排序方式： 共有34条查询结果，搜索用时 31 毫秒
1.
Monthon?Ganmanee Teruyoshi?Narita Hideo?SekiguchiEmail author 《Journal of Oceanography》2004,60(6):1071-1083
Based on our long-term data from megabenthos sampling from 1993 to 2002 in Ise Bay, central Japan, we examined spatio-temporal variations in taxon composition, species richness and its distribution of megabenthos in the bay in relation to the occurrence of the oxygen-poor water (i.e. oxygen content less than 3 ppm) in bottom waters of the bay. A total of 261 species were identified including 6 cnidarians, 1 tentaculate, 5 annelids, 71 molluscs, 72 crustaceans, 16 echinoderms, 12 urochordates and 78 pisces. Of the most abundant 10 megabenthos species, the following 4 species of echinoderms made up more than the half of megabenthos biomass: Luidia quinaria, Echinocardium cordatum, Asterias amurensis and Astropecten scoparius. Species richness of megabenthos varied significantly between seasons and among stations. The severity and period of occurrence of the oxygen-poor water developing every summer play an important role in determining spatial distributions of species richness in the bay. 相似文献
2.
3.
Abstract. Chemistry and sulfur isotopes are analyzed for a series of rocks in the chert‐dominant sequence around the stratiform manganese ore deposit of the Noda‐Tamagawa mine in the northern Kitakami Terrane, northeast Japan. The sequence is litholog‐ically classified into six units in ascending order: lower bedded chert, lower black shale, massive chert, manganese ore, upper black shale, and upper bedded chert. The rocks around the manganese ore deposit exhibit anomalous enrichment in Ni (max. 337 ppm), Zn (102) and U (30) in the upper part of lower bedded chert, Mo (122), Tl (79) and Pb (33) in the lower black shale, MnO, Cu (786) and Co (62) in the manganese ore, and As (247) and Sb (17) in the upper black shale. The aluminum‐normalized profiles reveal zonal enrichment of redox‐sensitive elements around the manganese bed: Zn‐Ni‐Fe‐Mo‐U(‐Co), Tl‐Pb(‐Mo), Mn‐Fe‐Cu‐V‐Cr‐Co(‐Zn) and As‐Sb in ascending order. The uppermost part of the lower bedded chert and black shale exhibit negative Ce/Ce* values, whereas the massive chert, manganese ore and lower part of the upper bedded chert display positive values. The isotopic δ34S values are 0±6 % in the lower part of the lower bedded chert, ‐19 to ‐42 % in the upper part of the lower bedded chert, ‐36 to ‐42 % in the lower black shale, ‐28 to ‐35 % in the massive chert, manganese ore and upper black shale, and ‐23±5 % in the upper bedded chert. Thus, there is a marked negative shift in δ34S values in the lower bedded chert, and an upward‐increasing trend in δ34S through the manganese ore horizon. The present data provide evidence for a change in the paleoceanographic environmental resulting from inflow of oxic deepwater into the stagnant anoxic ocean floor below the manganese ore horizon. This event is likely to have triggered the precipitation of manganese oxyhydroxides. The redistribution of redox‐sensitive elements through the formation of metalliferous black shale and manganese carbonate ore may have occurred in association with bacterial decomposition of organic matter during early diagenesis of initial manganese oxyhydroxides. 相似文献
4.
5.
