New experimental determination of Li and B partition coefficients during upper mantle partial melting   总被引：1，自引：1，他引：0  

Luisa Ottolini  Didier Laporte  Nicola Raffone  Jean-Luc Devidal  Brieuc Le Fèvre 《Contributions to Mineralogy and Petrology》2009,157(3):313-325

Despite the growing interest for Li and B as geochemical tracers, especially for material transfer from subducting slabs to overlying peridotites, little is known about the behaviour of these two elements during partial melting of mantle sources. In particular, mineral/melt partition coefficients for B and to a lesser extent Li are still a matter of debate. In this work, we re-equilibrated a synthetic basalt doped with ~10 ppm B and ~6 ppm Li with an olivine powder from a spinel lherzolite xenolith at 1 GPa–1,330°C, and we analyzed Li and B in the run products by secondary ion mass spectrometry (SIMS). In our experiment, B behaved as a highly incompatible element with mineral/melt partition coefficients of the order of 10⁻² (D ^ol/melt = 0.008 (0.004–0.013); D ^opx/melt = 0.024 (0.015–0.033); D ^cpx/melt = 0.041 (0.021–0.061)), and Li as a moderately incompatible element (D ^ol/melt = 0.427 (0.418–0.436); D ^opx/melt = 0.211 (0.167–0.256); D ^cpx/melt = 0.246 (0.229–0.264)). Our partition coefficients for Li are in good agreement with previous determinations. In the case of B, our partition coefficients are equal within error to those reported by Brenan et al. (1998) for all the mineral phases analyzed, but are lower than other coefficients from literature for some of the phases (up to 5 times for cpx). Our measurements complement the data set of Ds for modelling partial melting of the upper mantle and basalt generation, and confirm that, in this context, B is more incompatible than previously anticipated.  相似文献   

Comparative behavior of Sr, Nd and Hf isotopic systems during fluid-related deformation at middle crust levels     

Béatrice Luais  Christian Le Carlier de Veslud  Yves Géraud 《Geochimica et cosmochimica acta》2009,73(10):2961-2977

We have carried out a comparative Rb-Sr, Sm-Nd and Lu-Hf isotopic study of a progressively deformed hercynian leucogranite from the French Massif Central, belonging to the La Marche ductile shear zone, in order to investigate the respective perturbation of these geochronometers with fluid induced deformation. The one-meter wide outcrop presents a strongly deformed and mylonitized zone at the center, and an asymmetric deformation pattern with a higher deformation gradient on the northern side of the zone. Ten samples have been carefully collected every 10 cm North and South away from the strongest deformed mylonitic zone. They have been analyzed for a complete major, trace element data set, oxygen isotopes, Rb-Sr, Sm-Nd and Lu-Hf isotopic systematics.We show that most of major and trace elements except SiO₂, alkaline elements (K₂O, Rb), and some metal transition elements (Cu), are progressively depleted with increasing deformation. This depletion includes REE + Y, but also HFS elements (Ti, Hf, Zr, Nb) which are commonly considered as immobile elements during upper level processes. Variations in elemental ratios with deformation, e.g. decrease in LREE/MREE- HREE, Nd/Hf, Th/Sr, increase in Rb/Sr, U/Th and constant Sr/Nd, lead to propose the following order of element mobility: U ? Th > Sr = Nd ? Hf + HREE. We conclude in agreement with previous tectonic and metallogenic studies that trace element patterns across the shear zone result from circulation of oxidizing F-rich hydrothermal fluids associated with deformation. A temperature of the fluid of 470-480 °C can be deduced from the δ¹⁸O equilibrium between quartz-muscovite pairs.Elemental fractionation induces perturbation of the Rb-Sr geochronometer. The well-defined ⁸⁷Rb/⁸⁶Sr-⁸⁷Sr/⁸⁶Sr correlation gives an apparent age of 294 ± 19 Ma, slightly younger than the 323 ± 4 Ma age of leucogranites in this area. This apparent age is interpreted as dating event of intense deformation and fluid circulation associated with mass transfer, and exhumation of the ductile crust shortly after the leucogranite emplacement. Sm-Nd and Lu-Hf isochron-type diagrams do not define any correlation, because of the low fractionated Sm/Nd and Lu/Hf ratios. Isotopic data demonstrate that only the Lu-Hf geochronometer system is not affected by fluid circulation and gives reliable T_DM age (1.29 ± 0.03 Ga) and ε_Hf signatures. By contrast, the Sm-Nd geochronometer system gives erroneous old T_DM ages of 2.84-4 Ga. There is no positive ε_Nd-ε_Hf correlation, because of decreasing ε_Nd values with deformation at constant ε_Hf values. However, ε_Nd-ε_Hf values remain in the broad ε_Nd-ε_Hf terrestrial array, which strongly indicates that fluid-induced fractionation can contribute to the width of the terrestrial array. The strong ε_Hf negative values of the leucogranite are similar to metasedimentary granulitic xenoliths from the French Massif Central and confirm the generation of the leucogranite by several episodes of reworking of the lower crust.  相似文献   

