Geochemical Characteristics of Apatite in Heavy REE‐rich Deep‐Sea Mud from Minami‐Torishima Area,Southeastern Japan     

Yoshiaki Kon  Mihoko Hoshino  Kenzo Sanematsu  Sayaka Morita  Maiko Tsunematsu  Nobuyuki Okamoto  Nobuhiko Yano  Mikiya Tanaka  Tetsuichi Takagi 《Resource Geology》2014,64(1):47-57

We have conducted geochemical and mineralogical investigations of the rare earth and yttrium (REY)‐rich mud from the Minami‐Torishima area in the Pacific in order to clarify the concentration of REY and their host‐phase in the mud. X‐ray diffraction analysis shows that the mud is mainly composed of phillipsite, fluorapatite, quartz, albite, illite and montmorillonite. Whole‐rock CaO, P₂O₅ and total REY contents of the mud are positively correlated. Relative abundance of apatite is also positively correlated to P₂O₅ and total REY contents. These correlations suggest that apatite is the main host of the P₂O₅ and REY in the mud. We make in situ compositional analyses of constituent minerals in the REY mud. The results show that the apatite is abundant in REY (9300–32,000 ppm) and is characterized by a negative Ce anomaly and enrichment in heavy rare‐earth elements. This abundance and composition of REY of the mud is similar those of fish debris apatites. In contrast, phillipsite is less abundant in REY (60–170 ppm). Therefore we conclude that the main REY host phase of the mud is apatite.  相似文献   

Evolutionary spectral energy distribution diagnostics of starburst galaxies: signature of bimodality     

T. Takagi  N. Arimoto  H. Hanami 《Monthly notices of the Royal Astronomical Society》2003,340(3):813-831

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The SCUBA HAlf Degree Extragalactic Survey (SHADES) – V. Submillimetre properties of near-infrared-selected galaxies in the Subaru/XMM–Newton deep field     

T. Takagi  A. M. J. Mortier  K. Shimasaku  K. Coppin  A. Pope  R. J. Ivison  H. Hanami  S. Serjeant  D. L. Clements  R. S. Priddey  J. S. Dunlop  T. Takata  I. Aretxaga  S. C. Chapman  S. A. Eales  D. Farrah  G. L. Granato  M. Halpern  D. H. Hughes  E. van Kampen  D. Scott  K. Sekiguchi  I. Smail  M. Vaccari 《Monthly notices of the Royal Astronomical Society》2007,381(3):1154-1168

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Chemical overprinting of magmatism by weathering: A practical method for evaluating the degree of chemical weathering of granitoids     

Atsushi Kamei  Keisuke Fukushi  Tetsuichi Takagi  Hitoshi Tsukamoto 《Applied Geochemistry》2012

Quantitative determination of the degree of chemical weathering of rocks is a fundamental task in environmental and engineering geology, and many weathering indices based on whole-rock chemistry have been proposed. However, most classical indices are of limited application to granitoids in a wide area, because these lithotypes generally exhibit wide chemical variation arising from their petrogenesis. The chemical evolution produced during rock weathering, therefore, overprints pre-existing magmatic chemical variation. This problem can cause many classical weathering indices to yield misleading results. This study proposes a method that compensates for the influence of petrogenesis on calculation of the weathering index. The method is based on a bivariate plot of the magmatic chemical variation (MCV) in granitoids, and the degree of chemical weathering (DCW). The MCV axis must be based on an element that reflects magmatic processes and is also relatively immobile during rock weathering. In this study TiO₂ contents are utilized for the MCV. The DCW axis is fundamentally defined by the ratios of more-mobile to less-mobile elements during weathering, and hence many classical indices can be applied. The improved value of the degree of chemical weathering (DCW_i) for a weathered rock is derived by:where MCV₁ is the measured composition (e.g. TiO₂ content) of the weathered rock. DCW₁ denotes the ratios of more-mobile to less-mobile elements of the weathered rock. The “s” parameter is the slope of the least square linear regression for fresh granitoids in the MCV–DCW relationship. MCV_CV is a correction factor which is given by the average point on the MCV axis (e.g. average TiO₂) of the fresh rocks. This method is useful for evaluating the degree of weathering of various granitoids, and enhances the practical application of many weathering indices.  相似文献   

Characteristics of planetary-scale waves simulated by a new venusian mesosphere and thermosphere general circulation model     

N. Hoshino  H. Fujiwara  M. Takagi  Y. Takahashi  Y. Kasaba 《Icarus》2012,217(2):818-830

We have developed a new general circulation model (GCM) for the venusian mesosphere and thermosphere (80-about 180 km). Our GCM simulations show that winds in the subsolar-to-antisolar direction (SS–AS) are predominant above about 90 km. A weak return flow of the SS–AS is seen below about 90 km. We performed GCM simulations imposing the planetary-scale waves (thermal tides, Rossby wave, and Kelvin wave) at the lower boundary. Although the diurnal and semidiurnal tides are damped below 95 km, the Rossby wave propagates up to around 130 km. However, the amplitude of the Rossby wave is too small (<1 m/s) to affect the general circulation. On the other hand, the Kelvin wave propagates up to about 130 km with a maximum zonal wind fluctuation of approximately 5.9 m/s on average. The amplitude of the Kelvin wave sometimes exceeds 10 m/s around the terminator. The Kelvin wave causes a temporal variation in the wind velocity at the altitude of the O₂-1.27 μm nightglow emission (about 95 km). Using a newly developed 1-D nightglow model and the composition distribution calculated from our GCM, we investigated the impact of the Kelvin wave on the nightglow distribution. Our results suggest that the Kelvin wave would cause temporal variations in the nightglow emission in the 23:50–00:20 LT region with an intensity of 1.1–1.3 MR and a period of approximately 4 days.  相似文献   

