Kinetics of decompressional reactions in eclogitic rocks – formation of plagioclase coronas around kyanite     

D. Nakamura 《Journal of Metamorphic Geology》2002,20(3):325-333

This paper describes a kinetic study on reaction textures in eclogitic rocks from the Sulu region, eastern China. Some of the eclogitic rocks display a decompressional reaction texture, whereby kyanite grains are surrounded by plagioclase coronas and are never in contact with quartz. The change in mineral parageneses with progress of the reaction was predicted by constructing chemical potential diagrams in a model system. The chemical potential diagrams indicated that the chemical potential of 2Na₂O + CaO (2µ_Na2O + µ_CaO) in intergranular regions between kyanite and quartz should decrease with decreasing pressure, whereas 2µ_Na2O + µ_CaO in intergranular regions between garnet and omphacite should increase with decreasing pressure. Thus, upon decompression, an inequality in chemical potential arises in the rock. To reduce this inequality, garnet and omphacite react to produce amphibole and plagioclase and release Na₂O and CaO. Then, the released Na₂O and CaO components diffuse into the regions between kyanite and quartz grains and react to produce plagioclase between them. This model also indicates that the chemical potential of SiO₂ should decrease around kyanite grains during the progress of the decompressional reaction, and Si‐undersaturated conditions should have formed around kyanite grains in spite of the presence of quartz in these eclogitic rocks. Thus, spinel or corundum that are not stable in the system with excess quartz can form as a metastable phase, as observed in eclogitic rocks from the study areas. Phase diagrams in the system with excess quartz should be carefully applied for analysis of such reaction textures.  相似文献   

Natural superrotation of a rarefied planetary atmosphere     

P. A. Bespalov  O. N. Savina 《Astronomy Letters》2003,29(1):50-57

We consider the kinetics of a rarefied rotating planetary atmosphere. The spatial distributions of the atmospheric-gas density and mean angular velocity were determined by analyzing the exact solution of the two-dimensional kinetic equation. We show that the angular velocity of the gas at some distance from the planet could be higher than that in the initial layer starting from which the atmosphere is rarefied. Our model calculations elucidate the superrotation mechanism under consideration.  相似文献   

40 ℃时MgO·2B2O3-18%MgSO4-H2O过饱和溶液结晶动力学研究          下载免费PDF全文

马玉涛  夏树屏  朱黎霞  王波 《盐湖研究》2002,10(1)

针对我国盐湖硼资源的特点 ,模拟合成MgO·2B2 O3-1 8%MgSO4 -H2 O过饱和溶液 ,在 40℃恒温静置条件下 ,跟踪结晶动力学过程。拟合并给出结晶动力学方程 ,同时对结晶机制进行了探讨。析出固相采用X射线粉末衍射、红外光谱和热分析进行物相鉴定。  相似文献   

Sorption of lanthanides on smectite and kaolinite   总被引：2，自引：0，他引：2  

Frédéric Coppin  Gilles BergerAndreas Bauer  Sylvie CastetMichel Loubet 《Chemical Geology》2002,182(1):57-68

Experiments were carried out to investigate the sorption of the complete lanthanide series (Ln or rare earth elements, REE) on a kaolinite and an a Na-montmorillonite at 22°C over a wide range of pH (3-9). Experiments were conducted at two ionic strengths, 0.025 and 0.5 M, using two different background electrolytes (NaNO₃ or NaClO₄) under atmospheric conditions or N₂ flow (glove box). The REE sorption does not depend on the background electrolyte or the presence of dissolved CO₂, but is controlled by the nature of the clay minerals, the pH and the ionic strength. At 0.5 M, both clay minerals exhibit the same pH dependence for the Ln sorption edge, with a large increase in the sorption coefficient (K_D) above pH 5.5. At 0.025 M, the measured K_D is influenced by the Cation Exchange Capacity (CEC) of the minerals. Two different behaviours are observed for smectite: between pH 3 and 6, the K_D is weakly pH-dependent, while above pH 6, there is a slight decrease in log K_D. This can be explained by a particular arrangement of the particles. For kaolinite, the sorption coefficient exhibits a linear increase with increasing pH over the studied pH range. A fractionation is observed that due to the selective sorption between the HREEs and the LREEs at high ionic strength, the heavy REE is being more sorbed than the light REE. These results can be interpreted in terms of the surface chemistry of clay minerals, where two types of surface charge are able to coexist: the permanent structural charge and the variable pH-dependent charge. The fractionation due to sorption observed at high ionic strength can be interpreted either because of a competition with sodium or because of the formation of inner-sphere complexes. Both processes could favour the sorption of HREEs according to the lanthanide contraction.  相似文献   

煤岩有机质成油、成气热模拟动力学模型及其标定   总被引：8，自引：0，他引：8       下载免费PDF全文

卢双舫  付晓泰  王振平  曲佳燕 《地质科学》1996,31(1):15-21

借助热解实验技术和PY-GC分析技术分别建立了有机质成油和成气的动力学模型,并在数学优化求解上作了比较深入的工作。所得模型的理论计算值与实验结果在不同条件下均有良好的吻合关系,初步显示了该模型的可行性及其应用前景。  相似文献   

