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.

本项目对岩浆体系中的卤素分布、卤素分馏和卤素同位素分馏进行了系统的研究，重点研究了氯和溴。这项研究将对过碱性岩石进行研究，因为这些岩石富含卤素，并含有丰富的方钠石和透析物族矿物(EGM)，它们是过碱性岩浆系统中主要的氯和溴载体。我们的初步数据表明：(1)在岩浆分异过程中，氯和溴可能相互分馏；(2)方钠石分馏的数量和时间对残留熔体的氯/溴演化有重要影响。因此，将对四个经过充分研究的过碱性杂岩进行研究，它们包含(I)丰富的正岩浆方钠石-EGM组合(Ilímaussaq)，(Ii)少量的正岩浆但丰富的晚期岩浆方钠石-EGM组合(Khibina)，(Iii)罕见的晚期岩浆方钠石-EGM组合(Tamazeght)和(Iv)以EGM为唯一主要富氯相(Norra Kärr)的不含方钠石的组合，并就卤素丰度(F，Cl，Br，该项目首次系统地研究了氯(和溴)稳定同位素在岩浆体系中的行为，并将研究这两个同位素体系在解释岩浆和热液作用(包括分离结晶和流体出溶/脱气)方面的适用性。将所有四个地点的卤素浓度数据和卤素同位素数据结合在一起，结合质量平衡和瑞利型计算，考虑到方钠石和EGM分馏的相对影响，还将能够限制这些岩石各自地幔来源中关于卤素比率和卤素同位素组成的成分不均一性。这将有助于限制与卤素有关的地幔不均一性的规模和幅度，这一点已经在卤素浓度和氯同位素组成方面提供了证据。