Chemical variations of magmas at Izu-Oshima volcano,Japan: plagioclase-controlled and differentiated magmas     

Shun Nakano  Takahiro Yamamoto 《Bulletin of Volcanology》1991,53(2):112-120

Systematic analyses of the major-element chemistry of products of several eruptions during syn-and post-caldera stages of Izu-Oshima volcano were compiled. Comparisons of the products of large-scale eruptions in 1338?, 1421? and 1777–1778, of intermediate-scale eruptions in 1950–1951 and 1986, and of small-scale eruptions in 1954, 1964 and 1974 clearly show the existence of two types of magmas. One is “plagioclase-controlled” and the other is “differentiated” magma (multimineral-controlled); i.e. the bulk chemistry of the first magma type is controlled by plagioclase addition or removal, while that of the second type is controlled by fractionation of plagioclase, orthopyroxene, clinopyroxene, and titanomagnetite. Eruptions of Izu-Oshima volcano have occurred at the summit and along the flanks. Summit eruptions tap only plagioclase-controlled magmas, while flank eruptions supply both magma types. It is considered unlikely that both magma types would coexist in the same magma chamber based on the petrology. In the case of the 1986 eruption, the flank magma was isolated sometime in the past from the summit magma chamber or central conduit, and formed small magma pockets, where further differentiation occurred due to relatively rapid cooling. In a period of quiescence prior to the 1986 eruption, new magma was supplied to the summit magma chamber, and the summit eruption began. The dike intrusion or fracturing around the small magma pockets triggered the flank eruption of the differentiated magma. This model can be applied to the large-scale flank eruption in 1338(?) which erupted differentiated magmas. In 1421(?), the flank eruption tapped plagioclase-controlled magma. In this case, the isolated magmas from the summit magma chamber directly penetrated the flank without differentiation.  相似文献   

Rejuvenated-stage volcanism after 0.6-m.y. quiescence at West Maui volcano, Hawaii: new evidence from K–Ar ages and chemistry of Lahaina Volcanics     

Takahiro Tagami  Yoshitomo Nishimitsu  David R. Sherrod   《Journal of Volcanology and Geothermal Research》2003,120(3-4):207-214

West Maui’s rejuvenated-stage Lahaina Volcanics were erupted from four discrete sites. New K–Ar ages indicate two pulses of volcanism, the older about 0.6 Ma and the younger about 0.4 Ma. Compositionally the lava flows are entirely basanitic, but each pulse is diverse. The underlying postshield-stage Honolua Volcanics were emplaced by about 1.2 Ma on the basis of previously published ages. Therefore the duration of volcanic quiescence prior to rejuvenation is about 0.6 m.y. at West Maui, much longer than estimated previously.  相似文献   

Accuracy assessment of QuickBird stereo imagery   总被引：2，自引：0，他引：2  

Mayumi Noguchi  Clive S. Fraser  Takayuki Nakamura  Takahiro  Shimono  Shoichi Oki 《The Photogrammetric Record》2004,19(106):128-137

The Geographical Survey Institute of Japan has recently carried out an evaluation of the metric performance of QuickBird stereo satellite imagery. This paper describes the accuracy assessment of the sensor orientation and geopositioning phases of the study, the aim of which was twofold. First, it was desired to confirm the metric potential of QuickBird imagery for 1:25 000 scale topographic mapping. Second, a determination was to be made of the accuracy attainable from the Basic image product. The techniques of rational functions and affine bundle adjustment were employed, the former with bias compensation. The results obtained both reassert the high precision of the rational functions approach and cast doubt upon the applicability of the 3D affine model for accurate geopositioning from QuickBird imagery.  相似文献   

Late cretaceous to early paleogene paleomagnetic results from Sikhote Alin, far eastern Russia: implications for deformation of East Asia   总被引：1，自引：0，他引：1  

Yo-ichiro Otofuji  Takaaki Matsuda  Tetsumaru Itaya  Takeshi Shibata  Michiko Matsumoto  Takahiro Yamamoto  Chiyo Morimoto  Ruslan G. Kulinich  Petr S. Zimin  Anatoly P. Matunin  Vladimir G. Sakhno  Katsuhiro Kimura 《Earth and Planetary Science Letters》1995,130(1-4):95-108

