Geneses of Two Types of Mafic Rocks to Carry Placer‐Magnetite Ores in the Sanin Granitic Belt,SW Japan          下载免费PDF全文

Shunso Ishihara  Hideo Hirano 《Resource Geology》2017,67(1):103-108

Two types of mafic rocks from the central Sanin district, and their mafic minerals, were studied chemically and microscopically. They are classified into pyroxene‐containing gabbroid and hornblende–biotite quartz diorite. The gabbroid had higher color index but lower magnetite content; while the quartz diorite had lower color index, but higher magnetite content. The magnetite contents are also related to the amounts of hydrous mafic silicates. The gabbroic magma having pyroxene–amphibole assemblage, originated in the upper mantle, was considered essentially anhydrous, but became partly hydrous on the way to the site of solidification in the continental crust, and crystallized some magnetites with hypersthene and amphibole. The quartz dioritic magma was formed by partial melting of possibly subducting ocean‐floor basalts, once exposed to the sea‐floor then altered; thus the magmas became hydrous and oxidized originally, and precipitated abundant magnetite and hydrous mafic silicates from the early crystallization stage onward. Their weathered parts provided the most placer magnetite ores in the history.  相似文献   

Deep Flows on the Slope Inshore of the Kuril-Kamchatka Trench Southeast off Cape Erimo, Hokkaido     

Kazuyuki Uehara  Hideo Miyake 《Journal of Oceanography》1999,55(5):559-573

Deep flows on the slope inshore of the Kuril-Kamchatka Trench southeast off Cape Erimo, Hokkaido were observed for about five years from June 1989 to March 1995, using a mooring system with two current meters. In 1991 and 1993 directionally stable southwestward flows were observed at the upper layer (1000 m). These appear to be typical of the Oyashio because the characteristics of the flows were high mean kinetic energy, low eddy energy and high stability. However, the magnitudes of other mean flows at the upper layer, except for 1991 and 1993, were less than their standard deviations. This suggests that the Oyashio was observed for only a limited period of time. On the other hand, at the lower layer (3000 m) the magnitudes of the mean flows for 10–11 months were 1–3 cm s^-1 and ellipses of their eddy kinetic energy were extremely flattened in the direction of the local isobath. The directions of the mean flows in 1990, 1991 and 1993 were southwestward along the local isobath. The relationships between the upper and the lower flows are discussed in terms of monthly change of kinetic energy, since the low-frequency fluctuations longer than 30-day are predominant from the eddy kinetic energy spectra. The results show that there are cases when the kinetic energy of the monthly mean flows at the lower layers are larger than those at the upper layers. This suggests the possibility that the lower flows are in part a southward deep western boundary current.  相似文献   

Obituary     

Hideo Miyake 《Journal of Oceanography》1999,55(3):383-383

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Nonlinear behaviour of scoria soil sediments evaluated from borehole records in eastern Shizuoka prefecture,Japan     

Toshimi Satoh  Masanori Horike  Yoshihiro Takeuchi  Tomiichi Uetake  Hideyo Suzuki 《地震工程与结构动力学》1997,26(8):781-795

We evaluate the non-linear behaviour of soil sediments, analysing five weak and four strong motions observed at depths of 1 m and 28 m, in eastern Shizuoka prefecture, Japan. We identify S-wave velocities and frequency-dependent damping factors by minimizing the residual between observed and theoretical spectral ratios, based on a linear one-dimensional model. We find that S-wave velocities identified from strong motions, whose peak ground acceleration are 440, 210, 176, and 140 cm/s², are significantly smaller than those identified from weak motions. The shear modulus reduction ratios estimated from identified S-wave velocities become clear above an effective shear strain of 10^-4 and agree with laboratory test results below an effective shear strain of 8×10^-4. The differences of damping factors between weak and strong motions are not clear below this effective shear strain, as the laboratory test suggested. The equivalent linear one-dimensional model, with frequency-dependent damping factors, is confirmed to be valid to simulate strong motions at least an effective shear strain of less than 4×10^-4. © 1997 John Wiley & Sons, Ltd.  相似文献   

Sea level response to wind field fluctuation around the tip of the Izu Peninsula   总被引：1，自引：0，他引：1  

Hirofumi Hinata  Tetsuo Yanagi  Chizuru Satoh 《Journal of Oceanography》2008,64(4):605-620

The mechanism of a characteristic sea level response (barotropic coastal ocean response) to wind field fluctuation around the tip of the Izu Peninsula observed during the middle of December 2000 to the middle of January 2001 was investigated based on three types of numerical experiments using the Princeton Ocean Model with various parameters. The response was characterized by the relaxation of sea level falling (rising) during eastward upwelling (westward downwelling) favorable wind regime. Analyses of quasi-realistic numerical model results in terms of the vertically integrated momentum balances and vorticity balance for the barotropic mode revealed that: 1) development/abatement of two anomalous circulations generated around the tip of the Izu Peninsula controls the sea level response through the acceleration/deceleration of a quasi-geostrophic barotropic coastal current between the circulations; 2) nonlinear vorticity advection by the Kuroshio Current and by the coastal current, coupled with vorticity diffusion, decelerates the quasi-geostrophic coastal current in the latter half of the wind regimes, which induces the relaxation of sea level rise/fall. The results of the quasi-realistic numerical experiment suggest that an analysis of the vorticity balance for the barotropic mode contributes to a better understanding of sea level responses to wind in coastal regions with strong currents and complex topography. In addition, a numerical experiment with idealized spatially uniform density stratification and a quasi-realistic wind field shows that if the Kuroshio Current had been shifted far offshore from the Izu Peninsula during the observation period, westward propagating continental shelf waves would have controlled the coastal sea level response.  相似文献