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101.
Giant Megamullion in the Parece Vela Backarc Basin 总被引:1,自引:0,他引:1
Ohara Yasuhiko Yoshida Tsuyoshi Kato Yukihiro Kasuga Shigeru 《Marine Geophysical Researches》2001,22(1):47-61
We present results of high-resolution bathymetric studies of the extinct intermediate-spreading Parece Vela Basin in the northwestern Pacific, where we have identified an extremely large mullion structure, here termed a giant megamullion. We find that the giant megamullion is nearly an order of magnitude larger than the similar structures in the slow-spreading Mid-Atlantic Ridge (`megamullions'). The giant megamullion has slightly elevated mantle Bouguer anomaly, and yields serpentinized peridotites and gabbros, suggesting that they are exposing oceanic crust and upper mantle. An off-axis rugged `chaotic terrain' was also identified in the Parece Vela Basin. The terrain consists of isolated and elevated blocks capped by corrugated axis-normal lineations, and associated deeps. We thus interpret it as analogues to the Mid-Atlantic Ridge megamullions. We propose that amagmatic tectonics producing the giant megamullion and the chaotic terrain occupied a significant part in crustal construction in the Parece Vela Basin evolution. 相似文献
102.
Variability of the central region in active galactic nuclei 总被引:3,自引:0,他引:3
Summary We review implications of the observed optical and X-ray variability (periodicities and light-curves), relevant for the understanding of physical conditions in the deep interiors of active galactic nuclei. We discuss in detail kinematical, hydrodynamical, thermal and radiative transfer effects which may be responsible for observed variability patterns. We put emphasis on theoretical options which can predict basic accretion parameters, such as the mass of the central black hole, the accretion rate and the inclination angle, in terms of observable quantities. Closed analytical results are given whenever available. 相似文献
103.
Naoto Hirano Hirochika Sumino Taisei Morishita Shiki Machida Takaomi Kawano Kazutaka Yasukawa Takafumi Hirata Yasuhiro Kato Teruaki Ishii 《Island Arc》2021,30(1):e12386
The West Pacific Seamount Province (WPSP) represents a series of short-lived Cretaceous hotspot tracks. However, no intraplate volcanoes in advance of petit-spot volcanism erupted near a trench have been identified after the formation of the WPSP on the western Pacific Plate. This study reports new ages for Paleogene volcanic edifices within the northern WPSP, specifically the Ogasawara Plateau and related ridges, and Minamitorishima Island. These Paleogene ages are the first reported for basaltic rocks on western Pacific seamounts, in an area that has previously only yielded Cretaceous ages. The newly found Paleogene volcanisms overprint the Early–middle Cretaceous volcanic edifices, because the seamount or paleo-island material-covered reefal limestone caps on these edifices are uniformly older than the Paleogene volcanism identified in this study. This study outlines several possible causative factors for the Paleogene volcanism overprinting onto existing Cretaceous seamounts, including volcanism related to lithospheric stress, or a younger hotspot track within the northern part of the WPSP that records magmatism from ~60 Ma. 相似文献
104.
