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61.
Double-planed deep seismic zone and anomalous structure in the upper mantle beneath northeastern Honshu (Japan) 总被引:1,自引:0,他引:1
Seismicity located by using the most recent data obtained from the high-gain seismograph network of Tohoku University shows that the deep seismic zone beneath northeastern Honshu, Japan, is composed of two thin planes which are parallel to each other and are 30–40 km apart. Focal mechanisms derived from the earthquakes in the upper plane are reverse-faulting, or, some of them, down-dip compression. As a contrast, those in the lower plane are down-dip extension. The location of the upper boundary of the descending lithospheric slab, inferred from the arrival-time difference between ScS and ScSp waves and from the travel-time anomaly of intermediate-depth earthquakes observed at the small-scale seismic array, coincides exactly with the upper plane of the double-planed deep seismic zone. Anelasticity (1/Q) structure of the upper mantle consists of three distinct zones: a high-Q (Qs− 1500) inclined lithospheric slab, an intennediate-Q (Qs−350) land-side mantle between the Pacific coast and the volcanic front, and a low-Q (Qs − 100) land-side mantle between the volcanic front and the coast of the Japan Sea.The evidence obtained here provides valuable information as to the definition of the type of mechanism producing the plate motion beneath island arcs. 相似文献
62.
Akira Mizuta Tatsuya Yamasaki Shigehiro Nagataki Shin Mineshige 《Astrophysics and Space Science》2007,307(1-3):23-27
We investigate the outflow propagation in the collapsar in the context of gamma-ray bursts (GRBs) with 2D relativistic hydrodynamic
simulations. We vary the specific internal energy and bulk Lorentz factor of the injected outflow from non-relativistic regime
to relativistic one, fixing the power of the outflow to be 1051erg s−1. We observed the collimated outflow, when the Lorentz factor of the injected outflow is roughly greater than 2. To the contrary,
when the velocity of the injected outflow is slower, the expanding outflow is observed. The transition from collimated jet
to expanding outflow continuously occurs by decreasing the injected velocity. Different features of the dynamics of the outflows
would cause the difference between the GRBs and similar phenomena, such as, X-ray flashes. 相似文献
63.
64.
Yosuke IIDA Akira TSUCHIYAMA Toshihiko KADONO Kanako SAKAMOTO Tomoki NAKAMURA Kentaro UESUGI Tsukasa NAKANO Michael E. ZOLENSKY 《Meteoritics & planetary science》2010,45(8):1302-1319
Abstract– We investigated three‐dimensional structures of comet Wild 2 coma particle impact tracks using synchrotron radiation (SR) X‐ray microtomography at SPring‐8 to elucidate the nature of comet Wild 2 coma dust particles captured in aerogel by understanding the capture process. All tracks have a similar entrance morphology, indicating a common track formation process near the entrance by impact shock propagation irrespective of impactor materials. Distributions of elements along the tracks were simultaneously measured using SR‐XRF. Iron is distributed throughout the tracks, but it tends to concentrate in the terminal grains and at the bottoms of bulbs. Based on these results, we propose an impact track formation process. We estimate the densities of cometary dust particles based on the hypothesis that the kinetic energy of impacting dust particles is proportional to the track volume. The density of 148 cometary dust particles we investigated ranges from 0.80 to 5.96 g cm?3 with an average of 1.01 (±0.25) g cm?3. Moreover, we suggest that less fragile crystalline particles account for approximately 5 vol% (20 wt%) of impacting particles. This value of crystalline particles corresponds to that of chondrules and CAIs, which were transported from the inner region of the solar system to the outer comet‐forming region. Our results also suggest the presence of volatile components, such as organic material and perhaps ice, in some bulbous tracks (type‐C). 相似文献
65.
Jean-Alix Barrat Akira Yamaguchi Claire Bollinger Marcel Bohn 《Geochimica et cosmochimica acta》2010,74(21):6218-6231
The eucrites and diogenites are meteorites that probably originate from asteroid 4-Vesta. The upper part of the crust of this body is certainly composed of eucrites which are basaltic or gabbroic rocks. Diogenites are ultramafic cumulates whose relationships with eucritic lithologies are unknown. Here, we show that the orthopyroxenes of some diogenites display very deep negative Eu anomalies (Eu/Eu∗ close to 0.1 or lower). The contamination of the parental magmas of diogenites by melts derived by partial melting of the eucritic crust can satisfactorily explain the range of the Eu anomalies displayed by diogenites. Thus, these anomalies are the first firm indication that parental melts of diogenites have intruded the eucritic crust, and consequently are younger than eucrites. 相似文献
66.
