Boron isotope compositions of fluids and plumes from the Kueishantao hydrothermal field off northeastern Taiwan: Implications for fluid origin and hydrothermal processes

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• 作者：Zhigang Zeng ; Xiaoyuan Wang ; Chen-Tung A. Chen ; Xuebo Yin ; Shuai Chen ; Yunqi Ma ; Yingkai Xiao
• 关键词：Boron ; Hydrothermal fluid and plume ; Kueishantao hydrothermal field
• 刊名：Marine Chemistry
• 出版年：20 December, 2013
• 年：2013
• 卷：157
• 期：Complete
• 页码：59-66
• 全文大小：1088 K

文摘

Boron is a common element in vent fluids of seafloor hydrothermal fields, and it has been used to understand the hydrothermal flux and water-rock interaction in hydrothermal systems. We have measured the boron concentration and isotope composition of seawater, andesite, hydrothermal fluid and plume samples from the Kueishantao hydrothermal field. The 未¹¹B value of ambient seawater near the field is 40.05 卤 0.01鈥? and the boron concentration is 3.81 mg/L. Andesite rocks from the hydrothermal field have an average boron content of 15.3 ppm. The hydrothermal fluids from the yellow spring and white spring span a small range of 未¹¹B values, from 33.27 卤 0.22 to 36.84 卤 0.11鈥? and plumes from both springs also cover a small range, from 37.56 卤 0.01 to 40.37 卤 0.21鈥?

Hydrothermal fluids from both springs in the Kueishantao hydrothermal field have variable B enrichments relative to seawater between 7 and 21%. They have B concentrations (4.10-4.64 mg/L) that are slightly higher and 未¹¹B values (33.27-36.84鈥? that are lower than those of the hydrothermal plumes (3.94-4.17 mg/L, 37.56-40.37鈥?. Hydrothermal fluids and plumes display a very regular array of data points in a 未¹¹B-B diagram, suggesting that the boron of hydrothermal fluids and plumes is mainly from seawater and that little of it is, from andesite. This implies that the interaction of subseafloor fluid and -andesite at the Kueishantao hydrothermal field is of short duration. In all the fluids, from springs to hydrothermal plumes, the pH values, B concentrations and B isotopic compositions show significant correlations with each other suggesting that the 未¹¹B/B and pH/B ratios of hydrothermal plumes have stable values over the small distance form vent to plume (< 15 m). Thus the B concentrations and B isotopic compositions of hydrothermal plumes can be used to describe the diffusive processes governing the chemical compositions of hydrothermal plumes in the seawater environment.

The water/rock ratios, based on the B concentrations and 未¹¹B values, are between 1.96 and 3.63. The hydrothermal flux of boron from the yellow spring into the oceans is between 1.17 脳 10⁵ mol/yr and 1.32 脳 10⁵ mol/yr, and from the white spring it is between 6.69 脳 10⁴ mol/yr and 7.17 脳 10⁴ mol/yr, assuming that only andesites are present in the reaction zone.