Ion probe dating of a migmatite in SW Sweden: the fate of zircon in crustal processes     

A. Scherstn  S. . Larson  D. H. Cornell  J. Stigh 《Precambrian Research》2004,130(1-4):251-266

A migmatitic orthogneiss in the Western Segment in the Sveconorwegian Province of the Baltic Shield was dated using the ion-probe U–Pb method on zircon grains, which were also analysed for rare earth elements. Mesosome zircons have 1.605±0.010 Ga magmatic cores, which places the gneiss protolith in the same 1.61–1.59 Ga time bracket as continental arc-related gneisses, abundant in this part of the Sveconorwegian Province. These cores show REE profiles with strong HREE enrichment, positive Ce- and negative Eu-anomalies, typical of magmatic zircon. Migmatite leucosomes are folded and parallel with or slightly discordant to the fabric. They contain a small population of zircon with cores and metamorphic rims, which are interpreted as xenocrysts incorporated in the leucosome during melting of the mesosome. CL-bright metamorphic embayments and rims on xenocrysts reflect 1.01±0.05 Ga Sveconorwegian metamorphic reworking. Ce-anomalies are nearly absent and Eu-anomalies are reduced relative to igneous spots. This is probably a feature of fluid controlled environments where Ce and Eu oxidation states are buffered by the metamorphic fluid. From this and discordant rims from the mesosome we also conclude that the rims formed by reworking of the older zircon where the Pb-loss was also fluid induced. In the leucosome veins, magmatic acicular zircon gives 0.92±0.01 Ga, ascribed to the crystallisation of the veins. They originated by local melting, probably augmented by magma that formed at a deeper level. Widespread granitic and noritic late-Sveconorwegian magmatism close to 0.92 Ga in other parts of the Western Segment has equivalents in the Norwegian sectors of the Sveconorwegian Province. Leucosome formation was therefore part of a regional event related to exhumation of the Sveconorwegian Eastern Segment. We also provide the first unequivocal evidence for ductile deformation related to late-Sveconorwegian magmatism.  相似文献   

基于集对分析的水资源变化趋势的统计预测   总被引：15，自引：2，他引：15  

冯利华张行才  龚建林 《水文》2004,24(2):11-14

根据集对分析(SPA)的原理和方法，对水资源变化趋势的预测进行了研究。利用前期的预测因子进行计算，可以使集对分析具有预测功能。通过反复调整预测因子各区段的分界值，可以使水资源要素计算等级和实际等级的历史拟合率达到最大，其结果是比较好的。这是对水资源变化趋势的预测研究的一种新尝试。  相似文献   

基于集对分析和模糊集合论的水体营养化评价模型的应用研究   总被引：15，自引：0，他引：15  

王栋朱元姓  赵克勤 《水文》2004,24(3):9-13,41

尝试在水环境评价领域引入并应用集对分析和模糊集合论，结合水体营养化等水环境评价中模式识别、等级评价问题的实际应用，将相关的概念和理论进行拓广，定义了广义联系熵和广义相对隶属度。分别建立了基于集对分析的水体营养化评价一级模型和基于集对分析一模糊集合论的水体营养化评价二级模型。我国12个有代表性的湖库营养化程度评价的应用实例表明：所建模型的评价结果与调查结果相符，与单一模糊模式识别结果基本相符；二级模型与一级模型和单一模糊模式相比，评价结果相对全面，更符合用水障碍调查结果的实际情况；而且从广义联系熵判断，二级模型的广义联系熵较一级模型和单一模糊模式大一些，即更好地反映了待评价水样与评价标准两个集合的确定不确定关系和联系程度，从而在一定程度上验证了所建模型的有效性和简便性。文中所用理论方法和所建模型也可推广应用于其他领域。  相似文献   

Electrokinetic remediation of an electroplating site: design and scale-up for an in-situ application in the unsaturated zone   总被引：1，自引：0，他引：1  

