板块俯冲过程中的Mg-Li-Fe-Cr同位素分馏  

Mg-Li-Fe-Cr Isotopic Fractionation during Subduction

作　　者：李东永 肖益林[1] 王洋洋 沈骥 刘海洋 Li Dongyong;Xiao Yilin;Wang Yangyang;Shen Ji;Liu Haiyang(CAS Key Laboratory of Crust-Mantle Materials and Environments,School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China)

机构地区：[1]中国科学院壳幔物质与环境重点实验室中国科学技术大学地球和空间科学学院

出　　处：《地球科学》2019年第12期4081-4085,共5页Earth Science

基　　金：国家重点基础研究发展计划项目(No.2015CB856102);国家自然科学基金项目(No.41703002)

摘　　要：金属稳定同位素体系是示踪板块俯冲对壳幔物质再循环影响的全新工具,因此其在俯冲带的地球化学行为备受关注.Mg同位素在俯冲过程中不发生显著分馏,但大陆玄武岩具有低于洋中脊玄武岩的Mg同位素,这可能是碳酸岩的俯冲再循环导致的.与角闪岩继承原岩的Li同位素组成不同,榴辉岩具有轻于原岩的Li同位素组成,可归因于俯冲折返过程中的动力学扩散、脱水反应或低Li同位素的流体交代.作为变价元素,Fe和Cr的同位素在榴辉岩的形成过程中均不发生显著分馏,但是蛇纹岩的Fe同位素和Cr同位素与氧逸度指标具有相关性,指示氧化还原条件变化时脱水过程或流体交代会导致同位素分馏.In order to investigate mantle heterogeneities induced by subducted crustal plate,many studies have been focused on geochemical characteristics of stable metal isotopic systematics in subduction zone in recent years.Limited Mg isotopic fractionation occurred during subduction and exhumation,thus lighter Mg isotopic composition of continental basalts might be caused by carbonatite metasomatism.Instead of inherited Li isotopes of amphibolite,eclogite has lighter Li isotopies,which are attributed to kinetic diffusion,dehydration,or rehydration.Isotopes of Fe and Cr have insignificant fractionation during formation of eclogite,however,Fe and Cr isotopic composition of serpentinite are related to oxidation index,suggesting dehydration or alteration of fluids during serpentinization could shift Fe and Cr isotopic composition of serpentinite.

关 键 词：俯冲带 Mg-Li-Fe-Cr同位素 分憎 地球化学. 

分 类 号：P581[天文地球—岩石学]