Initial 87Sr/86Sr ratios of plutonic rocks from Japan     

Ken Shibata  Shunso Ishihara 《Contributions to Mineralogy and Petrology》1979,70(4):381-390

Initial ⁸⁷Sr/⁸⁶Sr rations were determined for more than 80 plutonic rocks in Japan. The ⁸⁷Sr/⁸⁶Sr ratios of gabbroic and granitic rocks show no significant difference in plutonic terranes where both rocks occur closely associated, implying a genetic relationship between them (e.g., Green Tuff belt) or reequilibration at deep level (e.g., Ryoke belt). Wherever granitic rocks occur independently from gabbroic rocks, the granites have higher ratios than the gabbros.Initial ⁸⁷Sr/⁸⁶Sr ratios of the granitic rocks are low (<0.706) in Northeast Japan but high (<0.706) in Southwest Japan, the boundary being the Tanakura Tectonic Line. Within Southwest Japan, the ratios are low along the Japan Sea side of the southernmost area. This regional variation is generally correlated with thickness of the continental crust as deduced from the Bouguer anomaly.Initial ⁸⁷Sr/⁸⁶Sr ratios of the granitic rocks vary from 0.7037 to 0.7124. The low group (<0.706) is considered to consist of essentially mantle-derived magmas contaminated by crustal material in lesser but varying degree, because of its geological setting and initial ⁸⁷Sr/⁸⁶Sr values. The high group may have been formed by contamination of a deep-seated magmas by crustal material or by generation of the main part of the magmas within the continental crust. The ratios of individual belts reflect their own history depending upon age and Rb/Sr ratio of the crustal material.Initial ⁸⁷Sr/⁸⁶Sr ratios of granitic rocks are generally low for the magnetite-series but high for the ilmenite-series. Thus, a negative correlation is observed between initial ratios and ³⁴S for most Cretaceous-Paleogene granites. However, Neogene ilmenite-series granites are low in both initial ⁸⁷Sr/⁸⁶Sr and ³⁴S indicating interaction of the granitic magma with young sedimentary rocks enriched in ³²S.  相似文献   

Modelling of depth phases and source processes of some central Aleutian earthquakes     

Tai-Lin Hong  Kazuya Fujita 《Earth and Planetary Science Letters》1981,53(3):333-342

Short-period synthetic seismograms are computed to determine the relative amplitudes and arrival times of P, pP, pwP (water surface reflection), and sP phases. Except along nodal planes of upgoing p, pwP is of greater amplitude than sP. For central Aleutian earthquakes, pwP dominates over sP and pP at North American stations for thrust mechanisms and modelled crustal structures. The pwP phase is clearly identified in three Aleutian events and can be used to constrain focal depths. Complex fracturing processes are identified in two of the events. In simple events, smaller phases which are consistent from station to station can be identified as sub-surface reflections and used for modelling the structure of the forearc.  相似文献   

Plutonium diffusivity in compacted bentonite     

Kazuya Idemitsu  Katsuhiko Ishiguro  Yasuhisa Yusa  Noriaki Sasaki  Naomi Tsunoda 《Engineering Geology》1990,28(3-4):455-462

Measurements on plutonium diffusivity in water-saturated compacted bentonite were carried out. Representative specimens of sodium bentonite were taken from the Tsukinuno and Kuroishi mines situated in northeast Japan. Tsukinuno bentonite was divided into three types: raw type, purified Na-type, and H-type which was prepared by treating Na-type bentonite with hydrochloric acid. Kuroishi bentonite contained chlorite as impurity. H-type bentonite was used as reference for the convenience of profile measurement in bentonite, since plutonium diffusivity in H-type bentonite was considered to be larger than that in Na-type bentonite because of low pH and low swelling pressure of H-type bentonite.

Sampled bentonite was compacted into pellets of 20 mm in diameter and 20 mm in height. Bulk densities of these specimens were 1200–1800 kg/m³ for purified Na-type and H-type bentonite and 1600 kg/m³ for raw type bentonite.

