共查询到18条相似文献，搜索用时 156 毫秒
1.
氧的非质量同位素分馏（mass—independent isotope fractionation）为全球变化研究提供了新方法。在介绍非质量同位素分馏的基础上,评述了氧同位素异常[△（^17O）3的表示方法以及氧的非质量同位素分馏的产生机制,重点综述了氧的非质量同位素分馏在地球科学中的应用。基于△（^17O）评估的生物圈生产力是全球总的生物生产力,打破了以往只能孤立地评估陆地或海洋生物生产力的瓶颈,奠定了在更广时空尺度上评估生物生产力的基础;△（^17O）能量化形成气溶胶硫酸盐和硝酸盐的气相与液相氧化反应路径的相对比例,为研究气溶胶和气候的互馈作用提供了新途径;冰芯中S同位素和△（^17O）的联合运用,不仅解决了冰芯中硫酸盐、硝酸盐的来源和运移问题,而且还为其形成的氧化过程提供了细节信息;而干旱区硫酸盐、硝酸盐矿物中△（^17O）的发现在解决一些长期有争议的沉积物成因和来源问题中起关键作用。氧的非质量同位素分馏还将在（古）大气臭氧活性、火山喷发柱化学和O、S、N生物地球化学循环等研究中发挥更大作用。 相似文献
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硫酸盐的氧同位素测量方法 总被引：7，自引：0，他引：7
硫酸盐不仅是常见矿物,还是自然界少数几个具有氧同位素非质量分馏效应的矿物之一。硫酸盐矿物的氧同位素组成,特别是硫酸盐的氧同位素非质量分馏效应,可以为研究其形成过程和条件提供大碹有用信息,揭示一些元素浓度甚至单个同位素比值测量无法获得的特殊作用过程。但由于硫酸盐的氧同位素分析技术难度大,这一方法在国内尚未建立起来。论文介绍了BrF5法测量硫酸盐氧同位素组成的实验装置、分析流程和测量结果。该方法是目前唯一可以同时测量硫酸盐^17O／^16O和^18O／^16O比值的方法。对BaSO4国际氧同位素标准样品NBS-127和一种BaSO4化学试剂进行了多次重复测量。测量的NBS-127国际标样的δ^18Ov-SMOW=（9．20±0．11）‰,与标准值完全一致;BaSO4化学试剂的δ^18Ov-SMOW=（14．64±0．13）‰。分析精度（标准偏差）达到0．13％。（1σ）,优于国外（0．15～0．29）‰（1σ）的水平 相似文献
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氧同位素组成是一个非常有效的示踪硫酸盐的起源和形成环境的工具.过去主要针对硫酸盐中的氧同位素δ(18O)的研究,近年来,随着硫酸盐中氧同位素质量不相关分馏现象的陆续发现,其δ(17O)的研究成为热点与前沿.在综述了硫酸盐三氧同位素测试技术的研究现状及进展情况后,重点介绍了从硫酸盐中直接提取O2供质谱计同时测定δ(17O)与δ(18O)值的CO2-激光氟化法;同时介绍了硫酸盐中氧同位素异常[Δ(17O)]的研究历程,探讨了硫酸盐中氧同位素质量不相关分馏的机理及三氧同位素的应用前景,展望了今后的研究趋势. 相似文献
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矿物和化合物内不等价结构位置上的同位素取代,造成了分子内同位素效应,即分子内同位素的分馏效应。例如云母类矿物,至少—OH和Si—O—Al中氧所处结构位置不同,会产生明显的氧同位素分馏。 相似文献
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硝酸盐的氮和三氧同位素(δ15N, δ17O和δ18O)及氧同位素非质量分馏(△17O)综合研究, 可以更有效地示踪硝酸盐的来源和形成过程、制约硝酸盐的形成条件。本文详细描述了细菌反硝化法测定10–6级硝酸盐氮和三氧同位素的分析测试方法和实验要点。综合优化改良的细菌反硝化前处理方法、全自动气体预浓缩富集纯化系统和测试流程, 实现了实验室长期测定数据的稳定性, 以及多批次标准样品测定的良好重现性。10 nmol NO– 3标准样品的δ18O和δ15N测试精度分别是0.25‰(1σ)和0.40‰(1σ)。80 nmol NO– 3标准样品的δ18O、δ17O和δ15N的测试精度分别是0.5‰(1σ)、0.4‰(1σ)和0.1‰(1σ), 据此计算出的Δ17O精度为0.46‰(1σ)。 相似文献
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白云鄂博富稀土元素碳酸岩墙的
碳和氧同位素特征 总被引：7，自引：0，他引：7
重点解剖了一条距白云鄂博超大型REE-Nb-Fe矿床东矿北东方向2 k m、切割白云鄂 博群H1及H3岩性段的细粒方解石碳酸岩岩墙的碳和氧同位素地球化学特征。结果表明,碳酸 岩的碳同位素组成变化范围较小(δ13C值为－6.6‰ ～ －4.6‰),与正常地幔碳δ 13C值－5±2‰一致;而氧同位素组成变化范围较大(δ18O值为11.9‰～17.7‰ ),显著高于地幔的δ18O值5.7±1.0‰,表明碳酸岩浆在结晶过程中或之后曾与 低 温热液流体发生了同位素交换。碳酸岩墙中白云石与方解石之间的碳和氧同位素分馏均小于 0‰,处于不平衡状态,说明该碳酸岩墙中的白云石与方解石并非同成因矿物,白云石可能 为次生成因的。 相似文献
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铜陵冬瓜山层控矽卡岩型铜金矿床的成因机制:硫同位素制约 总被引：7，自引：5，他引：2
冬瓜山铜金矿床是铜陵矿集区乃至长江中下游成矿带中的一个重要矿床。矿床上部受石炭系层位控制,发育层状、似层状层控矽卡岩型矿体;下部受岩体及其接触带控制,在岩体及其接触带围岩中发育脉状、细脉浸染状矿体。上部层控矽卡岩型矿体中的矿石类型以含铜(金)石英硫化物为主,矿石硫化物矿物的硫同位素组成显示主要成矿阶段的硫同位素基本达到了平衡。矿石矿物中的硫化物和硫酸盐的硫同位素组成对比表明,冬瓜山矿床与斑岩型矿床相似,而与Sedex型和VHMS型矿床不同。结合矿床成矿物理化学条件和矿石矿物共生组合关系,根据硫同位素储库效应,认为冬瓜山矿床硫化物阶段成矿热液中的含硫物种以H2S为主(XH2S0.99),硫化物的结晶沉淀对成矿热液的δ34S值影响不大。应用大本模式,高温岩浆来源的热液与熔体之间的硫同位素分馏Δ34S为0‰～+5‰,依据岩浆岩全岩硫同位素组成可以确定岩浆来源热液的硫同位素组成为+0.3‰～+12.0‰。在高温(600～350℃)硅酸盐阶段和氧化物阶段,硬石膏与成矿热液之间的硫同位素分馏Δ34S为+5.0‰～+19.0‰,而在高温(450～350℃)氧化物阶段后期及低温(350～200℃)硫化物阶段,黄铁矿与成矿热液之间的硫同位素分馏Δ34S分别为-1.0‰～0‰和0‰～+1.5‰。据此计算的含硫矿物硫同位素组成理论值与冬瓜山矿床实测值基本一致,显示成矿热液流体中的硫源为岩浆来源。综合前人对区域及冬瓜山矿床的研究,本文认为冬瓜山矿床为与燕山期岩浆作用密切相关的层控矽卡岩型铜金矿床。岩浆及其平衡热液中较高的总硫同位素组成暗示岩浆混染了区域沉积地层中广泛发育的膏盐成分。虽然硫同位素组成特征显示区域沉积岩成岩过程中经历了明显的海水沉积作用和细菌硫酸盐还原作用,但冬瓜山矿床矿石没有保存海西期沉积成矿的硫同位素证据。 相似文献
