Fluid geochemical characteristics and tectonic significance of hot springs in eastern Yunnan

<p indent="0mm"> In order to evaluate the seismic risk of different sections of the Mile-Fuyuan fault zone, to clarify the key monitoring area for future earthquake in eastern Yunnan, and to explore the geochemical characteristics of hot springs and their genesis, the geochemical characteristics of major and trace elements, hydrogen, oxygen and strontium isotopes, and silica concentration of six hot spring water samples and three gas samples collected in eastern Yunnan from 2016 to 2020 were studied. The results show that: 1) the recharge source of hot spring water in the Mile-Fuyuan fault zone is mainly atmospheric precipitation, and the recharge elevation of the hot springs is about <sc>2167~2383 m;</sc> 2) the hot spring circulation depths in the Mile-Fuyuan fault zone calculated by the SiO₂ geothermometer and the silicon-enthalpy model are <sc>552~828 m</sc> and <sc>929~1089 m,</sc> respectively, which are shallower than the hot spring circulation depths on the eastern boundary of the Sichuan-Yunnan Block; 3) the hot spring gases in the Mile-Fuyuan fault zone are mainly of crustal origin and are less affected by mantle sources; 4) small and moderate earthquakes are relatively frequent in the Mile area at the southern end of the Mile-Fuyuan fault zone, which may be related to the smaller fracture strength there and the weakening of the rocks caused by groundwater.