Calcium isotopic geochemistry of geothermal systems in the tectonically active southeastern Tibetan Plateau

Bei-Bei Chen; Si-Liang Li; Philip A E Pogge von Strandmann; Jun Zhong; Ting-Ting Ma; Jian Sun; Wen-Yan He; Cong-Qiang Liu

doi:10.1016/j.scitotenv.2023.161534

Calcium isotopic geochemistry of geothermal systems in the tectonically active southeastern Tibetan Plateau

Sci Total Environ. 2023 Apr 1:867:161534. doi: 10.1016/j.scitotenv.2023.161534. Epub 2023 Jan 10.

Authors

Bei-Bei Chen¹, Si-Liang Li², Philip A E Pogge von Strandmann³, Jun Zhong⁴, Ting-Ting Ma⁴, Jian Sun⁵, Wen-Yan He⁶, Cong-Qiang Liu⁴

Affiliations

¹ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China; State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing. Electronic address: chenbeibei@tju.edu.cn.
² Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China; State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin 300072, China. Electronic address: Siliang.li@tju.edu.cn.
³ London Geochemistry and Isotope Centre (LOGIC), Institute of Earth and Planetary Sciences, University College London and Birkbeck, University of London, Gower Street, London WC1E 6BT, UK; Institute of Geosciences, Johannes Gutenberg University, 55122 Mainz, Germany.
⁴ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China.
⁵ Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources, MNR Key Laboratory of Isotope Geology, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China.
⁶ State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing.

PMID: 36638984
DOI: 10.1016/j.scitotenv.2023.161534

Abstract

The global Calcium (Ca) cycle is closely coupled to the carbon cycle, and Ca isotopes have potential in tracing it. Even though groundwater is one of the main reservoirs of Ca at the Earth's surface, few data are available for groundwater, and the behavior of Ca and its isotopes in geothermal systems remains unknown. Here we analysed the stable Ca and radiogenic Sr isotope compositions of thermal waters distributed along the Jinsha and Yalong river valleys in the southeastern Tibetan Plateau. The Ca isotopic composition of the thermal water ranges from 0.45 to 2.16 ‰ (δ^44/40Ca values relative to SRM 915a). The thermal waters collected from carbonate aquifers have higher δ^44/40Ca values than bedrocks, which was attributed to secondary carbonate precipitation accompanied by CO₂ degassing. In contrast, δ^44/40Ca values in thermal waters collected from clastic and igneous rocks are similar to bedrock. Despite some thermal waters undergoing secondary silicates formation and CaNa ion exchange, such processes maybe not play a significant role in governing the Ca isotopic composition of these thermal waters. This suggests that Ca isotopes can be used to trace secondary carbonate precipitation driven by CO₂ degassing (e.g. travertine) in geothermal systems located in tectonically active areas.

Keywords: Calcium cycling; Calcium isotopes; Geothermal system; Groundwater; Tibetan Plateau; Water-rock interaction.