| Title | Applicability of the Na-K geothermometer in Slate Formations of Taiwan |
|---|---|
| Authors | Y. Lu, S. Song, C. Wang, T. Sachihiro, B.B. Chen, R.K. Tu |
| Year | 2019 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Na-K geothermometer, argillite/slate formations, water-rock interaction, tNa/K( albite-muscovite) |
| Abstract | More than 2/3 of hot springs in Taiwan are located in the Central Range metamorphic terrane, where argillite, slate, phyllite and black schist are predominated. Rapid uplift and erosion generate a higher geothermal gradient. The meteoric water infiltrated downward, was heated, then rose to the surface as hot springs by regional faults or fractured systems. The SiO2 geothermometer has been proved to be suitable in the argillite/slate formations of Taiwan (Chen, 1985; Huang et al., 2018). However, the applicability of the Na-K geothermometer has been debated for a long time. The widely used formula proposed by Fournier and Truesdell (1973) isn’t suitable in argillite/slate formations, because K-feldspar is absence. Chen (1985) proposed an albite-muscovite equilibrium formula of the Na-K geothermometer for argillite/slate formations. However, the 60-days argillite-fluid interactions showed that the Na-K geothermometer has a reverse relationship with experimental temperature (Huang et al., 2018). In this paper, we advocate that the reverse relationships of Na-K geothermometer and experimental temperature in Huang et al. (2018) may be affected by reaction time and redox state. The good correlation of Na/K and silica temperatures from well fluids implies that the Na-K geothermometer is worth considering. A new empirical formula of Na-K geothermometer is proposed by the fluids from deep production wells and based on quartz geothermometers above 180°C in this study. log(Na/K)=2.474*103T-1–3.7267 R2=0.71 From which the TNa/K (°C) 227°C >T>180°C, T(℃) = 2474/log(Na/K)+3.73 − 273.15 Most of the calculated errors between TNa-K and Tquartz we proposed are less than 8°C in the Chingshui, Tuchun, and Lushan geothermal fields. Poor coefficient of determination (R2 value) may be due to the equilibrium involved with H+ and complex clay mineral interactions. |