Possible fluid-rock interactions on differentiated asteroids recorded in eucritic meteorites     

J.A. Barrat  A. Yamaguchi  T.E. Bunch  C. Bollinger  G. Ceuleneer 《Geochimica et cosmochimica acta》2011,75(13):3839-3852

The eucritic meteorites are basaltic rocks that originate from the upper part of the crust of some small bodies as exemplified possibly by asteroid 4-Vesta. A few eucrites appear to have been modified by different degrees of a late stage alteration process that caused significant variations in mineralogy. Three distinct alteration stages are identified: (1) Fe-enrichment along the cracks that cross cut the pyroxene crystals (“Fe-metasomatism”); secondary olivine and minute amounts of troilite are found only occasionally in cracks at this stage; (2) deposits of Fe-rich olivine (Fa_64-86) and minor amounts of troilite are frequent inside the cracks; sporadic secondary Ca-rich plagioclase (An_97-98) is associated with the fayalitic olivine; (3) at this stage, the Fe-enrichment of the pyroxene is accompanied by a marked Al-depletion; moreover, secondary Ca-rich plagioclase is more frequent and partly fills some cracks or rims of the primary plagioclase crystals. The composition of the secondary phases on one hand, the lack of incompatible trace element enrichment in the metasomatized pyroxenes on the other hand, rule out a silicate melt as the metasomatic agent. Although no hydrous phase has been yet identified in the studied samples, aqueous fluids are plausible candidates for explaining the deposits of ferroan olivine and anorthitic plagioclase inside the fractures of the studied unequilibrated eucrites.  相似文献   

Primordial,thermal, and shock features of ordinary chondrites: Emulating bulk X‐ray diffraction using in‐plane rotation of polished thin sections     

Naoya Imae  Makoto Kimura  Akira Yamaguchi  Hideyasu Kojima 《Meteoritics & planetary science》2019,54(4):919-937

Using an X‐ray diffractometer, powder‐like diffraction patterns were acquired from in‐plane rotation of polished thin sections (PTSs) of 60 ordinary chondrites (23 H, 21 L, and 16 LL), in order to explore the thermal and shock metamorphism and its modifications of primordial features. The olivine (Ol) 130 peak position shown as Bragg indices clearly correlates with the chemical group for equilibrated ordinary chondrites (EOCs), while the peak is split or broad for unequilibrated ordinary chondrites (UOCs). The intensity ratio of kamacite may be useful for distinguishing the chemical group between H and L‐LL, but it is not definite because of heterogeneous terrestrial weathering of kamacite, especially in H chondrites. The summed intensities of the orthoenstatite (Oen) 511 and 421 peaks positively correlates with the metamorphic sequence from 3 to 6, while that of clinoenstatite (Cen) 22 is inversely correlated. The shock stage positively correlates with the summed full width of half maximum values of the Oen 511 and 421 peaks and the FWHM of Ol 130 peak for each class. Significant amount of Oen (Pbca) transformed through Cen (C2/c) finally to Cen (P2₁/c) is stable at high pressure for shock stage S6 (Tenham and NWA 4719). The shock melted LL chondrite is characterized by the occurrence of Cen and abundant homogeneous olivine. The effects of both thermal and shock metamorphism are thus incorporated into the bulk X‐ray diffraction (XRD) data. The bulk XRD method is useful for determining the bulk mineralogy, resulting in the classification of ordinary chondrites. The method is also applicable to samples other than PTS.  相似文献   

Eutrophication-induced changes in Lake Nakaumi,southwest Japan     

Kota Katsuki  Yasushi Miyamoto  Kazuyoshi Yamada  Hiroyuki Takata  Keiko Yamaguchi  Daisuke Nakayama  Hugo Coops  Hidenobu Kunii  Ritsuo Nomura  Boo-Keun Khim 《Journal of Paleolimnology》2008,40(4):1115-1125

Lake Nakaumi, southwest Japan, is an enclosed lagoon characterized by polyhaline and halocline conditions. Since the last century, its ecological state has been altered by eutrophication. We used a paleolimnological approach and studied multiple proxies, including chemical compounds, diatoms, foraminifera and molluscs, to infer the eutrophication history of the ecosystem. Eutrophication in Lake Nakaumi was associated with several factors, including increased nutrient loading, input of herbicides, and dike building since the 1920s. The ecological condition of this lake was divided into several stages that reflect the eutrophication process after the 1940s. A catastrophic “regime shift” from a clear state with aquatic vegetation to a turbid one with phytoplankton occurred in the early 1950s. Environmental degradation in the Honjo area, a part of Lake Nakaumi, was attributed primarily to physical changes caused by the construction of an enclosing dike. Eutrophication occurred almost simultaneously with the physical changes to the Honjo area in the 1970s. Until recently, no regime shift was observed in this area, though the core-top sediments show possible symptoms of incipient change.  相似文献   

