Tectonic variations in NS-trending rifts, southern Tibetan Plateau: insights from hydrothermal emissions and seismic activities

A series of NS-trending rifts in the Tibetan Plateau interior provide a window for unraveling its rifting properties and geodynamic mechanisms. In this study, we focused on hydrothermal degassing and seismic activities to identify the differential tectonic status of each rift. Analysis of hydrothermal gaseous components reveals that crustal metamorphic products accumulate in the western rifts and the easternmost rift while growing mantle-derived volatiles contribute in the northeast rifting zones. The flow rate of uprising mantle-derived fluids ranges from 0.01 mm/yr to 2972 mm/yr and the total ³He fluxes vary in 1.0 × 10⁻⁷ – 1.2 × 10⁻⁵ mol/km²/yr. The distribution of H₂-enriched hot springs coincides with the young initiation time of the rifts, indicating the young active tectonic setting in the eastern rifts. Spatially discernible characteristics are also observed in seismic activity. Earthquakes occurring in western rifts have relatively shallow focal depths and low frequencies and magnitudes, suggesting that faulting structures are active within the middle-shallow crust. In contrast, more frequent strong and deep-focus earthquakes occurred in the northeastern rifting areas, outlining the large-scale fault planes that dipped into the lower crust or even the bottom of the lithosphere and served as an enhanced conduit for the growing contribution of mantle-derived volatiles at the surface. Our interpretation emphasizes that the underlying Indian slab is unlikely to experience wide tearing beneath Tibet and that eastward-enhanced seismic activity and degassing are likely driven by eastward-propagating lateral slab detachment. These findings have profound implications for the post-collisional evolution of the Tibetan Plateau.