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991.
Yilin Xiao Jochen Hoefs Zhenhui Hou Klaus Simon Zeming Zhang 《Contributions to Mineralogy and Petrology》2011,162(4):797-819
In order to better understand the role of fluids during subduction and subsequent exhumation, we have investigated whole-rock
and mineral chemistry (major and trace elements) and Li, B as well as O, Sr, Nd, Pb isotopes on selected continuous drill-core
profiles through contrasting lithological boundaries from the Chinese Continental Scientific Drilling Program (CCSD) in Sulu,
China. Four carefully selected sample sets have been chosen to investigate geochemical changes as a result of fluid mobilization
during dehydration, peak metamorphism, and exhumation of deeply subducted continental crust. Our data reveal that while O
and Sr-Nd-Pb isotopic compositions remain more or less unchanged, significant Li and/or B isotope fractionations occur between
different lithologies that are in close contact during various metamorphic stages. Samples that are supposed to represent
prograde dehydration as indicated by veins formed at high pressures (HP) are characterized by element patterns of highly fluid-mobile
elements in the veins that are complementary to those of the host eclogite. A second sample set represents a UHP metamorphic
crustal eclogite that is separated from a garnet peridotite by a thin transitional interface. Garnet peridotite and eclogite
are characterized by a >10% difference in MgO, which, together with the presence of abundant hydroxyl-bearing minerals and
compositionally different clinopyroxene grains demonstrate that both rocks have been derived from different sources that have
been tectonically juxtaposed during subduction, and that hydrous silicate-rich fluids have been added from the subducting
slab to the mantle. Two additional sample sets, comprising retrograde amphibolite and relatively fresh eclogite, demonstrate
that besides external fluids, internal fluids can be responsible for the formation of amphibolite. Li and B concentrations
and isotopic compositions point to losses and isotopic fractionation during progressive dehydration. On the other hand, fluids
with isotopically heavier Li and B are added during retrogression. On a small scale, mantle-derived rocks may be significantly
metasomatized by fluids derived from the subducted slab. Our study indicates that during high-grade metamorphism, Li and B
may show different patterns of enrichment and of isotopic fractionation. 相似文献
992.
Tong Hou Zhaochong Zhang Timothy Kusky Yangsong Du Junlai Liu Zhidan Zhao 《Ore Geology Reviews》2011,41(1):133-143
Based on published data, we reappraise the classification of high-Ti and low-Ti basalt from the Emeishan large igneous province (ELIP) and the correlations between basalts and mafic–ultramafic intrusions. Because of the lack of clear spatial and temporal variations of different types of basalts, we suggest that the basalts in the ELIP cannot be classified into high-Ti and low-Ti groups, by TiO2 contents and/or Ti/Y ratios. The distinctive characteristics of these high-Ti and low-Ti lavas probably result largely from the different fractionating assemblages. Whether or not fractional crystallization of the Fe–Ti oxides occurred probably is the key factor that controls the Ti abundances and Ti/Y ratios in the residual melts, e.g., lavas, although the nature of the mantle sources, variable degrees of partial melting of mantle and crustal contamination also influence the geochemical signatures of the lavas. Therefore, neither Ti abundance nor Ti/Y ratios in basalts can reflect the nature of their mantle source. Moreover, the different types of mafic–ultramafic intrusions in the ELIP cannot simply be attributed to be genetically related special types of basalts, either high-Ti or low-Ti basalts. It is likely that they are merely the cumulus phases, i.e. chamber or conduit of the basaltic lavas. Hence, caution should be exercised in the use of high-Ti or low-Ti basalts as prospecting vectors for ore deposits in the region. Potential implications are proposed that both the Fe–V–Ti oxide and Cu–Ni–(PGE) sulfide mineralization in the ELIP intrusions is largely due to the variable differentiation and crustal contamination during magmatic processes. 相似文献
993.
强震条件下碎裂岩体崩塌机理及崩塌后壁对堆积体稳定性影响研究 总被引:2,自引:0,他引:2
5 12 汶川地震的强震作用诱发产生了大量崩塌地质灾害,且多发生于碎裂结构岩体中。崩塌后斜坡后缘岩体及前缘堆积体的稳定性和后缘岩体对前缘堆积体稳定性的影响研究同样是震后灾害所面临的问题。以干河沟沟口斜坡为例,在分析该斜坡结构特征及崩塌机理的基础上,采用二维离散元软件UDEC模拟了斜坡在天然或强震条件下的稳定状态和可能失稳过程; 运用极限平衡法对陡壁岩体再次崩塌,产生新物质堆载在现有崩塌堆积体后缘前、后分别建立模型进行了稳定性分析。研究结果表明:碎裂岩体崩塌过程可分为应力重分布、潜在崩塌体形成和地震诱发崩塌3个阶段。崩塌堆积体在考虑后缘堆载作用之前,在天然或地震环境下均处于相对稳定状态,考虑堆载作用之后,其可能会在地震条件下失稳。离散元法和极限平衡法的组合使用,对于解决同类斜坡的同类问题切实可行。 相似文献
994.
995.
996.
