Geochronological review of Sambagawa metamorphic belt in Southwest Japan     

LIU Yong-jiang  Akira Takasu  Tsuyoshi Sakurail 《世界地质(英文版)》2005,8(1)

Based on almost all available published age data, the protolith ages, peak metamorphic ages and cooling rate of the Sambagawa metamorphic belt have been discussed and the latest constraints on the ages of the Sambagawa metamorphism and subduction-related accretionary evolutions were summarized. Peak metamorphic conditions attained within the Kuma nappe complex at ca. 145～185 Ma, and uplift through ca. 500℃ at ca. 150 Ma and 350～400℃ at ca. 110～ 115 Ma. The protolith sediments of the Besshi nappe complex were accumulated and subsequently progressively subducted and suffered high P-T prograde metamorphism during the Kuma nappe complex uplifting. The Besshi nappe complex arrived maximum metamorphic conditions at ca. 110 ～ 120 Ma and subsequently started rapid uplift with the cooling rate of ca. 14.2℃/Ma at ca. 75 ～85 Ma, followed with the cooling rate of ca. 6.0 ～8.9℃/Ma. The Oboke nappe complex started subduction later than other tectonic units and arrived the peak metamorphic conditions at ca. 75 Ma, which followed by the uplift with a cooling rate of ca. 8℃/Ma.  相似文献   

Seasonal dynamics of the phytoplankton community in Sendai Bay,northern Japan     

Yukiko Taniuchi  Tsuyoshi Watanabe  Shigeho Kakehi  Tomoko Sakami  Akira Kuwata 《Journal of Oceanography》2017,73(1):1-9

Sendai Bay is located on the Pacific coast of northern Japan and suffered serious damage following the 2011 off the Pacific coast of Tohoku earthquake and tsunami in March 2011. To assess the impact on the marine ecosystem, information was needed on the phytoplankton communities and their seasonal variation. However, such information was limited. Therefore, an intensive monitoring of the phytoplankton was carried out from March 2012 to April 2014. Seasonal variation of the phytoplankton community was similar at coastal and offshore stations. Total phytoplankton biomass, based on Chl a concentration, peaked in spring and then decreased to a minimum in summer, before gradually increasing during early winter and peaking again in the following spring. This seasonal pattern was consistent with previous studies conducted before the earthquake and tsunami. Also, size structure of the phytoplankton community and its four main groups was estimated from the size-fractioned samples of Chl a. Our results also showed that the spring bloom consisted of large diatoms, with their growth ceasing due to nitrogen depletion. The bloom was followed by a summer period where cyanobacteria and picoeukaryote became dominant, with high cell densities in spite of low nutrient concentrations. In addition, sporadic environmental changes, such as those following typhoons, were observed. These resulted in large increases/decreases in individual phytoplankton groups.  相似文献   

Seasonal succession in the diatom community of Sendai Bay,northern Japan,following the 2011 off the Pacific coast of Tohoku earthquake     

Tsuyoshi Watanabe  Yukiko Taniuchi  Shigeho Kakehi  Tomoko Sakami  Akira Kuwata 《Journal of Oceanography》2017,73(1):133-144

Sendai Bay in northern Japan suffered serious damage from massive tsunamis generated by the 2011 off the Pacific coast of Tohoku earthquake. The physical disturbance caused by a tsunami may affect the coastal ecosystem, including the planktonic diatom community. We investigated seasonal changes in the diatom community structure at a coastal and an offshore station in Sendai Bay, from June 2011 (3 months after the tsunami) to April 2014. Diatom abundance increased at both stations during the spring. Sporadic increases were also recorded at the coastal station during the summer because of silicate input from river discharge. Seasonal succession of the diatom communities was similar at both the coastal and offshore stations. The onset of the spring bloom consisted mainly of Chaetoceros spp. when water temperatures were low. Subsequently, species such as Skeletonema costatum s.l. became dominant as salinity and nutrient concentrations decreased. Cell density decreased from summer into early winter. Leptocylindrus danicus became dominant in the summer, but was replaced by Thalassiosira cf. mala from autumn into winter. Redundancy analysis (RDA) showed that most of the variation in the diatom community could be explained by temperature, salinity, NO₃ ^?, NO₂ ^?, PO₄ ^3?, and SiO₂. In addition, the occurrence of diatom species before the tsunami showed a similar pattern to that after the tsunami, suggesting that the tsunami did not have a serious impact on the diatom community in Sendai Bay.  相似文献   