Shiki Machida Kentaro Nakamura Tetsu Kogiso Ryo Shimomura Koichi Horinouchi Kyoko Okino Yasuhiro Kato 《Island Arc》2021,30(1):e12395
A broad area densely covered by ferromanganese nodules was recently discovered around Minamitorishima (Marcus) Island, representing a high-potential metal resource, particularly for Co, Ni, Mo, and W. We studied 16 nodule samples from nodule fields around Minamitorishima Island. To define the fine-scale chemostratigraphy of the nodules, polished cross-sections of the samples were analyzed by microfocus X-ray fluorescence. Our results show that a general pattern of compositional variation was common throughout the growth history of the nodules in all the regions we studied. Chemical mapping clarified changes in the chemical signature and proportion of five lithological components throughout the growth history: Mn represented columnar δ-MnO2; Fe represented layered amorphous FeOOH*xH2O; Ti represented TiO2*2H2O intergrown with an amorphous FeOOH phase; P, Ca and Y represented particles of biogenic calcium phosphate; and Si, Al, K, Cu, and Ni represented pelagic sediment infills. We proposed a method for a creating a multi-dimensional compositional map of the fine-scale chemostratigraphy observed in the ferromanganese oxide layers on the basis of merging the mapped Mn, Fe, Ti, P, Si and Cu intensities. Multi-dimensional compositional mapping of the sampled nodules from the western North Pacific revealed two fundamental findings: (1) previously recognized first-order Fe–Mn layers, L0, L1, and L2, were further divided into two, three, and four sublayers, respectively, and (2) a delayed supply of material to be nuclei of nodule or a growth hiatus of Fe–Mn layer(s), leading to missing sublayers in the layers L0 and L2, regulated the nodule size. In contrast, layer L1, which does not have any missing sublayers, was commonly observed in the samples for this study and has been reported in studies of other regions in the western Pacific. We propose, therefore, that the layer L1 is a key facies for examining chemostratigraphic correlations with other areas of seafloor. 相似文献
105.
106.
Riko Iizuka Hiroyuki Kagi Kazuki Komatsu Daichi Ushijima Satoshi Nakano Asami Sano-Furukawa Takaya Nagai Takehiko Yagi 《Physics and Chemistry of Minerals》2011,38(10):777-785
The pressure responses of portlandite and the isotope effect on the phase transition were investigated at room temperature
from single-crystal Raman and IR spectra and from powder X-ray diffraction using diamond anvil cells under quasi-hydrostatic
conditions in a helium pressure-transmitting medium. Phase transformation and subsequent peak broadening (partial amorphization)
observed from the Raman and IR spectra of Ca(OH)2 occurred at lower pressures than those of Ca(OD)2. In contrast, no isotope effect was found on the volume and axial compressions observed from powder X-ray diffraction patterns.
X-ray diffraction lines attributable to the high-pressure phase remained up to 28.5 GPa, suggesting no total amorphization
in a helium pressure medium within the examined pressure region. These results suggest that the H–D isotope effect is engendered
in the local environment surrounding H(D) atoms. Moreover, the ratio of sample-to-methanol–ethanol pressure medium (i.e.,
packing density) in the sample chamber had a significant effect on the increase in the half widths of the diffraction lines,
even at pressures below the hydrostatic limit of the pressure medium. 相似文献
107.
����GPS���ݷ������ձ���������ɱ���齻�紦��Ӧ����Ƚ� 总被引:1,自引:0,他引:1
??????????????????????????GPS???????????(1997-01~1999-12)??????Hori???????????????????齻????????????????????????????:????????????С??????????????????????????????7 cm/a??50%?????????????10~30 km??????????????????齻??????????????Yabuki-Matu??ura????????????????????????????Hori???????????б?????????????????????????????????????????????????в?????????Ч????????????????????????????????Hori????????????????????????????????????????????????????????????????????????? 相似文献
108.
Postseismic relaxation due to Bhuj earthquake on January 26, 2001: possible mechanisms and processes
C. D. Reddy P. S. Sunil Roland B��rgmann D. V. Chandrasekhar Teruyuki Kato 《Natural Hazards》2013,65(2):1119-1134
Earthquakes cause static stress perturbations in the nearby crust and mantle. Obeying rheological laws, this stress relaxes in a time frame of months to years with the spatial extent of few km to hundreds of km. While postseismic relaxation associated with major inter-plate earthquakes is well established, there have been few opportunities to explore its occurrence following intraplate earthquakes. The M w 7.6 Bhuj earthquake on January 26, 2001 in western India is considered to be an intraplate event and provided a unique opportunity to examine post-earthquake relaxation processes sufficiently away from plate boundaries. To study the characteristics of transient postseismic deformation, six Global Positioning System campaigns were made at 14 sites. The postseismic transients were delineated after removing plate motions from the position time series. Postseismic deformation has been observed at all the sites in the study area. During 2001?C2007, the site closest to the epicenter exhibited postseismic deformation of about 30 and 25?mm in the north and east components, respectively. Time series of the NS and EW components of the postseismic transients can be fitted to both logarithmic and exponential functions. Close to the epicenter, the logarithmic function fits well to the initial transient, and an exponential function fits well to the later phases. The remaining sites (located east and west of the epicentral region) exhibited significantly diminished north?Csouth relaxation. Rapidly decaying afterslip and poroelastic mechanisms seem to be responsible for postseismic relaxation in the vicinity of epicenter during the initial period subsequent to the Bhuj earthquake. Postseismic relaxation by viscoelastic flow below the seismogenic zone seems to affect displacements across the entire Bhuj region. This paper presents the characteristics of postseismic transients and deformation processes in the scenario of the highly heterogeneous crust in the Bhuj region. 相似文献
109.
