新疆北部富蕴县沙尔布拉克玻安岩的地球化学特征及构造意义   总被引：19，自引：1，他引：19  

张海祥  牛贺才  于学元  Hiroaki Sato  Junichi Ito  单强 《地球化学》2003,32(2):155-160

详细的地球化学研究表明，新疆北部富蕴县沙尔布拉克中泥盆统北塔山组的辉石安山岩具有中等的SiO2含量（52.13%-60.45%)；高MgO(3.91%-9.31%)和相容元素（包括Ni、Cr、Co等）含量，以及高Mg^#和Al2O3／TiO2比值；低TiO2含量（0.21%-0.35%)；同时具有U型稀土元素分布模式；并强烈亏损高场强元素。这些特征均与玻安岩的地球化学特征一致，应属于玻安岩，形成于前弧环境。沙尔布拉克玻安岩的存在表明，古亚洲洋在早－中泥盆世向南发生了洋壳俯冲作用。  相似文献   

Deformable backstop as seaward end of coseismic slip in the Nankai Trough seismogenic zone     

Ayako Nakanishi  Shuichi KodairaJin-Oh Park  Yoshiyuki Kaneda 《Earth and Planetary Science Letters》2002,203(1):255-263

Wide-angle seismic surveys performed in the last decade have clarified the 3-D crustal structure along the Nankai Trough. The geometry and velocity structure of the southwestern Japan subduction zone are now well constrained. Comparing these observations with the rupture distribution of historic great thrust earthquakes, it appears that the coseismic rupture occurred along plate boundaries deeper than the wedge/backstop boundary (the boundary between the Neogene-Quaternary accretionary wedge and the crust forming the backstop). From the view of spatial relationship, both rupture distributions of the last two large events and the crust forming the backstop are considerably retreated from the trough axis in the west and east off the Kii Peninsula. In both areas, seamount or ridge subduction is apparent in seismic results, geomorphological data and geomagnetic data. The landward indentation of the deformable backstop, which corresponds to the crustal block of old accreted sediments, may be formed by seamount subduction according to published results of sandbox modeling. In particular, the subducted seamount may be a structural factor affecting the recession of the crustal block forming the backstop.  相似文献   

Structural factors controlling the rupture process of a megathrust earthquake at the Nankai trough seismogenic zone   总被引：7，自引：0，他引：7  

S. Kodaira  E. Kurashimo  J.-O. Park  N. Takahashi  A. Nakanishi  S. Miura  T. Iwasaki  N. Hirata  K. Ito  Y. Kaneda 《Geophysical Journal International》2002,149(3):815-835

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Assessment of metal concentrations in lake sediments of southwest Japan based on sediment quality guidelines   总被引：1，自引：0，他引：1  

M. Hawa Bibi  Faruque Ahmed  Hiroaki Ishiga 《Environmental Geology》2007,52(4):625-639

Geochemical analysis of the bottom sediments of Lakes Banryoko, Onbe, Hamahara and Kijima in Shimane prefecture of southwest Japan was carried out to determine their metal concentrations, and to assess the potential for ecological harm by comparison with sediment quality guidelines. The work conducted includes water quality measurement, and analyses of trace and major elements and rare earth element (REE) of sediments. Results showed that water quality of the lakes contrasts slightly between their upper and lower parts. Average abundances of As, Pb, Zn, Cu, Ni, and Cr in Banryoko sediments were 27, 33, 90, 27, 25, and 46 ppm, respectively, compared to 31, 52, 175, 44, 44, and 75 ppm at Onbe, 11, 26, 96, 13, 13, and 35 ppm at Hamahara, and 24, 43, 193, 31, 12, and 30 ppm at Kijima. These concentrations exceeded the lowest effect level that has moderate impact on aquatic organisms as proposed by the New York State Department of Environmental conservation. Pb and Cu abundances are comparable to the Coastal Ocean Sediment Database threshold, while As and Zn exceed this value, indicating the concentrations of these metals are potentially toxic. Increases in the abundances of these metals in lake sediments are probably related to the reducing condition of the sediments, anthropogenic sources and surface soil erosion. The REE patterns of sediments in the study areas are broadly comparable to the average upper continental crust, but show some contrast between lakes due to differing source litho type. Significant positive correlations between Fe₂O₃ and As, Pb, Zn, and Cu were found in the sediments, suggesting these metals may be adsorbed on Fe oxides in the lake sediments.  相似文献   

Environmental assessment of Dhaka City (Bangladesh) based on trace metal contents in road dusts   总被引：1，自引：0，他引：1  

Faruque Ahmed  M. Hawa Bibi  Hiroaki Ishiga 《Environmental Geology》2007,51(6):975-985

