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81.
Rates of magmatic processes in a cooling magma chamber wereinvestigated for alkali basalt and trachytic andesite lavaserupted sequentially from Rishiri Volcano, northern Japan, bydating of these lavas using 238U230Th radioactive disequilibriumand 14C dating methods, in combination with theoretical analyses.We obtained the eruption age of the basaltic lavas to be 29·3± 0·6 ka by 14C dating of charcoals. The eruptionage of the andesitic lavas was estimated to be 20·2 ±3·1 ka, utilizing a whole-rock isochron formed by UThfractionation as a result of degassing after lava emplacement.Because these two lavas represent a series of magmas producedby assimilation and fractional crystallization in the same magmachamber, the difference of the ages (i.e. 9 kyr) is a timescaleof magmatic evolution. The thermal and chemical evolution ofthe Rishiri magma chamber was modeled using mass and energybalance constraints, as well as quantitative information obtainedfrom petrological and geochemical observations on the lavas.Using the timescale of 9 kyr, the thickness of the magma chamberis estimated to have been about 1·7 km. The model calculationsshow that, in the early stage of the evolution, the magma cooledat a relatively high rate (>0·1°C/year), and thecooling rate decreased with time. Convective heat flux fromthe main magma body exceeded 2 W/m2 when the magma was basaltic,and the intensity diminished exponentially with magmatic evolution.Volume flux of crustal materials to the magma chamber and rateof convective melt exchange (compositional convection) betweenthe main magma and mush melt also decreased with time, from 0·1 m/year to 103 m/year, and from 1 m/yearto 102 m/year, respectively, as the magmas evolved frombasaltic to andesitic compositions. Although the mechanism ofthe cooling (i.e. thermal convection and/or compositional convection)of the main magma could not be constrained uniquely by the model,it is suggested that compositional convection was not effectivein cooling the main magma, and the magma chamber is consideredto have been cooled by thermal convection, in addition to heatconduction. KEY WORDS: convection; magma chamber; heat and mass transport; timescale; U-series disequilibria 相似文献
82.
Robin T.CLARK Xiquan DONG Chang-Hoi HO Jianhua SUN Huiling YUAN Tetsuya TAKEMI 《大气科学进展》2021,38(12):1977-1979
Throughout vast areas of Asia, the summer of 2020 was extraordinarily wet. After an exceptionally wet May in North-east India and Bangladesh, excessive rainfall hit at least 10 provinces in central and southern China in June and July, caus-ing extensive flooding in many rural and urban locations. Long standing rainfall, lake and river level records were con-sequently broken in several parts of the region with the Yangtze-Huaihe river valleys, particularly badly impacted, with con-sequential economic losses. Floods and landslides also affected parts of Japan with at least one location in Kumamoto province even experiencing a record-breaking 1000 mm of rainfall in just 3 days in early July. The 2020 wet season in South Korea was also exceptionally long, lasting 54 days, compared to their more usual 32. 相似文献
83.
Although changes in rainfall characteristics have been noted across the world, few studies have reported those in mountainous areas. This study was undertaken to clarify spatial and temporal variations in rainfall characteristics such as annual rainfall amount (Pr), mean daily rainfall intensity (η), and ratio of rain days (λ) in mountainous and lowland areas in Taiwan. To this aim, we examined spatial and year‐to‐year variations and marginal long‐term trends in Pr, η, and λ, based on rainfall data from 120 stations during the period 1978–2008. The period mean rainfall () at the lowland stations had strong relationships with the period mean daily rainfall intensity () and the period mean ratio of rain days () during those 31 years. Meanwhile, was only strongly related to at mountainous stations, indicating that influences on spatial variations in were different between lowland and mountainous stations. Year‐to‐year variations in Pr at each station were primarily determined from the variation in η at most stations for both lowland and mountainous stations. Long‐term trend analysis showed that Pr and η increased significantly at 10% and 31% of the total 120 stations, respectively, and λ decreased significantly at 6% of the total. The increases in Pr were mostly accompanied by increases in η. Although stations with significant η increases were slightly biased toward the western lowland area, increases or decreases in Pr and λ were not common. These results contribute to understanding the impacts of possible climate changes on terrestrial hydrological cycles. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
84.
