Evolution of subcontinental lithospheric mantle beneath eastern China: Re–Os isotopic evidence from mantle xenoliths in Paleozoic kimberlites and Mesozoic basalts     

Hong-Fu Zhang  Steven L. Goldstein  Xin-Hua Zhou  Min Sun  Jian-Ping Zheng  Yue Cai 《Contributions to Mineralogy and Petrology》2008,155(3):271-293

The ages of subcontinental lithospheric mantle beneath the North China and South China cratons are less well-constrained than the overlying crust. We report Re–Os isotope systematics of mantle xenoliths entrained in Paleozoic kimberlites and Mesozoic basalts from eastern China. Peridotite xenoliths from the Fuxian and Mengyin Paleozoic diamondiferous kimberlites in the North China Craton give Archean Re depletion ages of 2.6–3.2 Ga and melt depletion ages of 2.9–3.4 Ga. No obvious differences in Re and Os abundances, Os isotopic ratios and model ages are observed between spinel-facies and garnet-facies peridotites from both kimberlite localities. The Re–Os isotopic data, together with the PGE concentrations, demonstrate that beneath the Archean continental crust of the eastern North China Craton, Archean lithospheric mantle of spinel- to diamond-facies existed without apparent compositional stratification during the Paleozoic. The Mesozoic and Cenozoic basalt-borne peridotite and pyroxenite xenoliths, on the other hand, show geochemical features indicating metasomatic enrichment, along with a large range of the Re–Os isotopic model ages from Proterozoic to Phanerozoic. These features indicate that lithospheric transformation or refertilization through melt-peridotite interaction could be the primary mechanism for compositional changes during the Phanerozoic, rather than delamination or thermal-mechanical erosion, despite the potential of these latter processes to play an important role for the loss of garnet-facies mantle. A fresh garnet lherzolite xenolith from the Yangtze Block has a Re depletion age of ∼1.04 Ga, much younger than overlying Archean crustal rocks but the same Re depletion ages as spinel lherzolite xenoliths from adjacent Mesozoic basalts, indicating Neoproterozoic resetting of the Re–Os system in the South China Craton.  相似文献   

Comparison of arsenic concentrations in simultaneously-collected groundwater and aquifer particles from Bangladesh,India, Vietnam,and Nepal     

A. van Geen  K. Radloff  Z. Aziz  Z. Cheng  M.R. Huq  K.M. Ahmed  B. Weinman  S. Goodbred  H.B. Jung  Y. Zheng  M. Berg  P.T.K. Trang  L. Charlet  J. Metral  D. Tisserand  S. Guillot  S. Chakraborty  A.P. Gajurel  B.N. Upreti 《Applied Geochemistry》2008

One of the reasons the processes resulting in As release to groundwater in southern Asia remain poorly understood is the high degree of spatial variability of physical and chemical properties in shallow aquifers. In an attempt to overcome this difficulty, a simple device that collects groundwater and sediment as a slurry from precisely the same interval was developed in Bangladesh. Recently published results from Bangladesh and India relying on the needle-sampler are augmented here with new data from 37 intervals of grey aquifer material of likely Holocene age in Vietnam and Nepal. A total of 145 samples of filtered groundwater ranging in depth from 3 to 36 m that were analyzed for As (1–1000 μg/L), Fe (0.01–40 mg/L), Mn (0.2–4 mg/L) and S (0.04–14 mg/L) are compared. The P-extractable (0.01–36 mg/kg) and HCl-extractable As (0.04–36 mg/kg) content of the particulate phase was determined in the same suite of samples, in addition to Fe(II)/Fe ratios (0.2–1.0) in the acid-leachable fraction of the particulate phase. Needle-sampler data from Bangladesh indicated a relationship between dissolved As in groundwater and P-extractable As in the particulate phase that was interpreted as an indication of adsorptive equilibrium, under sufficiently reducing conditions, across 3 orders of magnitude in concentrations according to a distribution coefficient of 4 mL/g. The more recent observations from India, Vietnam and Nepal show groundwater As concentrations that are often an order of magnitude lower at a given level of P-extractable As compared to Bangladesh, even if only the subset of particularly reducing intervals characterized by leachable Fe(II)/Fe >0.5 and dissolved Fe >0.2 mg/L are considered. Without attempting to explain why As appears to be particularly mobile in reducing aquifers of Bangladesh compared to the other regions, the consequences of increasing the distribution coefficient for As between the particulate and dissolved phase to 40 mL/g for the flushing of shallow aquifers of their initial As content are explored.  相似文献   

