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矿物氧扩散与氧同位素退化交换作用 总被引：2，自引：0，他引：2
本文从理论上解论上解析了同位素封闭体系内的矿物氧扩散性质，火成岩从冷却为质岩从高峰变质温度冷却过程中的所发生的扩散作用会层致矿物晶体内部及晶粒间的氧同位素重新分配，两种不同的矿物氧扩散－同位素交换模式都可以用来模拟这种性质。实例研究进一步阐明了扩散对氧同位素组成的影响。 相似文献
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耦合的质量传输和动力学限制的同位素交换模型综合考虑了平流、扩散、热液弥散 ,以及岩石与水之间的不平衡同位素交换等项因素。把耦合模型应用于 2个构造环境下的古热液系统 ,进而解释稳定同位素数据。对于造成环绕浅成侵入岩体分布的18O亏损环带的流体的流动几何学 ,以及浅部正断层流体流动的几何学 ,耦合模型提供了不同于单一同位素交换模型的解释。耦合模型也提供了关于同位素相对交换速率和同位素交换机制的信息。结果表明 ,断层带的动态重结晶促进了表面反应 ,进而便利了同位素交换 ;在化学不反应性和未变形的矿物中 ,同位素交换可能受制于固态条件下的扩散。 相似文献
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矿物氧同位素模式温度计算 总被引：6，自引：1，他引：5
根据对现遥氧扩散模型的解析分析,通过模拟矿物之间的氧同位素交换轨迹进行模式温度计算,改进了常规矿物对氧同位素地质温度计方法。将模式温度计算与矿物氧－扩散封闭次上结合,建立了一个系统独立的同位素温度计算方法,因此所得到的同位素温度能够更好地反映矿物在高温岩石冷却过程中,的氧同位素交换行为;模式温度计算有如下优点：（１）考虑到了矿物之间扩散引起的同位素交换;（２）遵循质量守恒原理,更严格地适用于有限封 相似文献
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流体控制着地球系统中质量和能量的传输。流体岩石反应过程在岩石圈中是十分普遍的现象。在流体流动体系中 ,流体在岩石裂隙中通过平流、扩散、水动力弥散和动力学弥散等方式进行输运并与岩石发生同位素交换反应。文章首先对封闭体系、“封闭”体系、开放体系以及缓冲体系中的同位素交换模型进行了简单讨论 ,然后在讨论氧同位素动力学交换机制的基础上 ,建立了平衡交换模型和动力学交换模型。结合流体流动的归一化速率、弥散系数和流体岩石的反应速率等变量 ,对流体岩石交换反应的流体运动方程中的Peclet数和Damk¨ohler数进行了讨论 ,并详细解释了它们在流体岩石交换反应过程中的物理意义和地质用途。 相似文献
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方解石—橄榄石—流体三相体系氧同位素交换的实验研究 总被引：2，自引：2，他引：0
在６８０℃和５００ＭＰａ以及岩石学相平衡条件下,首次对方解石与镁橄榄石之间在大量超临界ＣＯ２－Ｈ２Ｏ流体存在的条件下进行了氧同位素交换实验。结果发现,在实验刚刚开始的一段时间内氧同位素交换很快,主要是以溶解／重结晶的机制进行的;而在以后的时间里氧同位素交换要慢得多,变成以扩散机制为主。进一步,反应产物方解石相对于镁橄榄石亏损＾１８Ｏ,指示方解石的溶解／重结晶速率大于镁橄榄石。流体相的存在导致具有不 相似文献
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扩散法——EA-IRMS测定天然水体铵态氮同位素实验条件研究 总被引：2，自引：0，他引：2
稳定氮同位素是研究氮循环和氮污染源示踪的一个有效手段。然而目前国内对水体中铵态氮同位素测定方法研究较少,限制了水体氮循环和污染机理的深入探讨。本文采用改进的扩散法(EA-IRMS)测定水中铵态氮同位素,探讨了样品制备过程中扩散溶液的体积、浓度和扩散时间对回收率及氮同位素测定值的影响。实验得出最佳扩散条件为:1.50 mg/L氯化铵溶液400 mL扩散14天,回收率大于95%,且不会产生氮同位素分馏。本研究为高精度测定天然水体中铵态氮同位素提供了更可靠的实验条件。 相似文献
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概述了同位素封闭体系内的矿物氧扩散和同位素交换机制及其在地质速率计上的应用。火成岩从高温冷却或变质岩从高峰主质温度冷却过程中，由于冷却速度不同，扩散作用导致的矿物晶体内部及晶粒间氧同位素再平衡也有所不同。通过实测岩石中各组成矿物氧同位素比值，模式含量和颗粒半径，据矿物氧扩散和同位素交换模型，可以估算出岩石的冷却速率。 相似文献
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Modeling isotopic signatures in systems affected by diffusion, advection, and a reaction which modifies the isotopic abundance of a given species, is a discipline in its infancy. Traditionally, much emphasis has been placed on kinetic isotope effects during biochemical reactions, while isotope effects caused by isotope specific diffusion coefficients have been neglected. A recent study by Donahue et al. (2008) suggested that transport related isotope effects may be of similar magnitude as microbially mediated isotope effects. Although it was later shown that the assumed differences in the isotope specific diffusion coefficients were probably overstated by one or two orders of magnitude (Bourg, 2008), this study raises several important issues: (1) Is it possible to directly calculate isotopic enrichment factors from measured concentration data without modeling the respective system? (2) Do changes in porosity and advection velocity modulate the influence of isotope specific diffusion coefficients on the fractionation factor α? (3) If one has no a priori knowledge whether diffusion coefficients are isotope specific or not, what is the nature and magnitude of the error introduced by either assumption? Here we argue (A) That the direct substitution of measured data into a differential equation is problematic and cannot be used as a replacement for a reaction-transport model; (B) That the transport related fractionation scales linearly with the difference between the respective diffusion coefficients of a given isotope system, but depends in a complex non-linear way on the interplay between advection velocity, and downcore changes of temperature and porosity. Last but not least, we argue that the influence of isotope specific diffusion coefficients on microbially mediated sulfate reduction in typical marine sediments is considerably smaller than the error associated with the determination of the fractionation factor. 相似文献
