蚀变洋壳和俯冲带变质流体的Fe-Mg同位素组成

黄建; 黄方; 肖益林

doi:10.3799/dqkx.2019.234

Volume 44 Issue 12

Dec. 2019

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Huang Jian, Huang Fang, Xiao Yilin, 2019. Fe-Mg Isotopic Compositions of Altered Oceanic Crust and Subduction-Zone Fluids. Earth Science, 44(12): 4050-4056. doi: 10.3799/dqkx.2019.234

Citation:

Huang Jian, Huang Fang, Xiao Yilin, 2019. Fe-Mg Isotopic Compositions of Altered Oceanic Crust and Subduction-Zone Fluids. Earth Science, 44(12): 4050-4056. doi: 10.3799/dqkx.2019.234

Huang Jian, Huang Fang, Xiao Yilin, 2019. Fe-Mg Isotopic Compositions of Altered Oceanic Crust and Subduction-Zone Fluids. Earth Science, 44(12): 4050-4056. doi: 10.3799/dqkx.2019.234

Citation:

Huang Jian, Huang Fang, Xiao Yilin, 2019. Fe-Mg Isotopic Compositions of Altered Oceanic Crust and Subduction-Zone Fluids. Earth Science, 44(12): 4050-4056. doi: 10.3799/dqkx.2019.234

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Fe-Mg Isotopic Compositions of Altered Oceanic Crust and Subduction-Zone Fluids

doi: 10.3799/dqkx.2019.234

CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China

Received Date: 2019-08-16
Publish Date: 2019-12-15

Abstract

Abstract

The origin of the light Fe and heavy Mg isotope enrichments in arc lavas remains unclear because of the lack of constraints on the Fe-Mg isotope compositions of altered oceanic crust (AOC) and metamorphic fluids in subduction zones. Carbonate-barren AOC has Mg isotope compositions similar to those of fresh mid-ocean ridge basalts, suggesting that low-to-high temperature alteration of oceanic crust by seawater and hydrothermal fluids results in limited Mg isotope fractionation. Fe-Mg isotope measurements show that the early omphacite-epidote veins have higher δ⁵⁶Fe and δ²⁶Mg compared to the host eclogites and that the δ⁵⁶Fe and δ²⁶Mg gradually decrease from the early omphacite-epidote through epidote-quartz to the late kyanite-epidote-quartz veins. These results indicate significant Fe-Mg isotope fractionation during fluid-rock interaction and fluid evolution due to the dissolution-precipitation processes of minerals in subduction zones. Compared to mid-ocean ridge basalts, the similar or higher δ⁵⁶Fe and δ²⁶Mg of AOC and metamorphic veins suggest that AOC-derived fluids are probably enriched in heavy Fe-Mg isotopes. Thus, contribution from AOC-derived fluids is unlikely to explain the light Fe and heavy Mg isotope compositions of arc lavas. We propose that the Fe-Mg isotope anomaly of arc lavas may result from a combination of prior melt depletion and addition of serpentinite-derived ⁵⁴Fe-²⁶Mg-rich fluids into the overlying mantle wedge.
- Fe-Mg isotopes,
- altered oceanic crust,
- eclogite,
- metamorphic fluids,
- fluid evolution,
- arc lavas,
- geochemistry

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References(38)

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