Coupling between finite and discrete element methods for the modelling of earth structures reinforced by geosynthetic     

P. Villard  B. Chevalier  B. Le HelloG. Combe 《Computers and Geotechnics》2009

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Managing environmental problems in Cuban karstic aquifers   总被引：1，自引：0，他引：1  

Leslie Molerio Leόn  Mario Parise 《Environmental Geology》2009,57(2):275-283

The study area is located along the Dead Sea Rift, the climate is considered arid in its southern margin near the Dead Sea, which is the lowest water reservoir found on the globe (412 m BSL), to semiarid in its northern part. During the last few decades, the water resources became depleted limiting the natural development of the agricultural settlements, which are the most common type of communities in the region. Previous studies suggested that a large amount of freshwater is lost as the result of salinization processes, which occur when fresh groundwater from the mountain aquifers, flow into the saline clastic Neogene aquifer complex. In order to comprehend this complex system, a detailed outlining of the regional hydrogeological system is essential. Since there are no boreholes, which penetrate the aquiferous rock sequences within the Rift, it was necessary to interpolate a large variety of data from several fields of geosciences. The methods applied included geological mapping, geophysical modeling based on interpretation of seismic profiles and geochemical modeling based on chemical and isotopic analysis of runoff, sediments and groundwater. The combined modeling based on results from the different types of analyses implied to several conclusions relevant to the regional water management policy: (1) groundwater becomes saline as it flows from the margins of the Rift to its center. Therefore, it is recommended to exploit it along the foothills of the rift escarpment. (2) Geophysical modeling indicated that the foothills and the Karstic mountain aquifer extend into the subsurface of the valley and can be farther exploited (up to 15 mm³ per annum) by relatively shallow wells. (3) Several mechanisms of groundwater salinization were deciphered: (a) the dense vertical faulting systems act as potential conduits for saline water, which flow-up from deep-seated sources and penetrate into the fresh aquifers. (b) Fresh groundwater in the clastic aquifer complex is rare, furthermore, two evaporates bodies were encountered (Auja and Zaharat el Qurein), also acting as sources for fresh water salinization. (c) Although the quantity of runoff recharge to the Jordan Valley aquifer complex is negligible, the increase in its salt-content (TDS) turns this negligible freshwater recharge to a significant contributor of salts.  相似文献   

MuSET: A multiparameter and high precision sensor for downhole spontaneous electrical potential measurements     

Philippe A. Pezard  Stéphanie Gautier  Tanguy Le Borgne  Bruno Legros  Jean-Luc Deltombe 《Comptes Rendus Geoscience》2009,341(10-11):957-964

On the basis of an existing multiparameter borehole fluid sensor (p, T, Cw, pH, Eh), a new downhole tool designed for 200 bars and 75 °C was developed to measure the spontaneous electrical potential in situ with great precision (better than a μV). To this end, the new sensor is based on the use of unpolarizable Pb/PbCl₂ electrodes either at the surface or downhole. In situ testing has demonstrated a capacity to identify several subsurface sources of natural electrical potential such as diffusion ones (membrane potential in the presence of clays, Fickian processes due to pore fluid salinity gradients), or else the electrokinetic mechanisms with gradients in pore fluid pressure. As a consequence, Multi-Sensors Electrical Tool (MuSET) might be used as an “electrical flowmeter” sensitive to both horizontal and vertical fluid flow in a vertical borehole.  相似文献   

