Zinc-rich Pyrite from the TAG Active Mound, the TAG Hydrotherma Field, Mid-Atlantic Ridge     

Su Young Lee    Masatsugu Ohnishi    Yasuhiro Shibata    Makoto Wwatanabe    Kenichi Hoshino    Mayumi Jige    Xiangping Gu  Hitoshi Chiba  Tamotsu Oomori    Kantaro Fujioka  Peter A. Rona 《Resource Geology》2001,51(1):63-68

Abstract: Pyrite rich in Zn, up to 3.1 wt%, was found in the TAG active mound of the TAG hydrothermal field, the slow-spreading Mid-Atlantic Ridge at 26°08'N and 44°49'W. The Zn-rich pyrite is characterized by an optical homogeneity, a homogeneous distribution of Zn in the back-scattered electron images, both at a magnification of about 500, a negative correlation between Fe and Zn contents of the pyrite and a rather small unit cell edge (a₀ = 5.4117 ± 0.0008Å), strongly indicating that the detected Zn is present in the pyrite in solid solution. Such Zn concentrations are observed exclusively in dendritic pyrite, suggesting that the Znrich pyrite grew from hydrothermal fluids of a high degree of supersaturation due to quenching on the seafloor.  相似文献   

New radiolarian ages from the Troodos ophiolite and their tectonic implications   总被引：3，自引：0，他引：3  

Soichi  Osozawa Makoto  Okamura 《Island Arc》1993,2(1):1-6

Abstract Newly obtained radiolarian biostratigraphic age combined with previous isotopic age of the Troodos ophiolite shows that the ophiolite becomes systematically younger from east to west: Turonian, early Campanian, and late Campanian. The youngest late Campanian part of the ophiolite is directly covered by the volcaniclastic sediment derived from an active island arc, whereas the older part is covered by pelagic radiolarite. These facts constitute evidence that the Troodos ophiolite was probably emplaced during the subduction of an active spreading ridge.  相似文献   

Chemical composition and rare gas content of four new detected antarctic meteorites     

Makoto Shima  Masako Shima  H. Hintenberger 《Earth and Planetary Science Letters》1973,19(2):246-249

Within a region of 5 km × 10 km on a downhill slope of the Yamato Mounties, in 1969 the Japanese Expedition Team collected many stones. 9 of them were recognized as meteorites. On 4 of these findings we determined the chemical composition and the rare gas content. According to the mineralogical and the chemical composition, Yamato (a) is an enstatite chondrite, Yamato (b) a Ca-poor achondrite, Yamato (c) seems to be a carbonations chondrite Type III and Yamato (d) a olivine bronzite chondrite. Exposure ages are 1.7, 31, 25 and 4.3 my respectively.  相似文献   

Wide-Field Camera for Gravitational Microlensing Survey: MOA-cam2     

Toshifumi Yanagisawa  Yasushi Muraki  Yutaka Matsubara  Fumio Abe  Kimiaki Masuda  Sachiyo Noda  Takahiro Sumi  Yuji Kato  Mitsuaki Fujimoto  Shuji Sato  Ian Bond  Nicholas Rattenbury  Philip Yock  Pam Kilmartin  John Hearnshaw  Micheal Reid  Denis Sullivan  Brian Carter  Richard Dodd  Garry Nankivell  Noiman Rumsey  Morihiro Honda  Maki Sekiguchi  Masanori Yoshizawa  Takashi Nakamura  Humitaka Sato  Seiji Kabe  Makoto Kobayashi  Yoshiyuki Watase  Jun Jugaku  Toshiharu Saito  Barbel Koribalsky 《Experimental Astronomy》2000,10(4):519-535

We have constructed a large, mosaic CCD camera called MOA-cam2 which has 4096 × 6144-pixelsto search for gravitational microlensing events. MOA-cam2 has three4096 × 2048-pixel SITe CCD chips, which have a very high quantum efficiency (nearly 80% in the wave region 500 to 800 nm),and three buttable sides. We have placed the threechips side by side with 100 m dead space. MOA-cam2 has been installed on the 61 cm Boller and Chivens telescope of the MOA collaboration at the Mt. John University Observatory (MJUO) in NewZealand since July 1998. The field coverage is 0.92° × 1.38° per exposure. The technical details of MOA-cam2 and the first images obtained with the Boller and Chivens telescope are presented. MOA-cam2 introduces a second phase of research on gravitational microlensing by the MOA collaboration.  相似文献   

Age model, physical properties and paleoceanographic implications of the middle Pleistocene core sediments in the Choshi area, central Japan     

Koji  Kameo  Makoto  Okada  Moamen  El-Masry  Toshio  Hisamitsu  Saneatsu  Saito  Hiroomi  Nakazato  Naohiko  Ohkouchi  Minoru  Ikehara  Hisato  Yasuda  Hiroshi  Kitazato  Asahiko  Taira 《Island Arc》2006,15(3):366-377

