A Fluid Inclusion Study on Columnar Adularia from the Hishikari Low-sulfidation Epithermal Gold Deposit, Japan   总被引：2，自引：1，他引：2  

Jiro ETOH  Eiji IZAWA  Sachihiro TAGUCHI 《Resource Geology》2002,52(1):73-78

Abstract: In the Hishikari low-sulfidation epithermal gold deposit, Japan, columnar adularia crystals commonly precipitated directly on to the fracture surface of wall rock, and then electrum precipitated on the columnar adularia with fine-grained adularia and quartz. To reveal the characteristics of mineralizing fluids and the elevation of paleo-water tables at the earliest stage of mineralization in the Honko-Sanjin zone of the Hishikari deposit, the fluid inclusions in the columnar adularia in gold-bearing quartz–adularia veins were studied.
Coexistence of vapor-rich and liquid-rich two–phase primary fluid inclusions indicates the deposition of columnar adularia from boiling fluids. The precipitation temperatures range from 175 to 215C, and generally increase with depth. The temperatures of final melting point of ice range from –1.2 to –0.1C with an average of –0.5C, corresponding to salinity ranging from 0.2 to 2.1 wt% NaCl equivalent with an average of 0.9 wt% NaCl (eq.). Concentrations of non-condensable gases such as CO₂ were under the detection limit of a laser Raman microprobe spectrometer. From the precipitation temperature of columnar adularia in the Hosen–2 vein and the boiling point – depth curve for a 0.9 wt% NaCl (eq.) fluid, paleo-water table was estimated to be at an elevation of about +170 m. The elevation of the paleo-water tables for other veins was estimated to range from +140 to +215 m.  相似文献   

Gas Measurement of Fluid Inclusions from the Hishikari Epithermal Gold Deposit, Southern Kyushu, Japan, Using Laser Raman Microprobe     

Jiro Etoh    Sachihiro Taguchi  Eiji Izawa 《Resource Geology》2002,52(4):405-408

Abstract. Laser Raman microprobe analysis was performed on the fluid inclusions from the Honko-Sanjin zone in the Hishikari epithermal gold deposit, southern Kyushu, Japan. Gas concentrations of fluid inclusions through the zone were below detection limits (e.g., 5 mmole/kg H₂O for CO₂), with an exception at shallow portion in which the CO₂/N₂ mole ratio was determined to be 5.3. Boiling of hydrothermal solutions probably separated gases from ore fluids at the deep portion of the deposit, and migration of gases to shallow portion resulted in CO₂-rich steam-heated water and related acid alteration.  相似文献   

Modification of North Pacific Intermediate Water around Mixed Water Region     

Ryuichiro Inoue  Jiro Yoshida  Yutaka Hiroe  Kousei Komatsu  Kiyoshi Kawasaki  Ichiro Yasuda 《Journal of Oceanography》2003,59(2):211-224

The mixing processes in the Mixed Water Region (MWR) that lead to changes in the properties of North Pacific Intermediate Water (NPIW) have been studied using observational data sets obtained in May–June 1998. Neutral surfaces, the equation of water mass conversion rate on neutral surfaces and the equation of vertical velocity across neutral surfaces have been used to distinguish dominant processes by assuming the horizontal scale to be the streamer scale (under 100 km). The possibility of double diffusive convection is also discussed in relation to the density ratio. These results may be summarized as follows: (1) the difference between the potential density surface and the neutral surface may rise to −0.04 kg/m³ around the source water of NPIW; (2) horizontal diffusion causes strong modifications of the source water of NPIW; (3) the density range within which strong modification of the source water of NPIW occurs becomes dense from the northern part of MWR near the Oyashio Front to the southern part near the Kuroshio Front, and to the eastern part. Our modeling of these processes shows that cabbeling has effects on the density increment of the source water of NPIW in the northern and southern part of MWR. Double diffusive convection has effects on the density increment of the source water of NPIW, mainly in the northern part of MWR. The possible density increment due to cabbeling in these areas is estimated to be 0.01≈0.03 kg/m³. The possible density increment due to double diffusive convection is 0.01≈0.03 kg/m³. The total density increment due to cabbeling and double diffusive convection amounts to 0.06 kg/m³. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Role of the wind in the control of the air temperature distribution     

Masahide Aikawa  Takatoshi Hiraki  Jiro Eiho  Hiroshi Miyazaki 《Meteorology and Atmospheric Physics》2008,102(1-2):15-22

