Br/Cl signature of hydrothermal fluids: liquid–vapour fractionation of bromine revisited
Br/Cl signature of hydrothermal fluids: liquid–vapour fractionation of bromine revisited
复制标题
热液的 Br/Cl 特征：重新审视溴的液-气分馏
DOI：
10.1111/j.1468-8123.2006.00135.x
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发表时间：
2006
期刊：
影响因子：
1.7
通讯作者：
G. Schettler
中科院分区：
文献类型：
--
作者：
A. Liebscher;V. Lüders;W. Heinrich;G. Schettler
热液的 Br/Cl 比率广泛用作海洋热液系统中的地球化学示踪剂，以证明流体相分离过程。然而，先前溴的液-气分馏结果并不明确。在这里，我们报告了在 380–450°C 和 22.9–41.7 MPa 系统中 H2O–NaCl–NaBr 中溴液气分馏的新实验结果。我们的数据表明，在液相中，溴通常比氯更富集。计算得出的反应 Brvapour + Clliquid = Brliquid + Clvapour 的交换系数 KD(Br-Cl) 液-汽在研究的 P-T 范围内介于 0.94 ± 0.08 和 1.66 ± 0.14 之间。它们与 DC 液体-蒸汽呈正相关，并表明随着液体-蒸汽固溶线开度的增加，即增加到 H2O-NaCl 系统中临界曲线的距离，溴-氯分馏也会增加。 KD(Br-Cl)液体-蒸汽形式 = a*ln[b*(DClliquid-vapour−1) + e1/a] 的经验拟合得出 a = 0.349 和 b = 1.697。基于这种经验拟合和 H2O-NaCl 系统中良好约束的相关系，我们计算了流体相分离对具有初始海水成分的热液的 Br/Cl 特征的影响，沿着 4.5 和 4.8 J g−1 K−1 等熵进行封闭和开放绝热上升。计算表明，流体相分离可以显着改变热液中的 Br/Cl 比率。预测的 Br/Cl 演变与 9°N 至 10°N 东太平洋海隆低盐度喷口流体中的 Br/Cl 特征一致。
Br/Cl ratios of hydrothermal fluids are widely used as geochemical tracers in marine hydrothermal systems to prove fluid phase separation processes. However, previous results of the liquid–vapour fractionation of bromine are ambiguous. Here we report new experimental results of the liquid–vapour fractionation of bromine in the system H2O–NaCl–NaBr at 380–450°C and 22.9–41.7 MPa. Our data indicate that bromine is generally more enriched than chlorine in the liquid phase. Calculated exchange coefficients KD(Br-Cl)liquid-vapour for the reaction Brvapour + Clliquid = Brliquid + Clvapour are between 0.94 ± 0.08 and 1.66 ± 0.14 within the investigated P–T range. They correlate positively with DClliquid-vapour and suggest increasing bromine–chlorine fractionation with increasing opening of the liquid–vapour solvus, i.e. increasing distance to the critical curve in the H2O–NaCl system. An empirical fit of the form KD(Br-Cl)liquid-vapour = a*ln[b*(DClliquid-vapour−1) + e1/a] yields a = 0.349 and b = 1.697. Based on this empirical fit and the well-constrained phase relations in the H2O–NaCl system we calculated the effect of fluid phase separation on the Br/Cl signature of a hydrothermal fluid with initial seawater composition for closed and open adiabatic ascents along the 4.5 and 4.8 J g−1 K−1 isentropes. The calculations indicate that fluid phase separation can significantly alter the Br/Cl ratio in hydrothermal fluids. The predicted Br/Cl evolutions are in accord with the Br/Cl signatures in low-salinity vent fluids from the 9 to 10°N East Pacific Rise.