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排序方式: 共有182条查询结果,搜索用时 15 毫秒
71.
In this study, based on a 2-D thermomechanical finite element model, the uplift of the Transantarctic Mountains (TAM) is discussed in relation to the flexural uplift of a rheologically layered lithosphere, which is described by Vening-Meinesz's cantilever kinematics. The general model behaviour shows that the thickness of the crust and the geothermal gradient in the lithosphere are the principal factors in controlling the effective elastic thickness ( T e ). Although T e is also significantly dependent on the magnitude of the uplift and the wet or dry rheological condition of rocks, these two factors do not have a dominant influence on the half-wavelength of the TAM. The model with a plausible crustal structure beneath Antarctica shows that the thermal structure beneath East Antarctica is the critical factor, controlling the half-wavelength of the TAM. If there is a significant radiogenic heat source in the Antarctic lithosphere, T e beneath East Antarctica is estimated to be 50 km, at most, and the lithosphere has no potential to explain an exceptionally large-scale half-wavelength of the TAM. Even for the model without a heat source, if East Antarctica is significantly thermally influenced by West Antarctica, T e is estimated to be about 60 km, and it is difficult to reproduce the half-wavelength of the TAM. Contrarily, when a radiogenic heat source is absent and the thermal structure beneath East Antarctica is not significantly affected by that beneath West Antarctica, the rheological structure beneath East Antarctica has the potential to reproduce the half-wavelength of the TAM ( T e ∼ 100 km). Thus, the presence of a radiogenic heat source in the crust and mantle and the thermal influence of West Antarctica on East Antarctica are crucial factors in the reproduction of the half-wavelength found in the TAM. 相似文献
72.
Lara M. Kueppers Mark A. Snyder Lisa C. Sloan Dan Cayan Jiming Jin Hideki Kanamaru Masao Kanamitsu Norman L. Miller Mary Tyree Hui Du Bryan Weare 《Global and Planetary Change》2008,60(3-4):250-264
In the western United States, more than 79 000 km2 has been converted to irrigated agriculture and urban areas. These changes have the potential to alter surface temperature by modifying the energy budget at the land–atmosphere interface. This study reports the seasonally varying temperature responses of four regional climate models (RCMs) – RSM, RegCM3, MM5-CLM3, and DRCM – to conversion of potential natural vegetation to modern land-cover and land-use over a 1-year period. Three of the RCMs supplemented soil moisture, producing large decreases in the August mean (− 1.4 to − 3.1 °C) and maximum (− 2.9 to − 6.1 °C) 2-m air temperatures where natural vegetation was converted to irrigated agriculture. Conversion to irrigated agriculture also resulted in large increases in relative humidity (9% to 36% absolute change). Modeled changes in the August minimum 2-m air temperature were not as pronounced or consistent across the models. Converting natural vegetation to urban land-cover produced less pronounced temperature effects in all models, with the magnitude of the effect dependent upon the preexisting vegetation type and urban parameterizations. Overall, the RCM results indicate that the temperature impacts of land-use change are most pronounced during the summer months, when surface heating is strongest and differences in surface soil moisture between irrigated land and natural vegetation are largest. 相似文献
73.
Hideki Ueyama 《Theoretical and Applied Climatology》2012,109(1-2):15-26
Methods are proposed to estimate the monthly relative humidity and wet bulb temperature based on observations from a dynamical downscaling coupled general circulation model with a regional climate model (RCM) for a quantitative assessment of climate change impacts. The water vapor pressure estimation model developed was a regression model with a monthly saturated water vapor pressure that used minimum air temperature as a variable. The monthly minimum air temperature correction model for RCM bias was developed by stepwise multiple regression analysis using the difference in monthly minimum air temperatures between observations and RCM output as a dependent variable and geographic factors as independent variables. The wet bulb temperature was estimated using the estimated water vapor pressure, air temperature, and atmospheric pressure at ground level both corrected for RCM bias. Root mean square errors of the data decreased considerably in August. 相似文献
74.
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
75.
