Hydrothermal alteration experiments of enstatite: Implications for aqueous alteration of carbonaceous chondrites     

Ichiro OHNISHI  Kazushige TOMEOKA 《Meteoritics & planetary science》2007,42(1):49-61

Abstract— Enstatite is one of the major constituent minerals in carbonaceous chondrites. Hydrothermal alteration experiments (26 in total) of enstatite were carried out at pH 0, 6, 7, 12, 13, and 14, at temperatures of 100, 200, and 300 °C, and for run durations of 24, 72, 168, and 336 h in order to provide constraints on the aqueous‐alteration conditions of the meteorites. The recovered samples were studied in detail by using powder X‐ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Under acidic and mildly acidic conditions (pH 0, 6), no significant alteration occurred, whereas under neutral to alkaline conditions (pH 7–14), serpentine and saponite formed in various proportions by replacing enstatite. At 300 °C for 168 h, serpentine formed under neutral to moderately alkaline conditions (pH 7, 12), and serpentine and saponite formed as unit cell‐scale coherent intergrowths under highly alkaline conditions (pH 13, 14). The amounts of phyllosilicates have a tendency to increase with increasing pH, temperature, and run duration. There is also a tendency for saponite to form at higher pH and temperature and under longer run‐durations than serpentine. The results indicate that alteration of enstatite is strongly dependent on the experimental conditions, especially pH. They suggest that CM chondrites experienced aqueous alteration under neutral to alkaline conditions, whereas CV and CI chondrites experienced aqueous alteration under more alkaline conditions. The results also suggest that aqueous alteration in CI chondrites occurred at higher temperatures than in CM chondrites, and aqueous alteration in CV chondrites occurred at even higher temperatures than in CI chondrites.  相似文献   

Can N-body systems generate periodic gravitational waves?     

T. Chiba  T. Imai  H. Asada 《Monthly notices of the Royal Astronomical Society》2007,377(1):269-272

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Effects of mixing on the subduction of South Pacific waters identified by a simulated passive tracer and its adjoint     

Shan Gao  Tangdong Qu  Ichiro Fukumori 《Dynamics of Atmospheres and Oceans》2011,51(1-2):45-54

Effects of mixing on water mass subduction are analyzed in the South Pacific Ocean. Model simulations using a passive tracer and its adjoint are employed in conjunction with a particle tracking method to distinguish effects of mixing from those of advection. The results show that mixing processes can contribute to as much as 20% of the overall subduction rate in the South Pacific. Of this mixing contribution, about 30% can be attributed to meso-scale eddies, including their associated bolus transport, while the major part (70%) is due to other diabatic processes. The impact of mixing reaches its maximum near the Sub-Antarctic Front, accounting for nearly 30% of the total subduction rate. Consequently, estimates based on tracing particles or on advection alone may significantly underestimate the subduction rate in the South Pacific Ocean.  相似文献   

Observation of a smoke ring on October 30, 1970     

Ichiro Kawaguchi  Nobuyuki Oda  Shun Mizuno 《Solar physics》1972,22(1):140-141

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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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Removal of water‐surface reflection effects with a temporal minimum filter for UAV‐based shallow‐water photogrammetry          下载免费PDF全文

I GD Yudha Partama  Ariyo Kanno  Motoyasu Ueda  Yoshihisa Akamatsu  Ryutei Inui  Masahiko Sekine  Koichi Yamamoto  Tsuyoshi Imai  Takaya Higuchi 《地球表面变化过程与地形》2018,43(12):2673-2682

