Linking hydrothermal He-CO2 degassing to regional seismicity in the volcanically and tectonically active Tengchong block, southeastern Tibetan Plateau

Abstract

The volcanically and tectonically active regions are manifest by the co-existence of hydrothermal degassing and seismic activities, but the potential links between them remain enigmatic. Here, we present flux estimates for hydrothermal He and CO₂ from the Tengchong block, southeastern Tibetan Plateau, to constrain the role of magmatic fluids in triggering earthquakes. The He-CO₂ systematics reveal significant anomalies of mantle He and CO₂ degassing in localized volcanically active regions (VAR) that are superposed upon a broader tectonically active region (TAR).This correlates well with geophysically detected melts at crustal depths and suggests focused supply of magmatic fluids to hydrothermal system. Higher fluxes of mantle He [(1.08 ± 0.84) × 10¹⁰ atoms m⁻² s⁻¹] and CO₂ [(1.29 ± 1.00) × 10⁴ mol km⁻² yr⁻¹] of magmatic origins concentrate in the VAR rather than the TAR [mantle He and CO₂ flux = (0.26 ± 0.16) × 10¹⁰ atoms m⁻² s⁻¹ and (0.32 ± 0.19) × 10⁴ mol km⁻² yr⁻¹, respectively]. Spatially, high magmatic He-CO₂ fluxes in the VAR correspond well with several earthquake swarms and deep low-frequency earthquakes, while the TAR with much lower fluxes of magmatic fluids generally hosts tectonic earthquakes that align along active faults. These observations offer plausible evidence for the crucial role of magmatic fluids in causing overpressure in seismogenic zone beneath the VAR, which differs from stress-dominated earthquake nucleation in the TAR, suggesting the interplay between magmatic fluids and tectonic faulting in driving regional seismicity.