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排序方式: 共有317条查询结果,搜索用时 15 毫秒
311.
Sulfur isotopic characteristics of late Cenozoic ore deposits at the arc junction of Hokkaido, Japan
Abstract Sulfide minerals of late Cenozoic vein-type deposits of southwest Hokkaido and Kuril Islands yielded δ34 CDT S values of 2 to 8 permil, which are typical green-tuff values of magnetite-series igneous terrane. Sulfides of the Kitami district of northeast Hokkaido, on the other hand, are characterized by negative δ34 SCDT values, ranging from 0 to - 7 permil. This unique value among ore deposits in the late Cenozoic back-arc terranes in the Japanese Islands is considered to have resulted from extraction of 32 S enriched sulfur from the basement rocks, because of well-developed N-S fracturing in the basement, which is characteristic of the axial belt and Kitami district of Hokkaido. 相似文献
312.
Characterization of drying-induced deformation behaviour of Opalinus Clay and tuff in no-stress regime 总被引:1,自引:0,他引:1
Aung Ko Ko Soe Masahiko Osada Manabu Takahashi Tai Sasaki 《Environmental Geology》2009,58(6):1215-1225
The drying-induced deformation behaviour of Opalinus Clay and tuff, which are being investigated under international and local
collaborative projects for nuclear waste disposal in Switzerland and Japan, was investigated under a no-stress condition in
the laboratory to evaluate their generic susceptibility to the formation of excavation damaged zone. The cylindrical core
samples of Opalinus Clay and tuff were prepared to a one-dimensional drying condition and submitted to an uncontrolled laboratory
environment. The strain evolution, evaporative water loss and environmental entities, such as temperature and relative humidity,
were recorded simultaneously and quasi-continuously. It was observed that the drying phase induced significant strain magnitude
and damage in Opalinus Clay samples, which was evidenced by the formation of hairy cracks on the surface parallel to the bedding.
On the contrary, the strain occurrences in tuff samples were relatively insignificant, and no tendency of cracking was observed.
In addition, the quasi-continuous availability of volumetric strains was further used in poroelastic relation for the estimation
of capillary suction evolution. The calculated results were validated with pore size distributions obtained from mercury intrusion
porosimetry. 相似文献
313.
Robert J. Stern Yoshihiko Tamura Robert W. Embley Osamu Ishizuka Susan G. Merle Neil K. Basu Hiroshi Kawabata Sherman H. Bloomer 《Island Arc》2008,17(1):70-89
Abstract West Rota Volcano (WRV) is a recently discovered extinct submarine volcano in the southern Mariana Arc. It is large (25 km diameter base), shallow (up to 300 m below sealevel), and contains a large caldera (6 × 10 km, with up to 1 km relief). The WRV lies near the northern termination of a major NNE‐trending normal fault. This and a second, parallel fault just west of the volcano separate uplifted, thick frontal arc crust to the east from subsiding, thin back‐arc basin crust to the west. The WRV is distinct from other Mariana Arc volcanoes: (i) it consists of a lower, predominantly andesite section overlain by a bimodal rhyolite‐basalt layered sequence; (ii) andesitic rocks are locally intensely altered and mineralized; (iii) it has a large caldera; and (iv) WRV is built on a major fault. Submarine felsic calderas are common in the Izu and Kermadec Arcs but are otherwise unknown from the Marianas and other primitive, intraoceanic arcs. 40Ar–39Ar dating indicates that andesitic volcanism comprising the lower volcanic section occurred 0.33–0.55 my ago, whereas eruption of the upper rhyolites and basalts occurred 37–51 thousand years ago. Four sequences of rhyolite pyroclastics each are 20–75 m thick, unwelded and show reverse grading, indicating submarine eruption. The youngest unit consists of 1–2 m diameter spheroids of rhyolite pumice, interpreted as magmatic balloons, formed by relatively quiet effusion and inflation of rhyolite into the overlying seawater. Geochemical studies indicate that felsic magmas were generated by anatexis of amphibolite‐facies meta‐andesites, perhaps in the middle arc crust. The presence of a large felsic volcano and caldera in the southern Marianas might indicate interaction of large normal faults with a mid‐crustal magma body at depth, providing a way for viscous felsic melts to reach the surface. 相似文献
314.
315.
The horizontal and vertical distributions of manganese in sea water, interstitial water and sediments in the Hiro Bay, Seto Inland Sea, Japan, have been investigated. The outflow from a pulp mill is the primary source of manganese in this bay. The industrial waste water contained 0.19 mg l–1 of manganese, mostly in a dissolved form. This manganese diffused out both horizontally and vertically into the surrounding sea water. The content of manganese in the liquid and solid phases in the sediments, however, are inverse with that in the sea water; namely the lowest concentration of manganese in the sediments was observed at the station near the outfall and manganese concentration increased with the distance from the outfall. 相似文献
316.
317.
Susumu Umino Kyoko Kanayama Keitaro Kitamura Akihiro Tamura Osamu Ishizuka Ryoko Senda Shoji Arai 《Island Arc》2018,27(1)
Boninites are widely distributed along the western margin of the Pacific Plate extruded during the incipient stage of the subduction zone development in the early Paleogene period. This paper discusses the genetic relationships of boninite and antecedent protoarc basalt magmas and demonstrates their recycled ancient slab origin based on the T–P conditions and Pb–Hf–Nd–Os isotopic modeling. Primitive melt inclusions in chrome spinel from Ogasawara and Guam islands show severely depleted high‐SiO2, MgO (high‐silica) and less depleted low‐SiO2, MgO (low‐silica and ultralow‐silica) boninitic compositions. The genetic conditions of 1 346 °C at 0.58 GPa and 1 292 °C at 0.69 GPa for the low‐ and ultralow‐silica boninite magmas lie on adiabatic melting paths of depleted mid‐ocean ridge basalt mantle with a potential temperature of 1 430 °C in Ogasawara and of 1 370 °C in Guam, respectively. This is consistent with the model that the low‐ and ultralow‐silica boninites were produced by remelting of the residue of the protoarc basalt during the forearc spreading immediately following the subduction initiation. In contrast, the genetic conditions of 1 428 °C and 0.96 GPa for the high‐silica boninite magma is reconciled with the ascent of more depleted harzburgitic source which pre‐existed below the Izu–Ogasawara–Mariana forearc region before the subduction started. Mixing calculations based on the Pb–Nd–Hf isotopic data for the Mariana protoarc basalt and boninites support the above remelting model for the (ultra)low‐silica boninite and the discrete harzburgite source for the high‐silica boninite. Yb–Os isotopic modeling of the high‐Si boninite source indicates 18–30 wt% melting of the primitive upper mantle at 1.5–1.7 Ga, whereas the source mantle of the protoarc basalt, the residue of which became the source of the (ultra)low‐Si boninite, experienced only 3.5–4.0 wt% melt depletion at 3.6–3.1 Ga, much earlier than the average depleted mid‐ocean ridge basalt mantle with similar degrees of melt depletion at 2.6–2.2 Ga. 相似文献