On the Assessment of Failure in Slope Stability Analysis by the Finite Element Method   总被引：3，自引：0，他引：3  

H. Zheng  D. F. Liu  C. G. Li 《Rock Mechanics and Rock Engineering》2008,41(4):629-639

  相似文献   

Considerations for conducting incubations to study the mechanisms of As release in reducing groundwater aquifers     

Kathleen A. Radloff  Anya R. Manning  Brian Mailloux  Yan Zheng  M. Moshiur Rahman  M. Rezaul Huq  Kazi M. Ahmed  Alexander van Geen 《Applied Geochemistry》2008

Microbial Fe reduction is widely believed to be the primary mechanism of As release from aquifer sands in Bangladesh, but alternative explanations have been proposed. Long-term incubation studies using natural aquifer material are one way to address such divergent views. This study addresses two issues related to this approach: (1) the need for suitable abiotic controls and (2) the spatial variability of the composition of aquifer sands. Four sterilization techniques were examined using orange-colored Pleistocene sediment from Bangladesh and artificial groundwater over 8 months. Acetate (10 mM) was added to sacrificial vials before sterilization using either (1) 25 kGy of gamma irradiation, (2) three 1-h autoclave cycles, (3) a single addition of an antibiotic mixture at 1× or (4) 10× the typical dose, and (5) a 10 mM addition of azide. The effectiveness of sterilization was evaluated using two indicators of microbial Fe reduction, changes in diffuse spectral reflectance and leachable Fe(II)/Fe ratios, as well as changes in P-extractable As concentrations in the solid phase. A low dose of antibiotics was ineffective after 70 days, whereas autoclaving significantly altered groundwater composition. Gamma irradiation, a high dose of antibiotics, and azide were effective for the duration of the experiment.  相似文献   

Composition and quality of coals in the Huaibei Coalfield, Anhui, China   总被引：3，自引：0，他引：3  

Liugen Zheng  Guijian Liu  Lei Wang  Chen-Lin Chou 《Journal of Geochemical Exploration》2008,97(2-3):59-68

The Huaibei Coalfield, Anhui Province, China, is one of the largest coalfields in China. The coals of Permian age are used mainly for power generation. Coal compositions and 47 trace elements of the No. 10 Coal of the Shanxi Formation, the No. 7, 5, and 4 Coals of the Lower Shihezi Formation, and the No. 3 Coal of the Upper Shihezi Formation from the Huaibei Coalfield were studied. The results indicate that the Huaibei coals have low ash, moisture, and sulfur contents, but high volatile matter and calorific value. The ash yield increases stratigraphically upwards, but the volatile matter and total sulfur contents show a slight decrease from the lower to upper seams. Magmatic intrusion into the No. 5 Coal resulted in high ash, volatile matter, and calorific value, but low moisture value in the coal. Among the studied 47 trace elements, Ba, Co, Cr, Cu, Hg, Mo, Ni, Pb, Sb, Th, U, V, and Zn are of environmental concerns. Four elements Hg, Mo, Zn, and Sb are clearly enriched in the coals as compared with the upper continental crust.  相似文献   

渤海湾盆地新生界生油岩系底界面温度分布   总被引：3，自引：1，他引：2       下载免费PDF全文

龚育龄  王良书  刘绍文  李成  韩用兵  李华  蔡进功 《地质科学》2008,43(1):1-11

依据渤海湾盆地2000余口测温井的地温梯度数据、地层岩性描述、分层数据以及钻井资料,计算了该盆地各生油岩系底界面的温度。统计结果表明:渤海湾盆地沙河街组大部分凹陷区地层底界面温度介于90℃至150℃,目前仍具有大量生油的温度条件,而在隆起或一些凸起地区,该地层组段温度普遍小于90℃,未能达到生油的温度指标。东营组和孔店组地层也仍具有一定的生油温度条件。研究还表明:地层温度与地层界面埋深密切相关,温度随界面埋深的增大而升高,沉积厚度大的凹陷区地层界面温度大于沉积厚度小的凸起区或斜坡地带,说明地层界面埋深是决定地温高低的主要控制因素,而地温梯度对地层界面温度的影响相对较小。  相似文献   

