Zinc isotopic fractionation between aqueous fluids and silicate magmas: An experimental study. (15th October 2021)

• Record Type: Journal Article
• Authors: Guo, Haihao; Xia, Ying; Wu, Fei; Huang, Fang
• Is Part Of: Geochimica et cosmochimica acta. Volume 311(2021)
• Page Start: 226
• Page End: 237
• Publication Date: 2021-10-15
• Subjects: Zn isotope -- Aqueous fluids -- Silicate magmas -- Igneous rocks -- Hydrothermal systems; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2021.06.028
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: Fluids in magmas play a key role in magma differentiation and transportation of economic metals for ore deposits. As a chalcophile and incompatible element, zinc and its isotopes have been increasingly applied to study the magmatic-hydrothermal processes. However, zinc isotopic fractionation between aqueous fluids and magmas has not been well constrained. Here we experimentally determined equilibrium fractionation factors of Zn isotopes between aqueous fluids and silicate magmas (Δ 66 Znfluid-magma = δ 66 Znfluid – δ 66 Znmagma ). The results reveal that aqueous fluids are isotopically heavier than the coexisting silicate magmas. No correlation between Δ 66 Znfluid-magma and temperature or chlorine contents in fluids is observed under our experimental conditions. Instead, Δ 66 Znfluid-magma is negatively corresponded with NBO/T of the melt (the ratio of non-bridge oxygen and tetrahedron ions), and positively correlated with the molar ratio of Al/(0.5 K + Ca + Fe) in the bulk magmas, suggesting the controlling of silicate composition on Zn isotope fractionation. Our data therefore indicate that the isotopically heavier Zn in the fluids exsolved from magmas may account for the higher δ 66 Zn of pegmatites and high-silica granitic rocks. Moreover, involvement of magmatic fluids can explain the highly variable and remarkably heavier Zn isotopic signatures of fumaroles, thermal spring waters, and seafloor hydrothermal fluids compared to the igneous rocks. This study provides information that can be used to guide research using Zn isotopes to trace fluid activity and magmatism.