Hydrothermal plumes in the eastern Manus Basin, Bismarck Sea: CH₄, Mn, Al and pH anomalies     

T. Gamo  H. Sakai  J. Ishibashi  E. Nakayama  K. Isshiki  H. Matsuura  K. Shitashima  K. Takeuchi  S. Ohta 《Deep Sea Research Part I: Oceanographic Research Papers》1993,40(11-12)

We present evidence for strong hydrothermal activity in the eastern Manus Basin (depth: 1700–2100 m), the existence of large scale triple-layered buoyant plumes at depths of 1100 m (“shallow plume”), 1700 m (“deep plume”), and 1400 m (“middle plume” with less extent than the other two plumes) that were revealed from water column anomalies of CH₄, Mn, Al and pH observed in November to December 1990. Judging from the horizontal distribution of these parameters, the deep plume seems to originate from two distinct hydrothermal sites (eastern and western sites) in the research area, the eastern site being visually ascertained with deep-tow observations at the same time. The CH₄/Mn ratio (mol mol⁻¹) of the deep plume (0.02–0.05) is the lowest yet observed in hydrothermal plumes. The order of magnitude difference of CH₄/Mn ratios between the shallow plume and the deep plume suggests that different kinds of fluid-rock interaction occurred to make the hydrothermal end members for the deep and shallow plumes. The shallow plume, which had an areal extent of more than 50 km, may be an episodic “megaplume”, because it was not recognized in the previous CH₄ profiles in 1986, and because it has a similar CH₄/Mn ratio as the megaplume observed in the North Fiji Basin. We found that the eastern deep plume is characterized by enormously high aluminium concentrations (0.6– 1.5 μmol kg⁻¹), pH anomalies (0.1) and high Al/Mn ratios (10–17). The endmember fluid for the eastern deep plume may have an unusually low pH value to dissolve this much aluminum during fluid-rock interaction, or this plume may originate from an eruption-influenced fluid.  相似文献   

Bifurcation of barotropic flow and homogenization of potential vorticity in a rotating laboratory model     

Satoshi Sakai 《Progress in Oceanography》1986,17(3-4)

Laboratory experiments with a rotating tank confirm the bifurcation character of a barotropic flow driven by an inflow and an outflow described by Sakai (1986). The model, a circular basin with a topographic β-effect, simulates a mid-latitude oceanic feature. At a low Rossby number, stationary Rossby waves are observed which are symmetrical with a line connecting the inlet and the outlet. As the Rossby number increases, a bifurcation occurs and two kinds of vortex flows are observed. In the vortex, potential vorticity is almost uniform. In addition to the two vortex flows, a jet-like inertial flow can also be observed. In general, thre results of these experiments agree well with those of a low-order model and a numerical model.  相似文献   

The role of crabs (Macrophthalmus japonicus) burrows on organic carbon cycle in estuarine tidal flat,Japan     

Sosuke Otani  Yasunori Kozuki  Ryoichi Yamanaka  Hiromitsu Sasaoka  Tetsu Ishiyama  Yoshihito Okitsu  Hajime Sakai  Yoji Fujiki 《Estuarine, Coastal and Shelf Science》2010,86(3):434-440

The objective of this study is to elucidate the burrow structure and to clarify the role of burrows in material cycle in the tidal flat. In our work, we focused on the dominant species in muddy tidal flat, crab Macrophthalmus japonicus.Burrow structure of Macrophthalmus japonicus was investigated on a Katsuura river tidal flat in Tokushima prefecture, Japan, using in situ resin casting. Sampling was conducted in August 2006, and a total of 48 burrow casts were obtained. Burrows consisted mainly of J-shaped structures (98%) while the rest belonged to U-shaped structures (2%). The maximum measured burrow volume was 120 cm³ and wall surface area was 224 cm², while maximum burrow length and depth were 23.2 cm and 16.5 cm, respectively. Burrow volume and surface area were strongly correlated with carapace width of M. japonicus. Investigation of the individual number of M. japonicus in 13 quadrats (50 × 50 × 20 cm) was conducted using 2 mm sieve. The number of M. japonicus was 15–31 ind./m². Using cohort analysis we estimated that surface area of burrows was 0.07–0.15 m²/m².CO₂ emission rate was measured at the surface sediment during the period from June to December 2008. Results varied from 13.8 ± 2.2 to 49.4 ± 3.2 mg CO₂/m²/h, and organic carbon decomposition was 3.8 ± 0.6–13.5 ± 0.9 mg C/m²/h. This leads the increase of organic carbon decomposition by 1.1 times, because of the expansion of the tidal flat surface area by burrowing activity. Organic carbon decomposition in burrow walls therefore contributed to organic matter decomposition in the tidal flat. These results indicated that in situ activities of Macrophthalmus japonicus significantly influence the material cycle and it is important to consider the existence of burrow in order to understand the fluxes of materials and to evaluate the purification function of the tidal flat.  相似文献   

