Petrogenesis of the EET 92023 achondrite and implications for early impact events          下载免费PDF全文

A. Yamaguchi  N. Shirai  C. Okamoto  M. Ebihara 《Meteoritics & planetary science》2017,52(4):709-721

We report petrology and geochemistry of an achondrite EET 92023 and compare it with normal and anomalous eucrites. EET 92023 is an unbrecciated achondrite and shows a granular texture mainly composed of low‐Ca pyroxene and plagioclase, petrologically similar to normal cumulate eucrites such as Moore County. However, this rock contains a significant amount of kamacite and taenite not common in unbrecciated, crystalline eucrites. EET 92023 contains a significant amount of platinum group elements (PGEs) (ca. 10% of CI), several orders of magnitude higher than those of monomict eucrites. We suggest that the metallic phases carrying PGEs were incorporated by a projectile during or before igneous crystallization and thermal metamorphism. The projectile was likely to be an iron meteorite rather than chondritic materials, as indicated by the lack of olivine and the presence of free silica. Therefore, the oxygen isotopic signature is indigenous, rather than due to contamination of the projectile material with different oxygen isotopic compositions. A significant thermal event involving partial melting and metamorphism after the impact event indicates that EET 92023 records early impact events which took place shortly after the crust formation on a differentiated protoplanet when the crust was still hot.  相似文献   

Seasonal transition of hydrological processes in a slow‐moving landslide in a snowy region          下载免费PDF全文

Hikaru Osawa  Yuki Matsushi  Sumio Matsuura  Takashi Okamoto  Tatsuya Shibasaki  Hiroyuki Hirashima 《水文研究》2018,32(17):2695-2707

A comprehensive understanding of seasonal hydrological dynamics is required to describe the influence of pore‐water pressure on the stability of landslides in snowy regions. This study reports on the results of continuous meteorological and hydrological observations over 2 years on a landslide body comprising Neogene sedimentary rocks in northern Japan, where a thick (3–5 m) seasonal snowpack covers the land surface. Monitoring of the volumetric water content in shallow unsaturated zones (<0.8 m depth) and pore‐water pressure in saturated bedrock at depths of 2.0 and 5.2 m revealed clear seasonality in hydrological responses to rainfall and meltwater supply. During snow‐free periods, both the shallow soil moisture and deep pore‐water pressure responded rapidly to intense rainwater infiltration. In contrast, during snowmelt, the deep pore pressure fluctuated in accordance with the daily cycle of meltwater input, without notable changes in shallow moisture conditions. During occasional foehn events that cause intense snow melting in midwinter, meltwater flows preferentially through the layered snowpack, converging to produce a localized water supply at the ground surface. This episodically triggers a significant rise in pore‐water pressure. The seasonal differences in hydrological responses were characterized by a set of newly proposed indices for the magnitude and quickness of increases in the pressure head near the sliding surface. Under snow‐covered conditions, the magnitude of the pressure increase tends to be suppressed, probably owing to a reduction in infiltration caused by a seasonal decrease in the permeability of surface soils, and effective pore‐water drainage through the highly conductive colluvial layer. Deep groundwater flow within bedrock remained in a steady upwelling state, enhanced by increasing moisture in shallow soils under snow cover, reflecting the convergence of subsurface water from surrounding hillslopes.  相似文献   

Experimental study on the collisional disruption of porous gypsum spheres     

Chisato Okamoto  Masahiko Arakawa 《Meteoritics & planetary science》2009,44(12):1947-1954

Abstract— In order to study the catastrophic disruption of porous bodies such as asteroids and planetesimals, we conducted several impact experiments using porous gypsum spheres (porosity: 50%). We investigated the fragment mass and velocity of disrupted gypsum spheres over a wide range of specific energies from 3 times 10³ J/kg to 5 times 10⁴ J/kg. We compared the largest fragment mass (m₁/M_t) and the antipodal velocity (V_a) of gypsum with those of non‐porous materials such as basalt and ice. The results showed that the impact strength of gypsum was notably higher than that of the non‐porous bodies; however, the fragment velocity of gypsum was slower than that of the non‐porous bodies. This was because the micro‐pores dispersed in the gypsum spheres caused a rapid attenuation of shock pressure in them. From these results, we expect that the collisional disruption of porous bodies could be significantly different from that of non‐porous bodies.  相似文献   