Plutonium profiles obtained in H-type bentonite can be explained by diffusion equation with constant concentration source. Diffusivity ranges from 10^-13 to 10¹² m²/s for H-type and Kuroishi impure sodium bentonite. Diffusivity in both raw type and purified Tsukinuno bentonite was was estimated to less than 10^-14 M²/s. Diffusivity in H-type bentonite showed a tendency to decrease with increasing density. Influence of in bentonite was also studied. Quartz content up to 50% or hematite content up to 1% did not influence diffusivity significantly in H-type bentonite.

The chemical species of plutonium in pore water of Na-type and H-type were estimated Pu(OH)₃^-; and PuO₂^- , respectively.  相似文献   

Crystal-ring microstructures in Oceanographer Fracture Zone basalts     

David Walker  Stephen E. DeLong  Tsugio Shibata 《Contributions to Mineralogy and Petrology》1980,74(1):1-6

Pillow basalt fragments from the Oceanographer Fracture Zone contain spherical microstructures seen in section as rings of equant microphenocrysts of olivine±plagioclase±augite. They are uniformly 1 mm in diameter and have the same vitreous or crystalline material on the inside and outside. These structures occur in the same sections as vesicles and segregation vesicles and are clearly distinguishable from them.The occurrence of these structures in pillow basalt fragments suggests a mode of formation resulting from pillow basalt extrusion. Mechanical disruption of the partially solidified inner surface of the pillow skin produces a dispersion of cool globules in the pillow interior. Crystals adhere to these tacky globules during continued pillow extrusion in a manner analogous to the formation of armored mud balls.  相似文献   

A monitoring result of polychlorinated biphenyls (PCBs) in deep-sea organisms and sediments off Tohoku during 2012–2014: temporal variation and the relationship with the trophic position     

Naohiko Ohkouchi  H. Shibata  Y. Chikaraishi  H. Nomaki  N. O. Ogawa  T. Nagata  T. Goto  K. Fujikura  H. Kitazato 《Journal of Oceanography》2016,72(4):629-639

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Evaluation of tsunami impacts on shallow marine sediments: An example from the tsunami caused by the 2003 Tokachi-oki earthquake, northern Japan     

Atsushi Noda  Hajime Katayama  Tsumoru Sagayama  Kazuya Suga  Yasuhito Uchida  Kenji Satake  Kohei Abe  Yukinobu Okamura 《Sedimentary Geology》2007,200(3-4):314-327

A combined approach of field geology and numerical simulation was conducted for evaluating the tsunami impacts on the shelf sediments. The 2003 Tokachi-oki earthquake, M 8.0, that occurred on 25 September 2003 off southeastern Hokkaido, northern Japan, generated a locally destructive tsunami. Maximum run-up height of the tsunami waves reached 4 m above sea level. In order to estimate the tsunami impacts on shallow marine sediments, we compared pre- and post-tsunami marine sediments in water depths of 38–112 m in terms of grain size, sedimentary structure, and microfossil content. Decreases of fine fractions, especially finer than very fine sand, which led to coarsen the mean grain size, were detected in the inner shelf of the northern part of the study area. Foraminiferal assemblages also changed in the coarsened sediments. On the other hand, the other shelf sediments largely unchanged or slightly fined. We also simulated the tsunami wave velocity and direction, and grain size entrained by the modeled tsunami. The numerical simulation resulted in that the 2003 tsunami could transport very fine sand in water depths shallower than 45–95 m at the northern part of the study area. This is comparable with the actual grain-size changes after the tsunami had passed. However, some storms and tidal currents might also be possible to stir the surface sediments after the pre-tsunami survey, so we could not conclude that the grain-size changes had been caused only by the tsunami. Nevertheless, a combined approach of sampling and modeling was powerful for estimating the tsunami impacts under the sea.  相似文献   

Degradation and dissolution of zooplanktonic organic matter and lipids in early diagenesis     

