Chemodynamical Evolution of Galaxies     

Chiaki Kobayashi 《Astrophysics and Space Science》2002,281(1-2):301-304

I simulate the chemodynamical evolution of the Milky Way and elliptical galaxies using the GRAPE-SPH code. By reproducing the observations, I discuss the origin of elliptical galaxies. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Seasonal Changes in Submarine Groundwater Discharge and Associated Nutrient Transport into a Tideless Semi-enclosed Embayment (Obama Bay,Japan)     

Ryo Sugimoto  Hisami Honda  Shiho Kobayashi  Yoshitake Takao  Daisuke Tahara  Osamu Tominaga  Makoto Taniguchi 《Estuaries and Coasts》2016,39(1):13-26

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Mineral chemistry of MUSES‐C Regio inferred from analysis of dust particles collected from the first‐ and second‐touchdown sites on asteroid Itokawa     

Tomoki Nakamura  Aiko Nakato  Hatsumi Ishida  Shigeru Wakita  Takaaki Noguchi  Michael E. Zolensky  Masahiko Tanaka  Makoto Kimura  Akira Tshuchiyama  Toshihiro Ogami  Takahito Hashimoto  Mitsuru Konno  Masayuki Uesugi  Toru Yada  Kei Shirai  Akio Fujimura  Ryuji Okazaki  Scott. A. Sandford  Yukihiro Ishibashi  Masanao Abe  Tatsuaki Okada  Munetaka Ueno  Junichiro Kawaguchi 《Meteoritics & planetary science》2014,49(2):215-227

The mineralogy and mineral chemistry of Itokawa dust particles captured during the first and second touchdowns on the MUSES‐C Regio were characterized by synchrotron‐radiation X‐ray diffraction and field‐emission electron microprobe analysis. Olivine and low‐ and high‐Ca pyroxene, plagioclase, and merrillite compositions of the first‐touchdown particles are similar to those of the second‐touchdown particles. The two touchdown sites are separated by approximately 100 meters and therefore the similarity suggests that MUSES‐C Regio is covered with dust particles of uniform mineral chemistry of LL chondrites. Quantitative compositional properties of 48 dust particles, including both first‐ and second‐touchdown samples, indicate that dust particles of MUSES‐C Regio have experienced prolonged thermal metamorphism, but they are not fully equilibrated in terms of chemical composition. This suggests that MUSES‐C particles were heated in a single asteroid at different temperatures. During slow cooling from a peak temperature of approximately 800 °C, chemical compositions of plagioclase and K‐feldspar seem to have been modified: Ab and Or contents changed during cooling, but An did not. This compositional modification is reproduced by a numerical simulation that modeled the cooling process of a 50 km sized Itokawa parent asteroid. After cooling, some particles have been heavily impacted and heated, which resulted in heterogeneous distributions of Na and K within plagioclase crystals. Impact‐induced chemical modification of plagioclase was verified by a comparison to a shock vein in the Kilabo LL6 ordinary chondrite where Na‐K distributions of plagioclase have been disturbed.  相似文献   

Space weathered rims found on the surfaces of the Itokawa dust particles     

Takaaki Noguchi  Makoto Kimura  Takahito Hashimoto  Mitsuru Konno  Tomoki Nakamura  Michael E. Zolensky  Ryuji Okazaki  Masahiko Tanaka  Akira Tsuchiyama  Aiko Nakato  Toshinori Ogami  Hatsumi Ishida  Ryosuke Sagae  Shinichi Tsujimoto  Toru Matsumoto  Junya Matsuno  Akio Fujimura  Masanao Abe  Toru Yada  Toshifumi Mukai  Munetaka Ueno  Tatsuaki Okada  Kei Shirai  Yukihiro Ishibashi 《Meteoritics & planetary science》2014,49(2):188-214

