Chlorine isotope fractionation in alkaline magmatic systems

该项目代表了一项系统的研究，以限制碱性岩浆中的氯同位素系统在热液系统中的行为和地幔中的氯同位素不均质性。由于碱性岩石一般来源于岩石圈地幔来源和富卤素的性质，因此对于理解岩浆系统侵位、分异和流体出溶/脱气过程中卤素从地幔到地壳的运移和卤素收支具有重要意义。根据我们的初步数据，在这个项目中将检验以下三个假设：(I)岩浆作用，如分离结晶和流体出溶/脱气，导致稳定的氯同位素分馏(Ii)在碱性岩浆中记录到地幔中氯同位素组成的不均一性(Iii)碱性岩石变质过程中的变形和流体-岩石相互作用不会显著改变其氯同位素组成。该项目将使用氯同位素数据(电感耦合等离子体质谱、SIMS)、卤素数据(F、氯、溴、碘)和S浓度数据(电子探针、化学气相色谱)以及关于矿物分离的氧和S同位素数据。结合物质平衡和瑞利型计算，这将允许(1)开发氯同位素数据在破译岩浆到热液过程中的应用，以及(2)限制(岩石圈)地幔中关于卤素比率(例如，F/氯、氯/溴、氯/碘)和氯同位素组成的全球成分不均一性，这方面已经有了证据。

This project represents a systematic study to constrain the behaviour of the Cl isotope system in alkaline magmatic to hydrothermal systems and the Cl isotope heterogeneity in the mantle. Because of their general derivation from lithospheric mantle sources and their halogen-rich nature, alkaline rocks are important to understand halogen transport from the mantle into the crust and halogen budgets during emplacement, differentiation, and fluid exsolution/degassing of magmatic systems. The extensive sample collection to be worked with includes plutonic, volcanic and metamorphosed alkaline rocks from more than 40 localities worldwide.Based on our preliminary data, the following three hypotheses will be tested during this project: (i) Magmatic processes, such as fractional crystallization and fluid exsolution/ degassing cause fractionation of stable Cl isotopes (ii) Heterogeneity of the mantle with respect to Cl isotope compositions is recorded in alkaline magmas (iii) Deformation and fluid-rock interaction during metamorphism of alkaline rocks does not significantly change their Cl isotopic composition. The project will use Cl isotope data (ICP-MS, SIMS), halogen (F, Cl, Br, I) and S concentration data (EPMA, CIC) as well as O and S isotope data on mineral separates. Combined with mass balance and Rayleigh-type calculations, this will allow to (i) develop applications of Cl isotope data for deciphering magmatic to hydrothermal processes and (ii) to constrain global compositional heterogeneities in the (lithospheric) mantle with respect to halogen ratios (e.g., F/Cl, Cl/Br, Cl/I) and Cl isotope compositions, for which already evidence was presented.