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镁（Mg）同位素有3个,24Mg、25Mg和26Mg,其中24Mg和26Mg的相对质量差较大,高达8.33%,这种大的相对质量差使地壳活动或其他地质过程中Mg同位素因化学物理条件的变化而发生明显的同位素质量分馏.目前,自然界可观测到的δ26Mg变化范围为-5.60‰~0.92‰,约6.5‰.镁在低温地球化学过程中分馏显著,而在高温环境下分馏不明显,因而Mg同位素是地质过程的潜在地球化学指标和示踪剂,在低温风化作用、高温部分熔融与岩浆结晶分异、变质作用、板片俯冲及壳幔物质循环、热液蚀变和矿床成因等方面取得重要进展.为此,简要介绍了镁同位素分析方法,系统总结了Mg同位素在地球各储库中的组成与分布特征以及地质作用过程中的镁同位素分馏机理;其次重点介绍了镁同位素近年来在碳酸岩研究中的应用;最后对有关问题进行了探讨,包括幔源岩石低δ26Mg成因解释（与俯冲再循环的碳酸盐岩、洋壳物质有关或与矿物分离结晶有关）和Li-Mg-Ca同位素联合示踪岩浆碳酸岩岩石成因.并对碰撞反应池多接收器电感耦合等离子体质谱仪（Nu Sapphire MC-ICP-MS）分析优势和Li-Mg-Ca等金属同位素联合示踪在稀土元素富集机制的应用进行了展望. 相似文献
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<正>The Turpan-Hami Basin in eastern Xinjiang is one of the driest regions on Earth and a premier environment to form and preserve nitrate.A large nitrate ore field in this basin was found recently.It is estimated there are about 2.5 billion tons of resources of nitrate,and the amount is as much as the Atacama Desert super-scale nitrate deposit in Chile.Nitrate is one of a few minerals with mass-independent fractionation(MIF),and the oxygen isotope MIF is an effective method to determine the source of nitrate.Theδ~(17)O,δ~(18)O of nitrate were measured by fluorination and thermal decomposition method.The date indicated that this is the first time that oxygen isotope MIF has been located in inland nitrate minerals.The results obtained by two methods are similar,⊿~(17)=δ~(17)O-0.52×δ~(18)O=12‰-17‰.The experiment and observation data proved that oxygen isotope MIF of nitrate are the result of photochemical reactions in the troposphere and stratosphere.Thus, evidence from MIF oxygen isotopic compositions indicate that long term atmospheric deposition of nitrate aerosol particles produced by photochemical reactions is the source of the deposits. 相似文献
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非质量硫同位素分馏效应是目前国际上最前沿的稳定同位素地球化学研究领域之一。在简要介绍非质量分馏理论的基础上,对近几年非质量硫同位素分馏效应的最新研究成果进行总结和分析。关于非质量硫同位素分馏的微观来源机制存在较多争议,有待于进一步探索;采用SF6为工作气体是现有硫同位素高精度测定的主要制样技术;非质量硫同位素分馏效应研究为火星大气演化及火星生命痕迹探询、古代大气氧化条件、地球早期硫循环、火山活动对气候的影响等重大地质科学问题的解释开辟了一条独特的新途径。最后对非质量硫同位素分馏领域研究趋势进行了探讨。 相似文献
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The influence of NaCl, CaCl2, and dissolved minerals on the oxygen isotope fractionation in mineral-water systems at high pressure and high temperature was studied experimentally. The salt effects of NaCl (up to 37 molal) and 5-molal CaCl2 on the oxygen isotope fractionation between quartz and water and between calcite and water were measured at 5 and 15 kbar at temperatures from 300 to 750°C. CaCl2 has a larger influence than NaCl on the isotopic fractionation between quartz and water. Although NaCl systematically changes the isotopic fractionation between quartz and water, it has no influence on the isotopic fractionation between calcite and water. This difference in the apparent oxygen isotope salt effects of NaCl must relate to the use of different minerals as reference phases. The term oxygen isotope salt effect is expanded here to encompass the effects of dissolved minerals on the fractionations between minerals and aqueous fluids. The oxygen isotope salt effects of dissolved