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101.
The Permian planktonic distribution is not well known, in contrast to other fossil distributions of nekton and benthos. Radiolaria are representative microfossils of plankton in the Permian palaeocean. This study compares both correlated radiolarian occurrences (Pseudotormentus De Wever et Caridroit and Quadriremis Nazarov et Ormiston) in literature data from the Pacific Rim and quantitative data from the Liuhuang and Gujingling sections in South China. Pseudotormentus distributions are concentrated in the Panthalassa, whereas Quadriremis occurrences are distributed over both the Panthalassa and the Palaeotethys. The uneven distribution of Pseudotormentus seems to have been controlled by a difference in the oceanic basins, indicating the presence of faunal differences in Permian planktonic microorganisms between the Panthalassa and the Palaeotethys. In other words, this study infers the provincialism of Permian planktonic microorganisms. The uneven distribution is explainable by a hypothesis that Pseudotormentus was strongly affected by a Panthalassan equatorial current. 相似文献
102.
Regional characteristics of the synoptic-scale wave disturbances in the tropical lower troposphere were examined by analyzing the FGGE level III-b data. Three tropical regions, western Pacific, eastern Pacific, and a region from the African Continent to the Atlantic, were selected for the present study. Spectrum analysis, trajectory analysis and composite analysis were used to obtain characteristics of the wave disturbances for each region.Main findings are as follows: 1.) The generation region of the western Pacific wave disturbances related to typhoon development are found around 5° N and 170° E. 2.) An interaction of the western Pacific wave disturbances with the upper Mid-Pacific trough was indicated statistically as an intensifying condition for typhoons. 3.) The wave disturbances in the eastern Pacific originate to the west of Panama and propagate west-north-westward with a period of 5.7 day and a wavelength of about 2700 km. 4.) The structure of the eastern Pacific wave disturbances is similar to that of the western Pacific disturbances. 5.) Two different paths of the African waves are found over the African Continent. The northern disturbance has a period of 4.4 days while the southern one has a period of 3.3–3.6 days. 6.) Disturbances along the northern path of the African waves are traced only to as far as 45° W, and those along the southern path are traced to the Caribbean Sea. 相似文献
103.
Tsuyoshi Tanaka 《Contributions to Mineralogy and Petrology》1975,52(4):233-246
Rare earth elements (REE), Ba, Sr as well as major elements in 47 pre-Cenozoic geosynclinal volcanics in Japan have been determined. The types of chondrite-normalized REE patterns can be classified into two large groups viz. log-linear REE pattern group and convex REE pattern group. Each group thus classified is also closely related to major element features. Although the REE pattern of the latter group is observed in the island arc tholeiite as well as abyssal tholeiite, the relative content of Ba to La indicates that the Japanese geosynclinal volcanics of this group are more akin to those of abyssal tholeiites than are the island arc ones. Two distinct types of REE fractionation are found in the volcanics of the Japanese geosyncline. The geographical distribution of two groups of the geosynclinal volcanics is different from that of the Cenozoic volcanics in Japan, and the petrochemical features of volcanics from northeast Japan can be distinguished from those of southwest Japan. By analogy with the current knowledge concerning a close relation between the tectonic settings and the geochemical features of the present-day volcanics, the geosynclinal basalts in question are inferred to have been formed during a tensional tectonic movement and have erupted along a local rift zone like the marginal seas and inter-arc basins in the Western Pacific Ocean or along part of a global rift system such as the Red Sea Trough. 相似文献
104.
Tsuyoshi Ishida 《Computers and Geotechnics》1990,9(4):341-353
To examine the accuracy and the chracteristics of the Distinct Element Method (DEM) which has non-deformable elements, the results simulated by the DEM were compared to the results of experiments and/or theories for three simple block models of a pillar, a mass and a toppling model. Consequently, it was elucidated that the DEM is a good numerical method which can be effectively applied to toppling failure of real fissured rock slopes. 相似文献
105.
106.
Tsuyoshi Komiya Shigenori Maruyama Takafumi Hirata Hisayoshi Yurimoto Susumu Nohda 《Island Arc》2004,13(1):47-72
Abstract Recent geological investigations of the Isua Supracrustal Belt (3.8 Ga), southern West Greenland, have suggested that it is the oldest accretionary complex on earth, defined by an oceanic plate‐type stratigraphy and a duplex structure. Plate history from mid‐oceanic ridge through plume magmatism to subduction zone has been postulated from analysis of the reconstructed oceanic plate stratigraphy in the accretionary complex. Comparison between field occurrence of greenstones in modern and ancient accretionary complexes reveals that two types of tholeiitic basalt from different tectonic settings, mid‐oceanic ridge basalt (MORB) and oceanic island basalt (OIB), occur. This work presents major, trace and rare earth element (REE) compositions of greenstones derived from Isua MORB and OIB, and of extremely rare relict igneous clinopyroxene in Isua MORB. The Isua clinopyroxenes (Cpx) have compositional variations equivalent to those of Cpx in modern MORB; in particular, low TiO2 and Na2O contents. The Isua Cpx show slightly light (L)REE‐depleted REE patterns, and the calculated REE pattern of the host magma is in agreement with that of Isua MORB. Analyses of 49 least‐altered greenstones carefully selected from approximately 1200 samples indicate that Isua MORB are enriched in Al2O3, and depleted in TiO2, FeO*, Y and Zr at the given MgO content, compared with Isua OIB. In addition, Isua MORB show an LREE‐depleted pattern, whereas Isua OIB forms a flat REE pattern. Such differences suggest that the Early Archean mantle had already become heterogeneous, depending on the tectonic environment. Isua MORB are enriched in FeO compared with modern MORB. Comparison of Isua MORB with recent melting experiments shows that the source mantle had 85–87 in Mg? and was enriched in FeO. Potential mantle temperature is estimated to be approximately 1480°C, indicating that the Early Archean mantle was hotter by at most approximately 150°C than the modern mantle. 相似文献
107.