Paleomagnetism of mid-Cretaceous red beds in west-central Kyushu Island, southwest Japan: paleoposition of Cretaceous sedimentary basins along the eastern margin of Asia     

Kazuto Kodama  Tetsuichi Takeda 《Earth and Planetary Science Letters》2002,201(1):233-246

A paleomagnetic study was carried out on the mid-Cretaceous sedimentary strata in west-central Kyushu Island, southwest Japan, to elucidate the origin of sedimentary basins along the Asian continental margin in the Cretaceous. We collected paleomagnetic samples from a total of 34 sites of the mid-Cretaceous Goshonoura Group, shallow-marine clastic deposits in west-central Kyushu, and characteristic remanent magnetizations were recognized from 18 horizons of red beds. Thermal demagnetization has revealed that the red beds contain three magnetization components, with low (<240°C), intermediate (240-480°C), and high (480-680°C) unblocking temperatures. The low unblocking temperature component is present-field viscous magnetization, and the intermediate one is interpreted as chemical remanent magnetization carried by maghemite that was presumably formed by post-folding, partial oxidation of detrital magnetite. Rock magnetic and petrographic studies suggest that the high unblocking temperature component resides largely in hematite (martite and pigmentary hematite) and partly in maghemite. Because of the positive fold test, this high temperature component can be regarded as primary, detrital remanent magnetization. The tilt-corrected mean direction of the high temperature component is Dec=65°, Inc=63° with α₉₅=5°, which yields a paleomagnetic pole at 39°N, 186°E and A₉₅=8°. A combination of this pole with those of the Late Cretaceous rocks in southwest Japan defines an apparent polar wander path (APWP), which is featured by a cusp between the Late Cretaceous and the Paleogene. A comparison of this APWP with the coeval paleomagnetic pole from northeast Asia suggests an approximately 50° post-Cretaceous clockwise rotation and 18±8° southward drift with respect to northeast Asia. The southward transport of the Cretaceous basin suggests that the proto-Japanese arc originated north of its present position. We propose that the coast-parallel translation of this landmass was caused by dextral motion of strike-slip faults, which previous geodynamic models interpreted to be sinistral through the Mesozoic. The change in strike-slip motion may have resulted from Mesozoic collision and penetration of exotic terranes, such as the Okhotsk microcontinent, with the northeastern part of Asia.  相似文献   

Double-planed structure of the deep seismic zone in the northeastern Japan arc   总被引：1，自引：0，他引：1  

Akira Hasegawa  Norihito Umino  Akio Takagi 《Tectonophysics》1978,47(1-2)

A double-planed structure of deep seismic zone has been found over a wide area more then 300 km × 200 km in the Tohoku District, the northeastern part of Honshu, Japan. This prominent feature of the configuration of the deep seismic zone has been ascertained through a precise determination of the microearthquake hypocenters by using the data from the seismic network of Tohoku University. The two planes are nearly parallel to each other, the distance between the two planes being from 30 to 40 km.Composite focal mechanism solutions are derived from the superposition of the distribution of first motions of P waves, and the different fault types are obtained for the two groups of earthquakes; the earthquakes which occurred in the upper plane are characterized by reverse faulting, some of them by down-dip compressional stresses, and those in the lower plane by down-dip extensional stresses. The evidence obtained here provides valuable information for the definition of the type of mechanism producing the plate motion beneath the island arc.  相似文献   

Short-period fluctuations in the atmospheric electric field over the ocean     

M. Takagi  N. Toriyama 《Pure and Applied Geophysics》1978,116(6):1089-1100

Fluctuations of short period in the atmospheric electric field were studied through the measurements of electric field and space charge density on the Mid-Pacific Ocean. The amplitude of fluctuation is about one third of the mean electric field, and the period mainly ranges from 2 to 5 min. The fluctuations are considered to be under the influence of spatial and temporal variation of space charge layer that possibly originates from the electrode effect above the sea surface. The unit of electrical irregularities in the atmosphere above the ocean has horizontal scale of the order of 1.5 km and indicates a tendency to become large as the wind speed increases. The vertical scale of space charge layer is estimated at several tens meters.  相似文献   

Segregation freezing as the cause of suction force for ice lens formation     

S. Takagi 《Engineering Geology》1979,13(1-4):93-100

We propose a new freezing mechanism, called segregation freezing, to explain the generation of the suction force that draws pore water up to the freezing surface of a growing ice lens. We derive the segregation freezing temperature by applying thermodynamics to a soil mechanics concept that distinguishes the mechanically effective pressure from the mechanically neutral pressure. The frost-heaving pressure is formulated as part of the solution of the differential equations of the simultaneous flow of heat and water, of which the segregation freezing temperature is one of the boundary conditions.  相似文献   

Cosmic-ray muon-induced ¹²⁹I in tellurium ores     

J. Takagi  W. Hampel  T. Kirsten 《Earth and Planetary Science Letters》1974,24(1):141-150

1.7 × 10⁷yr-lived ¹²⁹I has been positively detected in two natural tellurium ores by activation analysis with the help of low-level sum-coincidence gamma-ray spectrometry. The observed ¹²⁹I concentrations can be explained as induced by muon reactions on ¹³⁰Te. The detection of ¹²⁹I provides for the first time conclusive evidence for the occurrence of natural long-lived muon-induced nuclides. Most of the ¹²⁹Xe and ¹³¹Xe anomalies observed in natural tellurides are best interpreted in terms of reactions induced by muons and their secondary neutrons.  相似文献