Stardust in Antarctic micrometeorites     

Toru YADA  Christine FLOSS  Frank J. STADERMANN  Ernst ZINNER  Tomoki NAKAMURA  Takaaki NOGUCHI  A. Scott LEA 《Meteoritics & planetary science》2008,43(8):1287-1298

Abstract— We report the discovery of presolar silicate, oxide (hibonite), and (possibly) SiC grains in four Antarctic micrometeorites (AMMs). The oxygen isotopic compositions of the eighteen presolar silicate (and one oxide) grains found are similar those observed previously in primitive meteorites and interplanetary dust particles, and indicate origins in oxygen‐rich red giant or asymptotic giant branch stars, or in supernovae. Four grains with anomalous C isotopic compositions were also detected. ¹²C/¹³C as well as Si ratios are similar to those of mainstream SiC grains; the N isotopic composition of one grain is also consistent with a mainstream SiC classification. Presolar silicate grains were found in three of the seven AMMs studied, and are heterogeneously distributed within these micrometeorites. Fourteen of the 18 presolar silicate grains and 3 of the 4 C‐anomalous grains were found within one AMM, T98G8. Presolar silicate‐bearing micrometeorites contain crystalline silicates that give sharp X‐ray diffractions and do not contain magnesiowüstite, which forms mainly through the decomposition of phyllosilicates and carbonates. The occurrence of this mineral in AMMs without presolar silicates suggests that secondary parent body processes probably determine the presence or absence of presolar silicates in Antarctic micrometeorites.  相似文献   

Bulk mineralogical changes of hydrous micrometeorites during heating in the upper atmosphere at temperatures below 1000 °C     

Wataru Nozaki  Tomoki Nakamura  Takaaki Noguchi 《Meteoritics & planetary science》2006,41(7):1095-1114

Abstract— Small particles 200 μm in diameter from the hydrous carbonaceous chondrites Orgueil CI, Murchison CM2, and Tagish Lake were experimentally heated for short durations at subsolidus temperatures under controlled ambient pressures in order to examine the bulk mineralogical changes of hydrous micrometeorites during atmospheric entry. The three primitive meteorites consist mainly of various phyllosilicates and carbonates that are subject to decomposition at low temperatures, and thus the brief heating up to 1000 °C drastically changed the mineralogy. Changes included shrinkage of interlayer spacing of saponite due to loss of molecular water at 400–600 °C, serpentine and saponite decomposition to amorphous phases at 600 and 700 °C, respectively, decomposition of Mg‐Fe carbonate at 600 °C, recrystallization of secondary olivine and Fe oxide or metal at 700–800 °C, and recrystallization of secondary low‐Ca pyroxene at 800 °C. The ambient atmospheric pressures controlled species of secondary Fe phase: taenite at pressures lower than 10^?2 torr, magnesiowüstite from 10^?3 to 10^?1 torr, and magnetite from 10^?2 to 1 torr. The abundance of secondary low‐Ca pyroxene increases in the order of Murchison, Orgueil, and Tagish Lake, and the order corresponds to saponite abundance in samples prior to heating. Mineralogy of the three unmelted micrometeorites F96CI024, kw740052, and kw740054 were investigated in detail in order to estimate heating conditions. The results showed that they might have come from different parental objects, carbonaterich Tagish Lake type, carbonate‐poor Tagish Lake or CI type, and CM type, respectively, and experienced different peak temperatures, 600, 700, and 800?900 °C, respectively, at 60–80 km altitude upon atmospheric entry.  相似文献   

Remote sensing and modeling of landslides: detection,monitoring and risk evaluation     

Dalia Bach Kirschbaum  Hiroshi Fukuoka 《Environmental Earth Sciences》2012,66(6):1583-1583

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The Effect of Relative Density and Confining Stress on Shear Properties of Sands with Varying Grading     

Ogbonnaya Igwe  Hiroshi Fukuoka  Kyoji Sassa 《Geotechnical and Geological Engineering》2012,30(5):1207-1229

