Iron-Copper-Zinc Isotopic Compositions of Andesites from the Kueishantao Hydrothermal Field off Northeastern Taiwan

Zhigang Zeng,Yuxiang Zhang,Xiaohui Li,Zuxing Chen,Shuai Chen,Chen-Tung Arthur Chen

doi:10.3390/su14010359

Abstract

The studies of iron (Fe), copper (Cu), and zinc (Zn) isotopic compositions in seafloor andesites are helpful in understanding the metal stable isotope fractionation during magma evolution. Here, the Fe, Cu, and Zn isotopic compositions of andesites from the Kueishantao hydrothermal field (KHF) off northeastern Taiwan, west Pacific, have been studied. The majority of δ56Fe values (+0.02‰ to +0.11‰) in the KHF andesites are consistent with those of MORBs (mid-ocean ridge basalts). This suggests that the Fe in the KHF andesites is mainly from a MORB-type mantle. The Fe-Cu-Zn isotopic compositions (δ56Fe +0.22‰, δ65Cu +0.16‰ to +0.64‰, and δ66Zn +0.29‰ to +0.71‰) of the KHF andesites, which are significantly different from those of the MORBs and the continental crust (CC), have a relatively wide range of Cu and Zn isotopic compositions. This is most likely to be a result of the entrainment of the sedimentary carbonate-derived components into an andesitic magma. The recycled altered rocks (higher δ56Fe, lower δ66Zn) could preferentially incorporate isotopically light Fe and heavy Zn into the magma, resulting in relative enrichment of the lighter Fe and heavier Zn isotopes in the andesites. The majority of the δ56Fe values in the KHF andesites are higher than those of the sediments and the local CC and lower than those of the subducted altered rocks, while the reverse is true for δ66Zn, suggesting that the subseafloor sediments and CC materials (lower δ56Fe, higher δ66Zn) contaminating the rising andesitic magma could preferentially incorporate isotopically heavy Fe and light Zn into the magma, resulting in relative enrichment of the heavier Fe and lighter Zn isotopes in the andesites. Thus, the characteristics of the Fe and Zn isotopes in back-arc and island-arc volcanic rocks may also be influenced by the CC and plate subduction components.

Highlights

We present the first results of the Fe, Cu, and Zn isotope analyses of andesites from the Kueishantao hydrothermal field (KHF) off northeastern Taiwan, west
The majority of δ56 Fe and δ57 Fe values in the KHF andesites were higher than those in the sediments and the Taiwan local continental crust (CC) (Table 3) and lower than those in the subducted altered rocks [1,36,50–54], while the reverse was true for δ66 Zn and δ68 Zn
+0.29‰ to +0.71‰) of the KHF andesites are significantly different from those of the previously studied MORB and CC and have a relatively wide range of Cu and Zn isotopic compositions, which are most explained as being a result of the entrainment of sedimentary carbonate-derived components, which are from the plate subduction and CC components, into andesitic magma

Summary

Introduction

The stable isotopic systematics of iron, copper, and zinc (Fe-Cu-Zn) have been widely applied as tools for tracking fluid pathways and fingerprinting sources in volcanic and hydrothermal systems [1–7]. Only a few Fe-Cu-Zn isotope studies have been conducted on seafloor andesites. 0.12‰, n = 15) of subduction-related andesites from a variety of locations worldwide, including two high-Mg andesites from Liaoxi in the North China. Craton (NCC) [8], eight andesites from the Kamchatka [9,10], and two andesites from the Cordillera de Talamanca in the Central America arc [11], have been reported [5].

Results

Discussion

Conclusion