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21.
Daishido Tsuneaki Asuma Kuniyuki Ohkawa Tohru Obara Hirayoshi Komatsu Shinichi Nagane Kiyoshi 《Astrophysics and Space Science》1986,118(1-2):467-469
An FFT processor is being developed for the present pilot system of the large field radio patrol camera. A design of the processor is discussed.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
22.
Katsumi Marumo Tetsuro Urabe Akiko Goto Yoshinori Takano Miwako Nakaseama 《Resource Geology》2008,58(3):220-248
This report presents mineralogical, geochemical and isotopic data on samples obtained using the Benthic Multi‐coring System (BMS) to drill a submarine hydrothermal deposit developed in a caldera on the summit of the Suiyo Seamount in the Izu–Bonin Island Arc, south of Japan. This deposit is regarded as the first example of Kuroko‐type sulfide mineralization on a volcano at the volcanic front of an island arc. The mineralization and hydrothermal alteration below the 300 × 150‐m area of active venting was investigated to depths of 2–9 m below the sea floor. Drilling beneath the area of active venting recovered a sequence of altered volcanic rocks (dacite lavas, pyroclastic rocks of dacite–rhyolite compositions and pumice) associated with sulfide veining and patches/veins of anhydrite. No massive sulfide was found, however, and the subsea‐floor mineralization to 10 m depth is dominated by anhydrite and clay minerals with some sulfides. Sulfide‐bearing samples contained high Au (up to 42 ppm), Ag (up to 263 ppm), As (up to 1550 ppm), Hg (up to 55 ppm), Sb (up to 772 ppm), and Se (up to 24 ppm). Electron probe microanalyzer indicated that realgar, orpiment, and mimetite were major As‐bearing minerals. The sulfides were also characterized by high Zn (>10%) compared to Cu (<6.3%) and Pb (<0.6%). The δ202Hg/198Hg, δ202Hg/199Hg and δ202Hg/200Hg of the sulfide‐bearing dacite samples and a sulfide chimney decreased with increasing Hg/Zn concentration ratio. The variation of the δ202Hg/198Hg ranged from ?2.8 to +0.5‰ to relative to S‐HG02027. The large range of these δ202Hg/198Hg was greater than might be expected for such a heavy element and may be due to a predominance of kinetic effects. The variation of δ202Hg/198Hg of sulfide‐bearing dacite samples suggested that light Hg isotope in the vapor mixed with oxygenated seawater near sea floor during mineralization. Lead isotope ratios of the sulfide were very similar to those of the dacite lava, suggesting that lead is of magmatic origin. The 87Sr/86Sr ratio (0.70872) of anhydrite was different from that of the dacite lava, and suggests an Sr derivation predominantly from seawater. Hydrothermal alteration of the dacite in the Suiyo hydrothermal field was characterized by Fe‐sulfides, anhydrite, barite, montmorillonite, chlorite/montmorillonite mixed‐layer minerals, mica, and chlorite with little or no feldspar or cristobalite. Hydrothermal clay minerals changed with depth from montmorillonite to chlorite/montmorillonite mixed‐layer minerals to chlorite and mica. Hydrogen isotope ratios of chlorite/montmorillonite and mixed‐layer, mica‐chlorite composites obtained below the active venting sites ranged from ?49 to ?24‰, suggesting seawater as the dominant fluid causing alteration. Oxygen isotope ratios of anhydrite ranged from 9.2 to 10.4‰ and anhydrite formation temperatures were calculated to be 188–207°C. Oxygen isotope ratios ranged from +5.2 to +9.2‰ for montmorillonite, +3.2 to +4.5‰ for chlorite/montmorillonite mixed‐layer minerals, and +2.8 to +3.8‰ in mixtures of chlorite and mica. The formation temperatures of montmorillonite and of the chlorite–mica mixture were 160–250°C and 230–270°C, respectively. The isotope temperatures for clay minerals (220–270°C) and anhydrite (188°C) were significantly lower than the borehole temperature (308.3°C) measured just after the drilling, suggesting that temperature at this site is now higher than when clay minerals and anhydrite were formed. 相似文献
23.
