Variations of the Kuroshio Axis South of Kyushu in Relation to the Large Meander of the Kuroshio   总被引：1，自引：0，他引：1  

Toru Yamashiro  Masaki Kawabe 《Journal of Oceanography》2002,58(3):487-503

The characteristics of the Kuroshio axis south of Kyushu, which meanders almost sinusoidally, are clarified in relation to the large meander of the Kuroshio by analyzing water temperature data during 1961–95 and sea level during 1984–95. The shape of the Kuroshio axis south of Kyushu is classified into three categories of small, medium, and large amplitude of meander. The small amplitude category occupies more than a half of the large-meander (LM) period, while the medium amplitude category takes up more than a half of the non-large-meander (NLM) period. Therefore, the amplitude and, in turn, the curvature of the Kuroshio axis is smaller on average during the LM period than the NLM period. The mean Kuroshio axis during the LM period is located farther north at every longitude south of Kyushu than during the NLM period, with a slight difference west of the Tokara Islands and a large difference to the east. A northward shift of the Kuroshio axis in particular east of the Tokara Islands induces small amplitude and curvature of the meandering shape during the LM period. During the NLM period, the meandering shape and position south of Kyushu change little with Kuroshio volume transport. In the LM formation stage, the variation of the Kuroshio axis is small west of the Tokara Islands but large to the east due to a small meander of the Kuroshio. In the LM decay stage, the Kuroshio meanders greatly south of Kyushu and is located stably near the coast southeast of Kyushu. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Structure of Subsurface Intrusion of the Oyashio Water into the Kuroshio Extension and Formation Process of the North Pacific Intermediate Water     

Kuniaki Okuda  Ichiro Yasuda  Yutaka Hiroe  Yugo Shimizu 《Journal of Oceanography》2001,57(2):121-140

In order to understand the actual formation process of the North Pacific Intermediate Water (NPIW), structure of subsurface intrusions of the Oyashio water and the mixing of the Oyashio and the Kuroshio waters in and around the Kuroshio Extension (KE) were examined on the basis of a synoptic CTD observation carried out in May-June 1992. The fresh Oyashio water in the south of Hokkaido was transported into KE region through the Mixed Water Region (MWR) in the form of subsurface intrusions along two main paths. The one was along the east coast of northern Japan through the First Branch of the Oyashio (FBO) and the other along the eastern face of a warm streamer which connected KE with a warm core ring through the Second Branch of the Oyashio (SBO). The fresh Oyashio water extended southward through FBO strongly mixed with the saline NPIW transported by the Kuroshio in the south of Japan (old NPIW) in and around the warm streamer. On the other hand, the one through SBO well preserved its original properties and extended eastward beyond 150°E along KE with a form of rather narrow band. The intrusion ejected Oyashio water lens with a diameter of 50–60 km southward across KE axis and split northward into the MWR involved in the interaction of KE and a warm core ring, which were supposed to be primary processes of new NPIW formation.  相似文献   

Ce and Nd isotope geochemistry on island arc volcanic rocks with negative Ce anomaly: existence of sources with concave REE patterns in the mantle beneath the Solomon and Bonin island arcs   总被引：5，自引：0，他引：5  

Hiroshi Shimizu  Hideyuki Sawatari  Yousuke Kawata  Peter N. Dunkley  Akimasa Masuda 《Contributions to Mineralogy and Petrology》1992,110(2-3):242-252