http://dx.doi.org/10.1016/j.gsf.2016.06.013     

Tsuyoshi Komiya  Shinji Yamamoto  Shogo Aoki  Keiko Koshida  Masanori Shimojo  Yusuke Sawaki  Kazumasa Aoki  Shuhei Sakata  Takaomi D. Yokoyama  Kenshi Maki  Akira Ishikawa  Takafumi Hirata  Kenneth D. Collerson 《地学前缘(英文版)》2017,8(2):355-385

The Archean continental crusts account for ca.20% of the present volume,but the thermal history of the Earths' mantle suggests much more continental crusts were formed in the early Archean.Because the Archean continental crust underwent severe metamorphism,it is important to avoid influence by the later thermal events.We carried out a comprehensive geochronological work of Cathodoluminescence(CL) observation and U-Pb dating of zircons from orthogneisses and supracrustal rocks over the Saglek Block to obtain their protolith ages.The zircons were classified into three domains of core,mantle and rims,and the cores were further classified into three groups of inherited,altered and zoned cores based on the zonation on the CL images.We estimated the protolith ages from Pb-Pb ages of the zoned-cores of zircons with low U contents.We made a detailed sketch of a small outcrop in St.John's Harbour South(SJHS) area,and classified the orthogneisses and mafic enclaves into seven generations based on the geologic occurrence.The first and second generations comprise mafic rocks and lack magmatic zircons.We conducted CL imaging and U-Pb dating of zircons from the third,sixth and seventh generation of the orthogneisses to estimate the protolith ages at 3902 L 25,3892 ± 33 and 3897 ± 33 Ma for each,supporting the presence of the over 3.9 Ca Iqaluk Gneiss.The geological occurrence that the mafic rocks occur as enclaves within the 3.9 Ga Iqaluk Gneiss indicates that they are the oldest supracrustal rocks in the world.Our geochronological and geological studies show the Uivak Gneiss is quite varied in lithology and age from 3.6 to 3.9 Ga,and tentatively classified into six groups based on their ages.The oldest Uivak Gneiss components including the Iqaluk Gneiss are present around the SJHS area,and the orthogneisses become young as it is away.The lines of evidence of overprinting of younger granitoid on older granitoid in small outcrops and geological-map scale as well as presence of inherited zircons even in the oldest suite suggests that crustal reworking played an important role on erasing the ancient crusts.  相似文献   

High-pressure phase relations in the system CaAl4Si2O11–NaAl3Si3O11 with implication for Na-rich CAS phase in shocked Martian meteorites     