On the basis of observations using Cs‐corrected STEM, we identified three types of surface modification probably formed by space weathering on the surfaces of Itokawa particles. They are (1) redeposition rims (2–3 nm), (2) composite rims (30–60 nm), and (3) composite vesicular rims (60–80 nm). These rims are characterized by a combination of three zones. Zone I occupies the outermost part of the surface modification, which contains elements that are not included in the unchanged substrate minerals, suggesting that this zone is composed of sputter deposits and/or impact vapor deposits originating from the surrounding minerals. Redeposition rims are composed only of Zone I and directly attaches to the unchanged minerals (Zone III). Zone I of composite and composite vesicular rims often contains nanophase (Fe,Mg)S. The composite rims and the composite vesicular rims have a two‐layered structure: a combination of Zone I and Zone II, below which Zone III exists. Zone II is the partially amorphized zone. Zone II of ferromagnesian silicates contains abundant nanophase Fe. Radiation‐induced segregation and in situ reduction are the most plausible mechanisms to form nanophase Fe in Zone II. Their lattice fringes indicate that they contain metallic iron, which probably causes the reddening of the reflectance spectra of Itokawa. Zone II of the composite vesicular rims contains vesicles. The vesicles in Zone II were probably formed by segregation of solar wind He implanted in this zone. The textures strongly suggest that solar wind irradiation damage and implantation are the major causes of surface modification and space weathering on Itokawa.  相似文献   

Two overlapping plates subducting beneath central Japan as revealed by strontium isotope data     

K. Notsu  S. Aramaki  O. Oshima  Y. Kobayashi 《Journal of Volcanology and Geothermal Research》1987,32(1-3)

In central Japan, the Pacific plate subducts westward beneath the Eurasian plate and the Philippine Sea plate subducts northwestward into the mantle wedge between the Eurasian plate and the subducted Pacific slab. There, the Northeast Japan arc is joined to the Izu-Ogasawara arc. We determined ⁸⁷Sr/⁸⁶Sr ratios and Rb and Sr contents for 47 volcanic rock samples from 15 Quaternary volcanoes in central Japan and summarized the geographical distribution of the ratios. The general trend of slowly increasing ⁸⁷Sr/⁸⁶Sr ratio from the back-arc side toward the volcanic front in the Northeast Japan arc is broken by a marked high ratio (above 0.7060) centered around Akagi volcano located at the southernmost region of the arc. Elsewhere, the ratio along the volcanic front in this arc varies within the range 0.7038 to 0.7045. The marked high ⁸⁷Sr/⁸⁶Sr ratio is considered to be due to the addition of slab-derived components transported by the Philippine Sea plate to the magma-generating region in the mantle wedge beneath central Japan. Therefore, the geographical distribution of the high ratio may correspond to that of the Philippine Sea slab-derived components in the mantle wedge and we may draw the underground outline of the Philippine Sea plate. This outline implies that an aseismic portion of the Philippine Sea plate continues a few tens km ahead of the seismic one. A belt of low ⁸⁷Sr/⁸⁶Sr ratios from the Izu Peninsula northwestward along the northern end of the Izu-Ogasawara arc coincides with the zone where the subducting Philippine Sea plate is not observed seismologically, while it is detected seismologically on both sides of the belt.  相似文献   

Precursory activity in seismic belts containing the focal region of forthcoming large intraplate earthquake     

Akio Yoshida 《Tectonophysics》1987,140(2-4):131-143

Seismic activity in the region surrounding the foci is investigated for three severe earthquakes (two with a magnitude of 6.1 and one with a magnitude of 5.3) which have occurred in Japan in recent years. The most conspicuous feature commonly noticed is precursory activation of seismic belts which include the focal regions of main shocks. The repetition of the same pattern in the space-time distribution of earthquake occurrence along the seismic belt is also observed for each case. The precursory activity of seismic belts terminates in rather a short period and, after that, the area around the focus of the forthcoming large earthquake becomes quiescent, which demonstrates the appearance of the seismic gap of the second kind (Mogi, 1979). The periods of seismic quiescence for the cases investigated in this paper are longer than those which are given by the regression relationship between earthquake magnitude and precursor time proposed for example, by Sekiya (1977). However, our definition of anomalous seismic activity is clear, and it is possible to give a physical meaning to it as an increase in the local stress field in the seismic belt. We propose that a kind of coupling between intraplate tectonic blocks, analogous to interplate coupling in the subduction region, is responsible for the formation of the stress field relevant to these earthquakes. Although this is at present only one of the possible viewpoints on the formation of the focal region of large intraplate earthquakes, it may be worthwhile to study various precursory phenomena in-connection with this hypothesis.  相似文献   

Preferred orientation of phyllosilicate [001] in matrix of Murchison meteorite and possible mechanisms of generating the oriented texture in chondrites     

Akio Fujimura  Manabu Kato  Mineo Kumazawa 《Earth and Planetary Science Letters》1983

