oxygen isotopic equilibrium, we suggest that diffusion of oxygen occurred through an aqueous fluid phase. The timescale of formation of the oxygen isotopic profile around the wollastonite vein is calculated to be about 0.76 × 10⁶ years using the experimentally determined diffusion constant. Received: 14 January 1997 / Accepted: 23 April 1998  相似文献   

Statistical study of Am stars in spectroscopic binary systems     

Masatoshi Kitamura  Masayuki Kondo 《Astrophysics and Space Science》1978,56(2):341-362

Using the Am components in spectroscopic binaries, the region of metallicism in the (logm, logR) diagram is statistically discussed. The metallic-line characteristics appear in a slightly evolved stage near the Main Sequence within a belt characterized by logg=3.8–4.2, for which the radiiR/R =1.5–2.7. The distribution in the diagram indicates that appreciable differences should exist in the abundances as well as in the mixing lengths of the atmospheres of the Am components.Synchronism between rotation and revolution for the Am components is discussed, and it is clearly found that the synchronism holds accurately for the Am binaries with periods less than about six days, but for those with periods between six and ten days some Am components corotate and some do not, perhaps depending upon their ages.Using the Am spectroscopic binaries with periods less than twelve days, we find that the excess of metallicity is statistically correlated with the rotational velocity; and it is confirmed that the metallicity grossly decreases with increasing rotational velocity. If the effect of a non-Am secondary component is eliminated from a [m ₁]-value for the combined light, the correlation between metallicity excess and rotational velocity for the Am components only should approach [m ₁]/V (km s^–1)=–0.00077.  相似文献   

Influence of bedrock groundwater on streamflow characteristics in a volcanic catchment          下载免费PDF全文

Masamitsu Fujimoto  Nobuhito Ohte  Masatoshi Kawasaki  Ken'ichi Osaka  Masayuki Itoh  Izumi Ohtsuka  Masami Itoh 《水文研究》2016,30(4):558-572

Groundwater movements in volcanic mountains and their effects on streamflow discharge and representative elementary area (REA) have remained largely unclear. We surveyed the discharge and chemical composition of spring and stream water in two catchments: the Hontani river (NR) catchment (6.6 km²) and the Hosotani river (SR) catchment (4.0 km²) at the southern part of Daisen volcano, Japan. Daisen volcano is a young volcano (17 × 10³ years) at an early stage of erosion. Our study indicated that deep groundwater that moved through thick lava and pyroclastic flows and that could not be explained by shallow movements controlled by surface topography contributed dominantly to streamflow at larger catchment areas. At the NR catchment, the deep groundwater contribution clearly increased at a catchment boundary defined by an area of 3.0 km² and an elevation of 800 m. At the SR catchment, the contribution deep groundwater to the stream also increased suddenly at a boundary threshold of 2.0 and 700 m. Beyond these thresholds, the contributions of deep bedrock groundwater remained constant, indicating that the REA is between 2 and 3 km² at the observed area. These results indicate that the hydrological conditions of base flow were controlled mainly by the deep bedrock groundwater that moved through thick lava and pyroclastic flows in the undissected volcanic body of the upper part of the catchment. Our study demonstrates that deep and long groundwater movements via a deep bedrock layer including thick deposits of volcanic materials at the two catchments on Daisen volcano strongly determined streamflow discharge instead of the mixing of small‐scale hydrological conditions. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Formation of globular clusters induced by external ultraviolet radiation     

Kenji Hasegawa  Masayuki Umemura  Tetsu Kitayama 《Monthly notices of the Royal Astronomical Society》2009,397(3):1338-1347

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Further characterization of carbonaceous materials in Hayabusa‐returned samples to understand their origin     

Masayuki Uesugi  Motoo Ito  Hikaru Yabuta  Hiroshi Naraoka  Fumio Kitajima  Yoshinori Takano  Hajime Mita  Yoko Kebukawa  Aiko Nakato  Yuzuru Karouji 《Meteoritics & planetary science》2019,54(3):638-666

Carbonaceous materials in the sample catcher of the Hayabusa spacecraft were assigned as category 3 particles. We investigated the category 3 particles with a suite of in situ microanalytical methods. Possible contaminants collected from the cleanrooms of the spacecraft assembly and extraterrestrial sample curation center (ESCuC) were also analyzed in the same manner as category 3 particles for comparison. Our data were integrated with those of the preliminary examination team for category 3 particles. Possible origins for the category 3 particles include contamination before and after the operation of the Hayabusa spacecraft.  相似文献   