quartz, calcite, and phlogopite at 15 kbar and 750°C were measured in the three-phase systems quartz-calcite-water and phlogopite-calcite-water. Under these conditions, the oxygen isotope salt effects of the three dissolved minerals range from ∼0.7 to 2.1‰. In both three-phase hydrothermal systems, the equilibrium fractionation factors between the pairs of minerals are the same as those obtained by anhydrous direct exchange between each pair of minerals, proving that the use of carbonate as exchange medium provides correct isotopic fractionations for a mineral pair.When the oxygen isotope salt effects of two minerals are different, the use of water as an indirect exchange medium will give erroneous fractionations between the two minerals. The isotope salt effect of a dissolved mineral is also the main reason for the observation that the experimentally calibrated oxygen isotope fractionations between a mineral and water are systematically 1.5 to 2‰ more positive than the results of theoretical calculations. Dissolved minerals greatly affect the isotopic fractionation in mineral-water systems at high pressure and high temperature. If the presence of a solute changes the solubility of a mineral, the real oxygen isotope salt effect of the solute at high pressure and high temperature cannot be correctly derived by using the mineral as reference phase. 相似文献
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不同地质储库中的镁同位素组成及碳酸盐矿物形成过程中的镁同位素分馏控制因素 总被引：1，自引：1，他引：0
镁同位素在低温地球化学过程中显著的分馏效应,是其示踪地球表生环境演化及物质循环的基础。本文在前人研究的基础上,对地球上不同地质储库中的镁同位素组成及碳酸盐矿物形成过程中的镁同位素分馏控制因素进行了总结:火成岩的镁同位素组成较均一;风化产物总体富集重的镁同位素,且变化较大;碳酸盐岩中灰岩相对白云岩富集轻的镁同位素,但总体上富集轻的镁同位素;岩石类型、风化强度以及植被等因素对河流地表水的镁同位素组成影响较大,导致地表水的镁同位素组成总体变化较大;海水的镁同位素组成均一,平均值约为-0.83‰;低温条件下,控制碳酸盐矿物无机成因过程中镁同位素分馏的因素有矿物相、沉淀速率和温度,其中矿物相是主要控制因素;生物成因碳酸盐矿物镁同位素组成与生物体对含镁碳酸盐矿物的利用形式有关,除了需考虑与无机碳酸盐沉淀类似的控制因素外,还需考虑不同物种对轻、重镁同位素的选择性吸收能力;因生物成因海相碳酸盐矿物几乎都是由最初的无定形相碳酸盐转变而来,故生物成因海相碳酸盐矿物的镁同位素特征不能代表生成无定形相碳酸盐的流体的镁同位素特征。镁同位素在低温条件下具有良好的分馏效应,随着分析测试技术的发展及不同地质储库中镁同位素组成数据的积累和完善,有关表生环境中镁同位素分馏机制的许多问题将逐步得到解决,镁同位素在揭示地球表生环境演化及物质循环方面将发挥更大的作用。 相似文献
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碳酸钙-水体系氧同位素分馏系数的低温实验研究 总被引：4，自引：0，他引：4
碳酸钙是古气候和沉积岩稳定同位素地球化学研究中最常用的矿物 ,因此对碳酸钙水体系氧同位素分馏系数的实验校准已成为稳定同位素地球化学诞生以来的热点和前沿课题。但由于碳酸钙在自然界存在 3种同质多象变体 (方解石、文石和六方方解石 ) ,使人们对碳酸钙矿物与水之间氧同位素分馏系数的实验测定结果存在较大差别 ,当应用到同位素地质测温时 ,会给出显著不同的温度值。正确选用合理的方解石水或文石水体系分馏曲线 ,对低温和环境地球化学研究和应用具有重要价值。文章系统总结和评述了碳酸钙水体系氧同位素分馏系数实验校准的历史、方法和结果 ,对前人在表达方式上的不一致进行了统一 ,对氧同位素分馏的盐效应、动力氧同位素分馏效应和同质多象转变过程中的氧同位素继承性进行了讨论。通过对前人大量实验数据的系统处理并与理论计算相比较 ,推荐了热力学上平衡的方解石水体系氧同位素分馏方程 ,而对于文石水体系 ,理论计算结果尚有待于实验证实。 相似文献
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The apparent inconsistency in calcite-water fractionation does occur between the arithmetic combination of Zhou and Zheng [Zhou G.-T., and Zheng Y.-F. (2003) An experimental study of oxygen isotope fractionation between inorganically precipitated aragonite and water at low temperatures. Geochim. Cosmochim. Acta67, 387-399] and the experimental determination of Zhou and Zheng [Zhou G.-T., and Zheng Y.