The research investigated the influence of grain size distribution on the shear behavior of sand specimen in loose, medium and dense states. The investigation aimed at understanding the extent or degree at which static shear strength of soil is affected by its density. A standard indicator (coefficient of uniformity) was used in constituting four (4) different sand specimens—narrowly graded (NAG), intermediately graded (ING), well graded (WG) and gap graded (GAG). Different normal stress values were applied during the testing program. The specimens were sheared using a ring shear apparatus until a residual value of shear stress was obtained. Result obtained from the analysis shows two remarkable stress paths. Medium dense to dense specimens show dilative stress path while loose (less dense) specimens show contractive stress path. At loose state, WG specimens show higher peak and residual shear strengths than poorly graded ones. Of importance was the fact that all the NAG specimens underwent complete liquefaction but WG specimens did not undergo complete liquefaction. This was interpreted as strong inter-particle contacts/forces binding the grains which enhanced high shear resistance. The research also showed that increase in relative density leads to higher shear strength, particle size distribution notwithstanding. Also, result of the analysis showed that WG specimens in medium-and dense states have higher peak but lower residual strength than ING and NAG specimens-this phenomenon was termed reverse behavior by the author(s). GAG specimens when sheared have the lowest peak and residual strength at any given value of relative density.  相似文献   

RESEARCH IN CLIMATOLOGY BY GEOGRAPHERS IN JAPAN     

Yoshitaka Fukuoka 《The Professional geographer》1980,32(2):224-230

This is the last in a series of reports on various aspects of geographic research in Japan. The series has been sponsored by the United States Committee for the International Geographic Union in anticipation of the 1980 IGC in Tokyo. Like its predecessors, this report has been modified by H. Jesse Walker, member of the Committe, for the benefit of English-speaking readers of THE PROFESSIONAL GEOGRAPHER.  相似文献   

Structural evolutions of an obsidian and its fused glass by shock-wave compression     

K.?ShimodaEmail author  M.?Okuno  Y.?Syono  M.?Kikuchi  K.?Fukuoka  M.?Koyano  S.?Katayama 《Physics and Chemistry of Minerals》2004,31(8):532-542

Shock-recovery experiments for obsidian and its fused glass have been carried out with pressure up to 35 GPa. Structural evolution accompanying the shock compression was investigated using X-ray diffraction technique, Raman and infrared spectroscopy. The densities of obsidian and its fused glass increased with applied shock pressure up to 25 GPa. Densification reached a maximum of 4.7 and 3.6% for obsidian and its fused glass, respectively. The densification mechanism is attributed to reduction of the T–O–T angle, and changes in ring statistics in the structure. Density reduction observed at greater than 25 GPa of applied shock pressure is due to partial annealing of the high-density glass structures brought by high post-shock residual temperature. The density of fused glass is almost equal to its original value at 35 GPa while the shocked obsidian has a slightly lower value than its original value. Amorphization of crystallites present in the obsidian due to shock compression is probably the cause of the density decrease. The structural evolution observed in shock-compressed obsidian and its fused glass can be explained by densification resulting from average T–O–T angle reduction and increase of small rings, and subsequent structural relaxation by high post-shock temperature at applied shock compression above 25 GPa.  相似文献   

Evolution of Shear-Zone Structure in Undrained Ring-Shear Tests   总被引：4，自引：4，他引：0  

Muhammad?Wafid AgungEmail author  Kyoji?Sassa  Hiroshi?Fukuoka  Gonghui?Wang 《Landslides》2004,1(2):101-112

Undrained monotonic torque-controlled tests were conducted on fine-grained silica sand to study the shear-deformation process in granular materials by using a ring-shear apparatus. Shear-zone structures at various stages in the undrained shear tests were observed during a series of tests in which the experiments were terminated at different shear displacement. For undisturbed samples, the shear zone was only developed during the post-failure stage and its thickness increased with progressed shearing. First the shear surfaces had undulating and asymmetric structures; later they gradually became smooth and parallel to the shearing direction. During this process, pore water pressure was generated, and the effective friction angle decreased correspondingly. Generally, the shear zone could be divided into three parts: the compacted core, the adjacent zone above the core, and the adjacent zone below the core. Grain-size analysis on the sample from the shear zone revealed that grain crushing occurred during each stage and the extent of grain crushing differed for different shear stages. An interesting phenomenon occurred during the steady-state deformation where the coarse and fine particles within the shear zone segregated during motions and a parallel orientation structure developed. These results are helpful for understanding the mechanism of progressive failure in granular material as well as the rapid landslide with long runout study.  相似文献   

