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31.
在热液条件下合成了板状的和高度结晶的三八面体蒙脱石。用淬冷玻璃与脱水的钠基蒙脱石分别在(a)500°C,100MPa下1天和11天;(b)300°C,100MPa下7天的条件下进行反应。产物的结晶度和颗粒大小取决于初始玻璃的化学组成,合成温度和热液改性的时间。XRD尖锐的峰和一定相对湿度下水合作用证明了产物结构的高度有序和大尺寸。透射电镜也被用来表征产物颗粒尺寸。通过改变初始材料的化学成分,产物的颗粒大小可以在10nm到几个微米之间变化。有序度最高和尺寸最大的产物是在500°C,100MPa的条件下用Na0.33(Mg1.83Al0.67)Si4O11成分的玻璃反应… 相似文献
32.
Abstract The Miura Group (Miocene-Pliocene) of south-central Japan shows a number of unique lithological and structural features. The group is composed of volcanic arc-derived marine sediments, and those in the south of the Mineoka Tectonic Belt particularly show various kinds of complex structures such as layer-parallel faults, thrust duplexes, imbricate thrusts and vein structures, yet the degree of compaction of the sediments is still remarkably low. These structures involve deformations at a very early stage and at shallow depths. They arose shortly after sedimentation within the Izu fore arc, and continued during accretion to the Honshu fore arc. The deformational stages are classified here into three stages, the first comprises bedding-parallel faulting associated with gravitational sliding and sediment injection. The first vein structures formed during this stage in the Izu fore arc area. These structures are cut by features developed during the second and third stages: especially thrusting, including duplex and imbricate thrusts. This horizontal shortening occurred during the accretionary prism formation on the subduction plate boundary. The second vein structures formed during this stage in the accretionary prism formation. The origin of the vein structures was discussed both by field observation and laboratory experiments. The latter suggests earthquake origin and the formative process is explained in relation to the field evidence. 相似文献
33.
Generation and propagation of several-day period fluctuations along the southeast coast of Honshu, Japan, were investigated by analyzing sea level data and by using a numerical model. The sea level data obtained at twelve stations from Choshi to Omaezaki in fall in 1991, showed energy peaks at the 3–6 day period at the eastern stations in this coast. Time lags of the 3–6 day period fluctuations between station and station indicate westward propagation along the coast. However, the energy level of the 3–6 day period fluctuations suddenly decreased south of the Izu Peninsula. Numerical experiments using a two-layer model were performed to clarify the generation and propagation mechanism of the several-day period fluctuations by periodical wind in fall. The amplitude distributions of observed sea level were qualitatively explained by a coastal-trapped wave (CTW) in the numerical experiment. From the discussions on propagation of a free wave, CTW with the characteristics of a shelf wave generated by the wind along the northeast of the Boso Peninsula was separated into two types of wave at the southeast of the peninsula. One is an internal Kelvin wave with large interface displacement and the other is the shelf wave propagating over the northern part of the Izu Ridge. The sudden decrease in the surface displacement with the 3–6 day period observed at the western stations is considered to be due to the local effect of the wind and phase relation between the internal Kelvin wave and shelf wave. 相似文献
34.
Tetsuzo Seno Yujiro Ogawa Hidekazu Tokuyama Eiichiro Nishiyama Asahiko Taira 《Tectonophysics》1989,160(1-4):91-116
We discuss several models of the evolution of the trench-trench-trench triple junction off central Honshu during the past 1 m.y. on the basis of plate kinematics, morphology, gravity and seismic reflection profile data available for the area. The study area is characterized by large basins, 7–8 km deep on the inner lower trench slope on the Philippine Sea side and the deep (9 km) Izu-Bonin Trench to the east. Between the basins and the trench, there are 6–7 km-deep basement highs. The triple junction is unstable due to the movement of the Philippine Sea plate at a velocity of 3 cm/yr in WNW direction with respect to Eurasia (Northeast Japan), subparallel to the strike of the Sagami Trough. Generally we can expect the boundary area between the Philippine Sea and Pacific plates to be extended because the Pacific plate is unlikely to follow the retreating Philippine Sea plate due to the obstruction of the southeastern corner of Eurasia. The above peculiar morphology of the junction area could have resulted from this lack of stability. However, there are several possible ways to explain the above morphology.
