Volatile characteristics and fluxes of He-CO2 systematics in the southeastern Tibetan Plateau: Constraints on regional seismic activities

• Published in: Journal of hydrology (Amsterdam) Vol. 617; p. 129042
• Main Authors: Wang, Yingchun, Zhou, Xiaocheng, Tian, Jiao, Zhou, Jinlin, He, Miao, Li, Jingchao, Dong, Jinyuan, Yan, Yucong, Liu, Fengli, Yao, Bingyu, Wang, Yuwen, Zeng, Zhaojun, Liu, Kaiyi, Li, Liwu, Li, Zhongping, Xing, Lantian
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.2023
• Subjects: Geothermal system; He–CO2 systematics; Large fault zone; Tibetan Plateau; Volatiles flux; Tibetan Plateau; Volatiles flux; Geothermal system; Large fault zone; He–CO2 systematics
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/j.jhydrol.2022.129042

•The volatiles of the hot springs come mainly from the crust, with only a small amount from the mantle.•The tectonic stress field at the converging plate boundary limits the crustal helium flux.•Carbon sequestration of calcite precipitates slows down carbon flux in the collision zone.•Crust within the convergent boundary has the potential to produce a significant proportion of volatiles.•Coupled overpressure and stress fields in the rigid crust may lead to high seismic risk in this area. The spatial and temporal evolutionary mechanisms of volatile components at plate boundaries and their potential as earthquake precursors are not well understood. Based on observations of He–CO2 from 19 hot-spring gases in the Lancang River fault zone, Yunnan Province, the results show that the volatiles mainly come from the crust. The combined He isotope, He–CO2 relationships, and δ13C–CO2 values of the hot-spring volatiles indicate that it is a mixture of mantle and crustal fluids. These are related to the radiogenic He production caused by crustal U and Th elements with <5% mantle-derived He, whereas C is mainly from the metamorphic decarbonization of Tethyan marine carbonate rocks. Based on the He–CO2 isotopic relationship, crustal volatiles flux with a significant proportion were determined within a non-volcanic area, which was estimated to be 9–132 mol a−1, and CO2 degassing was estimated to be 2–120 × 109 mol a−1. These results are comparable to those of some volcanic areas and large seismically-active fault zones (such as the San Andreas Fault zone). The compressional stress field of the rigid crust near the study area leads to the low permeability of large faults and CO2 degassing from the hydrothermal system, resulting in chemical precipitation that further blocks the shallow crust conduits and deduced overpressure below the hydrothermal reservoir, which may be the cause of the presence of earthquakes with magnitudes greater than 7 in the Lancang River fault zone. The results are significant for elements cycling of converging plate boundaries and earthquake hazards monitoring.