Diverse nucleosynthetic components in barium isotopes of carbonaceous chondrites: Incomplete mixing of s- and r-process isotopes and extinct Cs in the early solar system     

Hiroshi Hidaka  Shigekazu Yoneda 《Geochimica et cosmochimica acta》2011,75(13):3687-3697

Barium isotopic compositions of chemical leachates from six carbonaceous chondrites, Orgueil (CI), Mighei (CM2), Murray (CM2), Efremovka (CV3), Kainsaz (CO3), and Karoonda (CK4), were determined using thermal ionization mass spectrometry in order to assess the chemical evolution in the early solar system.The Ba isotopic data from most of the leachates show variable ¹³⁵Ba excesses correlated with ¹³⁷Ba excesses, suggesting the presence and heterogeneity of additional nucleosynthetic components for s- and r-processes in the solar system. The isotopic deviations observed in this study were generally small (−1 < ε < +1) except in the case of the acid residues of CI and CM meteorites. Large deviations of ¹³⁵Ba (ε = −13.5 to −5.0) and ¹³⁷Ba (ε = −6.2∼−1.2) observed in the acid residues from one CI and two CM meteorites show significant evidence for the enrichment of s-process isotopes derived from presolar grains. Two models were proposed to estimate the ¹³⁵Cs isotopic abundances by subtraction of the s- and r-isotopic components from the total Ba isotopic abundances in the three CM meteorites, Mighei, Murchison (measured in a previous study), and Murray. The data points show individual linear trends between ¹³⁵Cs/¹³⁶Ba ratios and ¹³⁵Ba isotopic deviations for the three samples. Considering the different trends observed in the three CM meteorites, the Ba isotopic composition of the CM meteorite parent body was heterogeneous at its formation. Chronological information is unclear in the data for Murchison and Murray because of large analytical uncertainties imposed by error propagation. Only the Mighei meteorite data indicate the possible existence of presently extinct ¹³⁵Cs (¹³⁵Cs/¹³³Cs = (2.7 ± 1.6) × 10⁻⁴) in the early solar system. Another explanation of the data for the three CM meteorite is mixing of at least three components with different Ba isotopic compositions, although this is model-dependent.  相似文献   

日本东北9.0级地震的同震与震后滑动   总被引：3，自引：0，他引：3  

Hisashi Suito  Mikio Tobita  张慧 《华南地震》2011,31(3):11-18

大部分强震都发生在海沟,那里是海洋板块向大陆板块俯冲的地方.大量矩震级MW9.0以上的地震发生在若干区域,包括智利,阿拉斯加,堪察加半岛和苏门答腊岛等.位于太平洋板块俯冲鄂霍茨克板块的日本海沟,历史记载上没有发生过MW9.0地震,除了至今震级还有争议的公元869年Jogan大地震[1](可能超过MW9.0).然而,根据...  相似文献   

Spatial distribution and corresponding determining factors of metal concentrations in surface sediments of Beppu Bay, southwest Japan     

Amano A  Kuwae M  Agusa T  Omori K  Takeoka H  Tanabe S  Sugimoto T 《Marine environmental research》2011,71(4):247-256

This study determined the factors contributing to the spatial distribution of 14 metal concentrations in the surface sediments of Beppu Bay on the basis of comparisons of the organic geochemical properties and environmental parameters through principal component analysis (PCA) and redundancy analysis (RDA). The results of PCA and RDA showed that the concentrations of V, Cr, Co, and As were closely related to the distances between the sampling sites and the Oita River. This indicated that these metals originated from the river's drainage area. The Mn, Cu, Mo, and Cd concentrations were related to the water depth. These results indicated that the Mo, Cd, and Cu deposition processes were controlled by oxygen depletion, and that these elements accumulated in the deeper parts of the bay under anoxic conditions.  相似文献   

Deterministic Landslide Risk Assessment at a Past Landslide Site     

Mowen Xie  Tetsuro Esaki  Cheng Qiu  Chunxiang Wang  Zengfu Wang 《Geotechnical and Geological Engineering》2009,27(3):355-364

The slope failure and landslide hazard will possess the same properties within a range including the same engineering geological conditions. To assess the landslide risk of a mountainous area, the study of landslides previously having occurred is very important to evaluate the landslide risk around the area in which they took place. Based on the study of the mechanism of a previous landslide recorded in Kumamoto, Japan, this study initially proposes mechanical parameters for evaluating the landslide hazard using a 3D slope stability method. For each slope unit in the study area, the critical slip surface, which reveals the minimum safety factor of a slope, can be obtained. The affected streams and range of possible landslide masses are analyzed based on the debris flow simulation. This is initially applied to simulate the past landslide event and the result shows the landslide-deduced debris flow effectively re-displayed. Overlayered with layers of infrastructure in Geographic Information Systems (GIS), this risk map indicates which houses and road sections remain in dangerous areas.  相似文献   

