Origin of the Tonaru body in the Sanbagawa metamorphic belt,SW Japan     

Shogo Aoki  Kazumasa Aoki  Kentaro Chiba  Shuhei Sakata  Yuta Tsuchiya  Daichi Kato 《Island Arc》2020,29(1)

Zircon U–Pb dating of the Tonaru metagabbro body in the Sanbagawa metamorphic belt, southwest Japan, suggests that igneous events at ca 200–180 Ma were involved in the protolith formation. The trace element compositions of the Tonaru zircons are enriched in U (a fluid‐mobile element) and Sc (an amphibole‐buffered element), and depleted in Nb (a fluid‐immobile element), suggesting that the parental magmas related to the Tonaru metagabbros formed in an arc setting. Integration of our results with previous studies of the metasedimentary rocks in the Tonaru body clearly indicates that the protoliths of the Tonaru body were produced by oceanic‐arc magmatism. With the previous geochronological and geological studies, the tectono‐magmatic–metamorphic history of the Tonaru and other mafic bodies in the Sanbagawa metamorphic belt may be summarized as follows: (i) the protolith formation by the oceanic‐arc magmatic event had occurred at 200–180 Ma; (ii) the protoliths were accreted in the trench at ca 130–120 Ma; and (iii) they were completely subducted into the depth of the eclogite‐facies condition after 120 Ma.  相似文献   

Development of a numerical model for nitrates in groundwater in the reservoir area of the Komesu subsurface dam, Okinawa, Japan   总被引：1，自引：0，他引：1  

Shuhei Yoshimoto  Takeo Tsuchihara  Satoshi Ishida  Masayuki Imaizumi 《Environmental Earth Sciences》2013,70(5):2061-2077

A numerical model consisting of simplified equations was developed to simulate nitrate concentrations in groundwater in a reservoir area of a subsurface dam in a Quaternary limestone region. The model was composed of a water balance sub-model and a nitrogen balance sub-model; the water balance sub-model was built from tank models which can express the quick dilution near caves and the effect of dam construction; and the nitrogen balance sub-model was made to represent changes in nitrogen forms and movement of nitrogen in the soil and aquifer zones. The model was calibrated and verified by observed data before and after the dam construction and then applied to a predictive simulation under a simple assumption that rainfall descends gradually. The model seemed applicable to long-term prediction of changes in NO₃-N in the reservoir area.  相似文献   

Notes on extended–range atmospheric prediction in the Northern Hemisphere winter     

Shingo Yama  Shuhei Mae  K. Gambo 《大气科学进展》1997,14(1):23-40

We examined the characteristic feature and predictability of low frequency variability (LFV) of the atmosphere in the Northern Hemisphere winter (January and February) by using the empirical orthogonal functions (EOFs) of the geopotential height at 500 hPa. In the discussion, we used the EOFs for geostrophic zonal wind (Uznl) and the height deviation from the zonal mean (Zeddy). The set of EOFs for Uznl and Zeddy was denoted as Uznl-1. Uznl-2, …, Zeddy-1, Zeddy-2…, respectively. We used the data samples of 396 pentads derived from 33 years of NMC, ECMWF and JMA analyses, from January 1963 to 1995. From the calculated scores for Uznl-1, Uznl-2, Zeddy-1, Zeddy-2 and so on we found that Uznl-1 and Zeddy-1 were statistically stable and their scores were more persistent than those of the other EOFs. A close relationship existed between the scores of Uznl-1 and those of Zeddy-1 30-day forecast experiments were carried out with the medium resolution version of JMA global spectral model for 20 cases in January and February for the period of 1984-1992. Results showed that Zeddy-1 was more predicta?ble than the other EOFs for Zeddy Considering these results, we argued that prediction of the Zeddy-1 was to be one of the main target of extended range forecasting  相似文献   

Fission track and U–Pb zircon ages of psammitic rocks from the Harushinai unit,Kamuikotan metamorphic rocks,central Hokkaido,Japan: constraints on metamorphic histories          下载免费PDF全文

Ayumi S. Okamoto  Toru Takeshita  Hideki Iwano  Tohru Danhara  Takafumi Hirata  Hirotsugu Nishido  Shuhei Sakata 《Island Arc》2015,24(4):379-403