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A field method called gas push-pull test (GPPT) was previously developed for in-situ quantification of methane (CH4) oxidation by soil microorganisms. We examined whether natural-abundance stable carbon-isotope analysis of CH4, a common approach used to measure in-situ bioconversions, could be used as a quantitative tool to complement the GPPT method. During GPPTs strong isotope fractionation of CH4 due to molecular diffusion can occur. This effect was observed in laboratory experiments regardless of the GPPTs’ advective component (i.e., for different injection/extraction rates). Numerical simulations showed that if a GPPT is applied in soils with low microbial CH4 oxidation activities, isotope fractionation may be dominated by molecular diffusion rather than by consumption. Because diffusional and microbial isotope fractionation of CH4 occur simultaneously during a GPPT, CH4 isotope data alone from a single GPPT cannot be used to assess the bioconversion process. However, microbial fractionation may be estimated if the extent of diffusional fractionation is known. This can be achieved either by conducting two sequential GPPTs, with microbial activity being inhibited in the second test, or by estimating physical transport processes via co-injected tracers’ gas analysis. We present a case study, in which we re-analyzed GPPTs previously performed in the unsaturated zone above a petroleum-contaminated aquifer. At this field site the combination of sequential GPPTs, stable carbon-isotope analysis of CH4, and a modeling approach, which considers diffusion and microbial CH4 oxidation, was a powerful tool to estimate in situ both apparent Michaelis-Menten kinetic constants and the microbial kinetic isotope effect. 相似文献
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矿物水体系氢同位素平衡分馏系数和动力分馏系数是同位素地球化学研究中的重要参数。这些参数大多由实验测定。氢同位素分馏的实验研究主要包括矿物水体系氢同位素交换实验,交换实验前后矿物、水的氢同位素分析及分馏机理、平衡分馏、动力分馏理论研究。为确保氢同位素分馏系数和一系列动力学参数的准确可靠,实验中防止氢透过容器壁扩散,避免空气中水汽污染样品,正确控制实验温度等都很重要。本研究以石英管代替前人常用的金（银、铂）管作反应容器,建立了一套实验研究羟基矿物水体系氢同位素平衡分馏和动力分馏的新方法,并开展了电气石水、黑柱石水体系氢同位素分馏的实验研究。所得一系列参数的精度明显好于国外报道的资料。此研究方法可广泛应用于羟基矿物水体系的氢同位素分馏的实验研究。 相似文献
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John M. Eiler Lukas P. Baumgartner John W. Valley 《Contributions to Mineralogy and Petrology》1992,112(4):543-557
We formulated a numerical model for stable isotope interdiffusion which predicts the temperatures recorded between two or more minerals, and the intragranular distribution of stable isotopes in each mineral, as functions of mineral grain sizes and shapes, diffusivities, modes, equilibrium isotopic fractionations, and the cooling rate of a rock. One of the principal assumptions of the model is that grain boundaries are regions of rapid transport of stable isotopes. This Fast Grain Boundary (FGB) model describes interdiffusion between any number of mineral grains, assuming that local equilibrium and mass balance restrictions apply on the grain boundaries throughout the volume modeled. The model can be used for a rock containing any number of minerals, and number of grain sizes of each mineral, several grain shapes, and any thermal history or domain size desired. Previous models describing stable isotope interdiffusion upon cooling have been based on Dodson's equation or an equivalent numerical analogue. The closure temperature of Dodson is the average, bulk temperature recorded between a mineral and an infinite reservoir. By using Dodson's