Electrical conductivity of HCl-bearing aqueous fluids to 700 ºC and 1 GPa
Electrical conductivity of HCl-bearing aqueous fluids to 700 ºC and 1 GPa
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DOI：
10.1007/s00410-020-01754-5
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发表时间：
2020-11
影响因子：
3.5
通讯作者：
Steffen Klumbach;H. Keppler
中科院分区：
文献类型：
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作者：
Steffen Klumbach;H. Keppler
地下岩浆热液系统通常与地壳中高电导率有关。为了便于解释这些数据，并允许区分硅酸盐熔体和流体的影响，在外部加热的金刚石对顶砧单元中测量了H2 O-HCl系统中含水流体的电导率。数据收集到700 C和1 GPa，HCl浓度相当于0.01，0.1和1 mol/l在环境条件下。因此，这些数据使以前测量的压力范围增加了一倍以上，并将其扩展到地质现实的HCl浓度。电导率σ（单位：S/m）可通过数值模型log σ=− 2.032+ 205.8 T− 1+ 0.895 log c+ 3.888 log ρ+ log Λ 0（T，ρ）很好地再现，其中T为温度（单位：K），c为HCl浓度（单位：wt.%），ρ是纯水在相应压力和温度条件下的密度。Λ 0（T，ρ）是无限稀释时的极限摩尔电导率（单位：S cm 2 mol− 1），Λ 0（T，ρ）= 2550.14− 505.10 ρ− 429，437 T− 1。超过800个数据点与该模型的回归拟合得出R2 = 0.95。由于HCl的解离增强，电导率随着压力和流体密度而增加。然而，在恒定压力下，由于解离减少，电导率随温度降低。这种效应在地壳浅层压力为100-200 MPa时特别强烈，可使电导率降低两个数量级。因此，我们认为，有时在岩浆热液系统中火山中心以下的浅深度处观察到的低电导率可能只是反映了温度升高。强烈的负温度对流体电导率的影响，可能提供了一种可能性，遥感的温度变化，在这样的系统，并可能允许区分岩浆侵入的影响，从热液循环的变化。在地壳深部压力（500 MPa-1 GPa）下，HCl-NaCl-H2O流体的电导率通常很高，这意味着在地壳深部，如在高原岩浆区和其他地方，电导体至少部分可能是由于热液活动造成的。
Subsurface magmatic–hydrothermal systems are often associated with elevated electrical conductivities in the Earthʼs crust. To facilitate the interpretation of these data and to allow distinguishing between the effects of silicate melts and fluids, the electrical conductivity of aqueous fluids in the system H 2 O–HCl was measured in an externally heated diamond anvil cell. Data were collected to 700 C and 1 GPa, for HCl concentrations equivalent to 0.01, 0.1, and 1 mol/l at ambient conditions. The data, therefore, more than double the pressure range of previous measurements and extend them to geologically realistic HCl concentrations. The conductivities σ (in S/m) are well reproduced by a numerical model log σ=− 2.032+ 205.8 T− 1+ 0.895 log c+ 3.888 log ρ+ log Λ 0 (T, ρ), where T is the temperature in K, c is the HCl concentration in wt.%, and ρ is the density of pure water at the corresponding pressure and temperature conditions. Λ 0 (T, ρ) is the limiting molar conductivity (in S cm 2 mol− 1) at infinite dilution, Λ 0 (T, ρ)= 2550.14− 505.10 ρ− 429,437 T− 1. A regression fit of more than 800 data points to this model yielded R 2= 0.95. Conductivities increase with pressure and fluid densities due to an enhanced dissociation of HCl. However, at constant pressures, conductivities decrease with temperature because of reduced dissociation. This effect is particularly strong at shallow crustal pressures of 100–200 MPa and can reduce conductivities by two orders of magnitude. We, therefore, suggest that the low conductivities sometimes observed at shallow depths below the volcanic centers in magmatic–hydrothermal systems may simply reflect elevated temperatures. The strong negative temperature effect on fluid conductivities may offer a possibility for the remote sensing of temperature variations in such systems and may allow distinguishing the effects of magma intrusions from changes in hydrothermal circulation. The generally very high conductivities of HCl–NaCl–H 2 O fluids at deep crustal pressures (500 MPa–1 GPa) imply that electrical conductors in the deep crust, as in the Altiplano magmatic province and elsewhere, may at least partially be due to hydrothermal activity.