Measurements in a heated turbulent wall jet on a concave wall     

S. Okamoto  M. M. Gibson 《Mineralium Deposita》1994,29(1):291-297

The paper contains the results of extensive single-point hot-wire and resistance-thermometer measurements in a wall jet on a heated concave wall with an external free stream. It is found that the turbulence in the inner (wall) and outer layers is sensitive to the distortion produced by the curved wall, broadly confirming current views of these effects. The effect on the turbulence of streamline curvature is stabilising in the outer layer, destabilising in the inner. Consequently the point of zero shear stress is closer to the point of maximum mean velocity than in flat and convex wall jets with which these new results are compared. The rate of growth is about 80% of that of the equivalent flat wall flow, and about half that of the convex wall flow. Changes in the wall shear stress and heat flux, which are increased relative to the flat wall flow, are significant but less than the changes in the corresponding convex wall flow. The greatest changes occur in the triple products.List of Symbols c _f skin friction coefficient, 2 _w / U _M ² - q ² u ² +v ²+w ² - R radius of curvature of wall - r radius of curvature - St Stanton number,-q _w /c _p U _M (T –T _w ) - T mean temperature - U streamwise mean velocity - U _J initial wall-jet velocity - U ₁ initial free-stream velocity - U ₀ U _M –U _PW - u, v, w fluctuating velocity components - x, y distances measured along and normal to the wall - y _0.5,y _M wall-jet thicknesses defined in the text - y _S ,y _T wall-jet thicknesses defined in the text - T T _W –T - shear-layer thickness - ₂ momentum thickness - temperature fluctuation - M point of maximum velocity - P potential flow - s point of zero shear stress - W wall value - free stream value  相似文献   

Teleseismic synthetics obtained from 3-D calculations in 2-D media     

Taro Okamoto 《Geophysical Journal International》1994,118(3):613-622

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Phosphorus sorption from aqueous solution using natural materials     

Osama Eljamal  Junya Okawauchi  Kazuaki Hiramatsu  Masayoshi Harada 《Environmental Earth Sciences》2013,68(3):859-863

The sorption of phosphorus by using four different natural materials (marble dust, sawdust, soil, and rice husk) was studied by conducting batch tests and kinetic sorption model. The kinetic sorption model based on a pseudo equation was applied to predict the rate constant of sorption. Thorough investigations to understand the mechanism of phosphorus sorption onto the natural materials using kinetic sorption models, pseudo first- and second-order kinetic sorption model showed that the kinetic sorption is consistent with the second-order model, from which it can be inferred that the mechanism of sorption is chemisorption. Batch tests and kinetic sorption model results showed that by using marble dust as sorbent, among other materials, could remove more than 93 % of phosphorus from aqueous solution.  相似文献   

Fossil fluid reservoir beneath a duplex fault structure within the Central Range of Taiwan: implications for fluid leakage and lubrication during earthquake rupturing process     

Yu-Chang Chan  Kazuaki Okamoto  Tzen-Fu Yui  Yoshiyuki Iizuka  Hao-Tsu Chu 《地学学报》2005,17(6):493-499

In order to understand the kinematics which likely facilitated the speedy rupturing process of the 1999 Mw 7.6 Taiwan Chi-Chi earthquake, we examined exposed rocks in the Taiwan Slate belt, where the pressure and temperature conditions most resembled the hypocentre of the Chi-Chi earthquake, i.e. sub-greenschist facies. Field observations and composition analyses of the silicified vein-rich zones beneath the duplex structure suggest that impermeable slate layers may serve as cap rocks for confining deep-seated fluids. These fluids most likely come from the Taiwan metamorphic complex at deeper depths by the dehydration and decarbonation reactions (or partial melting). In addition, the gouge zone of a link fault above the detachment also indicates the presence of overpressured fluids during faulting. It is probable that episodic leakage of the confined fluid reservoirs may provide essential fluids for fault lubrication during earthquake ruptures.  相似文献   

