Experimental measurement of H2(aq) solubility in hydrothermal fluids: Application to the Piccard hydrothermal field, Mid-Cayman Rise
Experimental measurement of H2(aq) solubility in hydrothermal fluids: Application to the Piccard hydrothermal field, Mid-Cayman Rise
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DOI：
10.1016/j.gca.2020.05.020
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发表时间：
2020-08
影响因子：
5
通讯作者：
Peter P. Scheuermann;Yanlu Xing;K. Ding;W. Seyfried
中科院分区：
文献类型：
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作者：
Peter P. Scheuermann;Yanlu Xing;K. Ding;W. Seyfried
在大洋中脊热液系统中，流体的氧化还原状态受控于寄主岩石中亚铁的氧化和氢水溶液的生成，要定量解释氧化还原状态，需要将H2（aq）浓度转换为H2逸度fH 2。在这里，我们提出的热液实验的结果，校准thefH 2-浓度关系的盐水热液流体，YH 2-Cl。H2（aq）浓度在400和500 °C、210和510 bar之间在KCl-H2O系统中的单相流体和低密度蒸气中测量。赤铁矿-磁铁矿组合被用来缓冲H2。YH 2-克莱尔值远高于1，并随温度升高而降低。沿着等温线，YH 2-Cl随着流体密度的降低而降低。在400 °C、330巴和1000 mmol/kg KCl下，YH 2-Cl为316巴/摩尔，在500 °C、400巴和33 mmol/kg KCl下降至4巴/摩尔。结合先前确定的H2S（aq）在热液条件下的溶解度，这里提出的数据允许计算的自然喷口系统的氧化还原条件。为玄武岩托管的Piccard热液场计算的氧化还原条件表明，在深度存在角闪岩相矿物组合，与从喷口流体化学的其他方面（例如，Cl和SiO2）。皮卡德可能是第一个活跃的通风位置，通过其成分记录了以前只在化石化的海底热液系统中观察到的蚀变组合的证据。
In mid-ocean ridge hydrothermal systems the fluid redox state is controlled by oxidation of ferrous iron in the host rock and generation of aqueous hydrogen, H2(aq).A quantitative interpretation of redox state requires conversion of H2(aq)concentrations to H2fugacity,fH2. Here we present the results of hydrothermal experiments that calibrate thefH2-concentration relationship in saline hydrothermal fluids, YH2-Cl. H2(aq)concentrations were measured between 400 and 500 °C, 210 and 510 bar, in both single-phase fluids and low-density vapors in the KCl-H2O system. The assemblage hematite-magnetite was used to bufferfH2. Values of YH2-Clare well above unity and decrease as temperature increases. Along isotherms YH2-Cldecreases as the fluid density decreases. At 400 °C, 330 bar and 1000 mmol/kg KCl YH2-Clis 316 bar/molal and decreases to 4 bar/molal at 500 °C, 400 bar and 33 mmol/kg KCl. In combination with previous determination of H2S(aq)solubility at hydrothermal conditions, the data presented here permit calculation of the redox conditions of natural vent systems. Redox conditions calculated for the basalt-hosted Piccard hydrothermal field suggest amphibolite facies mineral assemblages are present at depth, consistent with the extremely hot temperatures (>500 °C) inferred from analysis of other aspects of vent fluid chemistry (e.g., Cl and SiO2). Piccard may be the first location of active venting that records, through its composition, evidence for an alteration assemblage that had been previously observed only in fossilized submarine hydrothermal systems.