Our gravity model across the trench-basement high-basin area shows that the basement highs are made of low-density materials (1.8–2 g/cm3). Thus we reject the mantle diapir model which proposes that the basement highs have been formed by diapiric injection of serpentinites between the retreating Philippine Sea plate and the Pacific plate.
The stretched basin model proposes that the basins have been formed by stretching of the Philippine Sea plate wedge. We estimated the extension to be about 10 km at the largest basin. We reconstructed the morphology at 1 Ma by moving the Philippine Sea plate 20 km farther to the east after closing the basins, and thus obtained 8 km depth of the 1 Ma trench, which is similar to that of the present Japan Trench to the north. Although this stretched basin model can explain the formation of the basins and the deep trench, other models are equally possible. For instance, the eduction model explains the origin of the basin by the eduction of the Philippine Sea basement from beneath the basement high, while the accretion model explains the basement highs by the accretion of the Izu-Bonin trench wedge sediments. In both of these models we can reconstruct the 1 Ma trench depth as about 8 km, similar to that of the stretched basin model.
The deformation of the basement of the basins constitutes the best criterion to differentiate between these models. The multi-channel seismic reflection profiles show that the basement of the largest basin is cut by normal faults, in particular at its eastern edge. This suggests that the stretched basin model is most likely. However, the upper part of the sediments shows that the basement high to the east has been recently uplifted. This uplift is probably due to the recent (0.5 Ma) start of accretion of the trench wedge sediments beneath this basement high. 相似文献
35.
Abstract The significance of timing and formation of mélange in accretionary prisms, particularly concerning basaltic and related rocks and pelagic sediments, is exemplified in the Sawadani area of the Jurassic Chichibu accretionary complex in Shikoku, southwest Japan. Major and trace element geochemistry of the basaltic and related rocks indicates that all are of a hot-spot origin which produced a seamount. Most of the rocks have a trend of differentiation from an alkalic parental magma. The time relationship between the blocks and matrices of the mélange deduced from radiolarian fossil evidence and macro- to microscopic characteristics of contacts between different lithologies indicates two stages of mixing of materials in the seafloor. The first mixing occurred on the flank of the seamount in the pelagic environments in the Late Permian, and the second occurred on the trench floor or in the accretionary prism after the Early Jurassic. These two stages show respectively the geological phenomena of a seamount within the Izanagi-Kula plate and its incorporation into the Asian continental margin. 相似文献
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37.
Guy Pautot Kazuaki Nakamura Philippe Huchon Jacques Angelier Jacques Bourgois Kantaro Fujioka Toshihiko Kanazawa Yasuo Nakamura Yujiro Ogawa Michel Sguret Akira Takeuchi 《Earth and Planetary Science Letters》1987,83(1-4)
Nine submersible dives were made in three trenches off central Japan, between 2990 and 5900 m of water depth. Our observations confirm the interpretation that Daiichi-Kashima Seamount is a Cretaceous guyot formed on the Pacific plate that has traveled into the Japan Trench. We also confirmed the previous interpretation of a large normal fault that splits the seamount in two halves, the lower one being now subducting beneath the Japan margin. Compressional deformation was identified within the lower part of the inner slope in front of the seamount. The pattern of deformation that affects Quaternary sediments is in agreement with the present kinematics of the convergence between the Pacific plate and Japan. Deep-water (5700 m) clam colonies are associated with advection of fluids, driven by the subduction-related overpressures. In the northern slope of the Boso Canyon, along the Sagami Trough system (Philippine Sea plate-Japan boundary), the deformation affecting a thick upper Miocene to lower Pliocene sequence indicates two directions of shortening: a N175°E direction which is consistent with the present relative motion along the Sagami Trough (N285–N300°E) and a N30°E direction which could be related to a more northerly direction of convergence that occured during the early Quaternary and earlier. 相似文献
38.