Welded tuffs in the Bogopol and Sijanov groups were sampled at 27 sites from 12 caldera formations in the Sikhote Alin mountain range around Kavalerovo (44.3°N, 135.0°E) for chronological and paleomagnetic studies. KAr age dates show that the welded tuffs erupted between 66 Ma and 46 Ma. All sites yield reliable paleomagnetic directions, with unblocking temperatures higher than 560°C. The high-temperature component at 12 sites and the medium-temperature component at 3 sites in the Bogopol Group show reversed polarity (D = 193.7°, I = −57.6°,₉₅ = 8.1°). The high-temperature component at 11 sites in the Sijanov Group showed both reversed and normal polarities and its mean direction reveals no detectable deflection from north (D = −2.9°, I = 59.6°,₉₅ = 11.2°). The combined paleomagnetic direction of the two groups yields a paleomagnetic pole of 250.5°E, 84.1°N (A₉₅ = 8.8°), which falls near Cretaceous paleomagnetic poles from Outer Mongolia, Inner Mongolia, the North China Block and the South China Block. The Sikhote Alin area appears not to have been subjected to detectable motion with respect to East Asia since about 50 Ma. This implies that the Sikhote Alin area behaved as an integral part of East Asia during the opening of the Japan Sea at about 15 Ma. However, significant separation between the paleomagnetic poles of East Asia and Europe during the Jurassic-Paleogene implies a major relative movement between these two blocks since the Paleogene.  相似文献   

Numerical Study of Formation of Dichothermal Water in the Bering Sea     

Takahiro Miura  Toshio Suga  Kimio Hanawa 《Journal of Oceanography》2003,59(3):369-376

A one-dimensional numerical model with a level-2.5 turbulent closure scheme to provide vertical mixing coefficients has been used to investigate the process by which the dichothermal water is formed in the Bering Sea, the density of which is about 26.6 sigma-theta. The water column to be simulated is assumed to move along a predetermined path. That is, the present model is of the Lagrangian-type. Surface boundary conditions are given using the climatologies of heat, freshwater and momentum fluxes. In order to obtain a plausible moving speed of the water column along the path, pre-liminary experiments were done using the surface fluxes in the central part of the Bering Sea for the initial temperature and salinity profiles at the entrance of the Sea. As a result, it was found that the temperature minimum layer, i.e., the dichothermal water with temperature similar to the climatology at the exit of the Bering Sea, was formed after about two years of integration. Based on the result, the movement speed of the water column along the path was set as 4.5 cm/s in the standard run. It was found that this model could plausibly reproduce the subsurface temperature minimum layer. That is, the dichothermal water was formed in the winter mixed layer process in the Bering Sea. The existence of the subsurface halocline (pycnocline) prohibited the deeper penetration of the winter mixed layer, and therefore water with a temperature colder than that under the mixed layer was formed in the mixed layer due to wintertime surface cooling. In the warming season this water remains as the subsurface temperature minimum layer between the upper seasonal thermocline and the lower halocline. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Reliability of ADCP data detided with a numerical model on the East China Sea shelf   总被引：2，自引：0，他引：2  

Atsuhiko Isobe  Takahiro Kuramitsu  Hirotaka Nozaki  Pil-Hun Chang 《Journal of Oceanography》2007,63(1):135-141

The reliability of a numerical tide model for detiding acoustic Doppler current profiler (ADCP) data is examined on the East China Sea shelf. The process is adopted for the ADCP data obtained on 12–13 May 2003. The ocean model accompanied by the most precise harmonic constants available to public is used to compute external tides. The root mean square difference is less than 10 cm/s between the detided currents and those using the least squares method, and so the detiding process using the numerical model is available to detect the East China Sea shelf circulation faster than this speed.  相似文献   

Winter Mixed Layer and Formation of Dichothermal Water in the Bering Sea     

Takahiro Miura  Toshio Suga  Kimio Hanawa 《Journal of Oceanography》2002,58(6):815-823