Melting of iron–silicon alloy up to the core–mantle boundary pressure: implications to the thermal structure of the Earth’s core     

Hidetoshi Asanuma  Eiji Ohtani  Takeshi Sakai  Hidenori Terasaki  Seiji Kamada  Tadashi Kondo  Takumi Kikegawa 《Physics and Chemistry of Minerals》2010,37(6):353-359

The melting temperature of Fe–18 wt% Si alloy was determined up to 119 GPa based on a change of laser heating efficiency and the texture of the recovered samples in the laser-heated diamond anvil cell experiments. We have also investigated the subsolidus phase relations of Fe–18 wt% Si alloy by the in-situ X-ray diffraction method and confirmed that the bcc phase is stable at least up to 57 GPa and high temperature. The melting curve of the alloy was fitted by the Simon’s equation, P(GPa)/a = (T _m(K)/T ₀) ^c , with parameters, T ₀ = 1,473 K, a = 3.5 ± 1.1 GPa, and c = 4.5 ± 0.4. The melting temperature of bcc Fe–18 wt% Si alloy is comparable with that of pure iron in the pressure range of this work. The melting temperature of Fe–18 wt% Si alloy is estimated to be 3,300–3,500 K at 135 GPa, and 4,000–4,200 K at around 330 GPa, which may provide the lower bound of the temperatures at the core–mantle boundary and the inner core–outer core boundary if the light element in the core is silicon.  相似文献   

Simple monitoring method for precaution of landslides watching tilting and water contents on slopes surface   总被引：2，自引：2，他引：0  

Taro Uchimura  Ikuo Towhata  Trinh Thi Lan Anh  Jou Fukuda  Carlos J. B. Bautista  Lin Wang  Ichiro Seko  Taro Uchida  Akira Matsuoka  Yosuke Ito  Yuichi Onda  Sho Iwagami  Min-Seok Kim  Naoki Sakai 《Landslides》2010,7(3):351-357

A low-cost and simple monitoring method for early warning of landslides is proposed. To detect abnormal deformation of a slope, this method employs a tilt sensor in place of an extensometer on the slope surface. In order to examine the relevance of measuring rotation angle on a slope surface by tilt sensor, model tests were conducted, and rotation on the slope surface was observed together with slide displacement along the surface. The rotation data responded 30 min before failure in a model test, which could be useful as a signal for early warning. However, the behavior of rotation before failure varies from case to case, and thus, criteria to issue warning should be defined more carefully. For a model slope made of uniform loose sand, measurement of slide displacement along the slope surface is sensitive to failure at the toe, while the measurement of rotation on the slope surface is useful to detect the development of progressive failure upward along the slope. Wireless sensor units with microelectromechanical systems (MEMS) tilt sensor and volumetric water content sensor were also examined on a real slope in Kobe City, and a long-term monitoring was attempted. A simple but possible way to define the criteria of judgment to issue warning can be proposed based on combination of data obtained by the tilt sensors and volumetric water content sensors.  相似文献   

Zonal distribution of oxygen isotope ratios in the Hiroshima granite complex,Southwest Japan     

H. Honma  H. Sakai 《Lithos》1976,9(3):173-178

¹⁸O/¹⁶O ratios have been obtained for 99 minerals from rocks of the Hiroshima granite complex and adjacent Ryoke granites. Zonal distribution of oxygen isotopes is observed on a regional scale almost parallel to the extension of the Ryoke plutono-metamorphic belt, granites in or around the metamorphic belt being 2–3%₀ richer in ¹⁸O than those farther away from the belt. Isotopic fractionations among coexisting minerals indicate that isotopic zonation existed at a magmatic stage. The zonal enrichment of ¹⁸O in the granite magma in the Ryoke belt and its periphery is a result of isotopic interaction between country rocks and the magma through fluid media. Genetic relationship between granites of the Ryoke and Chugoku belts are discussed with regard to the geological situation of the former belt.  相似文献   

Oxygen isotopic study of the Cretaceous granitic rocks in Japan     

Y. Matsuhisa  H. Honma  O. Matsubaya  H. Sakai 《Contributions to Mineralogy and Petrology》1972,37(1):65-74

The ( ¹⁸O values of nine Cretaceous granitic rocks from the low P/T type regional metamorphic zone of Japan are +10.0 to +13.2 relative to SMOW, while ten Cretaceous granitic rocks from the non-metamorphic zone are +7.9 to +9.8. The ¹⁸O-enrichment in the former rocks is mainly attributed to oxygen isotopic exchange between the granitic magma and the surrounding metamorphic rocks during regional metamorphism. The assimilation of ¹⁸O-rich country rocks is also possible in the cases such as gneissose granite and migmatite.The oxygen isotopic ratios of quartz-biotite pairs in the granitic rocks indicate that they are isotopically in near-equilibrium with each other. The quartz-biotite isotopic equilibrium temperatures estimated for these rocks range from 550° to 670° C. Feldspar is occasionally isotopically in disequilibrium with other minerals. This may be caused by exchange of oxygen isotopes between feldspar and hydrothermal or meteoric water after crystallization.  相似文献   