Regolith history of the aubritic meteorite parent body revealed by neutron capture effects on Sm and Gd isotopes     

Hiroshi Hidaka  Shigekazu Yoneda 《Geochimica et cosmochimica acta》2006,70(13):3449-3456

Enstatite achondrites (aubrites) when compared to other stone meteorites have unusually long cosmic-ray exposure (CRE) ages. We report here the ¹⁵⁰Sm/¹⁴⁹Sm and ¹⁵⁸Gd/¹⁵⁷Gd ratios in six different structural phases, i.e., light and dark (shocked) grains and in matrix materials of Pesyanoe, in three different fragments from Pena Blanca Spring, and in one from Norton County, Shallowater, and Khor Temiki, to investigate the regolith history on the aubrite parent body. The results from phases components of Pesyanoe confirm earlier reported evidence for regolith irradiation of several aubrites. The inferred neutron fluences for six Pesyanoe separates vary between (2.13 and 2.82) × 10¹⁶ n cm⁻². The fluences also significantly exceed those expected from cosmic-ray irradiation during transit to Earth and approach those observed in the lunar regolith. These observations confirm that the brecciated Pesyanoe meteorite, which contains solar wind (SW) gases only in dark phases, was processed in a regolith and that structural phases were differentially irradiated before compaction. On the other hand, in some aubrites (Mt. Egerton, Shallowater, Pena Blanca Spring, Norton County) neutron capture effects may entirely be due to space irradiation.  相似文献   

Temporal changes in the phytoplankton community of the southern basin of Lake Baikal over the last 24,000 years recorded by photosynthetic pigments in a sediment core     

Yukinori Tani  Kota Kurihara  Fumiko Nara  Nobuyasu Itoh  Mitsuyuki Soma  Yuko Soma  Atsushi Tanaka  Minoru Yoneda  Masashi Hirota  Yasuyuki Shibata 《Organic Geochemistry》2002,33(12)

Photosynthetic pigments and other indicators of phytoplankton were analyzed in a dated undisturbed sediment core obtained from the southern basin of Lake Baikal to reveal temporal changes in the phytoplankton community in the lake through the last glacial/post-glacial transition. The sedimentation age of the core spans the last 24 ¹⁴C ka. Chlorophyll a, its derivatives, carotenoids and total organic carbon (TOC) started to increase after 15 ¹⁴C ka, and the onset of biogenic silica occurred at 10 ¹⁴C ka. This indicated that the post-glacial growth of diatoms was preceded by that of other phytoplankton groups. In the record of the pigments and TOC, a temporary decrease was observed in the period 11.5–10.5 ¹⁴C ka, corresponding to the Younger Dryas cold period. The similarity found between the depth profiles of pyropheophytin a and steryl chlorin esters formed through predation of phytoplankton by zooplankton and that of TOC suggested the important contribution of fecal pellets to sedimentary organic matter in the lake.  相似文献   

Acid-sulphate Type Alteration and Mineralization in the Desmos Caldera, Manus Back-arc Basin, Papua New Guinea     

Kaul Gena    Toshio Mizuta    Daizo Ishiyama  Tetsuro Urabe 《Resource Geology》2001,51(1):31-44

Abstract: The Onsen acid‐sulphate type of mineralization is located in the Desmos caldera, Manus back‐arc basin. Hydrothermal precipitates, fresh and altered basaltic andesite collected from the Desmos caldera were studied to determine mineralization and mobility of elements under seawater dominated condition of hydrothermal alteration. The mineralization is characterized by three stages of advanced argillic alteration. Alteration stage I is characterized by coarse subhedral pyrophyllite with disseminated anhedral pyrite and enargite which were formed in the temperature range of 260–340°C. Alteration stage II which overprinted alteration stage I was formed in the temperature range of 270–310°C and is characterized by euhedral pyrite, quartz, natroalunite, cristobalite and mixed layer minerals of smectite and mica with 14–15 Å XRD peak. Alteration stage III is characterized by amorphous silica, native sulphur, covellite, marcasite and euhedral pyrite, which has overprinted alteration stages I and II. Relative to the fresh basaltic andesite samples, the rims and cores of the partly altered basaltic andesite samples have very low major, minor and rare earth elements content except for SiO₂ which is much higher (58–78 wt%) than SiO₂ content of the fresh basaltic andesite (55 wt%). REE patterns of the partly altered basaltic andesite specimens are variably depleted in LREE and have pronounced negative Eu anomalies. Normalization of major, minor and REE content of the partly altered basaltic andesites to the fresh basaltic andesite indicates that all the elements except for SiO2 in the partly altered basaltic andesite are strongly lost (e.g. Al₂O₃ = ‐8.3 to ‐10.9 g/100cm³, Ba = ‐2.2 to ‐5.6 mg/100cm³, La = ‐130 to ‐200 μg/100cm³) during the alteration process. Abnormal depletion of MgO, total Fe as Fe₂O₃, LREE especially Eu and enrichment of SiO₂ in the altered basaltic andesites from the Desmos caldera seafloor is caused by interaction of hot acidic hydrothermal fluid, which originates from a mixing of magmatic fluid and seawater.  相似文献   