Geomorphology Processes of Channel Planform Migration on Meandering Rivers     

LIN Zhipeng  SHAN Jingfu  and CHEN Le 《《地质学报》英文版》2017,91(Z1):134-135

<正>1 Introduction Morphological analysis on the planform migration structure of meandering river is an important basis for the reconstruction of evolution of paleochannel.Besides,it is a significant method for restoration of rivers through the  相似文献   

华北克拉通新太古代地壳增生:来自山西云中山地区TTG片麻岩和二长花岗片麻岩的证据   总被引：2，自引：2，他引：0  

康健丽  王惠初  肖志斌  孙义伟  曾乐  庞志斌  李建荣 《岩石学报》2017,33(9):2881-2898

通过详细的野外地质工作,本文在山西云中山地区识别出一套岩石组合完整的TTG片麻岩岩系,与TTG片麻岩共生的还有后期发育的二长花岗片麻岩。LA-ICP-MS锆石U-Pb定年结果表明,花岗闪长质片麻岩的形成时间为2486±9Ma,二长花岗片麻岩的形成时间为2448±11Ma。地球化学特征显示研究区TTG片麻岩为高铝TTG。奥长花岗质片麻岩总体表现为高SiO_2(69.82%~73.54%)、富Na_2O(4.19%~5.16%)、高CaO(1.45%~3.03%)的特征,Al_2O_3含量为14.31%~15.74%,铝饱和指数(A/CNK)为1.00~1.03,属富钠过铝质系列岩石;英云闪长质片麻岩的特征与奥长花岗片麻岩基本相似,但K_2O含量更低,CaO含量更高;花岗闪长质片麻岩SiO_2(61.23%~61.97%)含量相对偏低,Na_2O/K_2O为1.00~1.32,Al2O3含量为15.03%~15.73%,铝饱和指数(A/CNK)为0.96~1.05,为准铝质或过铝质系列岩石。与上述TTG片麻岩不同的是,本区出露的二长花岗片麻岩表现为富钾(K_2O/Na_2O=1.22~1.44)、贫Al_2O_3(12.81%~14.27%)的特征。岩石稀土总量较低(∑REE=52.71×10~(-6)~262.0×10~(-6)),轻稀土富集,重稀土亏损,轻、重稀土强烈分馏。微量元素具有富集K、Rb、Th等大离子亲石元素,亏损Nb、Ta、Sr、P、Ti等元素的特点,Cr、Ni等相容元素含量也较低,表现出岛弧岩浆的特征。花岗闪长片麻岩和二长花岗片麻岩εHf(t)值均为正值,前者成岩年龄与二阶段模式年龄较为接近,暗示其来源为2.5~2.6Ga的新生地壳,而后者成岩年龄与二阶段模式年龄则相差较多,其测点大都落在2.7~2.8Ga地壳演化线的区域内,表明二长花岗片麻岩来自于2.7~2.8Ga的古老地壳。根据上述地球化学特征,并结合区域地质特征,推测研究区高Al的TTG片麻岩是"平俯冲"状态下洋壳部分熔融的产物,而二长花岗片麻岩为底侵古老地壳部分熔融的产物,形成于大陆边缘弧的构造环境,代表云中山地区一次重要的以水平增生为主的地壳生长事件,同时也表明在新太古代末期,云中山地区已完成克拉通化,进入陆内演化阶段。  相似文献   

