Lake shoreline deformation in Tibet and mid‐crustal flow     

Simon R. Wallis  Hiroshi Mori  Kazuhiro Ozawa  Mayumi Mitsuishi  Chie Shirakawa 《Island Arc》2010,19(2):209-211

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Timescale of material circulation in subduction zone: U–Pb zircon and K–Ar phengite double‐dating of the Sanbagawa metamorphic complex in the Ikeda district,central Shikoku,southwest Japan     

Mitsuhiro Nagata  Kazuhiro Miyazaki  Hideki Iwano  Tohru Danhara  Hideyuki Obayashi  Takafumi Hirata  Koshi Yagi  Yoshikazu Kouchi  Koshi Yamamoto  Shigeru Otoh 《Island Arc》2019,28(4)

We have estimated the timescale of material circulation in the Sanbagawa subduction zone based on U–Pb zircon and K–Ar phengite dating in the Ikeda district, central Shikoku. The Minawa and Koboke units are major constituents of the high‐P Sanbagawa metamorphic complex in Shikoku, southwest Japan. For the Minawa unit, ages of 92–81 Ma for the trench‐fill sediments, are indicated, whereas the age of ductile deformation and metamorphism of garnet and chlorite zones are 74–72 Ma and 65 Ma, respectively. Our results and occurrence of c. 150 Ma Besshi‐type deposits formed at mid‐ocean ridge suggest that the 60‐Myr‐old Izanagi Plate was subducted beneath the Eurasian Plate at c. 90 Ma, and this observation is consistent with recent plate reconstructions. For the Koboke unit, the depositional ages of the trench‐fill sediments and the dates for the termination of ductile deformation and metamorphism are estimated at c. 76–74 and 64–62 Ma, respectively. In the Ikeda district, the depositional ages generally become younger towards lower structural levels in the Sanbagawa metamorphic complex. Our results of U–Pb and K–Ar dating show that the circulation of material from the deposition of the Minawa and Koboke units at the trench through an active high‐P metamorphic domain to the final exhumation from the domain occurred continuously throughout c. 30 Myr (from c. 90 to 60 Ma).  相似文献   

Redistribution and export of contaminated sediment within eastern Fukushima Prefecture due to typhoon flooding          下载免费PDF全文

Akihiro Kitamura  Hiroshi Kurikami  Kazuyuki Sakuma  Alex Malins  Masahiko Okumura  Masahiko Machida  Koji Mori  Kazuhiro Tada  Yasuhiro Tawara  Takamaru Kobayashi  Takafumi Yoshida  Hiroyuki Tosaka 《地球表面变化过程与地形》2016,41(12):1708-1726

Tropical cyclones expose river basins to heavy rainfall and flooding, and cause substantial soil erosion and sediment transport. There is heightened interest in the effects of typhoon floods on river basins in northeast Japan, as the migration of radiocaesium‐bearing soils contaminated by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident will affect future radiation levels. The five main catchments surrounding FDNPP are the Odaka, Ukedo, Maeda, Kuma and Tomioka basins, but little quantitative modelling has been undertaken to identify the sediment redistribution patterns and controlling processes across these basins. Here we address this issue and report catchment‐scale modelling of the five basins using the GETFLOWS simulation code. The three‐dimensional (3D) models of the basins incorporated details of the geology, soil type, land cover, and used data from meteorological records as inputs. The simulation results were checked against field monitoring data for water flow rates, suspended sediment concentrations and accumulated sediment erosion and deposition. The results show that the majority of annual sediment migration in the basins occurs over storm periods, thus making typhoons the main vectors for redistribution. The Ukedo and Tomioka basins are the most important basins in the region in terms of overall sediment transport, followed by the other three basins each with similar discharge amounts. Erosion is strongly correlated with the underlying geology and the surface topography in the study area. A low permeability Pliocene Dainenji formation in the coastal area causes high surface water flow rates and soil erosion. Conversely, erosion is lower in an area with high permeability granite basement rocks between the Hatagawa and Futaba faults in the centre of the study area. Land cover is also a factor controlling differences in erosion and transport rates between forested areas in the west of the study area and predominantly agricultural areas towards the east. The largest sediment depositions occur in the Ogaki and Takigawa Dams, at the confluence of the Takase and Ukedo Rivers, and at the Ukedo River mouth. Having clarified the sediment redistribution patterns and controlling processes, these results can assist the ongoing task of monitoring radioactive caesium redistribution within Fukushima Prefecture, and contribute to the design and implementation of measures to protect health and the environment. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Second‐mode tuned mass dampers in base‐isolated structures for reduction of floor acceleration          下载免费PDF全文

Yundong Shi  Kazuhiro Saburi  Masayoshi Nakashima 《地震工程与结构动力学》2018,47(12):2519-2538