¹³⁸Ce/¹⁴²Ce isotope ratios in Cenozoic island arc volcanic rocks are reported for the first time, together with isotope ratios of Nd and Sr and abundances of REE, Ba and Sr. The island arc volcanics studies here are boninites from Chichijima, the Bonin Islands, and basalts and andesites from the Solomon Islands. REE patterns of the island arc volcanic rocks from the Solmon Islands and the Bonin Islands are confirmed to have negative Ce anomalies. It is also disclosed that the majority of these island arc volcanic rocks show mainly positive values for both _Ce and _Nd. It is shown that these _Ce and _Ce values can hardly be interpreted by simple mixing between MORB and oceanic or continental crustal rocks; the former have positive _Nd and negative _Ce and the latter have negative _Ce and positive or negative _Nd. Existence of sources having positive _Ce and _Nd values is strongly suggested. If the sources are assumed to have been fractionated from CHUR (chondritic uniform reservoir) at the early or middle Precambrian era, the sources from which the volcanics were derived are concluded to have kept concave REE patterns with larger (La/Ce)_N and smaller (Nd/Sm)_N ratios than chondritic values over a substantial period of time, until the time of Cenozoic magmatism forming island arc volcanic rocks in question. During the periods of the Cenozoic magmatic activities and their related events, Ce anomalies are considered to have been created. From Ce and Nd isotope ratios, however, it is difficult to determine which of the following processes was responsible for the Ce anomaly; the incorporation process of subducted oceanic crust into magma at the mantle or the slab dehydration and metasomatism process. Nevertheless, so far as Ce and Nd isotopic ratios are concerned, incorporation of oceanic sediments did not take place to any clearly detectable degree.  相似文献   

Near-infrared and Visible Light Microthermometry of Fluid Inclusions in Sphalerite from a Possible Southeast Extension of the Toyoha Polymetallic Deposit, Japan   总被引：2，自引：0，他引：2  

Toru Shimizu    Masahiro Aoki  Taro Kabashima 《Resource Geology》2003,53(2):115-126

Abstract. Near-infrared (NIR) and visible light microthermometry was applied to the fluid inclusions in sphalerite from a possible southeast extension of the Toyoha polymetallic deposit. Sphalerite occurs as euhedral-subhedral crystals or collo-form aggregates with a variety of color, which contain a well-developed growth banding. Combined with morphological observations, fluid inclusions in dark-colored sphalerite were examined using a near-infrared light microscopic technique, whereas those in light-colored sphalerite and quartz were examined by a conventional visible light microscopy.
Salinities of fluid inclusions in dark-colored sphalerite have a wide variation (1.0–10.3 wt % NaCl equiv.) compared to that in light-colored sphalerite and quartz (0.0–3.4 wt % NaCl equiv.). These variations suggest that the conventional microthermometric data from light-colored sphalerite and quartz were inadequate to interpret the ore formation process. Dark-colored colloform sphalerite and a dark core of subhedral sphalerite formed from high-salinity fluids (6.5–10.3 wt % NaCl equiv.) under highly supersaturated conditions with respect to sphalerite.
The NIR and visible light microthermometry of fluid inclusions in sphalerite combined with its morphological observations is an invaluable method to infer the formation conditions of sphalerite. The NIR and visible light microthermometry is useful to reveal how the nature of ore fluids changed with time.  相似文献   

The anisotropy of surface morphology characteristics of rock discontinuities   总被引：1，自引：4，他引：1  

Ö. Aydan  Y. Shimizu  T. Kawamoto 《Rock Mechanics and Rock Engineering》1996,29(1):47-59

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Microcrack networks in granite affected by a fault zone: Visualization by confocal laser scanning microscopy     

Celia T. Onishi  Ichiko Shimizu   《Journal of Structural Geology》2005,27(12):170

Microcracks in the Cretaceous Ryoke-type granite in Japan were investigated by using deep drilling core samples collected in the Mizunami Underground Research Project of the Japan Nuclear Cycle Development Institute (JNC). The granite body suffered brittle deformation associated with Tertiary thrust movement. Based on core-scale and microscopic deformation features, the drill core from a depth of 300 to 700 m is divided into four domains, i.e. (A) undeformed granite, (B) granite intruded by cataclastic seams, (C) fractured granite in the fault damage zone, and (D) foliated cataclasite at the fault center. To characterize microcrack geometries in each domain, we employed the impregnation method using a low-viscous acrylic resin doped with fluorescent agents and captured the microcrack images by confocal laser scanning microscopy (CLSM). The CLSM image in the fault damage zone revealed anisotropic development of microcrack networks related to the fault movement. Both CLSM observation and porosity measurements reveal a drastic increase of micro-pores in the foliated cataclasite, possibly caused by fragmentation, and granulation and crack sealing in the fault zone.  相似文献   

