High-pressure phase relations in the system CaAl4Si2O11–NaAl3Si3O11 with implication for Na-rich CAS phase in shocked Martian meteorites     

M. Akaogi  M. Haraguchi  K. Nakanishi  H. Ajiro  H. Kojitani 《Earth and Planetary Science Letters》2010,289(3-4):503-508

High-pressure phase relations in the system NaAl₃Si₃O₁₁–CaAl₄Si₂O₁₁ were examined at 13–23 GPa and 1600–1900 °C, using a multianvil apparatus. A Ca-aluminosilicate with CaAl₄Si₂O₁₁ composition, designated CAS phase, is stable above about 13 GPa at 1600 °C. In the system NaAl₃Si₃O₁₁–CaAl₄Si₂O₁₁, the CAS phase dissolving NaAl₃Si₃O₁₁ component coexists with jadeite, corundum and stishovite below 22 GPa, above which the CAS phase coexists with Na-rich calcium ferrite, corundum and stishovite. At 1600 °C, the solubility of NaAl₃Si₃O₁₁ component in the CAS solid solution increases with increasing pressure up to about 50 mol% at about 22 GPa, above which the solubility decreases with pressure. The maximum solubility of NaAl₃Si₃O₁₁ component in the CAS phase increases with temperature up to around 70 mol% at 1900 °C at 22 GPa. The dissociation of NaAlSi₂O₆ jadeite to NaAlSiO₄ calcium ferrite plus stishovite occurs at about 22 GPa. Lattice parameters of the CAS phase with the hexagonal Ba-ferrite structure change with increase of the NaAl₃Si₃O₁₁ component: a-axis decreases and c-axis slightly increases, resulting in decrease of molar volume. Enthalpies of the CAS solid solutions were measured by high-temperature drop-solution calorimetry techniques. The results show that enthalpy of hypothetical NaAl₃Si₃O₁₁ CAS phase is much higher than the mixture of NaAlSi₂O₆ jadeite, corundum and stishovite and is close to that of the mixture of NaAlSiO₄ calcium ferrite, corundum and stishovite. When we adopt the Na:Ca ratio of 75:25 of the natural Na-rich CAS phase in a shocked Martian meteorite, Zagami, the phase relations determined above suggest that the natural CAS phase crystallized from melt at pressure around 22 GPa and temperature close to or higher than 2000–2200 °C. The inferred P, T conditions are consistent with those estimated using other high-pressure minerals in the shocked meteorite.  相似文献   

Bed morphological changes around a finite patch of vegetation          下载免费PDF全文

Hyung Suk Kim  Ichiro Kimura  Yasuyuki Shimizu 《地球表面变化过程与地形》2015,40(3):375-388

For the appropriate management and restoration of rivers, isolated vegetation is often a practical means for improving stream habitat and ecology. The effect of a finite vegetation patch on flow and bed morphology in an open channel was investigated using laboratory experiments. The patch containing emergent and submerged vegetation was modeled using circular cylinders and located mid‐channel along a side wall. Several configurations of the patch and submergence ratio (i.e. water depth to the height of vegetation), and two flow conditions (i.e. below and above the sediment motion threshold) were considered. For flows below the sediment motion threshold, erosion occurred primarily on the opposite side of the patch and near the leading edge of the patch. The degree of scouring depth observed in both these regions was affected by the submergence ratio and it increased with the non‐dimensional flow blockage (i.e. the product of the patch density and width). In contrast, for flows above the sediment motion threshold, sediment accumulated within and around the patch due to a reduction in bed shear stress, which was strongly influenced by the flow blockage and the obstruction ratio (i.e. the ratio of patch width to channel width). The eroded area observed within the patch was consistent with the interior adjustment region where the deceleration and diversion of flow occurred through the patch. As the flow blockage increased or as the obstruction ratio decreased, the deposition rate within and behind the patch decreased. Furthermore, the deposition rate increased with an increase in the ratio of flow rate through the patch to total flow rate regardless of the submergence ratio. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Platinum–Group Minerals in Podiform Chromitite from the Kamuikotan Zone, Hokkaido, Northern Japan     