Based on the geological tectonics, aftershock activity, earthquake surface rupture and peak ground motion, the geometric and dynamic characteristics of seismogenic tectonics about the 1995 Hanshin earthquake are analysed. Nojima fault and Rokko fault have the same trending direction, but opposite dips. Their rising and falling plates are in symmetrically diagonal distribution. The two faults can be defined as thrust-strike slip faults and constitute a pivotal strike-slip fault. The earthquake just occurred at the pivot, which is the seismotectonics for the earthquake to develop and occur. The pivotal movement along a strike-slip fault often leads to the occurrence of large earthquakes, whose dynamic process can be demonstrated by the stress analysis on the torsion of a beam with rectangle section. The displacement of earthquake surface rupture, aftershock density and peak acceleration change in a certain range of epicentral distance just similar as the shear stress changes from the center to the sides in the rectangle section. The distribution characteristics of the heaviest damage areas are also discussed in the article from the aspects of special geological tectonics and seismotectonic condition. The result obtained from the article can be applied not only to realizing the potencial earthquake sources in middle-long time, but also to build reasonably the prediction model about earthquake hazard. 相似文献
39.
A numerical experiment using a three dimensional level model was performed to clarify the mechanism generating a strong coastal
current, Kyucho, induced by the passage of Typhoon 0406 around the tip of the Tango Peninsula, Japan in June 2004. Wind stress accompanied
by Typhoon 0406 was applied to the model ocean with realistic bottom topography and stratification condition. The model well
reproduced the characteristics of Kyucho observed by Kumaki et al. (2005), i.e., the strong alongshore current with maximum velocity of 53 cm s−1 and its propagation along the peninsula with propagation speed of about 0.6 m s−1 one half-day after the typhoon’s passage. Coastal-trapped waves (CTW) accompanied by downwelling were induced along the northwest
coast of the peninsula by the alongshore wind stress. The energy density flux due to the CTW flowed eastward along the coast,
and indicated scattering of the CTW around the eastern coast of the peninsula. In addition, significant near-inertial internal
gravity waves were also caused in the offshore region from the west of the Noto Peninsula to the north of the Tango Peninsula
by the typhoon’s passage. The energy flux density of the near-inertial fluctuations flowed southward off the Fukui coast,
and part of the energy flux was trapped on the tip of the Tango Peninsula, flowing with the coast on its right. It was found
that the strong current, Kyucho, at the northeastern tip of the Tango Peninsula was generated by superposition of the near-inertial internal gravity waves
and subinertial CTW. 相似文献
40.
The cold-water belt (CWB) is frequently formed off the Soya Warm Current (SWC) during summer and autumn. The detailed distribution
of the flow and temperature fields observed by the R/V Sinyo-maru in the summer of 2001 captured the structures of the SWC
and the CWB. The temperature and density distributions showed that the vertical distribution of the CWB is associated with
the upwelling formed off the SWC. Numerical experiments using a two-layer model with realistic bottom topography have been
performed to understand the formation mechanism of CWB and the upwelling structure off the current. In the experiment, the
sea level difference between the Japan Sea and the Okhotsk Sea, and baroclinic flow assuming the Tsushima Warm Current were
given along the open boundary. The numerical model well reproduces the current system of the SWC and upwelling region off
it. The upwelling region is formed at the Soya Strait first, and then it spreads on the offshore side along the SWC as a developing
current system. Analysis of the model data indicated that the geostrophic balance mainly dominates in the current system,
while convergence of the bottom Ekman transport due to the SWC forms the upwelling region as the secondary circulation. In
addition, the advection effect due to the SWC is found to strengthen the upwelling. 相似文献