稳定氯同位素地球化学研究进展  

Advances in stable chlorine isotope geochemistry

作　　者：刘茜 王奕菁 魏海珍[1] LIU Xi;WANG Yijing;WEI Haizhen(School of Earth Sciences and Engineering,Nanjing University,State Key Laboratory for Mineral Deposits Research,Nanjing 210023,China)

机构地区：[1]南京大学地球科学与工程学院内生金属矿床成矿机制研究国家重点实验室,江苏南京210023

出　　处：《地学前缘》2020年第3期29-41,共13页Earth Science Frontiers

基　　金：国家自然科学基金项目(41973005,41673001,41422302)。

摘　　要：地球卤素元素含量相对稀少,相对而言氯为最常见的卤素元素。氯是一种挥发性元素,具有强烈的亲水性。自然界氯两个稳定同位素^35Cl和^37Cl,其相对丰度分别为75.76%和24.24%。文章综述了氯在各个地质储库的特征、稳定氯同位素分馏的控制因素以及氯同位素的地质应用三大方面的研究进展。地球主要储库中蒸发岩、海水、岩浆岩、沉积物、变质岩、地幔的氯同位素组成分别为-0.5‰^+0.8‰、0.00±0.05‰、-1.12‰^+0.79‰、-3.0‰^+2.0‰、-3.6‰~0、-1.9‰^+7.2‰。地外(月球、火星及其他小行星4-Vesta)氯同位素组成变化范围分别为-4‰^+81.1‰、-5.6‰^+8.6‰、-3.8‰^+7.7‰。相对地球上氯同位素δ^37Cl的变化范围(-14‰^+16‰),月球和火星δ^37Cl的变化范围可达-5.6‰^+81‰,表明挥发分氯在地内和地外迁移循环过程中有显著不同同位素分馏主控机制。已经探明氯同位素分馏受控于物理过程(如扩散、离子过滤、沉淀溶解作用、火山作用)和化学作用(如水岩作用、变质作用,尤其是蛇纹石化作用)等。扩散作用、淋滤作用和火山作用富集重同位素,沉淀作用结晶盐δ^37Cl先减小后上升,而蛇纹石化过程中多种因素共同影响。与其他指标结合,氯同位素地球化学可用于有效指示钾盐矿床远景区,评估示踪地下水的来源和演化路径、示踪污染物源区和量化生物修复、探究矿化流体来源、指示行星演化岩浆海洋脱气等过程。Halogen elements are relatively rare on earth and chlorine is the most abundant one.Chlorine is a strongly hydrophilic volatile element having two stable isotopes ^35Cl and ^37Cl with natural abundances of75.76%and 24.24%,respectively.In this work,we reviewed chlorine isotope geochemistry,including distribution of chlorine isotopes in various geological reservoirs,factors controlling equilibrium and kinetic fractionation behaviors of chlorine isotopes,and the relevant geological applications.The chlorine isotopic compositions(δ^37Cl)of evaporite,seawater,igneous rock,sediment,metamorphic rock and mantle are-0.5‰to+0.8‰,0.00±0.05‰,-1.12‰to+0.79‰,-3.0‰to+2.0‰,-3.6‰to 0 and-1.9‰to+7.2‰,respectively.The chlorine isotopic compositions(δ^37Cl)of Moon,Mars and other planets(4-Veata)are-4‰to+81.1‰,-5.6‰to+8.6‰and-3.8‰to+7.7‰,respectively.Compared to the relatively narrowδ^37Cl range(-14‰to+16‰)on Earth,largerδ^37Cl variations(-5.6‰to+81‰)are on the Moon and Mars,indicating dramatic differences in controlling mechanisms of chlorine isotope fractionation in terrestrial and extra-terrestrial processes.In nature,chlorine isotope fractionation is mainly controlled by physical(diffusion,ion filtration,salt precipitation,volcanic systems,etc.)and chemical(water-rock interaction,metamorphism,especially in serpentinization)processes.Heavy isotopes are enriched by diffusion,ion filtration and volcanism,andδ^37Cl first decreases and then increases during consecutive precipitation of salts from brine,while various factors influence the serpentine process.In combination with other geochemical indices,chlorine isotopes show great potentials in addressing a variety of geochemical issues,including prospecting for potash deposits,evaluating evolution paths of groundwater,tracing pollutant sources and quantifying bioremediation,tracking genesis of ore-forming fluid,as well as constraining planetary evolution and magma ocean degassing,and so on.

关 键 词：氯同位素 储库特征 平衡-动力学氯同位素分馏 地质应用 

分 类 号：P597.2[天文地球—地球化学]