Shusaku Goto Masataka Kinoshita Kyohiko Mitsuzawa 《Marine Geophysical Researches》2003,24(3-4):345-357
A low-temperature diffuse flow site associated with abundant vent fauna was found by submersible observations on the southern East Pacific Rise at 17°25′ S in 1997. This site was characterized by thin sediment covered pillow and sheet lavas with collapsed pits up to ∼15 m in diameter. There were three warm water vents (temperature: 6.5 to 10.5 °C) within the site above which the vented fluids rise as plumes. To estimate heat flux of the warm water vents, a temperature logger array was deployed and the vertical temperature distribution in the water column up to 38 m above the seafloor was monitored. A stationary deep seafloor observatory system was also deployed to monitor hydrothermal activity in this site. The temperature logger array measured temperature anomalies, while the plumes from the vents passed through the array. Because the temperature anomalies were measured in only specific current directions, we identified one of the vents as the source. Heat flux from the vent was estimated by applying a plume model in crossflow in a density-stratified environment. The average heat flux from September 13 to October 18, 1997 was 39 MW. This heat flux is as same order as those of high-temperature black smokers, indicating that a large volume flux was discharged from the vent (1.9 m3/s). Previous observations found many similar warm water flow vents along the spreading axis between 17°20′ S–30′ S. The total heat flux was estimated to be at least a few hundred mega-watts. This venting style would contribute to form effluent hydrothermal plumes extended above the spreading axis. 相似文献
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26.
Shuro?YoshikawaEmail author Toshiya?Kanamatsu Kazuhisa?Goto Izumi?Sakamoto Masatoshi?Yagi Mikio?Fujimaki Riichirou?Imura Kenji?Nemoto Hide?Sakaguchi 《Geo-Marine Letters》2015,35(4):315-328
Ongoing geological research into processes operating on the nearshore continental shelf and beyond is vital to our understanding of modern tsunami-generated sediment transport and deposition. This paper investigates the southern part of Sendai Bay, Japan, by means of high-resolution seismic surveys, vibracoring, bathymetric data assimilation, and radioisotope analysis of a core. For the first time, it was possible to identify an erosional surface in the shallow subsurface, formed by both seafloor erosion and associated offshore-directed sediment transport caused by the 2011 Tohoku-oki tsunami. The area of erosion and deposition extends at least 1,100 m offshore from the shoreline down to water depths of 16.7 m. The tsunami-generated sedimentological signature reaches up to 1.2 m below the present seafloor, whereas bathymetric changes due to storm-related reworking over a period of 3 years following the tsunami event have been limited to the upper ~0.3 m, despite the fact that the study area is located on an open shelf facing the Pacific Ocean. Tsunami-generated erosion surfaces may thus be preserved for extended periods of time, and may even enter the rock record, because the depth of tsunami erosion can exceed the depth of storm erosion. This finding is also important for interpretation of modern submarine strata, since erosion surfaces in shallow (depths less than ~1 m) seismic records from open coast shelves have generally been interpreted as storm-generated surfaces or transgressive ravinement surfaces. 相似文献
27.
Shock-loading experiments are performed on single-crystal specimens of BaZnGeO4 (BZG) between 13 and 51 GPa using a propellant gun and a two-stage light gas gun. Observation by an optical microscope reveals that all the shocked specimens are made of fragmented blocks of 10 ~ 100 μm in size. X-ray analyses indicate that the samples shocked to pressures above 41 GPa became a polycrystalline state of BZG with a weakly textured structure. A small amount of dissociation products of BaGeO3 (pyroxene type) and ZnO (wurtzite type) are detected in this pressure range. Between 27 and 19 GPa, a new phase which is thought to be produced by considerable deformations in the ring structure consisting of ZnO4 and GeO4 tetrahedra is observed. Below 19 GPa, shocked specimens are brought into a well aligned mosaic structure, but no significant change in the crystal structure is detected. 相似文献
28.