-F. (2005) Effect of polymorphic transition on oxygen isotope fractionation between aragonite, calcite and water: a low-temperature experimental study. Am. Mineral90, 1121-1130]. To resolve this issue is to acknowledge whether or not the isotope salt effect of dissolved minerals would occur on oxygen isotope exchange between water and the minerals of interest. The question is whether or not a term of mineral-water interaction should be taken into account when calculating mineral-water 103ln α factors by an arithmetic combination between theoretical 103ln β factors for mineral and water, respectively. The hydrothermal experiments of Hu and Clayton [Hu G.-X., and Clayton R.N. (2003) Oxygen isotope salt effects at high pressure and high temperature, and the calibration of oxygen isotope geothermometers. Geochim. Cosmochim. Acta67, 3227-3246] demonstrate the absence of isotope salt effect on the oxygen isotope fractionation between calcite and water, and this abnormal behavior reasonably explains the so-called inconsistency in the calcite-water fractionations of Zhou and Zheng (2003, 2005). We argue that the mineral-water correction is still necessary for calculation of fractionations in mineral-water systems. New experimental data for oxygen isotope fractionations involving dolomite and cerussite are consistent with the calculations of Zheng [Zheng Y.-F. (1999a) Oxygen isotope fractionation in carbonate and sulfate minerals. Geochem. J.33, 109-126], but also shed light on the assumptions used in modifying the increment method. We argue that the modified increment method has developed into a theoretical mean of predictive power for calculation of oxygen isotope fractionation factors for crystalline minerals of geochemical interest. 相似文献
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Oxygen isotope fractionation factors between calcium carbonates and water have been applied to ancient marine geochemistry
principally for the purpose of geothermometry. The problem was encountered, however, with respect to the direction and magnitude
of oxygen isotope fractionation between calcite and aragonite at thermodynamic equilibrium. This basically involves sound
understanding of both thermodynamics and kinetics of oxygen isotope fractionation between inorganically precipitated carbonate
and water at low temperatures. Thus the crucial issues are to acknowledge the processes of chemical reaction and isotopic
exchange during precipitation of CaCO3 minerals in solution, the kinetic mechanism of isotope equilibrium or disequilibrium, the effect of polymorphic transition
from metastable aragonite to stable calcite under hydrous or anhydrous conditions, and the presence or absence of isotope
salt effect on oxygen isotope exchange between carbonate and water in response to the hydrous or anhydrous conditions at thermodynamic
equilibrium. Because good agreements exist in carbonate–water oxygen isotope fractionation factors between theoretical calculations
and experimental determinations, it is encouraging to applying the thermodynamic and kinetic data to isotopic paleothermometry
and geochemical tracing. 相似文献
18.
