Earth Science Frontiers ›› 2020, Vol. 27 ›› Issue (3): 29-41.DOI: 10.13745/j.esf.sf.2020.4.10

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Advances in stable chlorine isotope geochemistry

LIU Xi(), WANG Yijing, WEI Haizhen*()   

  1. School of Earth Sciences and Engineering, Nanjing University; State Key Laboratory for Mineral Deposits Research, Nanjing 210023, China
  • Received:2019-07-01 Revised:2020-01-16 Online:2020-05-20 Published:2020-05-20
  • Contact: WEI Haizhen

Abstract:

Halogen elements are relatively rare on earth and chlorine is the most abundant one. Chlorine is a strongly hydrophilic volatile element having two stable isotopes 35Cl and 37Cl with natural abundances of 75.76% and 24.24%, respectively. In this work, we reviewed chlorine isotope geochemistry, including distribution of chlorine isotopes in various geological reservoirs, factors controlling equilibrium and kinetic fractionation behaviors of chlorine isotopes, and the relevant geological applications. The chlorine isotopic compositions (δ37Cl) of evaporite, seawater, igneous rock, sediment, metamorphic rock and mantle are -0.5‰ to +0.8‰, 0.00±0.05‰, -1.12‰ to +0.79‰, -3.0‰ to +2.0‰, -3.6‰ to 0 and -1.9‰ to +7.2‰, respectively. The chlorine isotopic compositions (δ37Cl) of Moon, Mars and other planets (4-Veata) are -4‰ to +81.1‰, -5.6‰ to +8.6‰ and -3.8‰ to +7.7‰, respectively. Compared to the relatively narrow δ37Cl range (-14‰ to +16‰) on Earth, larger δ37Cl variations (-5.6‰ to +81‰) are on the Moon and Mars, indicating dramatic differences in controlling mechanisms of chlorine isotope fractionation in terrestrial and extra-terrestrial processes. In nature, chlorine isotope fractionation is mainly controlled by physical (diffusion, ion filtration, salt precipitation, volcanic systems, etc.) and chemical (water-rock interaction, metamorphism, especially in serpentinization) processes. Heavy isotopes are enriched by diffusion, ion filtration and volcanism, and δ37Cl first decreases and then increases during consecutive precipitation of salts from brine, while various factors influence the serpentine process. In combination with other geochemical indices, chlorine isotopes show great potentials in addressing a variety of geochemical issues, including prospecting for potash deposits, evaluating evolution paths of groundwater, tracing pollutant sources and quantifying bioremediation, tracking genesis of ore-forming fluid, as well as constraining planetary evolution and magma ocean degassing, and so on.

Key words: chlorine isotope, isotopic characteristics in reservoirs, equilibrium-kinetic chlorine isotope fractionation, geological applications

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