S. Wieczorek  H. Weigand  M. Schmid  C. Marb   《Engineering Geology》2005,77(3-4):203-215

In-situ electrokinetic remediation of contaminated soils requires integrated approaches and adequately engineered setups to control relevant mass fluxes. Based on laboratory findings, this study presents the design of a pilot-scale remediation at an operating electroplating site. The fine-textured soil developed from Jurassic limestone exhibits a chromium, copper, nickel, and zinc contamination down to depths of more than 4 m. The feasibility of an electrokinetic remediation in the unsaturated zone was tested in a lab-scale experiment with subsoil material sampled at the site. The electrodes were placed in water-impermeable, ion-selective membrane wells. This construction allows the necessary watering of the electrodes, maintains unsaturated conditions in the soil compartment, and enables the transfer of contaminant ions into the wells. In addition, the soil is protected from pH changes caused by water electrolysis at the electrodes. The setup includes a watering and drainage system to compensate the electroosmotic water flux and impede desiccation of the anodic region. With a direct current of 70 V and an electric field strength of 2.2 V cm⁻¹, contaminant removal rates amounted up to 27% and 66% (w/w) of the initial zinc/copper and chromium/nickel concentrations. Copper, nickel, and zinc accumulated in the cathode well, while chromate species were enriched in the anode well. Given the successful lab-scale remediation, the pilot plant was designed for the in-situ treatment of a soil volume of 12 m³ below a production hall. A power of 500 V DC at a maximum current of 30 A is supplied by a transformer rectifier. This yields an electric field strength comparable to the lab-scale experiment and thereby similar contaminant transport velocities. A vacuum distillation unit is employed for process water reuse and to control electrolyte conductivity. To cope with chlorine gas generation at the anodes a gas absorber unit is employed. According to the lab-scale results, about 2, 9, 9, and 15 kg zinc, chromium, copper, and nickel, respectively, are expected to be removed from the field plot during an operation time of 10 months.  相似文献   

SIMS analyses of oxygen isotopes: Matrix effects in Fe-Mg-Ca garnets     

Daniel Vielzeuf  Michel Champenois  Fabrice Brunet 《Chemical Geology》2005,223(4):208-226

Large instrumental mass fractionation (IMF) may occur during measurements of oxygen isotope ratios by SIMS. Part of this fractionation depends on crystal structure and mineral composition. In order to improve the accuracy of SIMS measurements, we gathered 6 commonly used garnet standards and prepared 6 others to adequately cover the composition range Alm_0-73, Prp_0-99, Grs_0-20. Electron microprobe analyses were performed at UBP-Clermont to check the chemical homogeneity of these standards. Oxygen isotope compositions were determined by laser fluorination and mass spectrometry at UW-Madison. Ten SIMS sessions and 336 δ¹⁸O measurements at CRPG-Nancy, on a Cameca IMS1270 instrument, demonstrate that the standards are homogeneous with external reproducibility of 0.3‰ (1σ). In terms of δ¹⁸O, SIMS measurements indicate that, during a single session, IMF can vary up to 6.3‰ from one garnet standard to another. In most of the sessions, IMF can be correlated with the grossular content. However, for a satisfactory correction scheme, we suggest the combination of the 3 main components (Ca, Fe, Mg). This is done using a simple least square calculation routine. The correction coefficients determined for each session can be used to calculate the IMF and correct the measured isotopic ratio of a garnet of known chemical composition. This way, we were able to reproduce the δ¹⁸O values of most of the Fe-Mg-Ca garnet standards within ± 0.6‰. Interestingly, the use of only 3 end-member standards (AlmCMG, PrpMM, GrsSE) plus a standard of intermediate composition (e.g. UWG-2) is sufficient to reproduce δ¹⁸O within the same precision. Thus, linear interpolation among end-member standards is satisfactory in the case of the garnet solid-solutions. Two studies carried out on zoned garnets from the Alps and the Pyrenees indicate that matrix effects become significant when variations in grossular contents are important (> 10%). In order to obtain reliable isotope ratio measurements on Fe-Mg-Ca garnets using a SIMS, we suggest a correction scheme using at least 3 reliable end-member standards plus a standard of intermediate composition (a garnet standard closest to the average composition of the analysed garnet). This allows cross-checking and incorporates a correction based on the variations in composition of zoned crystals.  相似文献   