Takeshi Naganuma C. Julius Meisel Hideki Wada Yukihiro Kato Akira Takeuchi Katsunori Fujikura Jiro Naka & Kantaro Fujioka 《Island Arc》1999,8(2):232-244
A biological community was discovered in the Northern Okushiri Ridge, northeastern Japan Sea. The community was closely associated with sea-floor fissures, and presumed to be supported by methanotrophic and/or thiotrophic bacterial production. Sediments inside of and in the vicinity of the fissures were collected, and the short-chain (C9–20 ) sediment fatty acids were analyzed for amounts and compositions. The fatty acid compositions were compared with those from a known methane seep and a submarine volcano in the Sagami Bay, central Japan, and from a whale skeleton at the Torishima Seamount, northwestern Pacific Ocean. As a result, a close relationship between the sediments from the Northern Okushiri Ridge, the known methane-seep, and the whale skeleton was found. This finding represents the first discovery of methane seepage and associated biological communities in the Japan Sea. This also supports the hypothesis that the eastern margin of the northern Japan Sea is at the early stage of new subduction. 相似文献
76.
A method has been developed for determination of15N isotope ratio in nitrate nitrogen, which is a major analytical step in tracer experiments for studies of nitrate metabolism
in the marine environment. The method is based on diazotization of nitrite with sulfanilic acid following reduction of nitrate
to nitrite by a cadmium-copper column. The diazonium compound is then subject to the azo coupling reaction with 2-naphthol,
and the azo dye formed is extracted by a solid phase extraction column. The dye eluted from the column is collected, and total
nitrogen and15N content of the dye are determined by mass spectrometry. Sulfanilic acid can also remove preexisting nitrite by heating the
sample under acidic conditions before passing through the cadmium-copper reduction column. The average recovery of nitrate
nitrogen was 86%. A procedure for reducing the background nitrogen that derives from the analytical operations has been developed;
background nitrogen was limited to about 0.25 μg-atomN. The variation in the background nitrogen levels reflects the range of error in15N determination of nitrate nitrogen by this method. Application of the present method to a15NO3
− isotope dilution experiment for determination of nitrification rate in sea water is demonstrated. 相似文献
77.
78.
Detrital zircon multi‐chronology,provenance, and low‐grade metamorphism of the Cretaceous Shimanto accretionary complex,eastern Shikoku,Southwest Japan: Tectonic evolution in response to igneous activity within a subduction zone 下载免费PDF全文
Hidetoshi Hara Yoshihiro Nakamura Kousuke Hara Toshiyuki Kurihara Hiroshi Mori Hideki Iwano Tohru Danhara Shuhei Sakata Takafumi Hirata 《Island Arc》2017,26(6)
Detrital zircon multi‐chronology combined with provenance and low‐grade metamorphism analyses enables the reinterpretation of the tectonic evolution of the Cretaceous Shimanto accretionary complex in Southwest Japan. Detrital zircon U–Pb ages and provenance analysis defines the depositional age of trench‐fill turbidites associated with igneous activity in provenance. Periods of low igneous activity are recorded by youngest single grain zircon U–Pb ages (YSG) that approximate or are older than the depositional ages obtained from radiolarian fossil‐bearing mudstone. Periods of intensive igneous activity recorded by youngest cluster U–Pb ages (YC1σ) that correspond to the younger limits of radiolarian ages. The YC1σ U–Pb ages obtained from sandstones within mélange units provide more accurate younger depositional ages than radiolarian ages derived from mudstone. Determining true depositional ages requires a combination of fossil data, detrital zircon ages, and provenance information. Fission‐track ages using zircons estimated YC1σ U–Pb ages are useful for assessing depositional and annealing ages for the low‐grade metamorphosed accretionary complex. These new dating presented here indicates the following tectonic history of the accretionary wedge. Evolution of the Shimanto accretionary complex from the Albian to the Turonian was caused by the subduction of the Izanagi plate, a process that supplied sediments via the erosion of Permian and Triassic to Early Jurassic granitic rocks and the eruption of minor amounts of Early Cretaceous intermediate volcanic rocks. The complex subsequently underwent intensive igneous activity from the Coniacian to the early Paleocene as a result of the subduction of a hot and young oceanic slab, such as the Kula–Pacific plate. Finally, the major out‐of‐sequence thrusts of the Fukase Fault and the Aki Tectonic Line formed after the middle Eocene, and this reactivation of the Shimanto accretionary complex as a result of the subduction of the Pacific plate. 相似文献
79.