Episyenite formation in the Toki granite,central Japan     

Shoji?NishimotoEmail author  Hidekazu?Yoshida  Yoshihiro?Asahara  Tadahiko?Tsuruta  Masayuki?Ishibashi  Nagayoshi?Katsuta 《Contributions to Mineralogy and Petrology》2014,167(1):960

Episyenite is a quartz-depleted vuggy rock resulting from hydrothermal alteration of granitic rocks. This is the first report of its existence in an island arc, which is identified in a deep drill core of the Toki Cretaceous granite distributed in central Japan. In order to understand the petrographical features of the episyenite, neutron porosity measurement, geochemical analysis, microscopic observation, and X-ray computed tomography scanning were carried out. The results show remarkably high porosity (35.4 %) due to interconnecting vugs and the removal of quartz, plagioclase, and biotite. The Rb–Sr isotopic results and the paragenetic sequence of secondary minerals in the vugs suggest that the hydrothermal alteration process can be divided into an episyenitization stage and a later hydrothermal stage. At the episyenitization stage (70.6 ± 3.1 Ma) ca. 6 million years after the emplacement of the unaltered granite (76.3 ± 1.5 Ma), dissolution of quartz, biotite, and plagioclase occurred and was followed by the precipitation of albite, vermicular chlorite, and platy calcite. The episyenitization is considered as a local alteration of the Toki granite in an isotopically closed system. At the later hydrothermal stage, illite and secondary quartz precipitated from circulating meteoric-derived water in the dissolution vugs. Superimposing alteration at the later hydrothermal stage is limited, which results in the preservation of the episyenite in an almost primitive condition.  相似文献   

Statistical Analysis of Ground Motions Estimated on the Basis of a Recipe for Strong-motion Prediction: Approach to Quantitative Evaluation of Average and Standard Deviation of Ground Motion Distribution     

Masayuki Yamada  Shigeki Senna  Hiroyuki Fujiwara 《Pure and Applied Geophysics》2011,168(1-2):141-153

For seismic hazard assessment, we study the variabilities of predicted ground motion on the basis of a ??recipe for predicting strong ground motion?? and propose approximations to evaluate spatial distributions of the standard deviation for PGV, R1.0, R2.0, and R5.0 in the estimated ground motions. For strong-motion prediction, we use a finite difference method for a long period range (>1.0?s). To estimate variabilities, a Monte Carlo simulation is used and we adopt the Latin Hypercube Sampling (LHS) technique to reduce computations. In this article, we consider only aleatory variabilities in source parameters among all possible variabilities, such as those in the source parameters, the propagation characteristics and site characteristics. Model sources are assumed for dip-slip fault and strike-slip fault, and the variabilities are considered for parameters such as asperity location, rupture starting point, average asperity slip contrast, stress drop and rupture velocity. On the target site, 100 instances of PGV, R1.0, R2.0 and R5.0 data are obtained for 100 sets of parameters and an average and a standard deviation of the log normal distribution, corresponding to the variability for ground motion estimation, are statistically analyzed. For all target sites uniformly distributed in the area around the faults, the average and the standard deviation are statistically analyzed and spread to spatial maps. It is found that the spatial distributions of standard deviation values for both the dip-slip and strike-slip faults are not uniform. Approximations are attempted to develop a quantitative evaluation for spatial distributions of the standard deviation of the log normal distribution for PGV, R1.0, R2.0, and R5.0. The spatial distributions by these approximations are considered to almost reconstruct the characteristics, which are statistically analyzed by the finite difference method.  相似文献   

Kinetic stability of a melted iron globule during chondrule formation. I. Non‐rotating model     

Masayuki UESUGI  Minoru SEKIYA  Tomoki NAKAMURA 《Meteoritics & planetary science》2008,43(4):717-730