Geochemical analysis of street dusts was conducted to evaluate the environment of Dhaka City, Bangladesh. Dust samples were collected from different areas (industrial, commercial, and residential) of Dhaka City, and their major, trace and rare earth elements (REE) were determined. Samples from the commercial area had Pb concentrations double those of the industrial and residential areas. Contents of Zn, Cu, Ni, and Cr in the industrial areas were greater than those in the commercial and residential areas. The REE patterns of all dusts in Dhaka are similar and are comparable to the average upper continental crust. The condition of the Dhaka environment was compared to that in Japan and other baseline sediments using Zn–Fe₂O₃ and Pb–Fe₂O₃ diagrams. Zn–Fe₂O₃ trends for the dusts show steep inclination compared to the baseline sediment and the Japanese urban sediment trends. Dhaka lake data show enrichment of Zn over the dusts, suggestive of Zn pollution from poorly controlled industrial sources. In contrast, on the Pb–Fe₂O₃ diagram, Dhaka dusts have greater Pb contents than lake sediments, probably due to the higher traffic density in the commercial area compared to the residential area including the area around the lake. The results suggest that higher levels of Pb and Zn in street dusts in Dhaka can most likely be attributed to the anthropogenic sources like vehicle emissions to the atmosphere and a rapid development.  相似文献   

Notes on non-marine bivalve Trigonioides (Trigonioides?) from the mid-Cretaceous Goshoura Group, Kyushu, Japan     

Toshifumi Komatsu  Chen Jinhua  Hiroaki Ugai  Koji Hirose 《Journal of Asian Earth Sciences》2007,29(5-6):795-802

Trigonioides goshourensis n. sp. and Trigonioides amakusensis Kikuchi and Tashiro occur in the late Albian Eboshi Formation of the Goshoura Group in Kyushu, Japan. These Albian species are characterized by three radial pseudocardinal teeth on the thick and wide hinge plate, and are probably ancestors of Cenomanian species of Trigonioides (Kumamotoa) with four radial pseudocardinal teeth. This chronological relation may be important for the correlation of non-marine Cretaceous strata in East Asia. In addition, the habitat of T. amakusensis is interpreted as estuarine tidal flats under brackish water conditions, although Trigonioides is generally a freshwater bivalve genus.  相似文献   

Marine reservoir correction for the Pacific coast of central Japan using C ages of marine mollusks uplifted during historical earthquakes     

Masanobu Shishikura  Tomoo Echigo  Heitaro Kaneda 《Quaternary Research》2007,67(2):286-291

In this study we utilize marine shell samples from two levels of historically uplifted sessile mollusk assemblages and raised wave-cut benches to evaluate the marine reservoir correction (ΔR) for the Pacific coast of central Japan. Elevation measurements of the uplifted marine shells indicate that the lower assemblage emerged during the 1923 Taisho Kanto earthquake (M7.9), whereas uplift of the upper assemblage is most likely but less confidently ascribed to the 1703 Genroku Kanto earthquake (M8.2). Radiocarbon dating of carefully selected samples from the upper and lower assemblages yielded very similar ΔR values of 82 ± 33 and 77 ± 32 yr, respectively. We regard the former ΔR value as a representative and more reliable value given the uncertainty in correlation of the upper assemblage with the 1703 earthquake. This result is consistent with previously reported ΔR values for the Pacific coast of south-central Japan and areas around the Sea of Japan that are influenced by warm ocean currents. Radiocarbon dating of coseismically uplifted shells can aid in estimating marine reservoir ages in the tectonically active Japan Islands.  相似文献   

Fault configuration produced by initial arc rifting in the Parece Vela Basin as deduced from seismic reflection data   总被引：1，自引：0，他引：1  

Mikiya  Yamashita  Tetsuro  Tsuru  Narumi  Takahashi  Kaoru  Takizawa  Yoshiyuki  Kaneda  Kantaro  Fujioka  Keita  Koda 《Island Arc》2007,16(3):338-347

