Dissolved gas concentrations of the geothermal fluids in Taiwan
Date Issued
2010
Date
2010
Author(s)
Chen, Ai-Ti
Abstract
Taiwan, a geologically active island, is located on the boundary of the Philippine Sea Plate and the Eurasian Plate. High heat flow and geothermal gradient generated by the complex collision and orogeny, and heat up the meteoric water and/or the ground water. The heated water becomes geothermal fluids. In previous studies, some researchers tried to categorize hot springs based on their appearance, chemical compositions and lithological areas. Because of the chemical inertness, the concentrations and isotopic composition of dissolved noble gases are considered to be good indicators of the mantle degassing, climate changes, geothermal conditions, and so on. In this study, it is first time to classify the hot springs in Taiwan in terms of dissolved gases.
In order to discuss different origins of hot springs, 55 hot springs had been sampled in this study. Dissolved gases are distinguished as major and minor gases. Major gases include O2, N2, CH4 and CO2, while minor gases are He, Ne, Ar, Kr, Xe and Rn. Hot spring water was sampled and stored in pre-evacuated glass bottles for analyzing chemical compositions of minor gases. The abundance of five noble gases is determined by a quadrupole mass spectrometer (QMA200, Pfeiffer Vacuum Co.) based on the isotope dilution technique. Furthermore, helium isotopic ratios and helium-neon ratios are measured on a conventional noble gas mass spectrometer (MM5400, MicroMass Co.). For hydrochemistry analysis, water samples are analyzed by IC, ICP-MS and titration. Samples with glass vials are introduced to RAD 7 and GC for dissolved Rn and major dissolved gases analyses.
We can classify the hot springs into three major groups based on anion concentration data, and then subdivide them into nine minor groups by cation concentration data. Moreover, according to major dissolved gases compositions, three major gas components: CH4, N2 and CO2, are identified. The result indicates that there are three gas reservoirs in study area. Dissolved noble gases can provide more detailed clues about the sources of hot springs in Taiwan, such as the degree of mixing between meteoric water and deep-source water. The circulation model also can be identified.
Subjects
dissolved gas
geothermal fluid
noble gas
gas concentration
SDGs
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