Kazuya Yoshimura  Takeo Hama 《Journal of Oceanography》2012,68(1):205-214

A degradation experiment with zooplankton was carried out to investigate the diagenesis of zooplanktonic organic matter, lipids, and lipid classes. In addition, reactivities and the quantitative relation between bulk organic carbon and waxes (which are the biomarkers of zooplankton) were compared during the experiment to evaluate the possibility of estimating the contributions of zooplanktonic organic matter in organic carbon pools, such as settling particles and surface sediments, from the wax concentration. Lipids were found to be more labile than the bulk organic carbon. Major parts of the organic carbon and lipids which remained on day 120 were found in the particulate fraction, and the accumulations of stable organic carbon and lipids in the dissolved fraction were limited. Although the lipids were more labile than the bulk organic carbon in the early phase of the experiment, the degradation rate of lipids obviously decreased in the subsequent degradation period, demonstrating the presence of stable lipids in zooplankton. Whereas triglycerides readily decreased, phospholipids persisted, making a major contribution to particulate lipids throughout the experiment. Waxes and other structural lipids such as glycolipids were also stably preserved in particulate lipids, suggesting that stable lipids in particulate matter are composed of structural lipids and waxes during early diagenesis. The degradation rate of waxes showed values comparable to that of bulk organic carbon after 11 days of degradation, resulting in constant ratios of waxes/bulk organic carbon (0.8 ± 0.2%, n = 7) during the later incubation period (after 11 days). This result suggests that the ratio could prove useful in evaluating the zooplanktonic organic carbon in organic carbon pools such as surface sediments and settling particulates.  相似文献   

Preface     

Kohtaro Hosoda  Hiroshi Murakami  Akira Shibata  Futoki Sakaida  Hiroshi Kawamura 《Journal of Oceanography》2006,62(3):291-291

ADEOS-II Ocean: Advanced Earth Observing Satellite-II Ocean

Preface  相似文献   

One-dimensional electric field structure of an outer gap accelerator – II. γ-ray production resulting from inverse Compton scattering     

K. Hirotani  S. Shibata 《Monthly notices of the Royal Astronomical Society》1999,308(1):67-76

We study the structure of a stationary and axisymmetric charge-deficient region (or a potential gap) in the outer magnetosphere of a spinning neutron star. A large electric field along the magnetic field lines is created in this potential gap and accelerates migratory electrons (e⁻) and/or positrons (e⁺) to ultrarelativistic energies. Assuming that the gap is immersed in a dense soft photon field, these relativistic e^± radiate γ -ray photons via inverse Compton (IC) scattering. These γ -rays, in turn, produce yet more radiating particles by colliding with ambient soft photons, leading to a pair-production cascade in the gap. The replenished charges partially screen the longitudinal electric field, which is self-consistently solved together with the distribution of e^± and γ -ray photons. It is demonstrated that the voltage drop in the gap is not more than 10¹⁰ V when the background X-ray radiation is as luminous as 10³⁷ erg s⁻¹. However, this value increases with decreasing X-ray luminosity and attains 10¹² V when the X-ray radiation is 10³⁶ erg s⁻¹. In addition, we find useful expressions of the spatial distribution of the particle fluxes and longitudinal electric field, together with the relationship between the voltage drop and the current density. Amazingly, these expressions are valid not only when IC scattering dominates but also when curvature radiation dominates.  相似文献   

A Proposed Method to Estimate In Situ Dissolved Gas Concentrations in Gas‐Saturated Groundwater          下载免费PDF全文

Shuji Tamamura  Kazuya Miyakawa  Noritaka Aramaki  Toshifumi Igarashi  Katsuhiko Kaneko 《Ground water》2018,56(1):118-130

Gas‐saturated groundwater forms bubbles when brought to atmospheric pressure, preventing precise determination of its in situ dissolved gas concentrations. To overcome this problem, a modeling approach called the atmospheric sampling method is suggested here to recover the in situ dissolved gas concentrations of groundwater collected ex situ under atmospheric conditions at the Horonobe Underground Research Laboratory, Japan. The results from this method were compared with results measured at the same locations using two special techniques, the sealed sampler and pre‐evacuated vial methods, that have been developed to collect groundwater under its in situ conditions. In gas‐saturated groundwater cases, dissolved methane and inorganic carbon concentrations derived using the atmospheric sampling method were mostly within ±4 and ±10%, respectively, of values from the sealed sampler and pre‐evacuated vial methods. In gas‐unsaturated groundwater, however, the atmospheric sampling method overestimated the in situ dissolved methane concentrations, because the groundwater pressure at which bubbles appear (P_critical) was overestimated. The atmospheric sampling method is recommended for use where gas‐saturated groundwater can be collected only ex situ under atmospheric conditions.  相似文献