The recent development of structure‐from‐motion (SfM) and multi‐view stereo (MVS) photogrammetry techniques has enabled semi‐automatic high‐resolution bathymetry using aerial images taken by consumer‐grade digital cameras mounted on unmanned aerial vehicles (UAVs). However, the applicability of these techniques is sometimes limited by sun and sky reflections at the water surface, which render the point‐cloud density and accuracy insufficient. In this research, we present a new imaging technique to suppress the effect of these water‐surface reflections. In this technique, we order a drone to take a short video instead of a still picture at each waypoint. We then apply a temporal minimum filter to the video. This filter extracts the smallest RGB values in all the video frames for each pixel, and composes an image with greatly reduced reflection effects. To assess the performance of this technique, we applied it at three small shallow‐water sites. Specifically, we evaluated the effect of the technique on the point cloud density and the accuracy and precision of the photogrammetry. The results showed that the proposed technique achieved a far denser point cloud than the case in which a randomly chosen frame was used for each waypoint, and also showed better overall accuracy and precision in estimating water‐bottom elevation. The effectiveness of this new technique should depend on the surface wave state and sky radiance distribution, and this dependence, as well as the applicability to large areas, should be investigated in future research. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

Collapse behavior of a brick masonry house using a shaking table and numerical simulation based on the extended distinct element method   总被引：1，自引：1，他引：0  

T. Nakagawa  T. Narafu  H. Imai  T. Hanazato  Q. Ali  C. Minowa 《Bulletin of Earthquake Engineering》2012,10(1):269-283

Damage caused by devastating earthquakes has occurred in many developing countries. In order to mitigate such damage by promoting the study of adequate seismic design strategies, the authors conducted a dynamic collapse test on 3 m × 3 m × 3 m brick masonry house constructed with Pakistani bricks, using a one-direction horizontal large-scale shaking table. In order to analyze and simulate seismic performance of the masonry structures, the authors applied a new numerical simulating method based on the Extended Distinct Element Method (EDEM) and conducted collapse simulations of the brick masonry house behavior during the shaking table tests. In the numerical simulation model, bricks were assumed to be rigid bodies, and mortar was modeled using a mortar spring that consists of a normal spring and a shear spring. The parameters of each mortar spring were defined based on the results of material tests. Simulated results showed various collapsing processes, and the simulated aspects were found to be similar to the results of the shaking table tests.  相似文献   

‘Thailand was a desert' during the mid‐Cretaceous: Equatorward shift of the subtropical high‐pressure belt indicated by eolian deposits (Phu Thok Formation) in the Khorat Basin,northeastern Thailand     

Hitoshi Hasegawa  Suvapak Imsamut  Punya Charusiri  Ryuji Tada  Yu Horiuchi  Ken‐Ichiro Hisada 《Island Arc》2010,19(4):605-621

The Tibetan Plateau is a key factor in controlling the present‐day climate and atmospheric circulation pattern in Asia. The pattern of atmospheric circulation after the uplift of the plateau is well known, whereas direct evidence is lacking regarding the nature of the circulation pattern prior to the uplift. The distribution of desert directly reflects the position of the subtropical high‐pressure belt, and the prevailing surface‐wind pattern recorded in desert deposits reveals the position of its divergence axis. Cretaceous eolian sandstone of the Phu Thok Formation is extensively exposed in the northern Khorat Basin, northeastern Thailand. We conducted a sedimentological study on this formation to reconstruct temporal changes in the latitude of the subtropical high‐pressure belt in low‐latitude Asia during the Cretaceous. Spatio‐temporal changes in the paleo‐wind directions recorded in the Phu Thok Formation reveal that the Khorat Basin mainly belonged to the northeast trade wind belt and subtropical high‐pressure belt was situated to the north of the Khorat Basin during the initial stages of deposition, shifted southward to immediately above the basin during the main phase of deposition, and then shifted northward again to the north of the basin during the final stages of deposition. The paleomagnetic polarity sequence obtained for the Phu Thok Formation comprises three zones of normal polarity and two of reversed polarity, correlating to chrons M1n to C34n of the geomagnetic polarity time scale. This result suggests that the Phu Thok Formation is mid‐Cretaceous in age (from c. 126 Ma to c. 99–93 Ma), similar to the age of eolian sandstone in the Sichuan Basin, southern China (the Jiaguan Formation). These results, in combination with paleo‐wind direction data, suggest the development of low‐latitude desert and an equatorward shift of the subtropical high‐pressure belt (relative to the present‐day) in Asia during the mid‐Cretaceous.  相似文献   

Fluid Inclusion Study and Opaque Mineral Assemblage at the Deep and Shallow Part of the Batu Hijau Porphyry Copper-gold Deposit, Sumbawa, Indonesia     

