Distribution and genesis of geothermal waters in the Xianshuihe fault zone, Western Sichuan plateau, China: Constraints on fracture system and regional seismic activities

Abstract

The Xianshuihe fault zone (XSFZ), which is characterized by intense tectonic activities, frequent earthquakes and great number of hot springs, has significant potential for exploiting geothermal resources. Previous studies primarily focus on certain hydrothermal systems in southeastern segment of XSFZ, such as Kangding hydrothermal system, but lack the synthetical comparison and systematic analysis of geothermal waters along the XSFZ. Based on detailed geological investigation, the XSFZ hydrothermal system has divided into six geothermal activity areas: Luhuo (LH), Daofu (DF), Qianning-Bamei (QB), Yalahe-Zhonggu (YZ), Kangding (KD) and Moxi (MX). According to the ⁸⁷Sr/⁸⁶Sr ratios and elements behaving in water-rock interactions, the dissolution of silicate minerals is the primarily source of the hydrogeochemical compositions in geothermal waters. The δ_D and δ¹⁸O composition indicate that geothermal waters primarily originated from meteoric waters, but also affected by deep fluids. However, the contribution of deep fluids to the southeastern geothermal areas (YZ, KD and MX) with high concentrations of Cl^- is greater than that of the northwestern (LH, DF and QB). The reservoir temperatures and chlorine-enthalpy model reveal that there are three distinct geothermal systems along the XSFZ: YZ and KD geothermal waters are originated from a common deep reservoir (R1), MX are from R3, and LH, DF, and QB are from R4. Due to the uneven thermal structural distribution along XSFZ, the southeastern segments generated stronger thermal stress and have more frequent earthquake occurrence. Thus, the study of geothermal waters along XSFZ can provide valuable insights into deep tectonic activities and geochemical indicators of earthquake monitoring in the region.