Saori Imada Kei Hirose Tetsuya Komabayashi Toshihiro Suzuki Yasuo Ohishi 《Physics and Chemistry of Minerals》2012,39(7):525-530
Compression behaviors of two Al-rich phases in the lower mantle, hexagonal new aluminum-rich (NAL) phase and its high-pressure polymorph Ca-ferrite-type (CF) phase, were examined for identical Na0.4Mg0.6Al1.6Si0.4O4 (40?% NaAlSiO4–60?% MgAl2O4) composition. The volumes of the NAL and CF phases were obtained at room temperature up to 31 and 134?GPa, respectively, by a combination of laser-annealed diamond-anvil cell techniques and synchrotron X-ray diffraction measurements. Fitting of the third-order Birch–Murnaghan equation of state to such pressure–volume data yields bulk modulus K 0?=?199(6) GPa at 1?bar and its pressure derivative K 0′?=?5.0(6) for the NAL phase and K 0?=?169(5) GPa and K 0′?=?6.3(3) for the CF phase. These results indicate that the bulk modulus increases from 397 to 407 GPa across the phase transition from the NAL to CF phase at 43 GPa, where the NAL phase completely transforms into the CF phase on Na0.4Mg0.6Al1.6Si0.4O4. Density also increases by 2.1?% across the phase transition. 相似文献
85.
Masanao Noguchi Tetsuya Komabayashi Kei Hirose Yasuo Ohishi 《Physics and Chemistry of Minerals》2013,40(1):81-91
In order to examine pressure–volume–temperature (P–V–T) relations for CaSiO3 perovskite (Ca-perovskite), high-temperature compression experiments with in situ X-ray diffraction were performed in a laser-heated diamond anvil cell (DAC) to 127 GPa and 2,300 K. We also employed an external heating system in the DAC in order to obtain P–V data at a moderate temperature of 700 K up to 113 GPa, which is the reference temperature for constructing an equation of state. The P–V data at 700 K were fitted to the second-order Birch–Murnaghan equation of state, yielding K 700,1bar = 207 ± 4 GPa and V 700,1bar = 46.5 ± 0.1 Å3. Thermal pressure terms were evaluated in the framework of the Mie–Grüneisen–Debye model, yielding γ 700,1bar = 2.7 ± 0.3, q 700,1bar = 1.2 ± 0.8, and θ 700,1bar = 1,300 ± 500 K. A thermodynamic thermal pressure model was also employed, yielding α700,1bar = 5.7 ± 0.5 × 10?5/K and (?K/?T) V = ?0.010 ± 0.004 GPa/K. Computed densities along a lower mantle geotherm demonstrate that Ca-perovskite is denser than the surrounding lower mantle, suggesting that Ca-perovskite-rich rocks do not rise up through the lower mantle. One of such rocks might be a residue of partial melting of subducted mid-oceanic ridge basalt (MORB) at the base of the mantle. Since the partial melt is FeO-rich and therefore denser than the mantle, all the components of subducted MORB may not return to shallow levels. 相似文献
86.
Geologic Core Holder with a CFR PEEK Body for the X-ray CT-Based Numerical Analysis of Fracture Flow Under Confining Pressure 总被引:1,自引:0,他引:1
87.
Goro Komatsu Sergei G. Arzhannikov Alan R. Gillespie Raymond M. Burke Hideaki Miyamoto Victor R. Baker 《Geomorphology》2009,104(3-4):143-164
A suite of geomorphological and sedimentological features in the catchment of the upper Yenisei River in the Sayan mountains of southern Siberia testifies to the occurrence of cataclysmic floods that flowed down the river. Evidence of large-scale high-energy flood events includes: 1) gravel dunes, up to a few meters high and spaced 50 to 80 m apart, in the Kyzyl Basin 2) landforms such as hanging valleys and paleochannels and 3) flood sediments in a tributary valley. The origins of the Yenisei floods were likely diverse due to complex hydrological processes operating in the Sayan mountains. The possibilities include failures of multiple, variably impounded (ice, sedimentary, tectonic scarp, and lava flow dams) paleolakes in the two large intermontane basins of Darkhadyn Khotgor and Todza, and other minor basins, in the upper Yenisei River catchment. Dating techniques applied to the paleolakes in the Darkhadyn Khotgor and Todza basins revealed their formation during various periods in the middle–late Pleistocene and Holocene. Flooding from the Darkhadyn Khotgor appears to explain many of the inferred flood features, although contributions by flooding from other paleolake basins cannot be ruled out. Computer simulation of the flooding caused by a Darkhadyn Khotgor paleolake ice-dam failure indicates a probable peak discharge of 3.5 × 106 m3 s− 1, approximately one-fifth that of the floods that formed the Channeled Scabland in the U.S.A. Many of the outburst events probably occurred in the late Quaternary, but earlier floods could also have occurred. 相似文献
88.