Yuji?IchiyamaEmail author Akira?Ishiwatari Jun-Ichi?Kimura Ryoko?Senda Tsuyoshi?Miyamoto 《Contributions to Mineralogy and Petrology》2014,168(1):1019
The Mikabu and Sorachi–Yezo belts comprise Jurassic ophiolitic complexes in Japan, where abundant basaltic to picritic rocks occur as lavas and hyaloclastite blocks. In the studied northern Hamamatsu and Dodaira areas of the Mikabu belt, these rocks are divided into two geochemical types, namely depleted (D-) and enriched (E-) types. In addition, highly enriched (HE-) type has been reported from other areas in literature. The D-type picrites contain highly magnesian relic olivine phenocrysts up to Fo93.5, and their Fo–NiO trend indicates fractional crystallization from a high-MgO primary magma. The MgO content is calculated as high as 25 wt%, indicating mantle melting at unusually high potential temperature (T p) up to 1,650 °C. The E-type rocks represent the enrichment in Fe and LREE and the depletion in Mg, Al and HREE relative to the D-type rocks. These chemical characteristics are in good accordance with those of melts from garnet pyroxenite melting. Volcanics in the Sorachi–Yezo belts can be divided into the same types as the Mikabu belt, and the D-type picrites with magnesian olivines also show lines of evidence for production from high T p mantle. Evidence for the high T p mantle and geochemical similarities with high-Mg picrites and komatiites from oceanic and continental large igneous provinces (LIPs) indicate that the Mikabu and Sorachi–Yezo belts are accreted oceanic LIPs that were formed from hot large mantle plumes in the Late Jurassic Pacific Ocean. The E- and D-type rocks were formed as magmas generated by garnet pyroxenite melting at an early stage of LIP magmatism and by depleted peridotite melting at the later stage, respectively. The Mikabu belt characteristically bears abundant ultramafic cumulates, which could have been formed by crystal accumulation from a primary magma generated from Fe-rich peridotite mantle source, and the HE-type magma were produced by low degrees partial melting of garnet pyroxenite source. They should have been formed later and in lower temperatures than the E- and D-type rocks. The Mikabu and Sorachi Plateaus were formed in a low-latitude region of the Late Jurassic Pacific Ocean possibly near a subduction zone, partially experienced high P/T metamorphism during subduction, and then uplifted in association with (or without, in case of Mikabu) the supra-subduction zone ophiolite. The Mikabu and Sorachi Plateaus may be the Late Jurassic oceanic LIPs that could have been formed in brotherhood with the Shatsky Rise. 相似文献
67.
Akira Shimojuku Asmaa Boujibar Daisuke Yamazaki Takashi Yoshino Naotaka Tomioka Junshan Xu 《Physics and Chemistry of Minerals》2014,41(7):555-567
The growth rate of ringwoodite reaction rims between MgSiO3 perovskite and periclase was investigated at 22.5 GPa and 1,800 °C for 1–24 h using the Kawai-type high-pressure apparatus. The reaction was likely to proceed by a diffusion-controlled mechanism in which the dominant diffusion mechanism was grain-boundary diffusion. The reaction constant (the width of the ringwoodite reaction rim squared divided by time) determined from these experiments was between 1.3 × 10?15 and 5.6 × 10?15 m2/s. A Pt inert marker experiment indicated that the MgO component migrated faster than the SiO2 component in ringwoodite. Thus, either Mg or O having the slower diffusion rate controlled the reaction. Because previous diffusion studies have shown that diffusion rates of O are slower than those of Mg, O would be a rate-controlling element for ringwoodite formation from MgSiO3 perovskite and periclase. The growth rate appeared to be too fast to explain the observed topographic rise (~10 km) inside mantle plumes at the 660-km discontinuity. 相似文献
68.
69.
Seto Koji Katsuki Kota Tsujimoto Akira Kitagawa Junko Yamada Kazuyoshi Suzuki Yoshiaki 《Journal of Paleolimnology》2022,68(3):329-343
Journal of Paleolimnology - Sub-annual-scale environmental and ecosystem changes since the mid-18th century were reconstructed in a semi-closed lagoon, Lake Hiruga, located along the Sea of Japan... 相似文献
70.
Akiko M. Nakamura Akira Fujiwara Toshihiko Kadono 《Planetary and Space Science》1994,42(12):1043-1052
We describe the method and the result of a new experiment to obtain velocity distribution of fine ejecta fragments, from a few to a hundred microns in size, produced from basalt targets by impacts of nylon projectiles at a velocity of 3.7 km s−1. The size distribution of holes perforated by the ejecta fragments on thin films and foils placed around the targets was investigated, and the size-velocity relation was determined with the aid of an empirical formula for threshold penetration (McDonnell and Sullivan, Hypervelocity Impacts in Space, Unit for Space Sciences, University of Kent, 1992). The velocity of the fastest fragments, at a given size, is from the extrapolation of the size-velocity relation for 1–100 mm fragments (Nakamura and Fujiwara, Icarus92, 132–146, 1991; Nakamura et al, Icarus100, 127–135, 1992). The laboratory results are also compared with those obtained from the study of secondary craters around large lunar craters (Vickery, Icarus67, 224–236, 1986, Geophys. Res. Lett. 14, 726–729, 1987). All these data provide a smooth size-velocity relationship in the normalized fragment size range of four orders of magnitude. 相似文献