Abstract. Inorganic chemical compositions are determined for a series of rocks crossing an Early Jurassic stratiform manganese ore deposit in a chert‐dominant sequence at Katsuyama, in the Mino Terrane of central Japan. The lithology in the vicinity of the manganese ore bed is classified into lower bedded chert, black shale, massive chert, manganese ore and upper bedded chert, in ascending order. The rocks surrounding the manganese deposit are anomalously high in certain elements: Pb (max. 29 ppm), Ni (1140) and Co (336) in the lower bedded chert, Mo (438), As (149), Tl (29) and U (12) in the black shales, V (210) and Cr (87) in the massive chert, and MnO and W (24) in the manganese ore. The aluminum‐normalized profiles reveal a distinct zonation of redox‐sensitive elements: Pb‐Zn, Ni‐Co‐Cu(‐Zn) and U‐Cr in the lower bedded chert, Mo‐As‐Tl in the black shale, V(‐Cr) in the massive chert, and Mn‐Fe‐Ba‐W in the manganese ore, in ascending order. The lower and upper bedded cherts and manganese ore generally exhibit flat rare earth element patterns with positive Ce anomalies, whereas the uppermost part of the lower bedded chert, the black shale and massive chert have flat patterns with weak or nonexistent negative Ce anomalies and weak positive Eu anomalies. The strong enrichment in Ni, Co, W, Tl and As detected in the Katsuyama section is not recognized in other sediments, including those of anoxic deposition origin, but is identified in modern ferromanganese nodules, suggesting that metal enrichment in the Katsuyama section is essentially due to the formation of ferromanganese nodules rather than to deposition in an anoxic environment. The observed elemental zonation is well explained by equilibrium calculations, reflecting early diagenetic formation and associated gradual reduction with depth. The concentration profiles in combination with litho‐ and biostratigraphical features suggest that formation of these bedded manganese deposits was triggered by an influx of warm, saline and oxic water into a stagnant deep ocean floor basin in Panthalassa at the end of the middle Early Jurassic. Paleoceanographic environmental controls thus appear to be important factors in the formation and preservation of this type of stratiform manganese deposit. 相似文献
6.
The geological model about volcanism of the Green Tuff geosyncline deduced from the field observations consists of the following processes:
- Dome-shaped uplift with a mean diameter of 30 km.
- Collapse of the central part of the domes forming basins with a mean diameter of 10 km.
- Volcanic activity inside the collapse basins. It is considered that these consecutive processes resulted from the magmatic uplift from a deep part of the crust.
7.
Here, we examine spatiotemporal variations of Jurassic–Cretaceous magmatism along a c. 1000‐km transect across eastern Asia, including SW Japan, the Korean, Jiaodong and Liaodong peninsulas, and eastern Jilin Province. Integration of tectonic regime data with age data from igneous rocks in eastern Asia (from the Tan‐Lu Fault to SW Japan) suggests a shallowing of the subduction angle and subsequent flat‐slab subduction during the Jurassic, and slab rollback during the Early Cretaceous. The combination of a subducting plateau and root‐enhanced suction provides the best explanation for the flat‐slab subduction. In the final stage (Albian) of slab rollback, the geotectonic setting changed from subduction–accretion to a continental arc in the area close to the ancient trench (i.e. the Inner Zone of SW Japan). 相似文献
8.
Summary ?In cathodoluminescence (CL) images of synthetic low-quartz samples after He+ implantation at 4 MeV with a dose density over 1.14 × 10−4 C cm−2, bright CL halos of about 14 μm in width from the implantation surface are recognized. These widths are consistent with the
theoretical range. This confirms experimentally that the CL halos in low-quartz found in geological samples are formed by
alpha radiation. It also shows that CL colour continuously changes with dose density, demonstrating that it is possible to
use the CL halo as a new dosimeter that is useful for dating and analysis of radionuclide migration in natural geological
media.
Received December 3, 2001; revised version accepted February 27, 2002 相似文献
9.