Shoji ARAI  Hazel M. PRICHARD  Ichiro MATSUMOTO  Peter C. FISHER 《Resource Geology》1999,49(1):39-47

Abstract: Ru–Os–Ir alloys have been found in two podiform chromitites located at the Chiroro and Bankei mines in the Sarugawa peridotite complex in the Kamuikotan zone, Hokkaido, Japan. This is the first report on the occurrence of PGM (= platinum-group minerals) from chromitites in Japan. The Ru–Os–Ir alloys most typically form polyhedra associated with other minerals (Ni–Fe alloys and heazlewoodite) in chromian spinel. The PGM are possibly pseudomorphs after some primary PGM such as laurite and are chemically highly inhomogeneous, indicating a low-temperature alteration origin. This is consistent with intense alteration (formation of serpentine, uvarovite and kämmererite) imposed on the Kamuikotan chromitites. High-temperature primary PGE (platinum–group elements)–bearing sulfides were possibly recrystallized at low temperatures into a new assemblage of PGM, Ni-Fe alloys and sulfides. Placer PGM around the peridotite complexes are chemically different from the PGM in dunite and chromitite possibly due to the, as yet, incomplete search for the rock-hosted PGM. The PGE content in chromitites is distinctly higher in those in the Kamuikotan zone than in those in the Sangun zone of Southwest Japan, consistent with the more refractory nature (Cr# of spinel, up to 0.8) of the former than the latter (Cr# of spinel, 0.5).  相似文献   

Silicate darkening in the Kobe CK chondrite: Evidence for shock metamorphism at high temperature     

Kazushige Tomeoka  Ichiro Ohnishi  Noboru Nakamura 《Meteoritics & planetary science》2001,36(11):1535-1545

Abstract— The Kobe CK4 chondrite, like most metamorphosed CK chondrites, exhibits pronounced silicate darkening of matrix and chondrule mesostases. Our petrographic and scanning electron microscopic study reveals that the matrix of Kobe consists mostly of intermixtures of two types of fine‐grained olivine. One forms subhedral to anhedral normal crystals. The other fills interstices of the subhedral to anhedral olivine crystals, exhibiting a complex network of veinlets. The latter type of olivine contains high densities of small spherical vesicles (<0.05‐3 μm in diameter) and grains (<0.05‐5 μm) of magnetite and pentlandite as well as round to anhedral grains (1–10 μm) of plagioclase, low‐Ca pyroxene, diopside and chlorapatite. The vesicular olivine is particularly abundant in regions of matrix that exhibit a relatively high degree of darkening and commonly fills chondrule mesostases. The vesicular olivine is clearly the principal cause of the silicate darkening in Kobe. The internal texture of the vesicular olivine closely resembles those of local melts produced from the matrices of experimentally and naturally shocked carbonaceous chondrites. The occurrence and texture of the vesicular olivine suggest that it resulted from recrystallization of partially melted matrix olivine by shock. Kobe exhibits light shock effects in olivine that are consistent with shock stage S2 that is too low to explain the occurrence of olivine melting. We suggest that the vesicular olivine in Kobe was produced by shock metamorphism at a relatively mild shock pressure (<25 GPa) and a high temperature (>600 °C). Thus, it is probable that the shock effects in olivine, manifest as fracturing and deformation, were relatively minor, but heating was strong enough to cause partial melting of matrix olivine.  相似文献   

Table of Contents     

Mikio Nakanishi  Hiroshi Niino 《Boundary-Layer Meteorology》2004,112(3):619-620

Volume Contents

Table of Contents  相似文献   

V p/V s-ratios from the central Kolbeinsey Ridge to the Jan Mayen Basin,North Atlantic; implications for lithology,porosity and present-day stress field     

Mjelde  Rolf  Aurvåg  Roar  Kodaira  Shuichi  Shimamura  Hideki  Gunnarsson  Karl  Nakanishi  Ayako  Shiobara  Hajime 《Marine Geophysical Researches》2002,23(2):123-145