Accurate pressure–temperature–time (P–T–t) paths of rocks from sedimentation through maximum burial to exhumation are needed to determine the processes and mechanisms that form high‐pressure and low‐temperature type metamorphic rocks. Here, we present a new method combining laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) U–Pb with fission track (FT) dates for detrital zircons from two psammitic rock samples collected from the Harushinai unit of the Kamuikotan metamorphic rocks. The concordant zircon U–Pb ages for these samples vary markedly, from 1980 to 95 Ma, with the youngest age clusters in both samples yielding Albian‐Cenomanian weighted mean ages of 100.8 ± 1.1 and 99.3 ± 1.0 Ma (2σ uncertainties). The zircon U–Pb ages were not reset by high‐P/T type metamorphism, because there is no indication of overgrowth within the zircons with igneous oscillatory zoning. Therefore, these weighted mean ages are indicative of the maximum age of deposition of protolithic material. By comparison, the zircon FT data yield a pooled age of ca. 90 Ma, which is almost the same as the weighted mean age of the youngest U–Pb age cluster. This indicates that the zircon FT ages were reset at ca. 90 Ma while still at their source, but have not been reset since. This conclusion is supported by recorded temperature conditions of less than about 300 °C (the closure temperature of zircon FTs), as estimated from microstructures in the deformed detrital quartz grains in psammitic rocks, and no shortening of fission track lengths in the zircon. Combining these new data with previously reported white mica K–Ar ages indicates that the Harushinai unit was deposited after ca. 100 Ma, and underwent burial to its maximum depth before being subjected to a localized thermal overprint during exhumation at ca. 58 Ma.  相似文献   

Trace elements and stable isotope ratios (δC and δN) in fish from deep-waters of the Sulu Sea and the Celebes Sea     

Kwadwo Ansong Asante  Tetsuro Agusa  Reiji Kubota  Hiroko Mochizuki  Shuhei Nishida  Suguru Ohta  Annamalai Subramanian 《Marine pollution bulletin》2010,60(9):1560-1570

Trace elements (TEs) and stable isotope ratios (δ¹⁵N and δ¹³C) were analyzed in fish from deep-water of the Sulu Sea, the Celebes Sea and the Philippine Sea. Concentrations of V and Pb in pelagic fish from the Sulu Sea were higher than those from the Celebes Sea, whereas the opposite trend was observed for δ¹³C. High concentrations of Zn, Cu and Ag were found in non-migrant fish in deep-water, while Rb level was high in fish which migrate up to the epipelagic zone, probably resulting from differences in background levels of these TEs in each water environment or function of adaptation to deep-water by migrant and non-migrant species. Arsenic level in the Sulu Sea fish was positively correlated with δ¹⁵N, indicating biomagnification of arsenic. To our knowledge, this is the first study on relationship between diel vertical migration and TE accumulation in deep-water fish.  相似文献   

Is the Chandler period variable?   总被引：2，自引：0，他引：2  

Shuhei Okubo 《Geophysical Journal International》1982,71(3):629-646

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Time series analysis of natural remanent magnetization in deep-sea sediments     

Shuhei Okubo  Hitoshi Takeuchi 《Geophysical Journal International》1979,56(2):309-318

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Determination of U–Pb Ages for Young Zircons using Laser Ablation‐ICP‐Mass Spectrometry Coupled with an Ion Detection Attenuator Device     

Shuhei Sakata  Kentaro Hattori  Hideki Iwano  Takaomi D. Yokoyama  Tohru Danhara  Takafumi Hirata 《Geostandards and Geoanalytical Research》2014,38(4):409-420

We have developed new analytical procedures to measure precise and accurate ²³⁸U–²⁰⁶Pb and ²³⁵U–²⁰⁷Pb ages for young (~ 1 Ma) zircons using laser ablation‐ICP‐mass spectrometry. For young zircons, both careful correction for the background counts and analysis of very small Pb/U ratios (i.e., ²⁰⁶Pb/²³⁸U < 0.00016 and ²⁰⁷Pb/²³⁵U < 0.0001 for 1 Ma zircons) are highly desired. For the correction of the background, the contribution of the background signal intensities for the analytes, especially for the residual signal intensities for ²⁰⁶Pb and ²⁰⁷Pb, was defined through laser ablation of synthesised zircons (ablation blank) containing negligible Pb. The measured signal intensities for ²⁰²Hg, ²⁰⁶Pb and ²⁰⁷Pb signals obtained by the ablation blank were slightly higher than those obtained by data acquisition without laser ablation (gas blank). For the wider dynamic range measurements on Pb/U ratios, an attenuator device for the ion detection system was employed to extend the capability to monitor high‐intensity signals (i.e., > 3 Mcps). Through the attenuator device, the ion currents were reduced to 1/450 of the signal intensity without the attenuator. Because the switching time for the attenuator was shorter than 1 ms, signal intensities for only specific isotopes could be reduced. With attenuation of the ²³⁸U signal, counting statistics on ²⁰⁶Pb and ²⁰⁷Pb isotopes could be improved and counting loss on the ²³⁸U signal could be minimised. To demonstrate the reliability of this new analytical technique, ²³⁸U–²⁰⁶Pb and ²³⁵U–²⁰⁷Pb ages for three young zircon samples (collected from Osaka Group Pink Volcanic Ash, Kirigamine and Bishop Tuff) were measured. The data presented here demonstrate clearly that the present technique could become a major analytical tool for in situ U–Pb age determination of young zircons (~ 1 Ma).  相似文献   