REE abundances in ten chondrites (nine falls and one find) were determined very accurately by mass-spectrometric stable isotope dilution techniques. All of the chondrites have different relative and absolute REE patterns. Except for Eu and, rarely, for Ce, the REE abundances in chondrites are smoothly fractionated from sample to sample. Notwithstanding differences in the abundances of common REE, four of five L6 chondrites have very similar absolute Eu abundances; their mutually-normalized REE patterns are not curved, but are composed of two rectilinear segments.The Leedey-normalized REE pattern for St. Séverin (LL6) is composed of two concave curves. Yonozu's (H4,5) pattern shows negligibly concave curvature on both sides of Eu. Kesen's (H4) pattern is unusual in its overall pattern but also in irregularities for particular elements. The irregularity may be connected with the unusually high vapor pressure of metallic Yb. The REE pattern for the Allende bulk sample shows a discontinuity, presumably reflecting its considerable heterogeneity of composition and structure. It is evident that any pattern of ordinary chondrites cannot be produced from the Allende bulk pattern. A comparison is also made with the results on the chondrite composites previously investigated. 相似文献
108.
Hikaru Iwamori Hitomi Nakamura Masaki Yoshida Takashi Nakagawa Kenta Ueki Atsushi Nakao Tatsuji Nishizawa Satoru Haraguchi 《Comptes Rendus Geoscience》2019,351(2-3):209-220
Recent statistical analyses on the isotopic compositions of oceanic, arc, and continental basalts have revealed that the Earth's mantle is broadly divided into eastern and western hemispheres. The present study aimed to characterize the isotopically defined east–west geochemical hemispheres using trace-element concentrations. Basalt data with Rb, Sr, Nd, Sm, Pb, Th, and U in addition to the isotopic ratios 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb were selected mostly from the GEOROC and PetDB databases. A total of 4787 samples were used to investigate the global geochemical variations. The results show that the wide trace-element variations are broadly explained by the melting of melt-metasomatized and fluid-metasomatized mantle sources. The larger amount of the fluid component derived from subducted plates in the eastern hemisphere than that in the western hemisphere is inferred from the basalts. These characteristics support the hypothesis that focused subduction towards the supercontinent created the mantle geochemical hemispheres. 相似文献
109.
Baba Sotaro Osanai Yasuhito Adachi Tatsuro Nakano Nobuhiko Hokada Tomokazu Toyoshima Tsuyoshi 《Mineralogy and Petrology》2019,113(6):821-845
Mineralogy and Petrology - In this paper, we describe the metamorphic conditions of Fe-rich granulite and variations in rare earth elements (REE) between peak garnet porphyroblasts and secondary... 相似文献
110.
A simple geochemical technique using the ratio of total sulfur (TS) to total organic carbon (TOC) was successfully used to reconstruct paleoenvironments in the Jurassic–Cretaceous Tetori Group, central Japan. The TS to TOC ratio is often employed as an effective parameter to separate modern marine or brackish sediments from freshwater deposits. To test the TS/TOC method for paleoenvironmental interpretation of the Tetori Group, we first analyzed TS/TOC for samples for which depositional conditions (i.e. marine, brackish or freshwater) had been recognized paleontologically. The results indicate that the method can effectively separate sedimentary rocks deposited under freshwater from marine and brackish settings. Once we had established the effectiveness of this method, we applied it to three sections of the Tetori Group, central Japan. Stratigraphic fluctuations in TS/TOC values revealed episodic incursions of marine or brackish conditions in the dominantly freshwater depositional sequence in the middle of the Jobu Formation of the Itoshiro Subgroup at the Izumi section, Fukui Prefecture. The same paleoenvironment is also suggested to occur at the top of the Tetori Group in the Tateyama section, Toyama Prefecture. This research provides important information to paleogeographers who currently lack evidence from facies fossils to indicate if the uppermost part of the Tetori Group represents marine or brackish settings. A chemostratigraphy of TS/TOC parameters potentially could provide a correlation among Jurassic–Cretaceous sequences along continental margins over East Asia. 相似文献