Inundation behavior of the 2011 Tohoku earthquake tsunami in the Taro District,Miyako City,northeast Japan,as inferred from directional traces     

Toru Tachibana 《Natural Hazards》2015,75(3):2311-2330

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New isotopic evidence bearing on bonanza (Au-Ag) epithermal ore-forming processes   总被引：1，自引：0，他引：1  

James A. Saunders  Ryan Mathur  George D. Kamenov  Toru Shimizu  Matthew E. Brueseke 《Mineralium Deposita》2016,51(1):1-11

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Phase relation of CaSO<Subscript>4</Subscript> at high pressure and temperature up to 90 GPa and 2300 K     

Taku Fujii  Hiroaki Ohfuji  Toru Inoue 《Physics and Chemistry of Minerals》2016,43(5):353-361

Calcium sulfate (CaSO₄), one of the major sulfate minerals in the Earth’s crust, is expected to play a major role in sulfur recycling into the deep mantle. Here, we investigated the crystal structure and phase relation of CaSO₄ up to ~90 GPa and 2300 K through a series of high-pressure experiments combined with in situ X-ray diffraction. CaSO₄ forms three thermodynamically stable polymorphs: anhydrite (stable below 3 GPa), monazite-type phase (stable between 3 and ~13 GPa) and barite-type phase (stable up to at least 93 GPa). Anhydrite to monazite-type phase transition is induced by pressure even at room temperature, while monazite- to barite-type transition requires heating at least to 1500 K at ~20 GPa. The barite-type phase cannot always be quenched from high temperature and is distorted to metastable AgMnO₄-type structure or another modified barite structure depending on pressure. We obtained the pressure–volume data and density of anhydrite, monazite- and barite-type phases and found that their densities are lower than those calculated from the PREM model in the studied P–T conditions. This suggests that CaSO₄ is gravitationally unstable in the mantle and fluid/melt phase into which sulfur dissolves and/or sulfate–sulfide speciation may play a major role in the sulfur recycling into the deep Earth.  相似文献   

Temporal variations in the current structure and volume transport of the Coastal Oyashio revealed by direct current measurement     

Akira Kusaka  Yugo Shimizu  Toru Sato  Jiro Yoshida 《Journal of Oceanography》2016,72(4):601-615

Direct current measurements by a shipboard and bottom-mounted acoustic Doppler current profiler and concurrent hydrographic observations with a CTD were conducted off southeastern Hokkaido, Japan, between January and May 2005 to reveal temporal variations in the current structure and volume transport of the Coastal Oyashio (CO). The CO, which has a baroclinic jet structure with southwestward speeds exceeding 90 cm s^?1 and a width of 7–8 km, was associated with a surface-to-bottom density front and was formed on the offshore side of the shelf break. The volume transport of CO (T _CO) was estimated by integrating the fluxes of lower-density water that was trapped against the coast along the density front represented by the 26.2 σ _θ isopycnal line. This transport decreased monotonously from 0.79 Sv (1 Sv = 10⁶ m³ s^?1) in January to 0.21 Sv in March and subsequently to 0.12 Sv in May, possibly due to the decay of the East Sakhalin Current Water in the Okhotsk Sea. Accompanied by a decrease in T _CO, the location of the jet structure associated with the density front moved toward the coast while the maximum speed of the jet decreased and the tilt of the front became more horizontal. Consequently, more saline offshore Oyashio water flowed into the deep part of the shelf area, and the current structure altered from relatively barotropic in winter to baroclinic in spring. This study is the first to estimate the observed volume transport of the CO from direct current measurements.  相似文献