成矿区三维可视化与立体定量预测——以钦-杭成矿带庞西垌地区下园垌铅锌矿区为例   总被引：3，自引：1，他引：2  

高乐  卢宇彤  虞鹏鹏  肖凡 《岩石学报》2017,33(3):767-778

矿产资源是人类生存与社会进步的根本物质保障。近年来,随着地表矿、浅部矿产资源的日益枯竭,采用新技术、新方法的深部矿产资源预测成为地质勘查的主要研究方向。基于数字化、三维可视化及矿产定量预测为主的三维地质建模技术,为当前矿产资源远景预测与找矿工作提供了有力的工具。本文在现代成矿预测理论研究基础上,运用三维地质建模技术建立了钦杭成矿带下园垌矿区地质、地球物理、地球化学、钻孔等三维模型,揭示了区内构造地质特征、地球化学异常表征及地层岩体要素,据此探讨了矿床的成因及矿体分布特征。并在此基础上,采用证据权方法对研究区地质、地球物理、地球化学等多源信息进行融合,运用断裂缓冲区、地球化学异常、东岗岭组沉积岩地层等为证据因子来计算单位体积成矿后验概率,进行立体成矿预测,并圈定出铁锰矿、方铅闪锌矿、铅锌银综合矿等3处找矿有利靶区及估算出预测区内矿产资源储量总量为88710吨。研究结果表明:综合分析地质、地球物理、地球化学及钻孔数据进行矿区的三维地质空间定位、定量预测研究,可以有效的识别矿致异常信息,圈定找矿远景区,为成矿预测研究领域提供了新方向,可以将此方法应用至其他矿山。  相似文献   

伊宁地块石炭纪火山岩及其对构造演化的约束   总被引：6，自引：3，他引：3  

李永军  吴乐  李书领  李甘雨  沈锐  李钊  王祚鹏  汪振宇 《岩石学报》2017,33(1):1-15

西天山伊宁地块的构造格局及其演化之认识久存争议,倍受关注。分歧焦点有三:(1)石炭纪有无洋盆存在?(2)若有洋盆,何时闭合?(3)"沟-弧-盆"消亡时究竟是单向俯冲还是双向俯冲?若是单向俯冲,俯冲方向是由北向南或是相反(即俯冲极性)?因此,这些重大地质问题均聚焦于本区的火山岩。石炭纪火山岩是伊宁地块中的最主要建造和指示构造演化的关键层位,争论长久而激烈。本文认为,伊宁地块早石炭世发育弧前-岛弧-弧后盆地钙碱性火山-沉积建造,是塔里木板块北缘的主要组成部分;而晚石炭世碱性系列双峰式火山岩及其沉积组合则是大陆裂谷火山-沉积建造,形成于区域性伸展构造环境,是准噶尔板块与塔里木板块缝合后的陆内建造,因而古洋盆的关闭时限是早石炭世晚期(鄯善运动)。依据区内早石炭世建造的空间分布和变化规律,作者们认为古天山洋盆与当今地学界作为典型的日本沟-弧-盆体系有着极好的相似性和空间分布可对比性。石炭纪火山岩为本区的构造演化研究提供了重要的约束信息。  相似文献   

Estimation of undrained shear strength in moderately OC clays based on field vane test data     

Iok-Tong Ng  Ka-Veng Yuen  Le Dong 《Acta Geotechnica》2017,12(1):145-156

The undrained shear strength (s _u) of cohesive soils is a crucial parameter for many geotechnical engineering applications. Due to the complexities and uncertainties associated with laboratory and in situ tests, it is a challenging task to obtain the undrained shear strength in a reliable and economical manner. In this study, a probabilistic model for the s _u of moderately overconsolidated clays is developed using the Bayesian model class selection approach. The model is based on a comprehensive geotechnical database compiled for this study with field measurements of field vane strength (s _u), plastic limit (PL), natural water content (W _n), liquid limit (LL), vertical effective overburden stress (\(\sigma_{\nu }^{\prime }\)), preconsolidation pressure (\(\sigma_{\text{p}}^{\prime }\)) and overconsolidated ratio (OCR). Comparison study shows that the proposed model is superior to some well-known empirical relationships for OC clays. The proposed probabilistic model not only provides reliable and economical estimation of s _u but also facilitates reliability-based analysis and design for performance-based engineering applications.  相似文献