Halogen geochemistry and isotope geochemistry in magmatic systems

本项目主要对岩浆系统中的卤素分布、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Cl和Br。由于过碱性岩浆岩富含卤素，并含有丰富的钠石岩和易溶岩群矿物（EGM），是过碱性岩浆系统中主要的Cl和Br载体，因此本研究将对其进行研究。初步结果表明：(1)岩浆分异过程中Cl和Br可能相互分异；(2)钠石分异的数量和时间对残余熔体Cl/Br演化有重要影响。因此，研究人员将对四种经过充分研究的过碱性络合物进行研究，这些络合物包含(i)丰富的正岩浆型钠盐岩-EGM组合（Ilímaussaq）， （ii）少量的正岩浆型但丰富的晚期岩浆型钠盐岩-EGM组合（Khibina）， （iii）罕见的晚期岩浆型钠盐岩-EGM组合（tamazeg8）和（iv）以EGM为主要富Cl相的无钠盐岩组合（Norra Kärr），并相互比较卤素丰度(F, Cl, Br，I)和钠石和EGM的卤素同位素组成（δ37Cl和δ81Br）。本项目是首次系统研究岩浆系统中Cl（和Br）稳定同位素的行为，并将研究这两种同位素系统对岩浆和热液过程的适用性，包括分离结晶和流体脱气。结合所有四个地区的卤素浓度数据和卤素同位素数据，结合质量平衡和瑞利式计算，考虑钠石岩和EGM分馏的相对影响，也将允许限制这些岩石各自地幔源中卤素比和卤素同位素组成的非均质性。这将有助于限制与卤素有关的地幔非均质性的尺度和幅度，这方面已经有了卤素浓度和cl -同位素组成方面的证据。

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.