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Chapitre D'ouvrage Année : 2018

Halogens in Terrestrial and Cosmic Geochemical Systems: Abundances, Geochemical Behaviors, and Analytical Methods

Kenneth T. Koga

Résumé

Abstract The aims of this review chapter are to (i) summarize the distribution of halogens in different fluid (surficial, formation and crystalline shield waters, metamorphic, magmatic-hydrothermal-geothermal) and solid (oceanic and conti- nental crust, mantle and core) domains of the Earth, and various extra-terrestrial materials and bodies (meteorites, planets and moons, and the Sun); (ii) briefly discuss characteristic fractionation processes; and direct the reader to other chapters in this volume; (iii) provide an estimate of the total halogen abundance for the Earth and in its dominant reservoirs contributing to the Earth’s halogen endowment; and (iv) discuss some missing observations that could further improve our under- standing of halogen abundances and geochemical systematics. Determination of the distribution of the non-radioactive halogen elements (fluorine, F; chlorine, Cl; bromine, Br; and iodine, I) in, and the geochemical processes controlling their mass transfer between, solid and fluid repositories on Earth and in extraterrestrial envi- ronments has seen increasing attention in recent years. In part, this has been enabled by the development of dedicated analytical methodologies (e.g., in situ beam methods, secondary ion mass-spectrometer [SIMS], laser ablation-inductively coupled mass-spectrometer [LA-ICPMS], combined noble gas-halogen methods) that can provide a low detection level, accurate and precise determinations of halogen concentrations, and their isotope systematics in complex matrices (e.g., fluid inclusions, glasses, and minerals). However, a key motivation for this method development stems from an increased awareness of the value in halogen charac- terization for studying specific processes in Earth’s hydrosphere, crust, mantle, and core (e.g., crustal and mantle metasomatism; ore metal transfer; magmatic differ- entiation and volatile exsolution; fluid reservoir contamination and fluid mixing; mineral-melt-fluid partitioning; and basinal fluid evolution) in which the chemical and isotopic properties of the halogens provide significant advantages over other element groups. These properties include their (i) differential (i.e., temperature- and melt composition-dependent) incompatibility during fluid-melt and mineral-melt partitioning; (ii) collectively highly mobile and volatile nature but with only a few processes capable of fractionating the halogens from one another or leading to significant halogen mass transfer from one repository to another (e.g., the formation of evaporites, fluid phase separation [immiscibility, boiling], crystallization and degassing of magmas, subduction devolatilization and metamorphism); and (iii) strong systematic covariance of Cl and Br, but commonly differential behaviors of F and I (in response to organic processes) in most fluids in the hydrosphere, sediments, crustal rocks in general, the mantle, and mantle-derived lavas. Mass balance calculations show that F is dominantly hosted by mantle and crust, while Cl and Br show nearly identical distribution patterns in which a total of the seawater, formation waters, and evaporites comprise more than half of the Earth’s halogen budget. Experimentally determined metal-silicate partition coefficients suggest that a significant quantity of I is potentially hosted by the Earth’s core.
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Dates et versions

hal-02357705 , version 1 (10-11-2019)

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Jacob.J. Hanley, Kenneth T. Koga. Halogens in Terrestrial and Cosmic Geochemical Systems: Abundances, Geochemical Behaviors, and Analytical Methods. Daniel E. Harlov; Leonid Aranovich. The Role of Halogens in Terrestrial and Extraterrestrial Geochemical Processes, 2018, Springer Geochemistry, 978-3-319-61665-0. ⟨10.1007/978-3-319-61667-4_2⟩. ⟨hal-02357705⟩
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