Non‐iterative time integration scheme for non‐linear dynamic FEM analysis     

Riki Honda  Hisakazu Sakai  Sumio Sawada 《地震工程与结构动力学》2004,33(1):111-132

This paper proposes a non‐iterative time integration (NITI) scheme for non‐linear dynamic FEM analysis. The NITI scheme is constructed by combining explicit and implicit schemes, taking advantage of their merits, and enables stable computation without an iteration process for convergence even when used for non‐linear dynamic problems. Formulation of the NITI scheme is presented and its stability is studied. Although the NITI scheme is not unconditionally stable when applied to non‐linear problems, it is stable in most cases unless stiffness hardening occurs or the problem has a large velocity‐dependent term. The NITI scheme is applied to dynamic analysis of the non‐linear soil–structure system and computation results are compared with those by the central difference method (CDM). Comparison shows that the stability of the NITI scheme is superior to that of the CDM. Accuracy of the NITI scheme is verified because its results are identical with those by the CDM in which the time step is set as 1/10 of that for the NITI scheme. The application of the NITI scheme to the mesh‐partitioned FEM is also proposed. It is applied to dynamic analysis of the linear soil–structure system. It yields the same results as a conventional single‐domain FEM analysis using the Newmark β method. This result verifies the usability of mesh‐partitioned FEM analysis using the NITI scheme. Copyright © 2003 John Wiley& Sons, Ltd.  相似文献   

Geology of the summit limestone of Mount Qomolangma (Everest) and cooling history of the Yellow Band under the Qomolangma detachment     

Harutaka  Sakai  Minoru  Sawada  Yutaka  Takigami  Yuji  Orihashi  Tohru  Danhara  Hideki  Iwano  Yoshihiro  Kuwahara  Qi  Dong  Huawei  Cai  Jianguo  Li 《Island Arc》2005,14(4):297-310

Abstract   Newly discovered peloidal limestone from the summit of Mount Qomolangma (Mount Everest) contains skeletal fragments of trilobites, ostracods and crinoids. They are small pebble-sized debris interbedded in micritic bedded limestone of the Qomolangma Formation, and are interpreted to have been derived from a bank margin and redeposited in peri-platform environments. An exposure of the Qomolangma detachment at the base of the first step (8520 m), on the northern slope of Mount Qomolangma was also found. Non-metamorphosed, strongly fractured Ordovician limestone is separated from underlying metamorphosed Yellow Band by a sharp fault with a breccia zone. The ⁴⁰Ar–³⁹Ar ages of muscovite from the Yellow Band show two-phase metamorphic events of approximately 33.3 and 24.5 Ma. The older age represents the peak of a Barrovian-type Eo-Himalayan metamorphic event and the younger age records a decompressional high-temperature Neo-Himalayan metamorphic event. A muscovite whole-rock ⁸⁷Rb–⁸⁶Sr isochron of the Yellow Band yielded 40.06 ± 0.81 Ma, which suggests a Pre-Himalayan metamorphism, probably caused by tectonic stacking of the Tibetan Tethys sediments in the leading margin of the Indian subcontinent. Zircon and apatite grains, separated from the Yellow Band, gave pooled fission-track ages of 14.4 ± 0.9 and 14.4 ± 1.4 Ma, respectively. These new chronologic data indicate rapid cooling of the hanging wall of the Qomolangma detachment from approximately 350°C to 130°C during a short period (15.5–14.4 Ma).  相似文献   

Fault system of the 2004 Mid Niigata Prefecture Earthquake and its aftershocks     

Naoshi Hirata  Hiroshi Sato  Shin’ichi Sakai  Aitaro Kato  Eiji Kurashimo 《Landslides》2005,2(2):153-157

Data recorded by a seismic network deployed the day after the 2004 Mid Niigata Prefecture Earthquake (M6.8) in central Japan are used to determine the major source faults responsible for the mainshock and major aftershocks. Using this high-resolution seismic data, three major source faults are identified: two parallel faults dipping steeply to the west located 5 km apart, and the other dipping eastward and oriented perpendicular to the west-dipping faults. The analysis also reveals that the lateral variation in seismic velocity observed at the surface extends to a depth of 15 km, encompassing the source area of the mainshock. This strong heterogeneity of the crust, related to the complex geological and tectonic evolution of the area, is considered to be responsible for the prominent aftershock activity following the 2004 Niigata event.  相似文献