塔里木西部地区古生代断裂活动的方式和机制   总被引：15，自引：2，他引：13       下载免费PDF全文

李曰俊  吴根耀  孟庆龙  师骏  冯晓军  郑民 《地质科学》2008,43(4):727-745

基于系统的地震剖面解释及其与塔中地区的对比,本文探讨了塔里木西部地区古生代断裂活动的方式和机制。玛东断裂带是一条宽阔的北东向盖层滑脱型褶皱冲断带,前展式向东南扩展,冲断作用发生在奥陶纪末。巴东断裂(吐土休克Ⅱ号断裂)为北西向基底卷入型冲断带,奥陶纪末和中二叠世末发生冲断。巴西断裂和塔参2井南断裂是海西期的正断层。塔里木古板块古生代的发育受邻侧的造山带演化制约,近东西向和北东向断裂奥陶纪末的冲断是继承基底构造发育的。塔中地区的近北西向断裂是晚寒武世的新生断裂,加里东运动可分为两幕:奥陶纪末的冲断(艾比湖运动)和晚志留-中泥盆世的冲断-走滑,后者向西明显减弱。塔里木西部的部分北西向断裂(如康西断裂)可归入塔中北西向断裂系。北东向的玛东断裂带是其西的向北(东)冲断的吐木休克断裂带与其东的向南偏东冲断的塔中8-1井——塔中5井断裂带之间的调节断层。  相似文献   

冻融循环对塑料土工格栅拉伸性能的影响     

汪恩良  徐学燕  常俊德  钟华  高占坤 《冰川冻土》2008,30(4)

在-25～ 25 ℃环境温度条件下, 采用水中冻融和空气中冻融两种方式, 经过50次冻融循环后, 在15 ℃、 0 ℃、 -10 ℃、 -20 ℃和-35 ℃工况下对土工格栅试样进行了拉伸性能的试验研究, 获得了聚乙烯塑料土工格栅的极限承载力、最大延伸率、 不同延伸率对应的应力值等数据. 试验结果表明, 聚乙烯塑料土工格栅在低温时抗拉性能明显提高, 从 15 ℃降至-35 ℃时, 5%延伸率对应的抗拉强度提高107%, 极限承载力提高19%. 同时, 聚乙烯塑料土工格栅极限延伸率随温度降低呈线形关系降低, 从 15 ℃降至-35 ℃时, 极限延伸率降低80%.  相似文献   

四川大陆槽稀土矿床碳酸岩-英碱正长岩锆石U-Pb年代学和Hf同位素性质及其地质意义   总被引：5，自引：2，他引：3  

田世洪  侯增谦  杨竹森  杨志明  袁忠信  王彦斌  谢玉玲  刘英超  李政 《岩石学报》2008,24(3)

川西冕宁-德昌稀土成矿带是中国最重要的稀土成矿带之一,所有稀土矿床均与碳酸岩-正长岩杂岩体有关.前人研究表明,牦牛坪、木落寨和里庄碳酸岩-碱性杂岩体成岩年龄与其相应矿床的成矿年龄基本一致,而大陆槽正长岩年龄与REE矿床的成矿年龄相差甚远.本文对大陆槽碳酸岩、英碱正长岩进行了SHRIMP U-Pb锆石年代学和LA-MC-ICPMS锆石Hf同位素原位测量,它们的形成年龄分别为12.99±0.94Ma、14.53±0.31Ma,表明两者是同时形成的,且与其成矿年龄基本一致.碳酸岩和正长岩的εHf(t)值、Hf模式年龄与它们的εNd(t)值、Nd模式年龄所展现出来的特征一致,说明在其形成过程中有地壳物质的加入.  相似文献   

杞麓湖泄水暗河淤塞的不良环境效应分析   总被引：1，自引：0，他引：1  

康晓波  王宇  张华 《水文地质工程地质》2008,35(6):121-124

杞麓湖岩溶盆地为一封闭的汇水径流型断陷湖盆,汇水面积内的地表地下水流入杞麓湖后,从岳家营落水洞灌入式补给高寨暗河系统,通过地下暗河岩溶管道径流至东部的华宁盆地后以暗河形式排泄。由于泥砂堵塞暗河岩溶管道,导致落水洞最大泄流量不断减小,削弱了杞麓湖的水资源调节功能,引发洪涝灾害;淤塞物及径流迟缓引起污染、污染水置换缓慢又加剧了暗河污染;为解决淹蓄矛盾修建的调蓄水隧道施工以来,岩溶渗漏使得隧道沿线地下水位下降,疏干了山区农村水源,导致地面沉降变形,间接引出一系列新的环境地质问题。  相似文献