Preferred orientation of the dominant phyllosilicate phase (serpentine) in the matrix of the Murchison meteorite (C2) was determined by X-ray pole figure goniometry. The basal plane (001) of the phyllosilicate shows a clear preferred orientation of an axial concentration type. The preferred orientation is very weak in comparison with the orientations of known terrestrial tectonites, and it resembles the weakest case observed in the loosely consolidated clayey sediments from the deep ocean bottom. However, gentle sedimentation of platy phyllosilicate grains on a flat surface under a weak gravity field does not generate a sufficient preferred orientation. It is suggested that the preferred orientation in the matrix of Murchison was generated by uniaxial compaction, and the magnitude of strain to give rise to the observed degree of preferred orientation is evaluated as ?9%. There are two possible explanations of the deformation: dynamic compression caused by impact, and static compaction in a parent body. Though the latter case appears to be appropriate in the present case, it is not straightforward, however, to conclude that the suggested deformation is caused by burial compaction along gravity under lithostatic stress in a small primitive parent body.  相似文献   

Characteristics of vertical land movement and microearthquake activity in the northeastern Japan arc     

Hiroshi Ishii  Yoichiro Komukai  Akio Takagi 《Tectonophysics》1981,77(3-4)

Methods have been devised for analyzing vertical land movement and seismicity data using two-dimensional Chebychev functions and oblique projections. A filtering operation in the space domain is made possible by use of a two-dimensional Chebychev function. The oblique projections give an intuitive understanding of land deformation. Characteristic aspects of vertical land movement obtained by precise levelling and of the energy release of microearthquakes with depths shallower than 20 km in the northeastern Japan arc were investigated in detail applying these methods.Lineations with wavelength of about 20–60km trending towards NE—SW were found for both the land deformation and the seismicity. It should be noted that this trend is almost perpendicular to the direction of the strain migration and is related to other geophysical information.  相似文献   

Microstructural development of fine-grained quartz aggregates by syntectonic recrystallization     

Toshiaki Masuda  Akio Fujimura   《Tectonophysics》1981,72(1-2)

Experimental study of syntectonic recrystallization of fine-grained quartz aggregates was carried out in order to simulate the development of some natural microstructures of quartz tectonites and to understand their formation condition. Agate was axially compressed with a constant-strain-rate apparatus. Experiments were conducted at 4 kbar solid confining pressure, 700–1000°C and 10⁻⁴-10⁻⁶ sec⁻¹ to 10%–45% strain. In all runs, deformation has proceeded under wet condition caused by dehydration of pyrophyllite used as pressure medium.Two different types of microstructure were distinguished in the deformed specimens. One is P-type which is characterized by equant, equidimensional, and polygonal grains. The other is S-type which is characterized by the highly oblate grains with the largest dimension perpendicular to the compression axis. The P-type microstructure is developed at higher temperatures and slower strain rates, while the S-type developed at lower temperatures and faster strain rates. The transition between the S- and P-types is found to be very sharp.  相似文献   

Sub-Moho seismic profile in the Mariana Basin — Ocean bottom seismograph long-range explosion experiment     

S. Nagumo  T. Ouchi  J. Kasahara  S. Koresawa  Y. Tomoda  K. Kobayashi  A.S. Furumoto  M.E. Odegard  G.H. Sutton 《Earth and Planetary Science Letters》1981,53(1):93-102

Ocean bottom seismograph (OBS) long-range explosion experiments were carried out in the Mariana Basin in 1973 and 1976. Seven large shots (8.5–1.5 ton) as well as several tens of small shots were fired. The maximum range of observation was about 1900 km. As many as 25 OBS stations were deployed in an array of about 800 km. It is found that the sub-Moho P-wave velocity structure is of stratified nature, being composed of alternating high- and low-velocity layers. High-velocity layers with apparent velocities of 8.1, 8.2, 8.4, 8.6 and 8.7 km/s are identified. Low-velocity layers, sandwiched between the high-velocity layers of 8.4, 8.6 and 8.7 km/s, are very prominent. The sub-Moho high-velocity lid with an apparent velocity of 8.4 km/s is very thin. Thinning of this lid, thickening of the low-velocity layer, and the presence under it of another high-velocity layer (8.6 km/s) appear to characterize the uppermost mantle structure beneath the Mariana Basin.  相似文献