The temperature minimum layer, called “dichothermal water”, is a characteristic feature of the North Pacific subarctic gyre. In particular, dichothermal water having a density of approximately 26.6 sigma-theta (σ_θ), which corresponds to the densest water outcropping in winter in the North Pacific, is seen in the Bering Sea. In order to clarify the water properties, and the area in which and the process by which the dichothermal water is formed, a new seasonal mean gridded climatological dataset with a fine resolution for the Bering Sea and adjacent seas has been prepared using historically accumulated hydrographic data. Although the waters of the Alaskan Stream have temperature minimum layers, their temperature inversions are very weak in climatologies and the core densities of the temperature minimum layers are much lighter than 26.6σ_θ. On the other hand, in the Bering Sea one can see the robust structure of temperature minimum layers, the core density of the dichothermal water being around 26.6σ_θ. In addition, it has been found that the properties of the dichothermal water observed in the warming season are almost the same as those in the winter mixed layer. That is, the dichothermal waters are formed in the winter mixed layer in the Bering Sea. Since these waters are found in the Kamchatka Strait, i.e., the main exit of the Bering Sea waters, it can be supposed that the dichothermal waters are exported from the Bering Sea to the Pacific Ocean by the Kamchatka Current. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Twin formation in hematite during dehydration of goethite     

Genki Saito  Yuji Kunisada  Takahiro Nomura  Norihito Sakaguchi  Tomohiro Akiyama 《Physics and Chemistry of Minerals》2016,43(10):749-757

Twin formation in hematite during dehydration was investigated using X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy (TEM). When synthetic goethite was heated at different temperatures between 100 and 800 °C, a phase transformation occurred at temperatures above 250 °C. The electron diffraction patterns showed that the single-crystalline goethite with a growth direction of [001]_G was transformed into hematite with a growth direction of [100]_H. Two non-equivalent structures emerged in hematite after dehydration, with twin boundaries at the interface between the two variants. As the temperature was increased, crystal growth occurred. At 800 °C, the majority of the twin boundaries disappeared; however, some hematite particles remained in the twinned variant. The electron diffraction patterns and high-resolution TEM observations indicated that the twin boundaries consisted of crystallographically equivalent prismatic (100) (010), and (1\(\bar{1}\)0) planes. According to the total energy calculations based on spin-polarized density functional theory, the twin boundary of prismatic (100) screw had small interfacial energy (0.24 J/m²). Owing to this low interfacial energy, the prismatic (100) screw interface remained after higher-temperature treatment at 800 °C.  相似文献   

Data assimilation of sea ice concentration into a global ocean–sea ice model with corrections for atmospheric forcing and ocean temperature fields     

Takahiro Toyoda  Yosuke Fujii  Tamaki Yasuda  Norihisa Usui  Koji Ogawa  Tsurane Kuragano  Hiroyuki Tsujino  Masafumi Kamachi 《Journal of Oceanography》2016,72(2):235-262

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Cordilleran-type orogeny and episodic growth of continents: Insights from the circum-Pacific continental margins     

Takahiro Tagami  & Noriko Hasebe 《Island Arc》1999,8(2):206-217

A new material migration hypothesis for the plate subduction zone orogeny, so-called ‘the cordilleran-type orogeny’, is proposed on the basis of geological constraints as well as mechanics of accretionary wedges. The major tectonic processes of the hypothesis comprise: (i) episodic, extensive magmatism along the margin of an overriding plate; (ii) supply of voluminous igneous and eroded materials through forearc to trench, with an increase in the net sediment influx into trench; (iii) accelerated accretion of sediments beneath an overriding older accretionary wedge; and (iv) upward material migration within the wedge and resultant exhumation of high-P/T metamorphic rocks near the inland margin of the wedge. This hypothesis was validated by the test using available geo- and thermo-chronological data from two classical types of subduction-related orogens in Southwest Japan and California. The hypothesis, coupled with the thermochronologic point of view, requires the reconsideration of coevality of paired metamorphism. The temporal pairing is to be observed between the beginning of the regional high-T/P metamorphism and that of the uplift and exhumation of high-P/T metamorphism, with some time lag needed for material migration. Where the temporal pairing is examined therefore, the formation age of igneous rocks and related high-T/P metamorphic rocks should be compared to the exhumation age of high-P/T metamorphic rocks. The episodic, extensive magmatism that triggers the cordilleran-type orogeny shows a temporal correlation in the mid-Cretaceous for most circum-Pacific continental margins. The resultant widespread formation of accretionary complexes is also observed in the western part of the circum-Pacific margins. The deduced mid-Cretaceous circum-Pacific orogeny accompanied a gross increase in the continental crust production rate, and was approximately coeval with the Pangea breakup and the Central Pacific superplume episode, implying the orogeny as a part of the mid-Cretaceous pulsation of the Earth.  相似文献