Akira Imai    Yuki Nagai 《Resource Geology》2009,59(3):231-243

The Batu Hijau deposit is the only porphyry type deposit in production in the Sunda‐Banda arc, Indonesia. This study discusses the reason for the localization of copper grade at the deep part of the deposit based on the observation of opaque mineral assemblage. In addition, the formation condition of quartz veins and opaque minerals is discussed on the basis of the fluid inclusion microthermometry. Samples were selected from drill holes SBD100, SBD168, SBD194, SBD254, and SBD257 to cover the wide vertical range. At the Batu Hijau deposit, quartz veins have been classified mainly into four types called A, B, C and D veins, and the A veins contain mainly bornite, often associated with digenite and chalcocite. In addition, magnetite occurs in A veins. However, at the deep part of the deposit, there are quartz veins associated with magnetite, but few copper sulfides such as bornite and chalcopyrite in quartz veins, as observed in SBD257. Quartz veins at depth in SBD257 have abundant magnetite and pyrite. Pyrite in quartz veins at depth in SBD257 mainly occur at the rim of magnetite grains or interstices between them. In quartz veins in SBD254, there are abundant copper sulfides such as bornite and chalcopyrite in spite of the depth. Bornite and chalcopyrite occur as inclusions in magnetite grains in quartz veins in SBD254. Pyrite which often occurs in low grade zone in quartz veins in SBD254 is also recognized at the rims of copper sulfides. This indicates that pyrite in SBD257 and SBD254 formed later than magnetite. On the other hand, blebs of bornite and chalcopyrite inclusions in magnetite grains, which are recognized in quartz veins in SBD168 at shallow high grade part, suggest that the hydrothermal fluid, from which magnetite was deposited also brought the copper sulfides such as bornite and chalcopyrite to the deep part of the Batu Hijau deposit. Therefore, it is concluded that initially the high grade ore zone extended to depth without localization. However due to the later overprinting hydrothermal activity, copper sulfides and magnetite were replaced or dissolved and pyrite was formed, resulting the low grade zone at the deep part of the deposit. Dissolution temperatures (Td) of halite obtained by from fluid inclusion microthermometry show significant differences between SBD168 and other drill holes. The high Td obtained in SBD168 may indicate larger volume of NaCl crystals in hydrothermal fluid at the time of entrapment of the fluid inclusions and formation of other opaque minerals such as magnetite and copper‐iron sulfides. It suggests that the ratio of vapor to brine is also higher at the shallow part of the deposit. The higher vapor to brine ratio may suggest a higher degree of boiling. Removal of vapor phase separated from brine during boiling increases the concentration of substances dissolved in the brine, and this will result in saturation, as evidenced by the salinity and NaCl saturation. The higher degree of boiling suggested by the higher vapor to brine ratio at shallow part may have increased the copper concentration in the brine that may have lead the saturation, resulted in the deposition of copper‐bearing minerals.  相似文献   

Impact of flood events on macrobenthic community structure on an intertidal flat developing in the Ohta River Estuary     

Wataru Nishijima  Yoichi Nakano  Satoshi Nakai  Tetsuji Okuda  Tsuyoshi Imai  Mitsumasa Okada 《Marine pollution bulletin》2013

We investigated the effects of river floods on the macrobenthic community of the intertidal flat in the Ohta River Estuary, Japan, from 2005 to 2010. Sediment erosion by flood events ranged from about 2–3 cm to 12 cm, and the salinity dropped to 0‰ even during low-intensity flood events. Cluster analysis of the macrobenthic population showed that the community structure was controlled by the physical disturbance, decreased salinity, or both. The opportunistic polychaete Capitella sp. was the most dominant species in all clusters, and populations of the long-lived polychaete Ceratonereis erythraeensis increased in years with stable flow and almost disappeared in years with intense flooding. The bivalve Musculista senhousia was also an important opportunistic species that formed mats in summer of the stable years and influenced the structure of the macrobenthic community. Our results demonstrate the substantial effects of flood events on the macrobenthic community structure.  相似文献