摘要
锂(Li)作为新兴产业发展不可或缺的战略性关键金属,其两种同位素~6Li和~7Li相对质量差可达17%,在构造演化等过程中因物理化学条件的变化会发生显著的同位素质量分馏,地球上不同储库δ~7Li差异可达60‰,具有极大的地球化学示踪潜力。亲石性和强流体活动性使Li广泛分布于地壳,在随流体迁移过程中,~7Li更易于以四配位键的形式进入液相,使得自然储库流体中的δ~7Li普遍更高。在低温条件下,Li同位素发生较大分馏,次生黏土矿物的生成是影响Li同位素分馏的重要因素;高温环境中,Li同位素分馏程度较低,主要受扩散作用和不同矿物的分配系数控制。多接收电感耦合等离子体质谱(Multi-collector Inductively Coupled Plasma-Mass Spectrometry, MC-ICP-MS)和原位微区分析等Li同位素检测技术的快速发展与应用有效提高了Li同位素的分析精度(可达0.2‰),极大地推进了Li同位素在地学领域的应用。Li同位素很好地记录了板块俯冲阶段的脱水和交代作用,~7Li随流体脱出并影响地幔楔与岛弧岩浆Li同位素组成,深部高温环境下,Li的不分馏现象使得深部流体也具有与俯冲板块类似的低δ~7Li值的特征,幔源捕虏体的Li同位素差异也反映了不同程度的交代作用。同时,Li同位素有效地应用于成矿和找矿研究,盐湖卤水中Li的来源主要以富Li母岩风化和底部热液携带为主,沉积物的溶解进一步促进Li的富集。低δ~7Li的花岗伟晶岩型锂矿主要形成于岩浆分异后期。河流、雨水、气溶胶及黏土矿物形成等共同影响着表生作用下的Li同位素分馏。基于Li地球化学的特殊性和作为战略资源的重要性,本文介绍了Li及其同位素的地球化学性质和分布特征、分析技术及分馏机制,并全面综述了Li同位素在板块俯冲和壳-幔物质演化、成矿机制、地表风化、碳循环与人类活动等地学领域中的最新研究应用,以期为Li同位素在地球化学中的应用提供借鉴。若能在今后研究中提高Li同位素的测试精度,进一步明晰复杂条件下的Li同位素分离机制,必将发挥其在地学应用中的更多潜力。
Lithium(Li)as a non-traditional stable isotope is a strategic and critical metal for the development of emerging industries.This review summarizes the geochemical properties of Li as well as its isotope distribution characteristics,analytical techniques,and fractionation mechanisms,and provides a comprehensive discussion on the latest research application of Li isotopes in plate subduction,crust-mantle material evolution,metallogenic mechanism,surface weathering,carbon cycle,and human activities.The relative mass difference between the two stable isotopes,6 Li and 7 Li,can reach 17%.Significant Li isotopic fractionation occurs due to changes in environmental conditions(both physical and chemical)during tectonic evolution,andδ7Li can vary up to 60‰between different reservoirs.Lithium stable isotopes have great potential for ore prospecting and geochemical tracing.Lithium as a lithophile element with strong fluid activity is widely distributed in the crust,where 7 Li is more likely to enter the aqueous phase as tetravalent cations during fluid migration,which results in higherδ7Li in natural reservoirs.Lithium isotopic fractionation is significant at low temperature by forming secondary clay minerals,and it is less likely to occur at high temperature,where Li diffusivity and partition coefficient in minerals are the controlling factors.The rapid development of Li isotope detection techniques such as MC-ICP-MS and in-situ microanalysis greatly improves the accuracy of Li isotopic analysis(up to 0.2‰)and promotes use of Li isotopes in geoscience research.One example is in the study of dehydration and metasomatism during plate subduction.The preferential partitioning of 7 Li in the aqueous phase affects Li isotopic composition of mantle wedge fluid and island arc lavas,where the absence of Li isotopic fractionation in the deep,high temperature environment causes lowδ7Li values in the deep fluids,similar as in the subduction plate;whilst Li isotopic variations in mantle-derived xenoliths reflect different degrees of metasomatism.Li isotopes are also effectively used to study the genesis of ore deposits and ore prospecting.Lithium in salt brine are mainly sourced from weathering of Li-rich parent rocks and transported by bottom-up hydrothermal fluids,and the dissolution of sediments further promotes Li enrichment.The lowδ7Li granopegmatite type lithium deposits mainly formed during late-stage magmatic differentiation.Rivers,rainwater,aerosols,and clay formation jointly affect Li isotopic fractionation via epigenetic effects.This review provides a reference for the geochemical application of Li stable isotopes.Lithium isotopic analysis can be more broadly applied in geological studies as the accuracy of isotopic measurements is further improved and the mechanism of Li isotopic fractionation under complex conditions is further clarified.
作者
陈瑜
徐飞
程宏飞
陈贤哲
温汉捷
CHEN Yu;XU Fei;CHENG Hongfei;CHEN Xianzhe;WEN Hanjie(School of Earth Science and Resources,Chang’an University,Xi’an 710054,China;Engineering Technology Innovation Center of New Energy Minerals and Resource Information,Ministry of Natural Resources,Xi’an 710054,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China)
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2023年第5期469-490,共22页
Earth Science Frontiers
基金
国家自然科学基金项目(92162214,41773015,42172043,U1812402)
国家重点研发计划项目“稀散矿产资源基地深部探测技术示范(2017YFC0602500)”
云南省重点研发计划项目(202103AQ100003)
山西省科技重大专项(20181101003)。
关键词
锂同位素
分馏机制
成矿机制
洋壳示踪
地表风化
MC-ICP-MS
lithium isotope
fractionation mechanism
metallogenic mechanism
oceanic crust tracer
surface weathering
MC-ICP-MS