Abstract— We have investigated the kinematics of the separation of iron globules from chondrules during chondrule formation. A simple model, which assumes that the system has no angular momentum, was used to calculate the energy of a system with an iron globule and a chondrule. The energies of three different states were calculated: 1) a melted iron globule fully embedded in a melted chondrule, 2) a melted iron globule on the surface of a melted chondrule, and 3) a melted iron globule being separated from a melted chondrule. We also calculated the lowest energy shape for a melted iron globule on the surface of a melted chondrule, and compared our result with the shapes of four natural samples of chondrules and iron globules in thin sections. The shapes were calculated using an assumed value for the interface energy between the four couples of melted chondrules and the iron globules, and agree well with the natural shapes of chondrules and iron globules. The results of our calculations show that the iron globules of these four samples would be strongly bound to the surface of the melted chondrule during chondrule formation, and separation would be difficult, if the iron globules had been on the surface of precursors of these chondrules. Our results also show that if these iron globules were initially inside and transported to the surface of the melted chondrule, most of them would be ejected from the inside to outside because of surface tension forces, as long as the energy losses due to viscous dissipation when the globules pass through the surface of melted chondrules were sufficiently small. Although further improvement of the model is required, our results demonstrate that this ejection process may be responsible for the depletion of siderophile elements in natural chondrules.  相似文献   

Verifying optimality of rainfed agriculture using a stochastic model for drought occurrence   总被引：1，自引：1，他引：0  

Erfaneh Sharifi  Koichi Unami  Macarius Yangyuoru  Masayuki Fujihara 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(5):1503-1514

It may be paradoxical but subsistence rainfed agriculture is the predominant source of food in Sub-Saharan Africa where the production uncertainty is associated with the stochastic nature of rainfall. This paper attempts to comprehend the rationale of this situation by a mathematical approach. Considering the level of drought severity as the zero-reverting Ornstein–Uhlenbeck process, optimality of rainfed agriculture is investigated in the context of stochastic control theory. Occurrence of drought terminating growth of crops is modelled with the concept of first exit time. A stochastic control problem allowing for virtual cost of irrigation, water stress to crops, and benefits of farming is formulated with irrigation effort as the control variable. The Hamilton–Jacobi–Bellman equation governing the optimal control is studied to identify the set of cost functions optimizing rainfed agriculture in an inverse problem approach. Data and information were collected in the coastal savanna agro-ecological zone of Ghana, to identify model parameters, formulate the stochastic control problem, solve the inverse problem, and then verify optimality of rainfed agriculture. The results indicated that rainfed agriculture is not optimal when the crop is more tolerant to water stress.  相似文献   

High-frequency polarity swings during the Gauss-Matuyama reversal from Baoji loess sediment     

TianShui Yang  Masayuki Hyodo  ZhenYu Yang  ShiHong Zhang  Toshiaki Mishima  HuaiChun Wu  HaiYan Li  Yi Li  XingAn Shi  Kan Wang  YiMing Ma 《中国科学:地球科学(英文版)》2014,57(8):1929-1943

Paleomagnetic records of the Gauss-Matuyama reversal were obtained from two loess sections at Baoji on the Chinese Loess Plateau. Stepwise thermal demagnetization shows two obvious magnetization components. A low-temperature component isolated between 100 and 200–250°C is close to the present geomagnetic field direction, and a high-temperature component isolated above 200–250°C reveals clearly normal, reversed, and transitional polarities. Magnetostratigraphic results of both sections indicated that the Gauss-Matuyama reversal consists of a high-frequency polarity fluctuation zone, but the characteristic remanent magnetization directions during the reversal are clearly inconsistent. Rock magnetic experiments demonstrated that for all the specimens with normal, reversed, and transitional polarities magnetite and hematite are the main magnetic carriers. Anisotropy of magnetic susceptibility indicates that the studied loess sediments have a primary sedimentary fabric. Based on virtual geomagnetic pole latitudes, the Gauss-Matuyama reversal records in the two sections are accompanied by 14 short-lived geomagnetic episodes (15 rapid polarity swings) and 12 short-lived geomagnetic episodes (13 rapid polarity swings), respectively. Our new records, together with previous ones from lacustrine, marine, and aeolian deposits, suggest that high-frequency polarity swings coexist with the Gauss-Matuyama reversal, and that the Gauss-Matuyama reversal may have taken more than 11 kyr to complete. However, we need more detailed analyses of sections across polarity swings during reversals as well as more high-resolution reversal records to understand geomagnetic behavior and inconsistent characteristic remanent magnetization directions during polarity reversals.  相似文献