Morphology and propagation styles of Miocene submarine basanite lavas at Stanley, northwestern Tasmania, Australia 总被引:2,自引:0,他引:2
Miocene submarine basanite pillows, lava lobes, megapillows and sheet lavas in the Stanley Peninsula, northwestern Tasmania, Australia, are well-preserved in three dimensions. The pillows have ropy wrinkles, transverse wrinkles, symmetrical wrinkles, contraction cracks and three types of spreading cracks on their surfaces, and concentric and radial joints in the interior. The lava lobes have ropy wrinkles and contraction cracks on their surfaces. The megapillows are cylindrical with a smoothly curved upper surface and steep sides, and are characterized by distinct radial columnar joints in the interior. They are connected to pillows that propagate radially from its basal margin. The sheet lavas are tabular and have vertical columnar joints in the interior. The largest sheet lava shows a remarkable gradation from a lower 5-m-thick pillow facies to an upper massive facies. The pillows, lava lobes, megapillows and sheet lavas are inferred to have been emplaced completely below sea level but in a shallow marine environment. Their morphological features suggest that the pillows grew by episodic rupture of a near-solid crust and emergence of hot lava, whereas the lava lobes propagated by continuous stretching of the outer skin at the flow front. The megapillows and sheet lavas were master feeder channels by which molten lava was conveyed to the advancing pillows. The sheet lavas propagated by repeated processes of pillow formation and overriding by an upper massive part. Alternating pillow and massive facies commonly found in ocean-floor drill cores and exposed in cross-section in many subaqueous volcanic successions may have formed by propagation of pillows from the basal margins of advancing sheet lavas. 相似文献
29.
We have devised a new, simple and easy technique to measure the viscosity of hydrous silicate melts by combining an autoclave for melt hydration and the fiber elongation method for viscosity measurement. Using this, we measured the viscosity of hydrous rhyolitic melts whose water content ranges from 0.02 to 0.58 wt%. We observed a drastic decrease in viscosity against water content: 0.1 wt% water decreases the viscosity about an order of magnitude. Even when the water content is only 0.02 wt%, the viscosity decreased about half an order of magnitude. These results clearly demonstrate that the effect of water on viscosity should not be ignored even when it occurs as a trace constituent. We compared our experimental data with those derived from a non-Arrhenian viscosity model, which is considered to be applicable to calc-alkaline samples. This model succeeded in expressing the viscosity variation against water content but was unable to accurately predict the measured viscosity of liquids.Editorial responsibility: D. Dingwell 相似文献
30.
Tada-nori Goto 《Physics of the Earth and Planetary Interiors》2005,148(1):55-72
Seismicity along the Atotsugawa Fault, located in central Japan, shows a clear heterogeneity. The central segment of the fault with low-seismicity is recognized as a seismic gap, although a lot of micro-earthquakes occur along this fault. In order to elucidate the cause of the heterogeneity in seismicity, the electrical resistivity structure was investigated around the Atotsugawa Fault by using the magnetotelluric (MT) method. The regional geoelectrical strikes are approximately parallel to the fault in a low-frequency range. We constructed two-dimensional resistivity models across the fault using TM-mode MT responses to minimize three-dimensional effects on the modeling process. A smooth inversion algorithm was used, and the static-shifts on the apparent resistivity were corrected in the inversion process.A shallow, low resistivity zone along the fault is found from the surface to a depth of 1-2 km in the best-fit model across the high-seismicity segment of the fault. On the other hand, the corresponding low resistivity zone along the low-seismicity segment is limited to a shallower depth less than 1 km. The low resistivity zone along the Atotsugawa Fault is possibly due to fluid in the fracture zone; the segment with higher levels of seismicity may have higher fluid content in the fault zone compared with the lower seismicity segment. On a view of the crustal structure, a lateral resistivity variation in a depth range of 3-12 km is found below the fault trace in the high-seismicity segment, while a resistive layer of wide extent is found at a depth of about 5 km below the fault trace in the low-seismicity segment. The resistive layer is explained by less fluid condition and possibly characterized as high rigidity. Differences in the resistivity structures between low and high-seismicity segments of the fault suggest that the seismic gap in the central part of the Atotsugawa Fault may be interpreted as a locked segment. Thus, MT is an effective method in evaluating a cause and future activity of seismic gaps along active faults.The lower crust appears as a conductive zone beneath the low-seismicity segment, less conductive beneath the high-seismicity segment. Fluid is inferred as a preferable cause of the conductive zone in this study. It is suggested that the conductive lower crust beneath the low-seismicity segment is recognized where fluid is trapped by an impermeable layer in the upper crust. On the other hand, fluid in the lower crust may upwell to the surface along the high-seismicity segment of the fault. 相似文献