Age-related change and distribution of cadmium and zinc concentrations in the Steller sea lion (Eumetopias jubata) from the coast of Hokkaido,Japan     

Tsuneyasu Hamanaka  Tetsuro Itoo  Seikichi Mishima 《Marine pollution bulletin》1982,13(2):57-61

Tissue cadmium and zinc levels in Steller sea lions have been analysed to elucidate the body distribution of these metals and their age-related accumulation. A significant correlation between age (0.7–8.8 year old) and renal and hepatic cadmium concentration was noted. Of the tissues examined, the kidney manifested the highest cadmium content (mean: 20.9 μg g^?1 dry wt). A similar zinc distribution pattern was observed; its concentration was more uniform among tissues than that of cadmium. The tissue cadmium concentration in the Steller sea lion was lower than in other pinnipeds from various areas, possibly due to their feeding habits which may represent a major pathway of metal accumulation.  相似文献   

Structural characteristics controlling the seismicity crustal structure of southern Japan Trench fore-arc region, revealed by ocean bottom seismographic data     

Seiichi Miura  Shuichi Kodaira  Ayako Nakanishi  Tetsuro Tsuru  Narumi Takahashi  Naoshi Hirata  Yoshiyuki Kaneda 《Tectonophysics》2003,363(1-2):79-102

The Japan Trench is a plate convergent zone where the Pacific Plate is subducting below the Japanese islands. Many earthquakes occur associated with plate convergence, and the hypocenter distribution is variable along the Japan Trench. In order to investigate the detailed structure in the southern Japan Trench and to understand the variation of seismicity around the Japan Trench, a wide-angle seismic survey was conducted in the southern Japan Trench fore-arc region in 1998. Ocean bottom seismometers (15) were deployed on two seismic lines: one parallel to the trench axis and one perpendicular. Velocity structures along two seismic lines were determined by velocity modeling of travel time ray-tracing method. Results from the experiment show that the island arc Moho is 18–20 km in depth and consists of four layers: Tertiary and Cretaceous sedimentary rocks, island arc upper and lower crust. The uppermost mantle of the island arc (mantle wedge) extends to 110 km landward of the trench axis. The P-wave velocity of the mantle wedge is laterally heterogeneous: 7.4 km/s at the tip of the mantle wedge and 7.9 km/s below the coastline. An interplate layer is constrained in the subducting oceanic crust. The thickness of the interplate layer is about 1 km for a velocity of 4 km/s. Interplate layer at the plate boundary may cause weak interplate coupling and low seismicity near the trench axis. Low P-wave velocity mantle wedge is also consistent with weak interplate coupling. Thick interplate layer and heterogeneous P-wave velocity of mantle wedge may be associated with the variation of seismic activity.  相似文献   

Locations of Jovian decametric radiation sources     

Hiroshi Oya  Akira Morioka  Tetsuro Kondo 《Planetary and Space Science》1979,27(7):963-972

The location of the Jovian decametric radiation main source is determined to be the south magnetic pole while the location of the early source is found to be near the north magnetic pole, with an equal contribution from a region near the south magnetic pole. The results are based on calculations of the region observable from the Earth (ROE) for Jovian decametric radio waves that are emitted in the direction ± 10° centered on the direction perpendicular to the Jovian magnetic field and based on a Pioneer 11 model of the field at the level of the topside region of the Jovian ionosphere. Ground-based observations of the occurrence frequency of the decametric radiation as a function of Jovian longitude, which indicate a remarkable asymmetry between the early and main sources, agree with the calculated ROE area that varies as a function of CML observed from the Earth. The observations support a recent theory for the origin of the decametric radiation which is based on a wave-mode conversion from plasma waves into electromagnetic waves.  相似文献