Abstract   A continuous, well-preserved core was obtained from the Choshi area, on the Pacific side of Japan, to investigate paleoceanographic and paleoclimatic changes around the northwestern Pacific region during the middle Pleistocene. Siliciclastic sequences in the core are divided into five formations – the Obama, Yokone, Kurahashi and Toyosato Formations in the Inubo Group and the Katori Formation, in ascending order. Examination of calcareous nannofossils and magnetic polarities detected four datums in the core sediments of the Inubo Group: the top of Reticulofenestra asanoi , the base of Helicosphaera inversa , the top of Pseudoemiliania lacunosa and the Brunhes–Matuyama boundary. Fourteen marine isotope stages (MIS24–MIS11) were identified in the δ¹⁸O and δ¹³C records based on detected datums and the graphic correlation with the standard stack oxygen isotope curve. Magnetic susceptibility and gamma-ray attenuation porosity evaluator density were also measured and low values characterize the glacial intervals. Biogenic sedimentation by primary production may be larger during the glacial periods because of invasions of nutrient-rich northern surface-waters related to the southward shift of the Kuroshio front in the Choshi area.  相似文献   

Floral changes in calcareous nannofossils and their paleoceanographic significance in the equatorial Pacific Ocean during the last 500 000 years     

Shun  Chiyonobu  Tokiyuki  Sato  Reika  Narikiyo  Makoto  Yamasaki 《Island Arc》2006,15(4):476-482

Abstract   The late Quaternary calcareous nannofossil assemblages from Ocean Drilling Program Holes 807A and 846B, located in the western and eastern equatorial Pacific Ocean, respectively, were analyzed to clarify changes in surface-water conditions during the last 500 000 years. The uppermost Quaternary sediments in both holes contain abundant nannofossils, and their assemblages are characterized by high species diversity. The absolute abundances of coccoliths (specimens/g) and relative numbers of small reticulofenestrids decreased drastically in both holes between 0.3 and 0.2 Ma, whereas the relative abundance of warm-water species and Florisphaera profunda increased suddenly at this time. These data indicate that upwelling around the western and eastern equatorial Pacific regions weakened after 0.2 Ma, which was caused by a decrease in trade-wind strength.  相似文献   

Performance of a lithium fluoride bolometer for Tokyo dark matter search experiment     

Wataru Ootani  Makoto Minowa  Takayuki Watanabe  Yutaka Ito  Yasuhiro Kishimoto  Kentaro Miuchi  Yoshizumi Inoue  Youiti Ootuka 《Astroparticle Physics》1998,9(4):325-329

The performance of a 21-g lithium fluoride bolometer is presented. The background spectrum was measured in the surface laboratory. We derive an exclusion plot for the spin-dependent coupled Weakly Interacting Massive Particles (WIMPs) cross section.  相似文献   

Ca, Al-rich inclusions in Yamato 791717 (CO3) carbonaceous chondrite: Formation and alteration     

Yangting Lin  Daode Wang  Makoto Kimura 《中国科学D辑(英文版)》1998,41(5):513-521

In three polished thin sections of Yamato 791717 (CO3). fifty-five Ca, Al-rich inclusions were found, which include two hibonite-bearing, eight melilite-rich and forty-five spinel-pyroxene inclusions. Based on the petrography and mineral chemistry of the inclusions, it is proposed that the melilite-rich inclusions and spinel-pyroxene inclusions condensed in the solar nebula, and the hibonite-bearing inclusions crystallized from melts. The heavy alteration of the inclusions in Yamato 791717, which probably took place under a very oxidizing condition in the solar nebular, is also confirmed. Project supported by the National Natural Science Foundation of China (Grant No. 49673200). and by the Japanese Society for Promotion of Sciences (JSPS).  相似文献   

Introduction to the special volume on the Izu–Bonin – Mariana arc system     

Robert J. Stern  & Makoto Arima 《Island Arc》1998,7(3):295-300

  相似文献   

Characteristics of 3-dimensional earthquake ground motions     

Joseph Penzien  Makoto Watabe 《地震工程与结构动力学》1974,3(4):365-373

An orthogonal set of principal axes is defined for earthquake ground motions along which the component variances have maximum, minimum and intermediate values and the covariances equal zero. Corresponding axes are defined which yield maximum values for the covariances. The orthogonal transformations involved are identical in form to those used in the transformation of stress. Examination of real accelerograms reveals that the major principal axis points in the general direction of the epicentre and the minor principal axis is nearly vertical. It is concluded that artificially generated components of ground motion need not be correlated statistically provided they are directed along a set of principal axes.  相似文献