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Electromagnetometry at the sea floor     

Jiro Segawa  Hiroaki Toh 《Journal of Earth System Science》1990,99(4):639-656

Electromagnetometry at the sea floor has been developed over the last two decades taking advantage of the progress of positioning and acoustic technology in marine region. In spite of its risks and costs, electromagnetometry at the sea floor has significantly contributed to the study of conductivity anomalies through direct observations of electromagnetic variations at the sea floor. Some of the fruitful results of the ocean bottom observations around Japan as well as data processing of sea floor electromagnetic measurements are reviewed. Future problems in electromagnetometry at the sea floor are also discussed. In conclusion, the importance of establishing semipermanent electromagnetic observatories at the sea floor is emphasized.  相似文献   

Brane World Effective Action at Low Energies     

Sugumi Kanno  Jiro Soda 《Astrophysics and Space Science》2003,283(4):481-486

The low energy effective theory for the Randall-Sundrum two-brane system is investigated with an emphasis on the role of the non-linear radion in the brane world. It is shown that the gravity on the brane world is described by a quasi-scalar-tensor theory with a specific coupling function. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Ambient vibration test of an anchorage of South Bisan-seto suspension bridge     

Hiromichi Higashihara  Tamotsu Moriya  Jiro Tajima 《地震工程与结构动力学》1987,15(6):679-695

Dynamical properties of an anchorage of South Bisan-seto Suspension Bridge are determined by means of in situ measurement of the ambient vibrations. This anchorage, being located in the sea, is tall and slender; its natural frequencies are expected to be low. On the other hand, the elasticity of the ground estimated from the conventional geological data is highly dispersed. It even suggests the possibility of resonance between the towers and this anchorage. It is therefore necessary to know its natural frequencies precisely. Seismic motions and microtremors are acquired and used properly. The observation is repeated every year during the period of construction of the anchorage so that its inertial properties change significantly. First modes of the longitudinal and the transversal vibrations of the anchorage are identified and their frequencies determined. The elasticity modulus estimated from these natural frequencies is about five times as large as that of the geological survey while it is consistent with that obtained from the velocity of the elastic waves of the ground.  相似文献   

A possible Caledonide arm through the Barents Sea imaged by OBS data     

Asbjrn Johan Breivik  Rolf Mjelde  Paul Grogan  Hideki Shimamura  Yoshio Murai  Yuichi Nishimura  Asako Kuwano 《Tectonophysics》2002,355(1-4)

The assembly of the crystalline basement of the western Barents Sea is related to the Caledonian orogeny during the Silurian. However, the development southeast of Svalbard is not well understood, as conventional seismic reflection data does not provide reliable mapping below the Permian sequence. A wide-angle seismic survey from 1998, conducted with ocean bottom seismometers in the northwestern Barents Sea, provides data that enables the identification and mapping of the depths to crystalline basement and Moho by ray tracing and inversion. The four profiles modeled show pre-Permian basins and highs with a configuration distinct from later Mesozoic structural elements. Several strong reflections from within the crystalline crust indicate an inhomogeneous basement terrain. Refractions from the top of the basement together with reflections from the Moho constrain the basement velocity to increase from 6.3 km s⁻¹ at the top to 6.6 km s⁻¹ at the base of the crust. On two profiles, the Moho deepens locally into root structures, which are associated with high top mantle velocities of 8.5 km s⁻¹. Combined P- and S-wave data indicate a mixed sand/clay/carbonate lithology for the sedimentary section, and a predominantly felsic to intermediate crystalline crust. In general, the top basement and Moho surfaces exhibit poor correlation with the observed gravity field, and the gravity models required high-density bodies in the basement and upper mantle to account for the positive gravity anomalies in the area. Comparisons with the Ural suture zone suggest that the Barents Sea data may be interpreted in terms of a proto-Caledonian subduction zone dipping to the southeast, with a crustal root representing remnant of the continental collision, and high mantle velocities and densities representing eclogitized oceanic crust. High-density bodies within the crystalline crust may be accreted island arc or oceanic terrain. The mapped trend of the suture resembles a previously published model of the Caledonian orogeny. This model postulates a separate branch extending into central parts of the Barents Sea coupled with the northerly trending Svalbard Caledonides, and a microcontinent consisting of Svalbard and northern parts of the Barents Sea independent of Laurentia and Baltica at the time. Later, compressional faulting within the suture zone apparently formed the Sentralbanken High.  相似文献   