Yuto Kurumada Shogo Aoki Kazumasa Aoki Daichi Kato Mototaka Saneyoshi Khishigjav Tsogtbaatar Brian F. Windley Shinobu Ishigaki 《地学学报》2020,32(4):246-252
To verify the usefulness of calcite U–Pb measurement for vertebrate‐bearing strata in the Eastern Gobi, Mongolia, we performed laser ablation‐inductively coupled plasma‐mass spectrometry calcite U–Pb and trace element analyses of three caliche (calcrete) of the Bayn Shire Formation. The trace element analysis demonstrates high concentration of U in the calcites. Two meaningful calcite U–Pb ages were obtained; 95.9 ± 6.0 and 89.6 ± 4.0 Ma, which are consistent with published ages from the Bayn Shire Formation. Our results demonstrate that the calcite U–Pb method can be powerful tool for age determination of vertebrate‐bearing strata in the Gobi that do not contain index fossils or beds, but do contain caliches. This would make it possible for a comparison of biostratigraphy between the Gobi and other areas yielding abundant vertebrate fossils in Asia, North America and Europe, based on chronological data. 相似文献
110.
Advances in Understanding Top-of-Atmosphere Radiation Variability from Satellite Observations 总被引:1,自引:0,他引:1
Norman G. Loeb Seiji Kato Wenying Su Takmeng Wong Fred G. Rose David R. Doelling Joel R. Norris Xianglei Huang 《Surveys in Geophysics》2012,33(3-4):359-385
This paper highlights how the emerging record of satellite observations from the Earth Observation System (EOS) and A-Train constellation are advancing our ability to more completely document and understand the underlying processes associated with variations in the Earth’s top-of-atmosphere (TOA) radiation budget. Large-scale TOA radiation changes during the past decade are observed to be within 0.5?Wm?2 per decade based upon comparisons between Clouds and the Earth’s Radiant Energy System (CERES) instruments aboard Terra and Aqua and other instruments. Tropical variations in emitted outgoing longwave (LW) radiation are found to closely track changes in the El Ni?o-Southern Oscillation (ENSO). During positive ENSO phase (El Ni?o), outgoing LW radiation increases, and decreases during the negative ENSO phase (La Ni?a). The coldest year during the last decade occurred in 2008, during which strong La Nina conditions persisted throughout most of the year. Atmospheric Infrared Sounder (AIRS) observations show that the lower temperatures extended throughout much of the troposphere for several months, resulting in a reduction in outgoing LW radiation and an increase in net incoming radiation. At the global scale, outgoing LW flux anomalies are partially compensated for by decreases in midlatitude cloud fraction and cloud height, as observed by Moderate Resolution Imaging Spectrometer and Multi-angle Imaging SpectroRadiometer, respectively. CERES data show that clouds have a net radiative warming influence during La Ni?a conditions and a net cooling influence during El Ni?o, but the magnitude of the anomalies varies greatly from one ENSO event to another. Regional cloud-radiation variations among several Terra and A-Train instruments show consistent patterns and exhibit marked fluctuations at monthly timescales in response to tropical atmosphere-ocean dynamical processes associated with ENSO and Madden–Julian Oscillation. 相似文献