A comparison of techniques for hydrograph recession analysis     

Joko Sujono  Shiomi Shikasho  Kazuaki Hiramatsu 《水文研究》2004,18(3):403-413

A comparison between commonly used techniques for hydrograph recession analysis, namely the semi‐logarithmic plot of a single recession segment, the master recession and a relatively new approach based on wavelet transform was carried out. These methods were applied to a number of flood hydrograph events of two catchments in West Java, Indonesia. The results show that all the methods tested produce reasonable and comparable results. However, problems arise in the semi‐logarithmic plot and the master recession, i.e. determining the recession parameter K is not an easy task especially where the plotted data on a semi‐logarithmic plot is not a linear but a curved line. On a curved line, the end of direct flow or starting point of baseflow is not clear and it is quite difficult to identify. Hence, the best line as a basis for computing the recession parameter K becomes uncertain. The wavelet transform approach, however, produces promising results and minimizes a number of problems associated with hydrograph recession analysis. The end of direct flow and the location of the baseflow component are easily determined through the wavelet maps. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Deep-sea submersible survey in the Suruga, Sagami and Japan Trenches: preliminary results of the 1985 Kaiko cruise, Leg 2     

Guy Pautot  Kazuaki Nakamura  Philippe Huchon  Jacques Angelier  Jacques Bourgois  Kantaro Fujioka  Toshihiko Kanazawa  Yasuo Nakamura  Yujiro Ogawa  Michel Sguret  Akira Takeuchi 《Earth and Planetary Science Letters》1987,83(1-4)

Nine submersible dives were made in three trenches off central Japan, between 2990 and 5900 m of water depth. Our observations confirm the interpretation that Daiichi-Kashima Seamount is a Cretaceous guyot formed on the Pacific plate that has traveled into the Japan Trench. We also confirmed the previous interpretation of a large normal fault that splits the seamount in two halves, the lower one being now subducting beneath the Japan margin. Compressional deformation was identified within the lower part of the inner slope in front of the seamount. The pattern of deformation that affects Quaternary sediments is in agreement with the present kinematics of the convergence between the Pacific plate and Japan. Deep-water (5700 m) clam colonies are associated with advection of fluids, driven by the subduction-related overpressures. In the northern slope of the Boso Canyon, along the Sagami Trough system (Philippine Sea plate-Japan boundary), the deformation affecting a thick upper Miocene to lower Pliocene sequence indicates two directions of shortening: a N175°E direction which is consistent with the present relative motion along the Sagami Trough (N285–N300°E) and a N30°E direction which could be related to a more northerly direction of convergence that occured during the early Quaternary and earlier.  相似文献   

Response of Eucalanus bungii to oceanographic conditions in the western subarctic Pacific Ocean: Retrospective analysis of the Odate Collections     

Toru Kobari  Kazuaki Tadokoro  Hiroya Sugisaki  Hiroshi Itoh 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2748

To evaluate their response to oceanographic conditions, interannual variations in seasonal abundance of Eucalanus bungii were investigated in zooplankton samples collected from the Oyashio Current system from 1960 to 2002. Large decadal changes were observed in seasonal timing and population age-structure. During the early 1970s and 1990s, E. bungii were abundant until mid-summer, but during the late 1970s and early 1980s, the season of maximum abundance was limited to spring and early summer. From the late 1970s to early 1980s, spring–summer abundance of newly recruited young copepodites (C1–C2) declined significantly, and an even more pronounced decline was observed for the abundance of the late copepodite stages (C3–C5). Monthly population structure showed that young of the year stopped development at C3 during the late 1970s to early 1980s, but molted into late copepodite stages in the other decades. Seasonal weakening of the Aleutian Low Pressure System estimated from North Pacific Index (NPI) was rapid during the late 1970s to early 1980s, and the NPI was positively correlated with phosphate concentrations at sea surface, spring–summer abundance of the young copepodites stages, and the extended duration of the season of high abundance. These results suggest that the decadal decline of copepod abundance originated at the early life stages, and was associated with a shift of atmospheric and oceanographic conditions. As possible biological mechanisms, we propose reduced egg production, lower survival for the portion of the annual cohort with late birth date, and overwintering of the survivors at younger stages.  相似文献