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Li isotope fractionation in magmatic systems: Constraints from in situ analyses on magmatic minerals by femtosecond-laser ablation-MC-ICP-MS

岩浆系统中的锂同位素分馏：飞秒激光烧蚀-MC-ICP-MS 对岩浆矿物进行原位分析的限制

基本信息

批准号：
286789713
负责人：
Dr. Martin Oeser-Rabe
金额：
--
依托单位：
Institut für Geologie, Mineralogie und Geophysik
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2015
资助国家：
德国
起止时间：
2014-12-31 至 2020-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/286789713?language=en
关键词：
Li isotope fractionation magmatic systems

项目摘要

This project aims to investigate the fractionation of stable lithium (Li) isotopes in silicate minerals (i.e. olivine and clinopyroxene) from volcanic rocks in order to gain time information on magmatic processes. Since previous studies indicate (i) that stable isotope fractionation in magmas is largely driven by kinetic effects due to diffusive processes and (ii) that Li is a very fast diffusing trace element in minerals (and melts), one can expect large Li isotope variations, i.e. isotopic zoning, on the mineral scale. Therefore, in situ methods (e.g. laser ablation plasma mass spectrometry) have to be used which allow to performing high-precision isotope analyses with high spatial resolution.The first objective of this project comprises establishing an analytical routine for in situ Li isotope measurements on clinopyroxene and olivine. As the Li concentration in these silicate minerals is very low (usually a few ppm), such analyses are challenging. However, preliminary tests indicate that the analytical setup (femtosecond-laser ablation-multi collector-ICP-MS) available in Hannover is capable of in situ isotope measurements of trace elements in crystals with high precision and high spatial resolution.The second part of this project will focus on the investigation of Li isotopic zoning in chemically zoned clinopyroxene and olivine crystals in volcanic rocks in order to address the following questions:(a) Is chemical (and Fe-Mg isotopic) zoning commonly coupled with Li isotopic zoning?(b) Which mechanisms generate Li isotopic zoning and which (magmatic) processes are recorded by such zoning?(c) Can we obtain time information (durations) on these processes by using the observed intra-mineral zoning for diffusion modeling?(d) What are the spatial scales of Li diffusion in magmatic systems -- within or beyond hand-specimen scale?

该项目旨在研究火山岩中硅酸盐矿物（即橄榄石和斜辉石）中稳定锂（Li）同位素的分馏，以获得岩浆过程的时间信息。由于以往的研究表明(i)岩浆中的稳定同位素分馏主要是由扩散过程引起的动力学效应驱动的（ii） Li是矿物（和熔体）中非常快速扩散的微量元素，因此可以预期在矿物尺度上Li同位素的变化很大，即同位素分带。因此，必须使用原位方法（例如激光烧蚀等离子体质谱法），以便进行高空间分辨率的高精度同位素分析。该项目的第一个目标是建立斜辉石和橄榄石原位Li同位素测量的分析常规。由于这些硅酸盐矿物中的锂浓度非常低（通常为几ppm），因此这种分析具有挑战性。然而，初步测试表明，汉诺威现有的分析装置（飞秒激光烧蚀-多收集器- icp - ms）能够高精度和高空间分辨率地原位测量晶体中微量元素的同位素。本项目第二部分将重点研究火山岩中化学分带斜辉石和橄榄石晶体中的锂同位素分带，以解决以下问题：(a)化学（和铁镁同位素）分带是否与锂同位素分带普遍耦合？(b)哪些机制产生了锂同位素分带？这种分带记录了哪些（岩浆）过程？(c)我们能否利用观察到的矿物内分区进行扩散模拟，获得这些过程的时间信息（持续时间）？(d)岩浆系统中Li扩散的空间尺度是什么——在手标本尺度内还是超出手标本尺度？