Phosphoric acid digestion has been used for oxygen- and carbon-isotope analysis of carbonate minerals since 1950, and was recently established as a method for carbonate ‘clumped isotope’ analysis. The CO2 recovered from this reaction has an oxygen isotope composition substantially different from reactant carbonate, by an amount that varies with temperature of reaction and carbonate chemistry. Here, we present a theoretical model of the kinetic isotope effects associated with phosphoric acid digestion of carbonates, based on structural arguments that the key step in the reaction is disproportionation of H2CO3 reaction intermediary. We test that model against previous experimental constraints on the magnitudes and temperature dependences of these oxygen isotope fractionations, and against new experimental determinations of the fractionation of 13C-18O-containing isotopologues (‘clumped’ isotopic species). Our model predicts that the isotope fractionations associated with phosphoric acid digestion of carbonates at 25 °C are 10.72‰, 0.220‰, 0.137‰, 0.593‰ for, respectively, 18O/16O ratios (1000 lnα∗) and three indices that measure proportions of multiply-substituted isotopologues . We also predict that oxygen isotope fractionations follow the mass dependence exponent, λ of 0.5281 (where ). These predictions compare favorably to independent experimental constraints for phosphoric acid digestion of calcite, including our new data for fractionations of 13C-18O bonds (the measured change in Δ47 = 0.23‰) during phosphoric acid digestion of calcite at 25 °C.We have also attempted to evaluate the effect of carbonate cation compositions on phosphoric acid digestion fractionations using cluster models in which disproportionating H2CO3 interacts with adjacent cations. These models underestimate the magnitude of isotope fractionations and so must be regarded as unsucsessful, but do reproduce the general trend of variations and temperature dependences of oxygen isotope acid digestion fractionations among different carbonate minerals. We suggest these results present a useful starting point for future, more sophisticated models of the reacting carbonate/acid interface. Examinations of these theoretical predictions and available experimental data suggest cation radius is the most important factor governing the variations of isotope fractionation among different carbonate minerals. We predict a negative correlation between acid digestion fractionation of oxygen isotopes and of 13C-18O doubly-substituted isotopologues, and use this relationship to estimate the acid digestion fractionation of for different carbonate minerals. Combined with previous theoretical evaluations of 13C-18O clumping effects in carbonate minerals, this enables us to predict the temperature calibration relationship for different carbonate clumped isotope thermometers (witherite, calcite, aragonite, dolomite and magnesite), and to compare these predictions with available experimental determinations. The success of our models in capturing several of the features of isotope fractionation during acid digestion supports our hypothesis that phosphoric acid digestion of carbonate minerals involves disproportionation of transition state structures containing H2CO3. 相似文献