Yaping Liu Shugui Hou Sungmin Hong Soon-Do Hur Khanghyun Lee Yetang Wang 《Environmental Earth Sciences》2011,63(2):311-320
Samples collected from a 0.87 m snow pit at a high altitude site in the Cho Oyu range, Himalayas were measured for V, Cr,
Mn, Co, Ni, Cu, Zn, As, Rb, Sr, Cd, Sn, Sb, Ba, Tl, Pb, Bi, Th, and U using inductively coupled plasma mass spectrometry.
In addition, major ions, oxygen stable isotopes, and microparticles were also measured to assist the interpretation of seasonal
variation of trace elements. The trace elements show a distinct seasonality, i.e., higher concentrations during the non-monsoon
season than those during the monsoon season. Significant correlation is observed between Ba and the other trace elements.
Crustal enrichment factor (EFc) analysis indicates that V, Mn, Co, Ni, Rb, Sr, and Th originate mainly from crustal dust, while anthropogenic inputs make
an important contribution to the other trace elements (i.e., Cu, Zn, As, Cd, Sn, Sb, Ti, Pb, Bi, and U). Evidence from air
mass back trajectories suggests that atmospheric trace element pollution reaching the studied area is transported dominantly
by Indian summer monsoon during the monsoon season, while it is transported mainly by the westerlies during the non-monsoon
season. 相似文献
997.
998.
Using hydrographic data covering large areas of ocean for the period from June 21 to July 5 in 2009,we studied the circulation structure in the Luzon Strait area,examined the routes of water exchange between the South China Sea(SCS) and the Philippine Sea,and estimated the volume transport through Luzon Strait.We found that the Kuroshio axis follows a e-shaped path slightly east of 121uE in the upper layer.With an increase in depth,the Kuroshio axis became gradually farther from the island of Luzon.To study the water exchange between the Philippine Sea and the SCS,identification of inflows and outflows is necessary.We first identified which flows contributed to the water exchange through Luzon Strait,which differs from the approach taken in previous studies.We determined that the obvious water exchange is in the section of 121°E.The westward inflow from the Philippine Sea into the SCS is 6.39 Sv in volume,and mainly in the 100±500 m layer at 19.5°±20°N(accounting for 4.40 Sv),while the outflow from the SCS into the Philippine Sea is concentrated in the upper 100 m at 19°±20°N and upper 400 m at 21°±21.5°N,and below 240 m at 19°±19.5°N,accounting for 1.07,3.02 and 3.43 Sv in volume transport,respectively. 相似文献
999.
Fucoidan, a group of sulfated heteropolysaccharides, was extracted from Laminaria japonica, an important economic alga species in China. The anticoagulant activity of fucoidan and its derivatives (including sulfated, phosphorylated, and aminated fucoidan) was examined using in-vitro anticoagulant systems. The correlation between chemical variations within the fucoidan group and anticoagulant activity was determined. The in-vitro anticoagulant properties of fucoidan and its derivatives were determined by measuring activated partial thromboplastin time (APTT), prothrombin time (PT), and thrombin time (TT). The results indicate anticoagulant activity in all samples using APTT and TT assays; however, only the fucoidan derivatives affected the PT assay. Thus, the fucoidan derivatives were able to inhibit both intrinsic and extrinsic blood coagulants. Fucoidan (FPS) and its derivatives presented better anticoagulant activity than low molecular weight fucoidan (DFPS) and its derivatives, suggesting that molecular weight and proper conformation are contributing factors for anticoagulant activity of polysaccharides. Amino groups have a positive charge and can thus change the charge density of fucoidan. Accordingly, among the tested samples, aminated fucoidan (NF) was the most active reflecting the importance of charge density for anticoagulant activity. Available data obtained using in-vitro models suggest that the sulfate content, sulfate/total-sugar ratio, molecular weight, and the substituted group of fucoidan are important factors for anticoagulant activity but that the influence of sulfate, phosphate and amino groups on anticoagulant activity was different. 相似文献
1000.
土地利用变化对吴江市水田土壤有机碳储量的影响分析 总被引:2,自引:0,他引:2
农业表层土壤碳库容易受人为强烈干扰,而又可以在较短的时间尺度上进行调节,当今我国经济发达地区土地利用变化必然会对土壤固碳产生重要影响。本研究以江苏省吴江市水稻土为例,利用新一代中分辨率成像光谱仪(MODIS)和TM/ETM影像提取了1984年稻田面积,以及这部分稻田在2000-2005年的土地利用变化状况。研究中以最大似然法对TM/ETM、MODIS影像应用归一化植被指数(NDVI)、增强型植被指数(EVI)和陆地水分指数(LSWI)掩膜的方法作了识别提取;同时,结合第二次全国土壤普查、2003年耕地地力调查点和吴江市农林局土肥指导站长期定位点的土壤有机碳数据估算了1984年和2000-2005年土壤碳库变化情况。结果表明:近20多年来尽管吴江市水稻土水耕熟化过程中有机碳总体呈增加的趋势,但由于大量稻田被非农用地所取代,导致土壤固碳能力大幅度下降,尤其从2001年开始从"碳汇"变成"碳源"。因此,在我国经济发达区应密切关注耕地转换成非农用地而导致的土壤有机碳的损失。 相似文献