To reduce floor acceleration of base‐isolated structures under earthquakes, a tuned mass damper (TMD) system installed on the roof is studied. The optimal tuning parameters of the TMD are analyzed for linear base isolation under a generalized ground motion, and the performance of the TMD is validated using a suite of recorded ground motions. The simulation shows that a TMD tuned to the second mode of a base‐isolated structure reduces roof acceleration more effectively than a TMD tuned to the first mode. The reduction ratio, defined as the maximum roof acceleration with the TMD relative to that without the TMD, is approximately 0.9 with the second‐mode TMD. The higher effectiveness of the second‐mode TMD relative to the first‐mode TMD is attributed primarily to the unique characteristics of base isolation, ie, the relatively long first‐mode period and high base damping. The modal acceleration of the second mode is close to or even higher than that of the first mode in base‐isolated structures. The larger TMD mass ratio and lower modal damping ratio of the second‐mode TMD compared to the first‐mode TMD increases its effect on modal acceleration reduction. The reduction ratio with the second‐mode TMD improves to 0.8 for bilinear base isolation. Because of the detuning effect caused by the change in the first‐mode period in bilinear isolation, the first‐mode TMD is ineffective in reducing roof acceleration. Additionally, the displacement experienced by the second‐mode TMD is considerably smaller than that of the first‐mode TMD, thereby reducing the installation space for the TMD.  相似文献   

Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping     

S. M. White  K. Iwai  N. M. Phillips  R. E. Hills  A. Hirota  P. Yagoubov  G. Siringo  M. Shimojo  T. S. Bastian  A. S. Hales  T. Sawada  S. Asayama  M. Sugimoto  R. G. Marson  W. Kawasaki  E. Muller  T. Nakazato  K. Sugimoto  R. Brajša  I. Skokić  M. Bárta  S. Kim  A. J. Remijan  I. de Gregorio  S. A. Corder  H. S. Hudson  M. Loukitcheva  B. Chen  B. De Pontieu  G. D. Fleishmann  D. E. Gary  A. Kobelski  S. Wedemeyer  Y. Yan 《Solar physics》2017,292(7):88

The Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope has commenced science observations of the Sun starting in late 2016. Since the Sun is much larger than the field of view of individual ALMA dishes, the ALMA interferometer is unable to measure the background level of solar emission when observing the solar disk. The absolute temperature scale is a critical measurement for much of ALMA solar science, including the understanding of energy transfer through the solar atmosphere, the properties of prominences, and the study of shock heating in the chromosphere. In order to provide an absolute temperature scale, ALMA solar observing will take advantage of the remarkable fast-scanning capabilities of the ALMA 12 m dishes to make single-dish maps of the full Sun. This article reports on the results of an extensive commissioning effort to optimize the mapping procedure, and it describes the nature of the resulting data. Amplitude calibration is discussed in detail: a path that uses the two loads in the ALMA calibration system as well as sky measurements is described and applied to commissioning data. Inspection of a large number of single-dish datasets shows significant variation in the resulting temperatures, and based on the temperature distributions, we derive quiet-Sun values at disk center of 7300 K at \(\lambda = 3~\mbox{mm}\) and 5900 K at \(\lambda = 1.3~\mbox{mm}\). These values have statistical uncertainties of about 100 K, but systematic uncertainties in the temperature scale that may be significantly larger. Example images are presented from two periods with very different levels of solar activity. At a resolution of about \(25''\), the 1.3 mm wavelength images show temperatures on the disk that vary over about a 2000 K range. Active regions and plages are among the hotter features, while a large sunspot umbra shows up as a depression, and filament channels are relatively cool. Prominences above the solar limb are a common feature of the single-dish images.  相似文献   

Correction to: Landslide susceptibility mapping of the Sera River Basin using logistic regression model     

Raja  Nussaïbah B.  Çiçek  Ihsan  Türkoğlu  Necla  Aydin  Olgu  Kawasaki  Akiyuki 《Natural Hazards》2018,91(3):1423-1423

Natural Hazards - The article “Landslide susceptibility mapping of the Sera River Basin using logistic regression model,” written by Nussaïbah B. Raja, Ihsan Çiçek, Necla...  相似文献   

Osumilite and a spinel + quartz association in garnet–sillimanite gneiss from Rundvågshetta,Lützow-Holm Complex,East Antarctica     

Toshisuke Kawasaki  Nobuhiko Nakano  Yasuhito Osanai 《Gondwana Research》2011,19(2):430-445