M. Akaogi  M. Haraguchi  K. Nakanishi  H. Ajiro  H. Kojitani 《Earth and Planetary Science Letters》2010,289(3-4):503-508

High-pressure phase relations in the system NaAl₃Si₃O₁₁–CaAl₄Si₂O₁₁ were examined at 13–23 GPa and 1600–1900 °C, using a multianvil apparatus. A Ca-aluminosilicate with CaAl₄Si₂O₁₁ composition, designated CAS phase, is stable above about 13 GPa at 1600 °C. In the system NaAl₃Si₃O₁₁–CaAl₄Si₂O₁₁, the CAS phase dissolving NaAl₃Si₃O₁₁ component coexists with jadeite, corundum and stishovite below 22 GPa, above which the CAS phase coexists with Na-rich calcium ferrite, corundum and stishovite. At 1600 °C, the solubility of NaAl₃Si₃O₁₁ component in the CAS solid solution increases with increasing pressure up to about 50 mol% at about 22 GPa, above which the solubility decreases with pressure. The maximum solubility of NaAl₃Si₃O₁₁ component in the CAS phase increases with temperature up to around 70 mol% at 1900 °C at 22 GPa. The dissociation of NaAlSi₂O₆ jadeite to NaAlSiO₄ calcium ferrite plus stishovite occurs at about 22 GPa. Lattice parameters of the CAS phase with the hexagonal Ba-ferrite structure change with increase of the NaAl₃Si₃O₁₁ component: a-axis decreases and c-axis slightly increases, resulting in decrease of molar volume. Enthalpies of the CAS solid solutions were measured by high-temperature drop-solution calorimetry techniques. The results show that enthalpy of hypothetical NaAl₃Si₃O₁₁ CAS phase is much higher than the mixture of NaAlSi₂O₆ jadeite, corundum and stishovite and is close to that of the mixture of NaAlSiO₄ calcium ferrite, corundum and stishovite. When we adopt the Na:Ca ratio of 75:25 of the natural Na-rich CAS phase in a shocked Martian meteorite, Zagami, the phase relations determined above suggest that the natural CAS phase crystallized from melt at pressure around 22 GPa and temperature close to or higher than 2000–2200 °C. The inferred P, T conditions are consistent with those estimated using other high-pressure minerals in the shocked meteorite.  相似文献   

1-G model tests and hollow cylindrical torsional shear experiments on seismic residual displacements of fill dams from the viewpoint of seismic performance-based design     

Seda Sendir Torisu  Junichi Sato  Ikuo Towhata  Tsuyoshi Honda 《Soil Dynamics and Earthquake Engineering》2010

This paper concerns technological efforts for the general acceptance of performance-based seismic design principle of geotechnical structures. Among many problems to be solved, a particular emphasis was placed on the prediction of residual displacement that remains after a strong earthquake. Because of the complicated behavior of soils undergoing cyclic loading, the prediction is often either complicated/costly or not very accurate. The aim of this study is to examine the capability of existing prediction measures and propose some future scopes. To achieve these goals, shaking table model tests and laboratory shear tests were conducted by taking fill dams as an example target structure. It is concluded that performance-based design is possible if the necessary time and cost are spent and if the required accuracy of prediction is reasonable.  相似文献   

Preliminary health risk assessment for polybrominated diphenyl ethers and polybrominated dibenzo-p-dioxins/furans in seafood from Guangzhou and Zhoushan, China   总被引：1，自引：0，他引：1  

Miyake Y  Jiang Q  Yuan W  Hanari N  Okazawa T  Wyrzykowska B  So MK  Lam PK  Yamashita N 《Marine pollution bulletin》2008,57(6-12):357-364

Dietary intake is one of the important routes of human exposure to brominated flame retardants (BFRs) such as polybrominated diphenyl ethers (PBDEs). The use of PBDEs may also result in exposure to polybrominated dibenzo-p-dioxins and dibenzofurans (PBDDs/DFs), as these compounds are impurities in technical mixtures of BFRs and can also be formed unintentionally by the same processes that generate chlorinated dioxins. This study determined the concentrations of polybrominated compounds in common seafood in Guangzhou and Zhoushan, and assessed the health risks of these chemicals via consumption of contaminated seafood. Seafood samples (fish, bivalves, shrimp, crab, and cephalopods) purchased from local markets in 2003 and 2004 were analyzed for PBDEs and PBDDs/DFs. The highest concentration of total PBDEs (46.3 ng g(-1) lipid wt.) was detected in fish from Guangzhou, in which BDEs 47 and 209 were the two predominant congeners. The total daily intakes of PBDEs, PBDDs, and PBDFs were, 946, 6.39, and 6.54 pg kg(-1) body weight (bw) in Guangzhou, and 489, 4.99, and 7.65 pg kg(-1) bw in Zhoushan, respectively. The hazard ratios for PBDDs and PBDFs were both greater than unity, indicating that these compounds may pose some health risks to the local population.  相似文献   

Fourier transform infrared microspectroscopic characterization of Neoproterozoic organic microfossils from the Fifteenmile Group in Yukon,Canada     