Limits on isocurvature perturbations from non-Gaussianity in WMAP temperature anisotropy     

Chiaki Hikage  Kazuya Koyama  Takahiko Matsubara  Tomo Takahashi  Masahide Yamaguchi 《Monthly notices of the Royal Astronomical Society》2009,398(4):2188-2198

We study the effect of primordial isocurvature perturbations on non-Gaussian properties of cosmic microwave background (CMB) temperature anisotropies. We consider generic forms of the non-linearity of isocurvature perturbations which can be applied to a wide range of theoretical models. We derive analytical expressions for the bispectrum and the Minkowski Functionals for CMB temperature fluctuations to describe the non-Gaussianity from isocurvature perturbations. We find that the isocurvature non-Gaussianity in the quadratic isocurvature model, where the isocurvature perturbation S is written as a quadratic function of the Gaussian variable  σ,  S =σ²−〈σ²〉  , can give the same signal-to-noise ratio as   f _NL= 30  even if we impose the current observational limit on the fraction of isocurvature perturbations contained in the primordial power spectrum α. We give constraints on isocurvature non-Gaussianity from Minkowski Functionals using the Wilkinson Microwave Anisotropy Probe ( WMAP ) 5-year data. We do not find a significant signal of isocurvature non-Gaussianity. For the quadratic isocurvature model, we obtain a stringent upper limit on the isocurvature fraction  α < 0.070  (95 per cent CL) for a scale-invariant spectrum which is comparable to the limit obtained from the power spectrum.  相似文献   

A new one-dimensional simple energy balance and carbon cycle coupled model for global warming simulation     

Kazutaka Murakami  Takahiro Sasai  Yasushi Yamaguchi 《Theoretical and Applied Climatology》2010,101(3-4):459-473

Global warming and accompanying climate change may be caused by an increase in atmospheric greenhouse gasses generated by anthropogenic activities. In order to supply such a mechanism of global warming with a quantitative underpinning, we need to understand the multifaceted roles of the Earth's energy balance and material cycles. In this study, we propose a new one-dimensional simple Earth system model. The model consists of carbon and energy balance submodels with a north–south zonal structure. The two submodels are coupled by interactive feedback processes such as CO₂ fertilization of net primary production (NPP) and temperature dependencies of NPP, soil respiration, and ocean surface chemistry. The most important characteristics of the model are not only that the model requires a relatively short calculation time for carbon and energy simulation compared with a General Circulation Model (GCM) and an Earth system Model of Intermediate Complexity (EMIC), but also that the model can simulate average latitudinal variations. In order to analyze the response of the Earth system due to increasing greenhouse gasses, several simulations were conducted in one dimension from the years 1750 to 2000. Evaluating terrestrial and oceanic carbon uptake output of the model in the meridional direction through comparison with observations and satellite data, we analyzed the time variation patterns of air temperature in low- and middle-latitude belts. The model successfully reproduced the temporal variation in each latitude belt and the latitudinal distribution pattern of carbon uptake. Therefore, this model could more accurately demonstrate a difference in the latitudinal response of air temperature than existing models. As a result of the model evaluations, we concluded that this new one-dimensional simple Earth system model is a good tool for conducting global warming simulations. From future projections using various emission scenarios, we showed that the spatial distribution of terrestrial carbon uptake may vary greatly, not only among models used for climate change simulations, but also amongst emission scenarios.  相似文献   

Tasks and problems involved in the handling of disaster waste upon April 2016 Kumamoto Earthquake,Japan     

Amirhomayoun Saffarzadeh  Takayuki Shimaoka  Hirofumi Nakayama  Takao Hanashima  Kentaro Yamaguchi  Kazutoshi Manabe 《Natural Hazards》2017,88(3):1273-1295

The potential impacts of tsunamis along the Catalan Coast (NW Mediterranean) are analysed using numerical modelling. The region is characterized by moderate to low seismic activity and by moderate- to low-magnitude earthquakes. However, the occurrence of historical strong earthquakes and the location of several active offshore faults in front of the coast suggest that the possibility of an earthquake-triggered tsunami is not negligible although of low probability. Up to five faults have been identified to generate tsunamis, being the highest associated possible seismic magnitudes of up to 7.6. Coastal flooding and port agitation are characterized using the Worst-case Credible Tsunami Scenario Analysis approach. The results show a multiple fault source contribution to tsunami hazard. The shelf dimensions and the existence of submerged canyons control the tsunami propagation. In wide shelves, waves travelling offshore may become trapped by refraction causing the wave energy to reach the coastline at some distance from the origin. The free surface water elevation increases at the head of the canyons due to the sharp depth gradients. The effects of potential tsunamis would be very harmful in low-lying coastal stretches, such as deltas, with a high population concentration, assets and infrastructures. The Ebro delta appears to be the most exposed coast, and about the 20% of the delta surface is prone to flooding due to its extremely low-lying nature. The activity at Barcelona port will be severely affected by inflow backflow current at the entrance of up to 2 m/s.  相似文献   

