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841.
The notion that the Yakuno ophiolite and overlying Maizuru Group represents an accretionary prism formed during the Permian evolution of Japan on the Yakuno eruptive sequence, association of hemipelagic mudstone with silicic tuff, exotic fossiliferous limestones derived from previously accreted sea-mounts, upward coarsening of sequences terrigenous sandstone and conglomerate, and mildly deformed Permian and Triassic forearc basin formations. The most important indicator, however, is the seaward imbrication and repetition observed in both the Maizuru Group and the ophiolite itself. D1 deformation structures include axial–planar foliations (pressure-solution cleavage for the Maizuru Group and granulite–amphibolite metamorphic layering in the ophiolite), flattening type strain, symmetric pressure shadows and fringes, and isoclinal folds showing axial–planar foliations and thrust faulting at their overturned limb. The exceptional asymmetry observed indicates seaward-directed shearing near the thrust, while D1 structures in the Maizuru zone are explained by off-scraping, above the basal decollement. The later Jurassic D2 kink fold structure includes a first-order asymmetric kink with a brittle thrust at its overturned limb, more-or-less coeval with M2 retrograde metamorphism. Medium-pressure M1 prograde metamorphism in the Yakuno ophiolite produced layering of granulite and amphibolite, and in the Maizuru Group, formation of illite along pressure-solution cleavage of mudstones. The metamorphic grade is controlled by the stratigraphic relationships and appears typical of that in ocean floor regions. However, there was only one episode of M1 prograde metamorphism which occurred contemporaneously with D1 off-scraping. Given that subduction zones are normally characterized by high P/T metamorphic regimes, the observed P/T history appears to reflect relatively unusual conditions. Such high thermal gradients may plausibly reflect the approach of a young, hot oceanic plate which continued subducting beneath the Japanese arc. Accordingly, the Yakuno ophiolite was probably formed at the trench–trench–ridge triple junction. 相似文献
842.
843.
844.
Hiroshi Kinoshita Haruo Yoshida Hiroshi Nakai 《Celestial Mechanics and Dynamical Astronomy》1990,50(1):59-71
Symplectic integrators have many merits compared with traditional integrators: 相似文献
845.
Duplex of metamorphic units including ultramafic rocks in the central region of Tokunoshima,Southwest Japan 下载免费PDF全文
Geological observations in the central part of Tokunoshima in the Amami Islands, Southwest Japan, reveal that discrete layers of serpentinite, dioritic gneiss, and amphibolite are intercalated into pelitic schist and these rock bodies form a northwest‐dipping tectonic stack. A subhorizontal psammitic schist layer overlies them. These rocks underwent ductile deformation that is denoted by penetrative foliation and mineral lineation. Microstructures of the sheared metamorphic rocks and serpentinite indicate top‐to‐the‐east, ‐southeast or ‐south (hanging‐wall up) displacements. The en echelon array of rock bodies is interpreted as a duplex with the psammitic schist layer on its top and the pelitic schist layer on its bottom. It is inferred that the serpentinite‐bearing duplex was formed due to the tectonic erosion and the subsequent accretionary growth operated in a Cretaceous or older subduction zone. Tokunoshima has been considered to belong to the Shimanto Belt. However, regional low‐pressure and high‐temperature type amphibolite‐facies metamorphism and related ductile deformation have not been recognized in the other areas of the Shimanto Belt. There is no metamorphic rock occurrence comparable to that of Tokunoshima in the neighboring islands. The metamorphic rocks in Tokunoshima can be correlated to any of low‐pressure/temperature type metamorphic regions in Kyushu. 相似文献
846.
Xu Hui Zhang Weiping Lang Xuxing Guo Xia Ge Wenzhong Dang Renqing Takao Takeda 《大气科学进展》2000,17(3):403-412
During the Meiyu period in June and July of 1998, intensified field observations have been carried out for the project “Huaihe
River Basin Energy and Water Cycle Experiment (HUBEX)”. For studying Meiyu front and its precipitation in Huaihe River basin,
the present paper has performed analysis on the middle and lower level wind fields in the troposphere by using the radar data
obtained from the two Doppler radars located at Fengtai district and Shouxian County.
From June 29 to July 3 in 1998, the continuous heavy precipitation occurred in Huaihe River basin around Meiyu front. The
precipitation process on July 2 occurred within the observation range of the two Doppler radar in Fengtai district and Shouxian
County. The maximum rainfall of the Meiyu front was over 100 mm in 24 h, so it can be regarded as a typical mesoscale heavy
precipitation process related to Meiyu front.
Based on the wind field retrieved from the dual Doppler radar, we find that there are meso-γ scale vertical circulations in
the vertical cross-section perpendicular to Meiyu front, the strong upward motion of which corresponds to the position of
the heavy rainfall area. Furthermore, other results obtained by this study are identical with the results by analyzing the
conventional synoptic data years ago. For example: in the vicinity of 3 km level height ahead of Meiyu front there exists
a southwest low-level jet; the rainstorm caused by Meiyu front mainly occurs at the left side of the southwest low-level jet;
and the Meiyu front causes the intensification of the low-level convergence in front of it.
This research was supported by Project HUBEX (Project Number: 49794030) which is funded by the National Natural Science Foundation
of China (NSFC). 相似文献