Helium (including 3He and 4He isotopes) is an element mainly outgassing from Earth’s interior to the atmosphere. The fluxes and isotopic compositions of helium are critical parameters for monitoring the hazardous volcanic eruptions and earthquakes, estimating the fluxes of other volatile species (e.g., CO2 and N2) from the solid Earth, and exploring the helium resources and geothermal energy. Continental regions are essential for the outgassing of deeply-sourced helium in response to volcanic and tectonic processes. However, the helium fluxes remain largely unknown for continental collision settings such as the Tibetan Plateau.
We conducted a quantitative study on the magnitude of helium outgassing from hot springs in the Simao block of the Southeast Tibetan Plateau margin, which is located in a region influenced by the India-Asia continental collision. We report flux estimates of (0.03−32) × 105 atoms m−2 s−1 for 3He and (3.2−32) × 1010 atoms m−2 s−1 for 4He, with mantle fractions of helium fluxes up to 2−3 orders of magnitude greater than those of stable continents (Fig. 1). These mantle and crustal helium fluxes of the Simao block are comparable to those estimated for the representative continental regions worldwide. Geologically recent magma recharge beneath Quaternary volcanoes is proposed to account for the high mantle helium fluxes and 3He/4He up to 7.24 Ra (Fig. 2). Active tectonics driven by the India-Asia continental collision possibly maintained efficient release of crustal helium over geological timescales. These findings present the first flux estimates of hydrothermal helium degassing controlled by volcanic and tectonic processes in continental collision settings. We suggest that India-Asia continental collision zone is an important natural laboratory for studying helium degassing from solid Earth.
Fig. 1. Mantle 4He fluxes versus upward fluid flow rate (a) and crustal 4He fluxes (b) for hot springs in the Simao block.
Fig. 2. Genetic model showing helium degassing in the Simao block.
This study was supported by National Natural Science Foundation of China (42072327 and 41930642), National Key Research and Development Project (2020YFA0607700), China Seismic Experimental Site (2019CSES0104), and United Laboratory of High-Pressure Physics and Earthquake Science (2019HPPES02).
Full article: Zhang, M., Liu, W., Guan, L., Takahata, N., Sano, Y., Li, Y., Zhou, X., Chen, Z., Cao, C., Zhang, L., Lang, Y.-C., Liu, C.-Q., Xu, S., 2022. First Estimates of Hydrothermal Helium Fluxes in Continental Collision Settings: Insights from the Southeast Tibetan Plateau Margin. Geophysical Research Letters 49, e2022GL098228. https://doi.org/10.1029/2022GL098228