成岩流体－矿物反应的地球化学动力学数值模拟方法     

唐建武  倪师军  王绪本 《物探化探计算技术》1996,(4)

本文引用ＬｉｃｈｔｎｅｒＰ．Ｃ．（１９８８，１９９２）的渗透－扩散－化学反应三者耦合的时空连续性方程和准稳态近似法，建立了成岩作用过程中流体—矿物反应的地球化学动力学数学模型，并设计了数值模拟的计算方法和编写了计算程序。  相似文献   

流体—岩石相互作用中氧同位素地球化学及动力学研究现状   总被引：4，自引：0，他引：4       下载免费PDF全文

刘伟 《岩石矿物学杂志》1997,16(3):220-229

流体－岩石相互作用的研究突破了静止的固体地球观。开放体系、不平衡和动力学的研究构成了以地球内部流体为目标的前缘领域。矿物－流体体系氧同位素交换反应动力学模型主要分为５种：封闭、“封闭”、单向流动开放体系、流体缓冲体系和岩石缓冲体系。１８Ｏ／１６Ｏ交换机制主要为扩散控制和表面控制，后者通常伴随着强烈的矿物蚀变反应，前者则缺乏之。花岗岩－流体体系主要包括浅成系统、深成和／或者长期活动系统以及均一化平衡系统。花岗岩－流体氧同位素交换反应大多属于开放体系不平衡类型。同变形期流体－岩石相互作用的本质在于变形与流体化学反应的藕合作用。流体循环与质量传输机制主要包括平流或渗透、扩散以及平流－扩散复合机制。  相似文献   

东沟坝多金属矿床硫同位素交换动力学   总被引：1，自引：0，他引：1  

卢武长  杨绍全 《矿物岩石》1997,17(1):105-110

本文详细研究东沟坝多金属矿床的硫同位素特征，并根据同位素资料评估硫在成矿溶液中的最短停留时间和成矿机理。根据硫化物和硫酸盐在化学及同位素交换反应的过程中同样都包含有分子结构中的硫键断开和硫原子的交换，提出了化学平衡是同位素平衡的先决条件。指出在不少成矿温度低于３５０℃的热液矿床中，共沉淀的硫化物矿物和硫酸盐矿物之间的硫同位素时常没有达到平衡  相似文献   

Significance of oxides and particulate organic matter in controlling trace metal partitioning in a contaminated estuary     

Andrew Turner  Geoffrey E. Millward  Sophie M. Le Roux 《Marine Chemistry》2004,88(3-4):179-192

The sediment–water partitioning of radiolabelled Cd, Hg and Zn has been investigated along an estuarine salinity gradient using samples from the Mersey Estuary, UK. Partitioning was studied using untreated particles, and particles that had been extracted using either a reducing agent (NH₂OH.HCl–HOAc) or an oxidising agent (H₂O₂) in order to qualitatively evaluate the relative roles of Fe–Mn oxides and particulate organic matter (POM), respectively, on metal uptake. The extent of Cd partitioning between sediment and water, parameterised in terms of the distribution coefficient, K_D, exhibited a reduction with increasing salinity, regardless of whether or not particles had been digested. However, the magnitude of K_D decreased significantly following either chemical treatment, suggesting that both oxides and organic matter are important sorbents for Cd. The K_D for Hg in the presence of untreated particles increased with increasing salinity, and chemical reduction of the particles enhanced the uptake of Hg and reinforced this trend. Particle oxidation led to a significant reduction in the K_D for Hg, and uptake by the particles decreased with increasing salinity. These observations suggest that POM is considerably more important than Fe–Mn oxides in the removal of aqueous Hg, and that its presence is a prerequisite for enhanced sorption (or salting out) at elevated salinities. The salinity dependence of K_D for Zn displayed characteristics of both Cd (below salinities of about 5) and Hg (at greater salinities). However, the magnitude of K_D for Zn uptake was relatively insensitive to either chemical treatment, suggesting that oxides, POM, and residual phases contribute to the overall sorption of Zn by estuarine particles. Regression analyses of the metal partition data suggest that sorption to oxides and POM is nonadditive, and that the salinity dependence of metal partitioning results mainly from salinity-controlled interactions between metal and organic matter. Sequential extraction of metals bound to untreated and chemically treated particles in the partitioning experiments indicated that the exchangeability or lability of all metals increased on removal of either oxides or POM. This implies that sorption sites of relatively high energy are destroyed (or become less accessible), or sorption sites of relatively low energy are created (or become more accessible) on chemical treatment. These observations support a conceptual model for the particle surface whose integrity and binding properties are only maintained by the coexistence of and interaction between oxides and organic matter.  相似文献   

沉积物中多环芳烃在海岸带水域自然环境中的衰减研究     

张勇  庄一廷  张杰  Ka-Fai Poon  Michael H W Lam  洪华生  Rudolf S S Wu 《台湾海峡》2001,20(2):171-176

本文在现场情况下，研究了自然条件下受污染海岸带沉积物中的7种多环芳烃（Polynuclear Aromatic Hydrocarbons，简称PAHs）的解吸动力学行为。结果表明，7种PAHs）的解吸动力学行为。结果表明，7种PAHs的解吸动力学行为可以用二元模型模拟。文中并将所得数据与文献报道的数据进行了比较。  相似文献