Halogen geochemistry and isotope geochemistry in magmatic systems

岩浆系统中的卤素地球化学和同位素地球化学

• 批准号: 398824902
• 负责人: Privatdozent Dr. Michael Marks
• 金额: --
• 依托单位: IPREM - Institut des Sciences Analytiques
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/398824902?language=en
• 关键词: Halogen; geochemistry; isotope; magmatic; systems

The current project represents a systematic study on halogen distribution, halogen fractionation and halogen isotope fractionation in magmatic systems, focussing on Cl and Br. The study will investigate peralkaline rocks as these are halogen-rich and contain abundant sodalite and eudialyte-group minerals (EGM), the major Cl and Br carriers in peralkaline magmatic systems. Our preliminary data indicate that (i) Cl and Br may be fractionated from each other during magmatic differentiation and (ii) the amount and timing of sodalite fractionation has a major impact on the Cl/Br evolution of residual melts. Therefore, four otherwise well-studied peralkaline complexes that contain (i) abundant orthomagmatic sodalite-EGM assemblages (Ilímaussaq), (ii) minor orthomagmatic but abundant late-magmatic sodalite-EGM assemblages (Khibina), (iii) rare late-magmatic sodalite-EGM assemblages (Tamazeght) and (iv) sodalite-free assemblages with EGM as the only major Cl-rich phase (Norra Kärr), will be investigated and compared with each other with respect to halogen abundances (F, Cl, Br, I) and halogen isotope compositions (δ37Cl and δ81Br) of sodalite and EGM.This project is a first systematic study on the behaviour of Cl (and Br) stable isotopes in magmatic systems and will investigate the suitability of these two isotope systems for deciphering magmatic and hydrothermal processes, including fractional crystallization and fluid exsolution/degassing. The combination of the halogen concentration data and the halogen isotope data from all four localities, combined with mass balance and Rayleigh-type calculations accounting for the relative effects of sodalite and EGM fractionation will also allow for constraining compositional heterogeneities in the respective mantle sources for these rocks with respect to halogen ratios and halogen isotope compositions. This will help to constrain the scales and amplitudes of mantle heterogeneities concerning the halogens, for which already evidence was presented, both with respect to halogen concentrations and Cl-isotope compositions.

本项目是对岩浆体系中卤素分布、卤素分馏和卤素同位素分馏的系统研究，重点是Cl和Br。该研究将调查过碱性岩石，因为这些岩石富含卤素，含有丰富的方钠石和eudialyte族矿物（EGM），过碱性岩浆系统中的主要Cl和Br载体。我们的初步数据表明，（i）Cl和Br可能是分馏从对方在岩浆分异和（ii）方钠石分馏的量和时间有重大影响的Cl/Br演化的残留熔体。因此，四个其他研究充分的过碱性复合物，包含（i）丰富的正岩浆方钠岩-EGM组合（Ilímaussaq），（ii）少量正岩浆但丰富的晚岩浆方钠岩-EGM组合（Khibina），（iii）罕见的晚岩浆方钠岩-EGM组合（Tamazeght）和（iv）EGM作为唯一主要的富Cl相的无方钠岩组合（Norra Kärr），将进行调查，并相互比较卤素丰度（F，Cl，Br，I）和卤素同位素组成本文首次系统地研究了Cl（和Br）在方钠石和EGM中的行为。该项目将研究岩浆系统中的稳定同位素，并将研究这两种同位素系统是否适合解释岩浆和热液过程，包括分离结晶和流体出溶/脱气。的卤素浓度数据和卤素同位素数据从所有四个地方，结合质量平衡和瑞利型计算占方钠石和EGM分馏的相对影响，也将允许约束组成的不均匀性，在各自的地幔来源，这些岩石的卤素比和卤素同位素组成。这将有助于限制的规模和幅度的地幔不均匀性有关的卤素，其中已经提出的证据，无论是相对于卤素浓度和Cl-同位素组成。