Liquid waveguide spectrophotometric measurements of arsenate and particulate arsenic,as well as phosphate and particulate phosphorus,in seawater     

Fuminori Hashihama  Shuhei Suwa  Jota Kanda 《Journal of Oceanography》2017,73(4):439-447

Sensitive methods for the determination of arsenate and particulate arsenic (PAs), as well as phosphate and particulate phosphorus (PP), in seawater are described. The method for arsenate and phosphate was established by applying automated liquid waveguide spectrophotometry. Because the reaction time for the formation of the arsenate-molybdate complex is longer than that for the phosphate-molybdate complex, a long Teflon tube submerged in a heating bath was installed in the conventional phosphate flow system. The arsenate was quantified as the difference between absorbances of molybdenum blue dyes with (only phosphate) and without (phosphate + arsenate) arsenate reduction treatment. Contamination was observed in the reagent for arsenate reduction and must be corrected. Linear dynamic ranges up to 1000 nM were confirmed for arsenate and phosphate. The detection limits for arsenate and phosphate were 5 and 4 nM, respectively. Freezing was a reliable sample preservation technique for both arsenate and phosphate. The method for PAs and PP was established by combining conventional persulfate oxidation of PP and the automated liquid waveguide spectrophotometry of arsenate and phosphate. The digestion efficiencies of organic As analogs were >93%. Contamination in the glass fiber filter was negligible. Field tests confirmed that the coefficients of variation (CVs) of 10–19 nM arsenate and 4–151 nM phosphate were 7–20 and 1–25%, respectively, while the CVs of 0.9 nM PAs and 10.2 nM PP were 11 and 4%, respectively.  相似文献   

Age gap between the intrusion of gneissose granitoids and regional high‐temperature metamorphism in the Ryoke belt (Mikawa area), central Japan          下载免费PDF全文

Kota Takatsuka  Tetsuo Kawakami  Etienne Skrzypek  Shuhei Sakata  Hideyuki Obayashi  Takafumi Hirata 《Island Arc》2018,27(1)

The relationships between the intrusion of gneissose granitoids and the attainment of regional high‐T conditions recorded in metamorphic rocks from the Ryoke belt of the Mikawa area, central Japan, are explored. Seven gneissose granitoid samples (tonalite, granodiorite, granite) were collected from three distinct plutonic bodies that are mapped as the so‐called “Older Ryoke granitoids.” Based on bulk‐rock compositions and U–Pb zircon ages obtained by laser ablation inductively coupled plasma mass spectrometry, the analyzed granitoids can be separated into two groups. Gneissose granitoids from the northern part of the area give weighted mean ²⁰⁶Pb/²³⁸U ages of 99 ±1 Ma (two samples) and 95 ±1 Ma (one sample), whereas those from the southern part yield 81 ±1 Ma (two samples) and 78–77 ±1 Ma (two samples). Regional comparisons allow correlation of the northern granitoids (99–95 Ma) with the Kiyosaki granodiorite, and mostly with the Kamihara tonalite found to the east. The southern granitoids are tentatively renamed as “78–75 Ma (Hbl)?Bt granite” and “81–75 Ma Hbl?Bt tonalite” (Hbl, hornblende; Bt, biotite). and seem to be broadly coeval members of the same magmatic suite. With respect to available age data, no gneissose granitoid from the Mikawa area shows a U–Pb zircon age which matches that of high‐T metamorphism (ca 87 Ma). The southern gneissose granitoids (81–75 Ma), although they occur in the highest‐grade metamorphic zone, do not seem to represent the heat source which produced the metamorphic field gradient with a low dP/dT slope.  相似文献