This is the first report of osumilite occurring as fine isolated inclusions within garnet porphyroblasts, as observed in garnet–sillimanite gneiss from Rundvågshetta, Lützow-Holm Complex, East Antarctica. The osumilite is characterized by high Si content (10.60 and 10.95 atoms based on 30 oxygens per formula unit), low Al content (2.99 and 3.82), a high content of M site-occupying cations (2.51 and 3.03), and high X_Mg values (about 0.81). We also report a spinel + quartz association found as inclusions within garnet porphyroblasts. Spinel grains, which are in direct contact with quartz and are spatially associated with sillimanite, show extremely high Zn contents (X_Zn^Spl = 0.33 ? 0.46) and high X_Mg values (0.45–0.54). The garnet is rimmed by sillimanite, K-feldspar, plagioclase, and quartz. Biotite and cordierite are found only as inclusions within garnet porphyroblasts, where biotite coexists with spinel–quartz or with rutile. Porphyroblastic garnet contains rutile needles and has low X_Mg values (about 0.36). The sillimanite contains a high Fe content (about 1.2 wt.% Fe₂O₃).The occurrence of osumilite and spinel + quartz indicates a clockwise pressure–temperature path of ultrahigh-temperature metamorphism, involving the following events: (1) the Rundvågshetta granulites suffered prograde metamorphism within the kyanite and sapphirine + quartz fields; (2) subsequent retrograde metamorphism, involving near-isothermal decompression, occurred in the orthopyroxene + sillimanite + quartz field; (3) the granulites passed through the garnet + cordierite + sillimanite + quartz field during decreasing temperature; (4) the granulites entered the osumilite stability field at around 8 kbar and 950 °C; and (5) the granulites retain a final record of retrograde metamorphism within the biotite + sillimanite + K-feldspar and quartz field at 6.1 kbar and about 830 °C.  相似文献   

黑龙江杂岩蓝片岩—云母片岩矿物成分及变质作用P-T条件   总被引：1，自引：0，他引：1  

李蓉  孙德有  铃木和博  郑常青 《地球科学》2013,38(2):277-288

黑龙江构造混杂岩中保留着一套曾遭受过中高压变质作用的岩石,其代表性岩石为:蓝片岩-云母片岩;蓝闪石、铁蓝闪石和多硅白云母(单位结构中Si=3.37～3.46>3.30)等具有中高压性质的典型变质矿物在岩石中平衡共生.蓝片岩-云母片岩组合至少经历了早期和晚期两阶段变质,早期为绿帘蓝片岩相,变质温压条件为T=320～460℃,P=7.8×108～11×108Pa.晚期为高绿片岩相,出现富镁绿泥石(XMg=0.565～0.646)交代早期钠质角闪石和多硅白云母等高压变质矿物现象,变质温度升高而压力有所降低,由石榴石云母片岩所限定的高绿片岩相变质条件为T=536～598℃,P=6.8×108～9.5×108Pa,属中温和中高压变质.  相似文献   

Late Quaternary tephrostratigraphy of Baegdusan and Ulleung volcanoes using marine sediments in the Japan Sea/East Sea     

Chungwan Lim  Kazuhiro Toyoda  Ken Ikehara  David W. Peate 《Quaternary Research》2013

Only Ulleung and Baegdusan volcanoes have produced alkaline tephras in the Japan Sea/East Sea during the Quaternary. Little is known about their detailed tephrostratigraphy, except for the U–Oki and B–Tm tephras. Trace element analysis of bulk sediments can be used to identify alkaline cryptotephra because of the large compositional contrast. Five sediment cores spanning the interval between the rhyolitic AT (29.4 ka) and Aso-4 (87 ka) tephras were analyzed using an INAA scanning method. Source volcanoes for the five detected alkaline cryptotephra were identified from major element analyses of hand-picked glass shards: Ulleung (U–Ym, and the newly identified U–Sado), and Baegdusan (B–J, and the newly identified B–Sado and B-Ym). The eruption ages of the U–Ym, U–Sado, B–J, B–Sado, and B–Ym tephras are estimated to be 38 ka, 61 ka, 26 ka, 51 ka, 68–69 ka, and 86 ka, respectively, based on correlations with regional-scale TL (thinly laminated) layer stratigraphy (produced by basin-wide changes in bottom-water oxygen levels in response to millennium-scale paleoclimate variations). This study has allowed construction of an alkaline tephrostratigraphical framework for the late Quaternary linked to global environmental changes in the Japan Sea/East Sea, and improves our knowledge of the eruptive histories of Ulleung and Baegdusan volcanoes.  相似文献   

Sea surface temperature record off central Japan since the Last Glacial Maximum using planktonic foraminiferal Mg/Ca thermometry     

Takuya Sagawa  Kazuhiro Toyoda  Tadamichi Oba 《第四纪科学杂志》2006,21(1):63-73

We conducted paired measurements of the Mg/Ca ratio and δ¹⁸O of planktonic foraminifera, Globigerina bulloides, from a sediment core (MD01‐2420) off central Japan in the northwest Pacific, to reconstruct current movements since the Last Glacial Maximum (LGM). These methods make it possible to determine the magnitude and timing of the sea surface temperature (SST) changes and to reconstruct the variations of the past seawater δ¹⁸O (δ¹⁸Ow) off central Japan. The amplitude of Mg/Ca‐based SST changes between the Holocene and the LGM was about 10°C. The strong resemblance of the SSTs estimated from both methods, Mg/Ca‐based and δ¹⁸O‐based, suggests that the SST changes were caused primarily by latitudinal displacement of the Kuroshio–Oyashio currents and no distinct change in the carbonate dissolution of the core. The southward migration of the water mass was 5–6° in latitude at the LGM. The values for regional δ¹⁸Ow changes, which were obtained by subtracting the ice volume contribution from the calculated δ¹⁸Ow, describe the millennial‐scale water mass migration over the last 30 kyr. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献