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

Abstract : 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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Jacob.J. Hanley, Kenneth 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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