Pan-African Extensional Collapse Along the Gondwana Suture     

M. Santosh  M. Yoshida 《Gondwana Research》2001,4(2)

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Crustal Evolution in South and Southeast Asia: Introduction     

S. Hada  M. Yoshida  Z.X. Li  X. Wang 《Gondwana Research》2001,4(1)

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Non-local memory effects of the electromotive force by fluid motion with helicity and two-dimensional periodicity     

Kumiko Hori  Shigeo Yoshida 《地球物理与天体物理流体动力学》2013,107(6):601-632

In mean-field dynamo theory, the electromotive force term 〈u′ × B′〉 due to small-scale fields connects the small-scale magnetic field with the large-scale field. This term is usually approximated as the α-effect, assumed to be instantaneous in time and local in space. However, the approximation is valid only when the magnetic Reynolds number Rm is much less than unity, and is inappropriate when Rm ? 1, which is the condition satisfied in the Earth's core or solar convection zone. We introduce a function φ _qr as a non-local and non-instantaneous generalization of the usual α-effect and examine its behaviour as a function of Rm in the range 1/64 ≤ Rm ≤ 10 for a kinematic dynamo model. We use the flow of G.O. Roberts 1972 Roberts, GO. 1972. Dynamo action of fluid motions with two-dimensional periodicity. Phil. Trans. Roy. Soc. London Ser. A, 271: 411–454. [Crossref], [Web of Science ®] , [Google Scholar] (Phil, Trans. Roy. Soc. London Ser. A, 1972, 271, 411–454), which is steady and has non-zero helicities and two-dimensional periodicity. As a result, we identify three regions in Rm space according to the behaviour of the function φ _qr : (i) Rm ? 1/4, where the function φ _qr is local and instantaneous and can be approximated by the traditional α and β effects, (ii) 1/4 ? Rm ? 4, where the deviation from the traditional α and β effects increases and non-localness and non-instantaneousness increase, and (iii) Rm ? 4, where boundary layers develop fully and non-localness and non-instantaneousness are prominent. We show that the non-local memory effect for Rm ? 4 strongly affects the dynamo action and explains an observed augmentation of the growth rate in the dispersion relation. The results imply that the non-local memory effect of the electromotive force should be important in the geodynamo or the solar dynamo.  相似文献   

Permian Peri‐glacial Deposits from Central Mongolia in Central Asian Orogenic Belt: A Possible Indicator of the Capitanian Cooling Event     

Tatsuya Fujimoto  Shigeru Otoh  Yuji Orihashi  Takafumi Hirata  Takaomi D. Yokoyama  Masanori Shimojo  Yoshikazu Kouchi  Hokuto Obara  Yasuo Ishizaki  Kazuhiro Tsukada  Toshiyuki Kurihara  Manchuk Nuramkhan  Sersmaa Gonchigdorj 《Resource Geology》2012,62(4):408-422

A dropstone‐bearing, Middle Permian to Early Triassic peri‐glacial sedimentary unit was first discovered from the Khangai–Khentei Belt in Mongolia, Central Asian Orogenic Belt. The unit, Urmegtei Formation, is assumed to cover the early Carboniferous Khangai–Khentei accretionary complex, and is an upward‐fining sequence, consisting of conglomerates, sandstones, and varved sandstone and mudstone beds with granite dropstones in ascending order. The formation was cut by a felsic dike, and was deformed and metamorphosed together with the felsic dike. An undeformed porphyritic granite batholith finally cut all the deformed and metamorphosed rocks. LA‐ICP‐MS, U–Pb zircon dating has revealed the following ²⁰⁶Pb/²³⁸U weighted mean igneous ages: (i) a granite dropstone in the Urmegtei Formation is 273 ± 5 Ma (Kungurian of Early Permian); (ii) the deformed felsic dike is 247 ± 4 Ma (Olenekian of Early Triassic); and (iii) the undeformed granite batholith is 218 ± 9 Ma (Carnian of Late Triassic). From these data, the age of sedimentation of the Urmegtei Formation is constrained between the Kungurian and the Olenekian (273–247 Ma), and the age of deformation and metamorphism is constrained between the Olenekian and the Carnian (247–218 Ma). In Permian and Triassic times, the global climate was in a warming trend from the Serpukhovian (early Late Carboniferous) to the Kungurian long and severe cool mode (328–271 Ma) to the Roadian to Bajocian (Middle Jurassic) warm mode (271–168 Ma), with an interruption with the Capitanian Kamura cooling event (266–260 Ma). The dropstone‐bearing strata of the Urmegtei Formation, together with the glacier‐related deposits in the Verkhoyansk, Kolyma, and Omolon areas of northeastern Siberia (said to be of Middle to Late Permian age), must be products of the Capitanian cooling event. Although further study is needed, the dropstone‐bearing strata we found can be explained in two ways: (i) the Urmegtei Formation is an autochthonous formation indicating a short‐term expansion of land glacier to the central part of Siberia in Capitanian age; or (ii) the Urmegtei Formation was deposited in or around a limited ice‐covered continent in northeast Siberia in the Capitanian and was displaced to the present position by the Carnian.  相似文献   