Abstract   The Parece Vela Basin (PVB), which is a currently inactive back-arc basin of the Philippine Sea Plate, was formed by separation between the Izu-Ogasawara Arc (IOA) and the Kyushu-Palau Ridge (KPR). Elucidating the marks of the past back-arc opening and rifting is important for investigation of its crustal structure. To image its fault configurations and crustal deformation, pre-stack depth migration to multichannel seismic reflection was applied and data obtained by the Japan Agency for Marine-Earth Science and Technology and Metal Mining Agency of Japan and Japan National Oil Corporation (Japan Oil, Gas and Metals National Corporation). Salient results for the pre-stack depth-migrated sections are: (i) deep reflectors exist around the eastern margin of KPR and at the western margin of IOA down to 8 km depth; and (ii) normal fault zones distributed at the eastern margin of the KPR (Fault zone A) and the western margin of the IOA (Fault zone B) have a total displacement of greater than 500 m associated with synrift sediments. Additional normal faults (Fault zone C) exist 20 km east of the Fault zone B. They are covered with sediment, which indicates deposition of recent volcanic products in the IOA. According to those results: (i) the fault displacement of more than 500 m with respect to initial rifting was approximately asymmetric at 25 Ma based on PSDM profiles; and (ii) the faults had reactivated after 23 Ma, based on the age of deformed sediments obtained from past ocean drillings. The age of the base sediments corresponds to those of spreading and rotation after rifting in the PVB. Fault zone C is covered with thick and not deformed volcanogenic sediments from the IOA, which suggests that the fault is inactive.  相似文献   

Experimental study of a low-alkali tholeiite at 1–5 kbar: optimal condition for the crystallization of high-An plagioclase in hydrous arc tholeiite     

Daisuke?Takagi  Hiroaki?SatoEmail author  Mitsuhiro?Nakagawa 《Contributions to Mineralogy and Petrology》2005,149(5):527-540

We conducted melting experiments on a low-alkali tholeiite (SiO₂ ~52 wt%, MgO ~6.5 wt%, CaO/Na₂O~4.4, Al₂O₃/SiO₂ ~0.33) under both H₂O-undersaturated and H₂O-saturated conditions to investigate the effect of H₂O on the Ca–Na partitioning between plagioclase and melt. Experiments were performed in the temperature and pressure ranges of 1,000–1,300°C and 1–5 kbar, respectively, with varying H₂O contents of 0–12wt%. Redox condition was 0–2 log unit above NNO (nickel–nickel oxide) buffer. Temperature-bulk H₂O diagrams for the low-alkali tholeiite are constructed at 1, 2, and 5 kbar, and compositions of near-liquidus plagioclase and coexisting melt are determined. To exclude the effect of melt composition (CaO/Na₂O and Al₂O₃/SiO₂ ratios) on plagioclase composition and to reveal the effect of H₂O on An (=100×Ca/(Ca+Na)) content and (=(Ca/Na)_pl/(Ca/Na)_melt), we focused on the composition of near-liquidus plagioclases which crystallized from melts with nearly constant CaO/Na₂O and Al₂O₃/SiO₂ ratios. Our experimental results show that, at each experimental pressure, An content of the near-liquidus plagioclase and the K_D^Ca-Na almost linearly increases as H₂O content in melt increases. Each of the An content and the variations in a low-alkali tholeiitic system (CaO/Na₂O~4.0–4.5, Al₂O₃/SiO₂ ~0.27–0.33) can be described by one equation using temperature, pressure, and melt H₂O content as parameters. An content and of liquidus plagioclase increases with increasing melt H₂O and with decreasing pressure, elucidating that nearly H₂O-saturated conditions of 2–3 kbar is optimal for the crystallization of the most An-rich plagioclase (>An₈₈). We suggest this pressure condition of 2–3 kbar, corresponding to depth of 7–11 km, plays an important role for the origin of An-rich plagioclase in H₂O-rich low-alkali tholeiite. At pressures more than ca. 4 kbar, crystallization of liquidus Ca-rich clinopyroxene decreases the CaO/Na₂O ratio of liquid, thus prohibiting the crystallization of high-An plagioclase from hydrous tholeiite.  相似文献   

X-ray beaming caused by resonance scattering in the accretion column of magnetic cataclysmic variables     

Y. Terada  M. Ishida  K. Makishima  T. Imanari  R. Fujimoto  K. Matsuzaki  H. Kaneda 《Monthly notices of the Royal Astronomical Society》2001,328(1):112-126

Extremely strong ionized Fe emission lines, with equivalent widths reaching ∼4000 eV, were discovered by ASCA from a few Galactic compact objects, including AX J2315−0592, RX J1802.1+1804 and AX J1842.8−0423. These objects are thought to be binary systems containing magnetized white dwarfs (WDs). A possible interpretation of the strong Fe K line is the line-photon collimation in the WD accretion column, as a result of resonance scattering of line photons. The collimation occurs when the accretion column has a flat shape, and the effect is augmented by the vertical velocity gradient, which reduces the resonant trapping of resonant photons along the magnetic field lines. This effect was quantitatively confirmed with Monte Carlo simulations. Furthermore, with ASCA observations of the polar V834 Centauri, this collimation effect was clearly detected as a rotational modulation of the equivalent width of the Fe K emission line. The extremely strong emission lines mentioned above can be explained consistently by our interpretation. Combining this effect with other X-ray information, the geometry and plasma parameters in the accretion column were determined.  相似文献