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101.
Oliver E. Jagoutz J.-P. Burg S. Hussain H. Dawood T. Pettke T. Iizuka S. Maruyama 《Contributions to Mineralogy and Petrology》2009,158(6):739-755
We present major and trace element analyses and U–Pb zircon intrusion ages from I-type granitoids sampled along a crustal
transect in the vicinity of the Chilas gabbronorite of the Kohistan paleo-arc. The aim is to investigate the roles of fractional
crystallization of mantle-derived melts and partial melting of lower crustal amphibolites to produce the magmatic upper crust
of an island arc. The analyzed samples span a wide calc-alkaline compositional range (diorite–tonalite–granodiorite–granite)
and have typical subduction-related trace element signatures. Their intrusion ages (75.1 ± 4.5–42.1 ± 4.4 Ma) are younger
than the Chilas Complex (~85 Ma). The new results indicate, in conjunction with literature data, that granitoid formation
in the Kohistan arc was a continuous rather than punctuated process. Field observations and the presence of inherited zircons
indicate the importance of assimilation processes. Field relations, petrographic observations and major and trace element
compositions of the granitoid indicate the importance of amphibole fractionation for their origin. It is concluded that granitoids
in the Kohistan arc are derivative products of mantle derived melts that evolved through amphibole-dominated fractionation
and intra crustal assimilation. 相似文献
102.
Miyake Y Jiang Q Yuan W Hanari N Okazawa T Wyrzykowska B So MK Lam PK Yamashita N 《Marine pollution bulletin》2008,57(6-12):357-364
Dietary intake is one of the important routes of human exposure to brominated flame retardants (BFRs) such as polybrominated diphenyl ethers (PBDEs). The use of PBDEs may also result in exposure to polybrominated dibenzo-p-dioxins and dibenzofurans (PBDDs/DFs), as these compounds are impurities in technical mixtures of BFRs and can also be formed unintentionally by the same processes that generate chlorinated dioxins. This study determined the concentrations of polybrominated compounds in common seafood in Guangzhou and Zhoushan, and assessed the health risks of these chemicals via consumption of contaminated seafood. Seafood samples (fish, bivalves, shrimp, crab, and cephalopods) purchased from local markets in 2003 and 2004 were analyzed for PBDEs and PBDDs/DFs. The highest concentration of total PBDEs (46.3 ng g(-1) lipid wt.) was detected in fish from Guangzhou, in which BDEs 47 and 209 were the two predominant congeners. The total daily intakes of PBDEs, PBDDs, and PBDFs were, 946, 6.39, and 6.54 pg kg(-1) body weight (bw) in Guangzhou, and 489, 4.99, and 7.65 pg kg(-1) bw in Zhoushan, respectively. The hazard ratios for PBDDs and PBDFs were both greater than unity, indicating that these compounds may pose some health risks to the local population. 相似文献
103.
104.
Tsugunobu Nagai Masaynki Kuwashima Makoto Kawamura Tsuyoshi Kohno 《Planetary and Space Science》1979,27(7):1035-1037
It is suggested that the drop out of the 1.2–4 MeV proton flux, observed by the geostationary satellite GMS, was due to the Earthward shift of the particle boundary in all local time. The particle boundary motions are associated with substorm activities. 相似文献
105.
Ikawa Hiroki Kuwagata Tsuneo Haginoya Shigenori Ishigooka Yasushi Ono Keisuke Maruyama Atsushi Sakai Hidemitsu Fukuoka Minehiko Yoshimoto Mayumi Ishida Sachinobu Chen Charles P. Hasegawa Toshihiro Watanabe Tsutomu 《Boundary-Layer Meteorology》2021,179(3):447-476
Boundary-Layer Meteorology - Known as the heat-mitigation effect, irrigated rice-paddy fields distribute a large fraction of their received energy to the latent heat during the growing season. The... 相似文献
106.
The plate culture method using the two formulae for non-nitrogenous media was adopted in this investigation for the purpose
of counting and isolating nitrogen-fixing bacteria distributed in the open sea.
Sea water samples were collected at eighteen different stations in the region of Lat. 50°N–15°S along Long. 155°W and two
other stations in the Pacific Ocean. In order to compare with those samples from the open sea, water samples were also obtained
at four stations in Suruga and Sagami Bays.
Nitrogen-fixing bacteria appear to be widely but very unevenly distributed at all depths in sea water, in numbers approximately
ranging from nil to 104 per 100 ml of sea water, and denser vertical populations have been found in the area of Lat. 40°N and 5°N along Long. 155°W, even at
depths from 2,000 to 3,000m. A conparatively denser population of bacteria was found in sea water from Suruga Bay and Sagami
Bay.
The bacteria associated with plankton were abundantly demonstrated, in numbers ranging from 106 to 108 per 1 ml settling volume of plankton, in many plankton samples collected at four stations in the southern parts of the Pacific Ocean.
Almost all the bacteria isolated from the samples of blue green algal colonies,Trichodesmium, sp., were able to grow on nonnitrogeneous media. 相似文献
107.