Sumisu volcano,Izu-Bonin arc,Japan: site of a silicic caldera-forming eruption from a small open-ocean island     

Kenichiro Tani  Richard S. Fiske  Yoshihiko Tamura  Yukari Kido  Jiro Naka  Hiroshi Shukuno  Rika Takeuchi 《Bulletin of Volcanology》2008,70(5):547-562

Sumisu volcano was the site of an eruption during 30–60 ka that introduced ∼48–50 km³ of rhyolite tephra into the open-ocean environment at the front of the Izu-Bonin arc. The resulting caldera is 8 × 10 km in diameter, has steep inner walls 550–780 m high, and a floor averaging 900 m below sea level. In the course of five research cruises to the Sumisu area, a manned submersible, two ROVs, a Deep-Tow camera sled, and dredge samples were used to study the caldera and surrounding areas. These studies were augmented by newly acquired single-channel seismic profiles and multi-beam seafloor swath-mapping. Caldera-wall traverses show that pre-caldera eruptions built a complex of overlapping dacitic and basaltic edifices, that eventually grew above sea level to form an island about 200 m high. The caldera-forming eruption began on the island and probably produced a large eruption column. We interpret that prodigious rates of tephra fallback overwhelmed the Sumisu area, forming huge rafts of floating pumice, choking the nearby water column with hyperconcentrations of slowly settling tephra, and generating pyroclastic gravity currents of water-saturated pumice that traveled downslope along the sea floor. Thick, compositionally similar pumice deposits encountered in ODP Leg 126 cores 70 km to the south could have been deposited by these gravity currents. The caldera-rim, presently at ocean depths of 100–400 m, is mantled by an extensive layer of coarse dense lithic clasts, but syn-caldera pumice deposits are only thin and locally preserved. The paucity of syn-caldera pumice could be due to the combined effects of proximal non-deposition and later erosion by strong ocean currents. Post-caldera edifice instability resulted in the collapse of a 15° sector of the eastern caldera rim and the formation of bathymetrically conspicuous wavy slump structures that disturb much of the volcano’s surface.  相似文献   

Relative influence of biotic and abiotic processes on travertine fabrics,Satono‐yu hot spring,Japan     

Fumito Shiraishi  Yuki Eno  Yuki Nakamura  Yusaku Hanzawa  Jiro Asada  Anelize Manuela Bahniuk 《Sedimentology》2019,66(2):459-479

The relative influences of biotic and abiotic processes on travertine fabrics are still not well understood, despite increasing interest in the last decade to better understand the record of ancient microbial life and sedimentary fabrics in microbial hydrocarbon reservoirs. This study examines travertines at Satono‐yu hot spring in Japan (the temperature of water flowing over the travertine was ca 35°C), to better understand the interaction between depositional, hydrochemical and microbial parameters at different flow settings. Characteristics of the bulk hydrochemistry, mineralogy (exclusively aragonite) and the driving force for precipitation (primarily abiotic CO₂ degassing with some photosynthetic microbial contribution) were similar among all of the flow settings. Conversely, the increase in flow velocity suppressed the influence of photosynthesis and enhanced the abiotic precipitation due to the thinner diffusive boundary layer at the travertine surface–water interface. Additionally, the increase in flow velocity changed the microbial composition and decreased the bacterial diversity by reflecting their adhesion efficiency on the travertine substrate. The acidity of the cyanobacterial sheaths controls the aragonite nucleation rate and the resulting calcification, even at significantly high equilibrium CO₂ partial pressure (ca 22 to 28 matm), high dissolved inorganic carbon concentration (ca 35 to 38 mmol l^?1), and elevated aragonite saturation state (ca 20‐fold to 34‐fold). Therefore, the increase in flow velocity suppresses the microbial influence with respect to the increase in the saturation state, the nucleation site supply and pore space generation. Overall, this results in the predominance of abiotic precipitation under high flow velocities. Consequently, a sparse‐micritic fabric with abundant interlamina porosity forms under lower flow velocity where the microbial influence is effective, while a dense‐sparitic fabric with little inter‐crystalline porosity forms under higher flow velocity where abiotic precipitation prevails. These findings provide an essential base for assessing the formation processes of ancient travertines and comparable deposits from petrological fabrics.  相似文献