Horizontal distribution of calanoid copepods in the western Arctic Ocean during the summer of 2008   总被引：1，自引：1，他引：0  

Kohei Matsuno  Atsushi Yamaguchi  Koji Shimada  Ichiro Imai 《Polar Science》2012,6(1):105-119

The horizontal distribution of the epipelagic zooplankton communities in the western Arctic Ocean was studied during August–October 2008. Zooplankton abundance and biomass were higher in the Chukchi Sea, and ranged from 3,000 to 274,000 ind. m^?2 and 5–678 g WM m^?2, respectively. Copepods were the most dominant taxa and comprised 37?94% of zooplankton abundance. For calanoid copepods, 30 species belonging to 20 genera were identified. Based on the copepod abundance, their communities were classified into three groups using a cluster analysis. The horizontal distribution of each group was well synchronized with depth zones, defined here as Shelf, Slope and Basin. Neritic Pacific copepods were the dominant species in the Shelf zone. Arctic copepods were substantially greater in the Slope zone than the other regions. Mesopelagic copepods were greater in the Basin zone than the other regions. Stage compositions of large-sized Arctic copepods (Calanus glacialis and Metridia longa) were characterized by the dominance of late copepodid stages in the Basin. Both the abundance and stage compositions of large copepods corresponded well with Chl. a concentrations in each region, with high Chl. a in the Shelf and Slope supporting reproduction of copepods resulting in high abundance dominated by early copepodid stages.  相似文献   

Climatic physical snowpack properties for large-scale modeling examined by observations and a physical model     

Kazuyuki Saito  Satoru Yamaguchi  Hiroki Iwata  Yoshinobu Harazono  Kenji Kosugi  Michael Lehning  Martha Shulski 《Polar Science》2012,6(1):79-95

Here we have conducted an integral study using site observations and a model with detailed snow dynamics, to examine the capability of the model for deriving a simple relationship between the density and thermal conductivity of the snowpack within different climatic zones used in large-scale climate modeling. Snow and meteorological observations were conducted at multiple sites in different climatic regions (two in Interior Alaska, two in Japan). A series of thermal conductivity measurements in snow pit observations done in Alaska provided useful information for constructing the relationship. The one-dimensional snow dynamics model, SNOWPACK, simulated the evolution of the snowpack and compared observations between all sites. Overall, model simulations tended to underestimate the density and overestimate the thermal conductivity, and failed to foster the relationship evident in the observations from the current and previous research. The causes for the deficiency were analyzed and discussed, regarding a low density of the new snow layer and a slow compaction rate. Our working relationships were compared to the equations derived by previous investigators. Discrepancy from the regression for the melting season observations in Alaska was found in common.  相似文献   

“Cross-correlation analysis of seismic and volcanic data at Mount Etna volcano,Italy” by Cardaci et al.     

D. K. Yamaguchi 《Bulletin of Volcanology》1996,57(7):578-580

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Resistivity mapping using the VLF-MT method around surface fault ruptures of the 1995 Hyogo-ken Nanbu earthquake, Japan   总被引：1，自引：0，他引：1  

Satoru Yamaguchi  Takahisa Murakami  Hiroo Inokuchi 《Island Arc》2001,10(3-4):296-305

Abstract Distinctive fault ruptures, the Nojima Fault and Ogura Fault, appeared along the northwestern coast of Awaji Island at the time of the 1995 Hyogo-ken Nanbu earthquake (Kobe earthquake). In order to delineate the shallow resistivity structures around the faults just after they formed, Very Low Frequency Magnetotelluric (VLF-MT) surveys were made at five sites along the Nojima Fault and at one site along the Ogura Fault. Fourteen transects were made at the one site on the Ogura Fault, and another transect covers the area between the two faults. Changes in apparent resistivity or phase, or both, commonly occur when crossing the surface location of one of the faults, except for the northern transects at OGR-0 on the Ogura Fault. Apparent resistivity values of less than 100 Ωm were observed for Tertiary and Quaternary sediments and values larger than 200 Ωm for granitic rocks. The resistivity structures are related to the morphological characteristics of the fault ruptures. Remarkably conductive zones (less than 10 Ωm in apparent resistivity and 30–40 m in width) were found where the surface displacement is distinct and prominent along a single fault plane. If remarkably conductive zones were formed at the time of the 1995 Hyogo-ken Nanbu earthquake, the results provide a good constraint on the dimensions of a conductive zone near the surface that was made by one earthquake. Alternatively, if characteristic resistivity structures existed prior to the earthquake, the conductive zone was probably formed by some tens of earthquakes in relatively modern times. In this case, this phenomenon is inferred to be a concentration of fracturing in a narrow zone and is associated with the formation of clay minerals, which enhance rock conductivity.  相似文献