Seasonal appearance ofProchlorococcus was studied by flow cytometry in Suruga Bay, Japan in 1992–1993.Prochlorococcus cells were in high concentrations (>1×104 cells ml–1) from July to October 1992 and September 1993, when the water temperature was over 20°C. The 16S rRNA of the isolated cells showed 98.5% sequence homology with that ofP. marinus (Sargasso strain), indicating that they are the same species. The former has a high divinyl-chlorophyll (DV-Chl.)a/b ratio similar to the Mediterranean strain and different from the Sargasso strain. Maximum concentration ofProchlorococcus at the surface water was 2.5×104 cells ml–1 in August 1992 and their DV-Chl.a accounted for 4.0% of the total chlorophylla. A decrease in cell density to less than 5×103 cells ml–1 was observed from December to May with an exceptional rise in January 1993. WhileProchlorococcus showed a maximum concentration of 3.6×104 cells ml–1 at 10 m depth in September 1992, phycoerythrin (PE)-richSynechococcus spp. were dominant with their maximum concentration of 2.2×105 cells ml–1 in the same water body. On the other hand, phycocyanin (PC)-richSynechococcus spp. and the larger phytoplankters showed maximum concentrations in the surface waters in May and June. BothProchlorococcus and PE-richSynechococcus showed their lowest concentrations in April. A significant positive correlation was obtained between cell concentrations of the PE-richSynechococcus andProchlorococcus. 相似文献
108.
Giant Megamullion in the Parece Vela Backarc Basin 总被引:1,自引:0,他引:1
Ohara Yasuhiko Yoshida Tsuyoshi Kato Yukihiro Kasuga Shigeru 《Marine Geophysical Researches》2001,22(1):47-61
We present results of high-resolution bathymetric studies of the extinct intermediate-spreading Parece Vela Basin in the northwestern Pacific, where we have identified an extremely large mullion structure, here termed a giant megamullion. We find that the giant megamullion is nearly an order of magnitude larger than the similar structures in the slow-spreading Mid-Atlantic Ridge (`megamullions'). The giant megamullion has slightly elevated mantle Bouguer anomaly, and yields serpentinized peridotites and gabbros, suggesting that they are exposing oceanic crust and upper mantle. An off-axis rugged `chaotic terrain' was also identified in the Parece Vela Basin. The terrain consists of isolated and elevated blocks capped by corrugated axis-normal lineations, and associated deeps. We thus interpret it as analogues to the Mid-Atlantic Ridge megamullions. We propose that amagmatic tectonics producing the giant megamullion and the chaotic terrain occupied a significant part in crustal construction in the Parece Vela Basin evolution. 相似文献
109.
Evolution of the composition of seawater through geologic time, and its influence on the evolution of life 总被引:2,自引:2,他引:0
Tsuyoshi Komiya Takafumi Hirata Kouki Kitajima Shinji Yamamoto Takazo Shibuya Yusuke Sawaki Tomoko Ishikawa Degan Shu Yong Li Jian Han 《Gondwana Research》2008,14(1-2):159
The redox state of the surface environment of the early Earth is still controversial, and a detailed and quantitative estimate is still lacking. We carried out in-situ analyses of major, trace, and rare-earth elements of carbonate minerals in rocks with primary sedimentary structures in shallow and deep sea-deposits, in order to eliminate secondary carbonate and contamination of detrital materials, and to estimate the redox condition of seawater through time. Based on the Ce content and anomalies of the carbonate minerals at given parameters of atmospheric CO2 content (pCO2) and Ca content of seawater, we calculated the oxygen contents of shallow and deep seawater, respectively. The results show that the oxygen content of the deep sea was low and constant until at least 1.9 Ga. The oxygen content of shallow seawater increased after 2.7 Ga, but fluctuated. It became quite high at 2.5 and 2.3 Ga, but eventually increased after the Phanerozoic. In addition, the calculation of a high pCO2 condition shows that seawater was more oxic even in the Archean than at present, suggesting a relatively low pCO2 through geologic time.Our detailed calculations from compositions of carbonate minerals in Three Gorge area, south China show a low oxygen content of seawater after the Snowball Earth until the late Ediacaran, an increase in the late Ediacaran, and a significant decrease around the Precambrian–Cambrian and Nemakit/Daldynian–Tommotian boundaries. These variations were possibly caused by global regression and dissolution of methane hydrates. 相似文献
110.
Models on Snowball Earth and Cambrian explosion: A synopsis 总被引:5,自引:5,他引:0
During the late Proterozoic from 1000 to 542 Ma, the Earth is thought to have been frozen at least during two times: in the Sturtian (715–680 Ma) and in the Marinoan (680–635 Ma) global glaciations. Following the Marinoan Snowball Earth, large multi-cellular animals of the Ediacara fauna flourished as a prelude to the Phanerozoic world. Here we summarize the most popular models on the cause and cessation of Snowball Earth. Episodic decrease of greenhouse gas occurs through the effect of erosion and weathering promoted by either mountain building or by an increase in the coastlines during the break-up of supercontinents. Effects on the globe caused by true polar wander, eruption of voluminous flood basalts, or dramatic reduction in planetary obliquity can also lead to ice ages and mass extinction. A radically revised concept based on Earth's magnetic intensity has also been proposed, which explains the true polar wander through a quasi-polar dynamo model. The ‘switch-on’ and ‘switch-off’ of the Earth's strong dynamo can lead to the onset and disappearance of the Snowball Earth. The galactic model infers that gamma ray burst associated with starburst creates huge amounts of clouds which would cut off sun rays and freeze the Earth.The Snowball Earth event is considered to have exerted a significant control on the subsequent revolutionary changes in the evolution of life forms. Although according to the biological clock, extensive re-organisation of genome is thought to have been completed by around 900 Ma, the evolution of modern life in Cambrian occurred only after the geochemical bridge was in place with elevated oxygen and nutrient levels in lakes that developed within continental rifts where the hydrothermal system in the granitic basement created the chemical environment enriched in Ca2+, Fe2+, V, Mo, HCO3, phosphate and other elements required for building the skeleton and bone of the first modern animals. With cosmic radiation exerting a significant control on the mutation, the Neoproterozoic Earth history illustrates the possible link from Galaxy to the genome level. 相似文献