2 International Workshop on Water Dynamics     

Sujoy Ghosh  Asami Sano  Akira Shimojuku  Takaaki Kawazoe  Konstantin Litasov 《Gondwana Research》2005,8(2):291-292

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Glass veins in the unequilibrated eucrite Yamato 82202     

Paul C. Buchanan  Takaaki Noguchi  Donald D. Bogard  Ikuo Katayama 《Geochimica et cosmochimica acta》2005,69(7):1883-1898

The unequilibrated eucrite Yamato 82202 (Y82202) contains a network of relatively thick (up to 1 mm in width) glass veins. The host of the meteorite represents a monomict breccia composed of volcanic rock that crystallized > 4.3 Ga ago as a lava flow on the surface of 4 Vesta. The veins formed 3.90 ± 0.04 Ga ago, probably as a result of frictional melting associated with impact, under conditions of low effective oxygen fugacity and higher sulfur fugacity. The glass contains disordered structural elements characteristic of pyroxene and feldspar, reminiscent of the eucritic target lithology. The unequilibrated pyroxenes of the volcanic host and the pristine character of the glass indicate that this meteoritic material did not experience significant thermal metamorphism after initial crystallization of the lava. Hence, it was not affected by regional metamorphism caused by burial to a significant depth or by long-term contact metamorphism associated with a thick lava flow, large intrusion, or hot layer of impact ejecta. The meteorite resided at a shallow depth (though not at the surface) on 4 Vesta or on one of the vestoids until it was ejected and traveled to Earth, probably with other HED materials that have ³⁶Ar exposure ages of ∼13 Ma. These data suggest that the surface of the asteroid 4 Vesta has significant, though probably small, proportions of glass, as well as unequilibrated volcanic rock.  相似文献   

Downslope volume enlargement of a debris slide–debris flow in the 1999 Hiroshima, Japan, rainstorm     

Gonghui Wang  Kyoji Sassa  Hiroshi Fukuoka 《Engineering Geology》2003,69(3-4):309-330

Following a heavy rainstorm on 29 June 1999, hundreds of slope failures occurred in granitic mountains in Hiroshima Prefecture, Japan. Among these events, a highly mobile landslide (termed the Kameyama landslide in this paper), which occurred in Kameyama area of Hiroshima city, was the most catastrophic, and was investigated in detail. The displaced soil mass from the source area of this landslide traveled about 300 m and deposited a volume more than 10 times as great as that in the source area. The landslide originated in and traversed a valley-shaped concave slope covered by pre-existing colluvial debris deposits. In addition, a spring was visible in the source area and very shallow ground water was observed in an observation pit dug in the source area. Thus, it is inferred that the ground-water table rose quickly during the rainfall, and that this rise triggered the slope failure in the source area. Based on a field survey along the landslide cross section, a possible explanation for the mechanism of the landslide was obtained: the displaced soil mass from the source area impacted the debris deposit in the path of the landslide, thus triggering liquefaction failure of the saturated part of debris. The original landslide and the liquefied debris then moved downslope as a single mass. To examine this assumption, ring-shear tests were performed on samples taken from the source area. Undrained ring-shear tests on the saturated samples showed that the sample is highly liquefiable, and liquefaction failure could have been triggered in the debris deposits by a very small impact from the displaced soil mass of the initial failure. In addition, laboratory tests simulating the impacts on the debris deposits at natural water content, i.e., unsaturated (at the survey time, 2 days after the failure) showed that although shear failure could be caused by the assumed impact force, the displaced soils stopped after a few centimeters displacement, indicating that existence of a saturated zone in debris deposits is prerequisite for this kind of failure.  相似文献