This study investigates the structural performance of interior, exterior and corner traditional timber joints found in a traditional temple in Japan subjected to bi‐axial bending. A total of 36 half‐scale specimens were fabricated and tested under both uni‐axial and bi‐axial cyclic bending for comparison of their structural behaviour. The results show that the corner joints exhibit lower rotational stiffness than the interior and exterior joints. Further, connections subjected to only uni‐axial moments exhibit better performance with regard to moment resistance, energy dissipation and stiffness degradation as compared with those subjected to bi‐axial moments. Hence, this study suggests that if the timber joints are subjected to bi‐axial bending, this effect on timber joints should be considered during the design and evaluation process in the future. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
89.
Mooring and hydrographic observations were conducted from September 2012 to May 2014 at the mouth of Otsuchi Bay, a ria along the Pacific coast of Japan. Our observations quantitatively demonstrated that the circulation and the water properties of Otsuchi Bay are strongly influenced by the Tsugaru Warm Current (TWC) and Oyashio Current (OY) at seasonal and subseasonal time scales. Two bottom-mounted velocity profilers and temperature and salinity measurements beneath the near-surface halocline showed a counterclockwise lateral circulation pattern related to the TWC, which was enhanced from summer to autumn. From winter to early spring, the lateral circulation patterns related to the TWC weakened and the influence of the OY occasionally increased. When the OY was weak, surface flows became an overturning structure, with outflows in the upper layer and inflows in the lower layer. When the OY was strong and passed close to the Sanriku coast, the circulation became highly variable and intermittent. Intrusions of the markedly low-salinity OY water were observed on two occasions and persisted for periods of several weeks to several months. Salinity was sometimes less than 33.7, the lower limit of the typical TWC from late summer to autumn even when the TWC dominates. We suggested that this is the seasonal fluctuations of the TWC itself, as the upstream current of the Tsushima Warm Current is freshened in summer as a result of the influence of the Changjiang River. The surface water was generally fresher in the south of the bay than in the north, suggesting the Coriolis deflection of the river plume. 相似文献
90.
Masato Ueshima Takato Takemura Takeshi Saito Yoshiharu Ito Shoichiro Hamamoto Hirotaka Saito Toshiko Komatsu 《Environmental Earth Sciences》2017,76(18):633
Underground developments such as subways and shopping facilities have been increasing in number and magnitude in the relatively shallow subsurface of many urban areas where the earth materials commonly are composed of marine sediments. Marine sediments can contain significant amounts of toxic trace elements such as arsenic, boron, and lead. Changes in the subsurface environment caused by excavation and construction in underground developments could potentially cause these toxic elements to be dissolved into pore water of the sediments, which might lead to groundwater pollution. The purpose of this study is to investigate correlations among chemical properties of marine sediments, such as pH and electrical conductivity (EC), concentrations of toxic trace elements, and stratigraphic characteristics of the sediments. We selected three sites with different stratigraphic settings in the southern Kanto Plain around the Tokyo Metropolis. We collected core samples from shallow strata at a site in the Arakawa Lowland, southern Saitama, and at two sites in the Musashino Upland, Middle Tokyo. All sites have both marine and non-marine sediments up to 50–60 m in thickness. We determined trace element concentrations in the pore water, pH, EC, and loss on ignition. The results show that (1) the marine sediments tend to have low pH, high EC, and high sulfur concentration compared to the non-marine sediments (2) the concentration of most of the soluble heavy metals vary depending on the concentration of sulfate, the pH, and the formation processes of the strata, (3) the arsenic concentration is not related to sulfur concentration but apparently to Fe and Al concentrations, (4) the boron concentration is not related to any other properties implying that the boron level is independent of and cannot be predicted by common chemical properties, and (5) for all three sites, concentrations of most of the trace elements, EC, pH, and sulfate concentration were correlated with each other. This study shows that the concentration and potential mobilization of many toxic trace elements in marine sediments could be predicted by easily measurable pore water chemical properties such as pH and EC. This could be useful for predicting and avoiding the risk of groundwater pollution during underground development projects. 相似文献