Motoko Igisu  Tsuyoshi Komiya  Stanley M. Awramik  Yuka Ikemoto  Yechuan Geng  Hiroki Uehara  Ken Takai 《Island Arc》2019,28(5)

Conventional and synchrotron radiation‐based (SR) Fourier transform infrared microspectroscopies (micro‐FTIR) were applied to four types of ~ 810 Ma organic‐walled microfossils together with diffuse organic matter (OM) and one irregularly shaped structure from the Fifteenmile Group, in Yukon, Canada, for their chemical characterization. The microfossils comprised one filamentous type and three coccoidal types. Micro‐FTIR mapping analysis revealed the micrometer‐scale, spatial distribution of organic components (aliphatic C‐H bonds) and carbonate in the microfossils. Based on comparisons of CH₃/CH₂ peak height ratios (R_3/2) and morphologies of the microfossils (without the diffuse OM) to those of previously described Proterozoic microfossils, possible affinities of the microfossils are suggested, as follows. Palaeolyngbya? and Glenobotrydion belong to bacteria. Myxococcoides is not clearly characterized due to the significant mixing with diffuse OM containing abundant aliphatic C‐H groups. The irregularly shaped structure may represent a eukaryote. The diffuse OM may represent a mixture of decomposed microbial cells and extracellular polymeric substances (EPS). SR micro‐FTIR measurements of two coccoid types (Glenobotrydion and Unnamed Coccoid Form D) revealed that the R_3/2 values of the internal spots with wall structures are similar to those without wall structures in Glenobotrydion: those values from Unnamed Coccoid Form D were different. The results suggest that these two coccoids are different chemically as well as morphologically. Micro‐FTIR characterization of the organic‐walled microfossils together with morphological analysis provides new insight into their biological affinities.  相似文献   

GMS proton flux observation during February 1978     

Tsugunobu Nagai  Masaynki Kuwashima  Makoto Kawamura  Tsuyoshi Kohno 《Planetary and Space Science》1979,27(7):1035-1037

It is suggested that the drop out of the 1.2–4 MeV proton flux, observed by the geostationary satellite GMS, was due to the Earthward shift of the particle boundary in all local time. The particle boundary motions are associated with substorm activities.  相似文献   

Source distribution of acoustic emissions during an in-situ direct shear test: Implications for an analog model of seismogenic faulting in an inhomogeneous rock mass     

Tsuyoshi Ishida  Tadashi Kanagawa  Yuji Kanaori 《Engineering Geology》2010,110(3-4):66-76

We monitored acoustic emission (AE) events during an in-situ direct shear test on a specimen composed of a slate-dominant alternation of slate and sandstone, measuring 0.5 m long, 0.5 m wide and 0.2 m high. The test was conducted in a survey tunnel for an underground powerhouse in central Japan. The AE epicenters located on a fractured plane are compared with the locations of joints and a loosening seam, the height distribution of the fractured plane, and the horizontal movement of the test block prior to failure. We conclude that an initially intact region of rock bounded by the joints and the seam is fractured, generating the AE. Considering these results in connection with asperity models of seismogenic faulting for a subduction-zone earthquake, the significant contrast of stress conditions derived from the geological inhomogeneity and the uneven fractured plane is analogous to that due to subducted seamounts and horst-graben structures on a subducted oceanic plate. For an inland earthquake, the intact regions on an expected shear plane can be considered to be a portion of the fault asperity that causes strong ground motion, while the weakened portion can be considered to correspond to a region of aseismic creep. Consequently, large-scale inhomogeneous rock fracturing experiments such as the in-situ direct shear test may provide useful insights as analog models of seismogenic faulting. Furthermore, understanding of inhomogeneous rock-mass fracturing obtained from such experiments will not only contribute to a better understanding of the mechanism of earthquakes but also provide valuable knowledge for AE monitoring applications in rock engineering, such as the predictions of rockbursts in mines and the monitoring of fractures around large underground chambers.  相似文献