Quick clay—A case study of chemical perspective in Southwest Sweden     

Yvonne Andersson-Sköld  J. Kenneth Torrance  Karin Odén  Karin Rankka 《Engineering Geology》2005,82(2):107-118

Quick clay, a soil that changes from normal firm ground to a liquid mass when it is disturbed, has been involved in most of the large and serious clay slides in Sweden, Norway and Canada. The location, time of occurrence and size of quick clay slides are difficult to predict and large slides may cause great devastation. Some geochemical studies of Swedish quick clay were done in the 1960s and early 1970s, but no systematic studies of the interrelationships of pore water chemistry, mineralogy, geotechnical properties and other parameters on quick clays in Sweden have been published. Such studies are of national and general interest because of the many combinations of rock flour source areas and sedimentation conditions that occurred across central Sweden and into the Baltic Sea area during deglaciation. In this study, geotechnical properties related to the in situ chemistry at one quick clay site were extensively studied, and spot sampling was conducted at two other locations in Southwest Sweden. In this area the clay minerals mainly are non-expanding phyllosilicate minerals (illite) and primary minerals (quartz, feldspar), which is consistent with previous studies of quick clay mineralogy. Extensive leaching has occurred at all three locations. At the extensively studied site, Surte, the lowest salinity was found at the greatest depth, inferring that the leaching by fresh water was accomplished by water movement upward and laterally through the sediment from the underlying bedrock. This is consistent with the local setting where bedrock hills rise sharply to over 100 m above the marine sediment surface. An artesian pressure would also be anticipated at this location. There is a correlation (negative) between sensitivity and salinity but there is an indication that the maximum salinity or electrical conductivity consistent with the quick clay behaviour is higher than reported elsewhere. However, for high sensitivities the salinity is about the same as reported elsewhere. In the deepest part of the borehole, there is a higher content of Fe and Al in the pore water, indicating reduced state. Further work is needed to confirm the difference in salinity and to investigate the possible interplay of salinity and potential dispersing agents such as the role of anoxic conditions, in this region. Further work is especially needed in the locations where the sediment accumulation occurred under lower salinity conditions. At all three locations, high remoulded shear strength and low sensitivity have been seen near the surface together with a decrease in pore water cation concentrations.  相似文献   

Trace element fractionation during high-grade metamorphism and crustal melting—constraints from ion microprobe data of metapelitic, migmatitic and igneous garnets and implications for Sm–Nd garnet chronology     

