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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Effect of the hydrothermal alteration on the surface conductivity of rock matrix: Comparative study between relatively-high and low temperature hydrothermal systems
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Effect of the hydrothermal alteration on the surface conductivity of rock matrix: Comparative study between relatively-high and low temperature hydrothermal systems

机译：水热蚀变对岩石基质表面电导率的影响：高温和低温热液系统的比较研究

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摘要

In volcanic areas, hydrothermal systems are characterized by high bulk electrical conductivity, which is a combination of high-salinity/temperature pore water and hydrothermally-altered rock matrix. The present study focuses on better understanding the influence of the hydrothermal alteration on the surface conductivity associated with generation and stability of smectite. As a case study, the GSB borehole site at Beppu geothermal area in southwest Japan was selected; at this site, hydrothermal fluids with a relatively high temperature (150 °C) flow at a shallow depth. The physical properties related to electrical conductivity (formation factor, surface conductivity, and porosity) were estimated on the basis of Revil model using conductivity measurements of the drillcores. Strong hydrothermal alteration at the site GSB was shown by high surface conductivity (10~(-2)-10~(-1) S/m) and high cementation exponent (2.5-4.5). From the comparison between the vertical profiles of the bulk conductivity, pore water conductivity, and surface conductivity, it was shown that the rock matrix makes a non-negligible contribution to the bulk conductivity at the site. This contribution to bulk conductivity is quite different from that of low-temperature hydrothermal systems, where the contribution from the pore water dominates because there is little or no hydrothermal alteration. Furthermore, comparison between the findings of this study and low-temperature hydrothermal systems showed that the surface conductivity could simply reflect temperature to which the rock has been exposed. The surface conductivity maintains the small value at the low temperatures such as ＜40 ℃, and significantly increases at the relatively high temperatures (100-150 °C). At the higher exposed temperatures ＞ 150 ℃, its value decreases relative to that at the temperatures of 100-150 °C. This relationship is consistent with the generation and stability of smectite at active hydrothermal systems, and places strong constraints on the quantitative interpretation of the electrical conductivity structure of a volcano.
机译：在火山地区，热液系统的特征是高整体电导率，这是高盐度/高温孔隙水和热液改变的岩石基质的结合。本研究的重点是更好地理解水热蚀变对蒙脱石生成和稳定性相关的表面电导率的影响。作为案例研究，选择了日本西南部别府地热区的GSB钻孔位置。在该位置，温度较高（150°C）的热液在浅层流动。与电导率有关的物理性质（形成因数，表面电导率和孔隙率）是根据Revil模型使用钻芯的电导率测量值估算的。高的表面电导率（10〜（-2）-10〜（-1）S / m）和高的胶结指数（2.5-4.5）显示了GSB处强烈的水热变化。通过对体积电导率，孔隙水电导率和表面电导率的垂直分布图的比较，可以看出，岩石基质对现场的体积电导率的贡献不可忽略。这种对体积电导率的贡献与低温热液系统的差别很大，在低温热液系统中，孔隙水的贡献占主导地位，因为很少或没有热液变化。此外，本研究结果与低温热液系统之间的比较表明，表面电导率可以简单地反映岩石所处的温度。在较低的温度（例如＜40℃）下，表面电导率保持较小的值，而在较高的温度下（100-150°C），表面电导率则显着增加。在＞ 150℃的较高暴露温度下，其值相对于在100-150°C的温度下降低。这种关系与蒙脱石在活跃的热液系统中的产生和稳定性是一致的，并且对火山的电导率结构的定量解释提出了强烈的限制。

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