Distribution of nitrous oxide dissolved in water masses in the eastern subtropical North Pacific and its origin inferred from isotopomer analysis     

Ayako Fujii  Sakae Toyoda  Osamu Yoshida  Shuichi Watanabe  Ken’ichi Sasaki  Naohiro Yoshida 《Journal of Oceanography》2013,69(2):147-157

N₂O concentration and its isotopomer ratios were measured over a wide area from San Diego to Honolulu in the eastern subtropical North Pacific (ESNP). Waters in the study area had an N₂O maximum (38.2–50.5 nmol kg^?1) at 600–1000 m depth, which is similar to the profiles obtained previously in other areas in the North Pacific. We separated the seawater into five water masses (two for the surface layer, two for the middle layer, and one for the deep layer) and deduced N₂O production–consumption mechanisms in each water body by use of N₂O isotopomer ratios. The results showed that the mechanisms differ slightly among water masses. In the “coastal” surface layer, N₂O is produced by nitrification (NH₂OH oxidation). In the “open ocean” surface layer, it is produced mainly by nitrifier denitrification and to a lesser extent by nitrification under substrate-limited conditions. In both “upwelling” and “open ocean” middle layers it is produced mainly by denitrification and to a lesser extent by nitrifier denitrification. It is also partly reduced. In the deep layer, it is produced predominantly by denitrification with partial reduction. In this way, isotopomers aid elucidation of production–consumption mechanisms of N₂O in the sea even though the mechanisms cannot always be ascertained.  相似文献   

Geotechnical evaluation of slope and ground failures during the 8 October 2005 Muzaffarabad earthquake, Pakistan   总被引：4，自引：0，他引：4  

Ömer Aydan  Yoshimi Ohta  Masanori Hamada 《Journal of Seismology》2009,13(3):399-413

A large devastating earthquake with a magnitude of 7.6 struck in Kashmir on Oct. 8, 2005. The largest city influenced by the earthquake was Muzaffarabad. Balakot town was the nearest settlement to the epicenter, and it was the most heavily damaged. The earthquake caused extensive damage to housing and structures founded on loose deposits or weathered/sheared rock masses. Furthermore, extensive slope failures occurred along Neelum and Jhelum valleys, which obstructed both river flow and roadways. In this article, failures of natural and cut slopes as well as other ground failures induced by the earthquake and their geotechnical evaluation are presented, and their implications on civil infrastructures and site selection for reconstruction and rehabilitation are discussed. It is suggested that if housing and constructions on soil slopes containing boulders as observed in Balakot and Muzaffarabad are allowed, there should be a safety zone between the slope crest and allowable construction boundary.  相似文献   

http://dx.doi.org/10.1016/j.gsf.2016.06.013     

Tsuyoshi Komiya  Shinji Yamamoto  Shogo Aoki  Keiko Koshida  Masanori Shimojo  Yusuke Sawaki  Kazumasa Aoki  Shuhei Sakata  Takaomi D. Yokoyama  Kenshi Maki  Akira Ishikawa  Takafumi Hirata  Kenneth D. Collerson 《地学前缘(英文版)》2017,8(2):355-385