S. Jung  E. Hellebrand 《Lithos》2006,87(3-4):193-213

Rare earth element (REE) and other trace element (Y, Sr, Ti, Cr, V, Na) abundances in garnet from a garnet-bearing metapelite, a pelitic migmatite, a syn-tectonic granite and a post-tectonic leucogranite were measured by secondary ion mass spectrometry (SIMS) in order to identify the effective variables on the trace element distribution between garnet and the host rock. Garnet from the garnet-bearing metapelite, the pelitic migmatite and the syn-tectonic granite is zoned with respect to REE. The cores are enriched by a factor of 2–3 relative to the rims. For the garnets from the garnet-bearing metapelite equilibrium distribution following a simple Rayleigh fractionation is responsible for the decreasing concentrations in REE from core to rim. Garnet from the pelitic migmatite shows a more complex trace element pattern following distinct enrichment and depletion patterns for Ti, V, Cr and REE from core to rim. These features suggest disequilibrium between garnet and the associated melt in which the enrichment of trace elements probably correspond to a period of open-system behaviour in these rocks at a time when the garnet, originally nucleated in the metamorphic environment was incorporated into the melt. The garnet from the syn-tectonic granite shows stepwise decreasing concentrations in REE from core to rim: a REE-rich core can be distinguished from a broad REE-depleted rim. Notably, from core to rim an inflection of the Yb / Er and Yb / Dy ratios is visible. Whereas the decrease of HREE abundance in the core region of the garnet from the syn-tectonic granite may arise from equilibrium partitioning during garnet growth, the inflection can be interpreted as a result of partial melting. Garnet cores with high Yb / Er and Yb / Dy >  1 nucleated in the metamorphic environment without the presence of a melt whereas the rims with lower Yb / Er and Yb / Dy <  1 crystallized in the presence of a melt. Garnet from the leucogranite has lower REE abundances and is considered to be of igneous origin. In contrast to garnet from the other samples, its core has low trace element abundances, whereas its rim is significantly enriched in REE but depleted in Ti. These features suggest that only the outermost rim was in equilibrium with the melt. For this garnet, liquid diffusion controlled partitioning is more likely to explain the extreme trace element variation. An evaluation of Sm and Nd concentrations in garnet and a comparison of Sm–Nd and U–Pb garnet ages and U–Pb monazite ages form the terrane indicate that the observed LREE systematics in the different garnet species are a primary feature and are not homogenized by volume diffusion during high grade amphibolite facies conditions.  相似文献   

亚洲夏季风爆发与热源强迫下的热带大气Rossby波     

陈哲  李崇银 《大气科学》2006,30(6):1227-1235

对南海夏季风爆发前的风场和局地对流凝结加热强迫作用进行了合成分析, 表明南海夏季风爆发前局地对流凝结加热作用对与南海夏季风爆发密切相关的低频涡对的产生起着重要作用.然后, 从动力学的角度研究了带有外部热源强迫的赤道β平面上的Rossby波, 利用Gardner-Morikawa变换和摄动展开方法, 得到了热源强迫下描写赤道Rossby的mKdV方程, 进而得到了不同热源形式下切变气流中赤道非线性Rossby波的解析解.结果表明, 不同类型的热源对赤道Rossby波的结构起着非常重要的作用, 同时也为南海夏季风爆发前低频涡对的形成给出了一种动力学解释.  相似文献   

Solar activity effects in the ionospheric D region   总被引：2，自引：0，他引：2  

A. D. Danilov 《Annales Geophysicae》1998,16(12):1527-1533

Variations in the D-region electron concentration within the solar activity cycle are considered. It is demonstrated that conclusions of various authors, who have analyzed various sets of experimental data on [e], differ significantly. The most reliable seem to be the conclusions based on analysis of the [e] measurements carried out by the Faraday rotation method and on the theoretical concepts on the D-region photochemistry. Possible QBO effects in the relation of [e] to solar activity are considered and an assumption is made that such effects may be the reason for the aforementioned disagreement in conclusions on the [e] relation to solar indices.Paper Presented at the Second IAGA/ICMA (IAMAS) Workshop on Solar Activity Forcing of the Middle Atmosphere, Prague, August 1997  相似文献   

论造山带中超镁铁岩的成对分布     

张旗  张魁武  李达周 《岩石矿物学杂志》1987,6(2):97-103

文中把俯冲-碰撞型造山带中出露的超镁铁岩分为蛇绿岩型和火山弧型两类,后者又细分为义敦型、阿拉斯加型及橄榄岩-闪长岩型等三个亚类。在同一造山带内,如果蛇绿岩与火山弧型超镁铁岩在空间上相伴分布,侵位的时间相近,则可共同组成一对超镁铁岩带。蛇绿岩代表封闭的洋盆残迹,而火山弧型岩体则来自过渡壳之下、消减带之上的地幔楔。文中还概述了造山带中成对超镁铁岩的分布、产出条件及其在造山带研究中的意义。  相似文献