The Cretaceous Ofuku Pluton and Its Relation to Mineralization in the Western Akiyoshi Plateau,Yamaguchi Prefecture,Japan 
下载免费PDF全文
下载免费PDF全文 Yuka Sasaki Teruyoshi Imaoka Mariko Nagashima Kazuo Nakashima Takafumi Sonehara Koshi Yagi Tetsumaru Itaya 《Resource Geology》2016,66(2):85-113
The relationship between the magmatism of the Cretaceous Ofuku pluton and mineralization in and around the Akiyoshi Plateau, Yamaguchi Prefecture, Japan was investigated using a combination of field observation, petrographic and geochemical analyses, K–Ar geochronology, and fluid inclusion data. The Ofuku pluton has a surface area of 1.5 × 1.0 km, and was intruded into the Paleozoic accretionary complexes of the Akiyoshi Limestone, Ota Group and Tsunemori Formation in the western part of the Akiyoshi Plateau. The pluton belongs to the ilmenite‐series and is zoned, consisting mainly of early tonalite and granodiorite that share a gradational contact, and later granite and aplite that intruded the tonalite and granodiorite. Harker diagrams show that the Ofuku pluton has intermediate to silicic compositions ranging from 60.4 to 77.9 wt.% SiO2, but a compositional gap exists between 70.5 to 73.4 wt.% SiO2 (anhydrous basis). Modal and chemical variations indicate that the assumed parental magma is tonalitic. Quantitative models of fractional crystallization based on mass balance calculations and the Rayleigh fractionation model using major and trace element data for all crystalline phases indicate that magmatic fractionation was controlled mainly by crystal fractionation of plagioclase, hornblende, clinopyroxene and orthopyroxene at the early stage, and quartz, plagioclase, biotite, hornblende, apatite, ilmenite and zircon at the later stage. The residual melt extracted from the granodiorite mush was subsequently intruded into the northern and western parts of the Ofuku pluton as melt lens to form the granite and aplite. The age of the pluton was estimated at 99–97 Ma and 101–98 Ma based on K–Ar dating of hornblende and biotite, respectively. Both ages are consistent within analytical error, indicating that the Ofuku pluton and the associated Yamato mine belong to the Tungsten Province of the San‐yo Belt, which is genetically related to the ilmenite‐series granitoids of the Kanmon to Shunan stages. The aplite contains Cl‐rich apatite and REE‐rich monazite‐(Ce), allanite‐(Ce), xenotime and bastnäsite‐(Ce), indicating that the residual melt was rich in halogens and REEs. The tonalite–granodiorite of the Ofuku pluton contains many three‐phase fluid inclusions, along with daughter minerals such as NaCl and KCl, and vapor/liquid (V/L) volume ratios range from 0.2 to 0.9, suggesting that the fluid was boiling. In contrast, the granite and aplite contain low salinity two‐phase inclusions with low V/L ratios. The granodiorite occupies a large part of the pluton, and the inclusions with various V/L ratios with chloride daughter minerals suggest the boiling fluids might be related to the mineralization. This fluid could have carried base metals such as Cu and Zn, forming Cu ore deposits in and around the Ofuku pluton. The occurrence and composition of fluid inclusions in the igneous rocks from the Akiyoshi Plateau are directly linked to Cu mineralization in the area, demonstrating that fluid inclusions are useful indicators of mineralization. 相似文献
10.
Kosei Komuro Hiroshi Kubota Tokiyuki Sato Yoshimichi Kajiwara Shojiro Tanimura 《Resource Geology》2004,54(4):425-436
Abstract. A comprehensive investigation was carried out on the distribution of both trace fossils and sulfur isotopes in mud-stones in the Hokuroku district, northeast Japan, in the hope of delineating the depositional environment of the mudstones in which the Kuroko deposits are embedded. The mudstones are generally massive in structure and usually contain large trace fossils, being indicative of an aerobic biofacies. On the other hand, some mudstones in and above the Kuroko ore horizon are partly laminated and usually contain smaller trace fossils, being assignable to an anaerobic or dysaerobic biofacies. The δ34 S values of sulfides in the mudstones above and below the ore horizon range from -40 to -12 %o, indicating mostly oxic depositional conditions in equilibrium with the inferred aerobic biofacies. In the mudstones in the ore horizon, the δ34 S values exhibit regionally discriminated variations: -44 to -12 %o in areas far (>1 km) from the known Kuroko deposits and -24 to +6 %o in areas closer to them. The latter high δ34 S group implies the temporal occurrence of local anoxic basins in the vicinity of the known Kuroko deposits. At the time of late Nishikurosawa Stage (i.e. the currently assumed Kuroko metallogenic epoch), an intense oceanic stagnation is suggested to have taken place to form the local anoxic basins responsible for the formation and preservation of Kuroko deposits. This oceanic environmental event is considered to be most likely due to increasing biological productivity primarily triggered and enhanced by upwelling of NADW in the paleo-Sea of Japan at that time. 相似文献