The Archean continental crusts account for ca.20% of the present volume,but the thermal history of the Earths' mantle suggests much more continental crusts were formed in the early Archean.Because the Archean continental crust underwent severe metamorphism,it is important to avoid influence by the later thermal events.We carried out a comprehensive geochronological work of Cathodoluminescence(CL) observation and U-Pb dating of zircons from orthogneisses and supracrustal rocks over the Saglek Block to obtain their protolith ages.The zircons were classified into three domains of core,mantle and rims,and the cores were further classified into three groups of inherited,altered and zoned cores based on the zonation on the CL images.We estimated the protolith ages from Pb-Pb ages of the zoned-cores of zircons with low U contents.We made a detailed sketch of a small outcrop in St.John's Harbour South(SJHS) area,and classified the orthogneisses and mafic enclaves into seven generations based on the geologic occurrence.The first and second generations comprise mafic rocks and lack magmatic zircons.We conducted CL imaging and U-Pb dating of zircons from the third,sixth and seventh generation of the orthogneisses to estimate the protolith ages at 3902 L 25,3892 ± 33 and 3897 ± 33 Ma for each,supporting the presence of the over 3.9 Ca Iqaluk Gneiss.The geological occurrence that the mafic rocks occur as enclaves within the 3.9 Ga Iqaluk Gneiss indicates that they are the oldest supracrustal rocks in the world.Our geochronological and geological studies show the Uivak Gneiss is quite varied in lithology and age from 3.6 to 3.9 Ga,and tentatively classified into six groups based on their ages.The oldest Uivak Gneiss components including the Iqaluk Gneiss are present around the SJHS area,and the orthogneisses become young as it is away.The lines of evidence of overprinting of younger granitoid on older granitoid in small outcrops and geological-map scale as well as presence of inherited zircons even in the oldest suite suggests that crustal reworking played an important role on erasing the ancient crusts.  相似文献   

中国老挝跨境生物多样性保护区的林地变化(英文)   总被引：2，自引：1，他引：1  

叶艳妹  YOSHIDA A 《地理学报(英文版)》2010,20(6):889-898

This paper analyzed forest land use change in Trans-Boundary Laos-China Biodiversity Conservation Area which is called Namha National Biodiversity Conservation Areas (Namha NBCAs), with 1992 and 2002 TM (ETM). Based on GIS and statistical methods, the intensity, state index of land use change and transfer matrix were used to study spatiotemporal land use change in the region. The results showed that the area of forest land decreased greatly, also the area of bamboo and grassland decreased. The other way round, the area of unstocked forest, slash and burn and rice paddy land increased. As a whole, the intensity of forest land change was higher, but others were lower. From the transfer matrix, most of the forest land changed into unstocked forest and urban area, some to slash and burn. The grassland and bamboo were mainly transferred to forest and unstocked forest. The unstocked forest land mostly came from forest land and grassland. It was showed there were three main causes of the land use change namely: opium poppy cultivation, rubber plantation and also ecotourism activities and finally some policies were developed in order to address the land use change in the study areas.  相似文献   

Adsorption of tributyltin by tributyltin resistant marine Pseudoalteromonas sp. cells     

Mimura H  Sato R  Furuyama Y  Taniike A  Yagi M  Yoshida K  Kitamura A 《Marine pollution bulletin》2008,57(6-12):877-882

The isolate, Pesudoalteromonas sp. TBT1, could grow to overcome the toxicity of tributyltin chloride (TBTCl) up to 30 microM in the absence of Cl(-) in the medium until the cells reached an exponential phase of growth. The viability, however, was reduced after the cells reached a stationary phase. The degradation products, such as dibutyltin (DBT) and monobutyltin (MBT), were not detected in the growth medium, indicating that the isolate has no ability to degrade TBT into less toxic DBT and MBT. Up to about 10(7.5) TBT molecules were adsorbed by a single cell. The observation of morphological changes with an electron microscope showed that the cell surface became wrinkled after exposure to the lethal concentration of 10 mM TBTCl. These results indicate that the resistance of the isolate toward the toxicity of TBTCl is not related to the unique cell surface, which seems to play an important role in preventing the diffusion of TBTCl into the cytoplasm.  相似文献   

Adsorption of tributyltin by tributyltin resistant marine Pseudoalteromonas sp. cells     

Haruo Mimura  Ryusei Sato  Yuichi Furuyama  Akira Taniike  Masahiro Yagi  Kazutoshi Yoshida  Akira Kitamura 《Marine pollution bulletin》2008,57(6-12):877

The isolate, Pesudoalteromonas sp. TBT1, could grow to overcome the toxicity of tributyltin chloride (TBTCl) up to 30 μM in the absence of Cl⁻ in the medium until the cells reached an exponential phase of growth. The viability, however, was reduced after the cells reached a stationary phase. The degradation products, such as dibutyltin (DBT) and monobutyltin (MBT), were not detected in the growth medium, indicating that the isolate has no ability to degrade TBT into less toxic DBT and MBT. Up to about 10^7.5 TBT molecules were adsorbed by a single cell. The observation of morphological changes with an electron microscope showed that the cell surface became wrinkled after exposure to the lethal concentration of 10 mM TBTCl. These results indicate that the resistance of the isolate toward the toxicity of TBTCl is not related to the unique cell surface, which seems to play an important role in preventing the diffusion of TBTCl into the cytoplasm.  相似文献