equation, these models have treated the closure temperature as an innate characteristic of a given mineral, independent of the amounts and diffusion rates of other minerals. Such models do not accurately describe the mass balance of many stable isotope interdiffusion problems. Existing models for cation interdiffusion could be applied to stable isotopes with some modifications, but only describe exchange between two minerals under specific conditions. The results of FGB calculations differ considerably from the predictions of Dodson's equation in many rock types of interest. Actual calculations using the FGB model indicate that closure temperature and diffusion profiles are as strongly functions of modal abundance and relative differences in diffusion coefficient as they are functions of grain size and cooling rate. Closure temperatures recorded between two minerals which exchanged stable isotopes by diffusion are a function of modal abundance and differences in diffusion coefficient, and may differ from that predicted by Dodson's equation by hundreds of degrees C. Either or both of two minerals may preserve detectable zonation, which may in some instances be larger in the faster diffusing mineral. Rocks containing three or more minerals can record a large span of fractionations resulting from closed system processes alone. The results of FGB diffusion modeling indicate that the effects of diffusive exchange must be evaluated before interpreting mineral fractionations, concordant or discordant, recorded within any rock in which diffusion could have acted over observable scales. The predictions of this model are applicable to thermometry, evaluation of open or closed system retrogression, and determination of cooling rates or diffusion coefficients. 相似文献
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煤层甲烷碳同位素在煤层气勘探中的地质意义--以沁水盆地为例 总被引：30，自引：2，他引：28
根据沁水煤层气甲烷碳同位素的组成与分布特征,从煤层甲烷碳同位素在煤层气解吸-扩散-运移中的分馏效应,结合水文地质条件和构造条件,讨论了煤层甲烷碳同位素在煤层气勘探中的地质意义,认为沁水煤层气δ13C1值不仅总体上较高,而且随埋深增大而增高,说明沁水煤层气存在因煤层抬升而卸压所导致的煤层气解吸-扩散-运移效应,从而形成了该区甲烷碳同位素在平面上的分带现象。 相似文献
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Ding Tiping Liu Yushan Wan Defang Liu Zhijian Li Jincheng Zhang Guilan Institute of Mineral Deposits Chinese Academy of Geological Sciences Beijing 《《地质学报》英文版》1992,66(3):271-282
Experiments for oxygen isotope exchange between ferberite and water were carried out and the followingequation on oxygen isotope fractionation between ferberite and water against temperature was obtained:Combining this equation with the equation of Clayton et al. (1972) on oxygen isotope fractionation be-tween quartz and water, an equation on oxygen isotope fractionation between quartz and ferberite was ob-tained:The Bigeleison-Mayer function method was used to calculate the oxygen isotope fractionation betweenquartz and ferberite. The theoretical curve obtained agrees with the experimental calibration results quite wellin the temperature range of study.The above calibrated equation has been used in 5 world famous tungsten deposits to determine their tem-peratures of formation. The results show that the temperature range for an idividual deposit determined by thisgeothermometer agrees with those obtained from fluid inclusion determination and other isotopegeothermometers. 相似文献
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激光探针分析在氧同位素地球化学研究中的应用 总被引：6，自引：0，他引：6
简要介绍了氧同位素分析的最新方法———激光探针法的主要特点,并详细评述了激光探针分析在氧同位素地球化学研究中的应用。某些矿物内部存在氧同位素组成的变化,构成氧同位素环带。与其他化学成分环带一样,矿物氧同位素环带也可以分为生长环带（包括次生加大的环带）和扩散环带两种。变质岩中石榴石经常保存有明显的生长环带,而矽卡岩中石榴石、变质花岗质岩石中锆石和蚀变花岗岩中石英等矿物均可以记录岩石形成早期的某些氧同位素特征。由于这种差异与岩石的形成环境有关,因此通过对矿物氧同位素组成的微区分析可揭示岩石的某些成因信息。在缓慢冷却的变质岩中,磁铁矿的氧同位素环带常是扩散作用形成的,由此可以确定岩石的冷却速率。通过对脉石英的激光探针分析,可以研究流体的流动机理。变质岩的氧同位素微区分析为ｐ Ｔ ｔ ｆ轨迹研究提供了有力的武器,而氧同位素示踪可用来解决流体在变质岩形成过程中的作用问题。 相似文献