The horizontal components from twenty Ocean Bottom Seismometers deployed along three profiles near the Kolbeinsey Ridge, North Atlantic, have been modelled with regard to S-waves, based on P-wave models obtained earlier. Two profiles were acquired parallel to the ridge, and the third profile extended eastwards across the continental Jan Mayen Basin. The modelling requires a thin (few 100 m) layer with very high V _p/V _s-ratio (3.5–9.5) at the sea-floor in the area lacking sedimentary cover. The obtained V _p/V _s-ratios for the remaining part of layer 2A, 2B, 3 and upper mantle, correspond to the following lithologies: pillow lavas, sheeted dykes, gabbro and peridotite, respectively. All crustal layers exhibit a decreasing trend in V _p/V _s-ratio away-from-the-axis, interpreted as decreasing porosity and/or crack density in that direction. A significant S-wave azimuthal anisotropy is observed within the thin uppermost layer of basalt near the ridge. The anisotropy is interpreted as being caused by fluid-filled microcracks aligned along the direction of present-day maximum compressive stress, and indicates crustal extension at the ridge itself and perpendicular-to-the-ridge compression 12 km off axis. Spreading along the Kolbeinsey Ridge has most likely been continuous since its initiation ca. 25 Ma: The data do not suggest the presence of an extinct spreading axis between the Kolbeinsey Ridge and the Aegir Ridge as has been proposed earlier. The V _p/V _s-ratios found in the Jan Mayen Basin are compatible with continental crust, overlain by a sedimentary section dominated by shale.  相似文献   

Nitrogen and phosphorus distributions across the thermohaline front in Kii Channel in winter     

Ichiro Yuasa  Eisuke Hashimoto  Hideki Ueshima 《Journal of Oceanography》1993,49(4):407-424

We have studied nitrogen and phosphorus distributions across the thermohaline front in Kii Channel in winter by using engine-cooling sea water of a ferry boat. On Dec. 1986 and Jan. 1987, differences of PO₄–P and DIN across the front are recognized. Especially in the latter case, differences of nutrients concentrations across the front are very obvious. But differences of nutrients across the front on Feb. 1986, Feb. and Mar. 1987 are not obvious. Inspite of winter,Akashiwo had happened in Osaka Bay, nutrients mostly have already been utilized by phytoplankton in inner part of Osaka Bay. Consequently, differences of nutrients concentrations across the front are nearly zero.  相似文献   

Errata: 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(4):495-497

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Absolute Volume Transports of the Oyashio Referred to Moored Current Meter Data Crossing the OICE     

Kazuyuki Uehara  Shin-Ichi Ito  Hideo Miyake  Ichiro Yasuda  Yugo Shimizu  Tomowo Watanabe 《Journal of Oceanography》2004,60(2):397-409

During November 2000–June 2002, both direct current measurements from deployment of a line of five moorings and repeated CTD observations were conducted along the Oyashio Intensive observation line off Cape Erimo (OICE). All the moorings were installed above the inshore-side slope of the Kuril-Kamchatka Trench. Before calculating the absolute volume transports, we compared vertical velocity differences of relative geostrophic velocities with those of the measured velocities. Since both the vertical velocity differences concerned with the middle three moorings were in good agreement, the flows above the continental slope are considered to be in thermal wind balance. We therefore used the current meter data of these three moorings, selected among all five moorings, to estimate the absolute volume transports of the Oyashio referred to the current meter data. As a result, we estimated that the southwestward absolute volume transports in 0–1000 db are 0.5–12.8 × 10⁶ m³/sec and the largest transport is obtained in winter, January 2001. The Oyashio absolute transports in January 2001, crossing the OICE between 42°N and 41°15′ N from the surface to near the bottom above the continental slope, is estimated to be at least 31 × 10⁶ m³/sec. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Two-dimensional asymmetric vortex merger: Contour dynamics experiment   总被引：1，自引：0，他引：1  

Ichiro Yasuda  Glenn R. Flierl 《Journal of Oceanography》1995,51(2):145-170

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