The role of the grain boundary at chemical and isotopic fronts in marble during contact metamorphism
Hideki Wada Takamaru Ando Masayuki Suzuki 《Contributions to Mineralogy and Petrology》1998,132(4):309-320
Carbon and oxygen isotopic profiles around a low pressure metasomatic wollastonite reaction front in a marble of the Hida
metamorphic terrain, central Japan, display typical metamorphic fluid-enhanced isotopic zonations. Isotopic profiles obtained
from detailed microscale analyses perpendicular to the chemical reaction front in calcite marble show that diffusion-enhanced
isotopic exchange may control these profiles. Carbon and oxygen isotopic behaviour in grain boundaries is remarkably different.
Oxygen isotopic troughs (18O depleted rims) around the calcite-grain boundaries are widely observed in this contact aureole, demonstrating that diffusion
of oxygen in calcite grain boundary dominates over lattice diffusion in calcite. In contrast, no difference is observed in
carbon isotopic profiles obtained from grain cores and rims. There is thus no specific role of the grain boundary for diffusion
of carbonic species in the metamorphic fluid during transportation. Carbon chemical species such as CO2 and CO3 ions in metamorphic fluid migrate mainly through lattice diffusion. The carbon and oxygen isotope profiles may be modelled
by diffusion into a semi-infinite medium. Empirically lattice diffusion of oxygen isotopes is almost six times faster than
that of carbon isotopes, and oxygen grain-boundary diffusion is ten times faster than oxygen lattice diffusion. Oxygen isotopic
results around the wollastonite vein indicate that migration of the metamorphic fluid into calcite marble was small and was
parallel to the aquifer. From the stability of wollastonite and the attainment of oxygen isotopic equilibrium, we suggest
that diffusion of oxygen occurred through an aqueous fluid phase. The timescale of formation of the oxygen isotopic profile
around the wollastonite vein is calculated to be about 0.76 × 106 years using the experimentally determined diffusion constant.
Received: 14 January 1997 / Accepted: 23 April 1998 相似文献
80.
Futoshi Nanayama Jun Tajika Toru Yamasaki Hiroshi Kurita Hideki Iwano Tohru Danhara Takafumi Hirata 《Island Arc》2021,30(1):e12403
Greenstone bodies emplaced upon or into clastic sediments crop out ubiquitously in the Hidaka belt (early Paleogene accretionary and collisional complexes exposed in the central part of northern Hokkaido, NE Japan), but the timing and setting of their emplacement has remained poorly constrained. Here, we report new zircon U–Pb ages for the sedimentary complexes surrounding these greenstones. The Hidaka Supergroup in the northern Hidaka belt is divided into four zones from west to east: zones S, U, and R, which contain in situ greenstones; and zone Y, which does not. Detrital zircons in zones S, U, and R have early Eocene U–Pb ages (55–47 Ma) and these strata are intruded by early Eocene granites (46–45 Ma), indicating that they were deposited between 55 and 46 Ma. Therefore, in situ greenstones in the northern Hidaka belt can only be explained by the subduction of the Izanagi–Pacific Ridge during 55–47 Ma. In contrast, the deposition of zone Y (the Yubetsu Group, younging to the west) began by 73–71 Ma, indicating that the accretionary prism in front of the paleo-Kuril arc formed at the same time as that in the Idonnappu zone and grew continuously until 48 Ma. The plutonic rocks that intruded the Hidaka belt are roughly divided into three stages: (1) early Eocene granites intruded the northern Hidaka belt at 46–45 Ma, during subduction of the Izanagi–Pacific Ridge; (2) the upper sequence of the Hidaka metamorphic zone was metamorphosed by magmatism at 40–37 Ma associated with the collision of the paleo-Kuril arc and NE Asia; and (3) younger granites intruded the entire Hidaka belt at 20–17 Ma in association with asthenospheric upwelling caused by back-arc expansion. 相似文献