Fig. 1: Tectonic framework of the Himalayas and southern Tibet, CO₂ flux measurements, and sample distribution in the study area.

a Map of the Himalayan-Tibetan orogen showing major tectonic boundaries and extensional rift systems. Base map was created with GeoMapApp (www.geomapapp.org)/CC BY, and the hemisphere inset was generated using ArcGIS Earth software. Localities of the Himalayan domes and leucogranites are after ref. ⁵¹. The dash-dotted blue box shows the location of the TTYR. The yellow line represents the seismically inferred northern extent of the Indian crustal front¹⁹. b Distribution of CO₂ flux measurements and thermal springs in the southern, central, and north segments of the TTYR. Profiles AA′, BB′, CC′, and DD′ represent soil CO₂ measurements across active fault zones, as shown in Supplementary Fig. 8. The base map is from a 30-meter SRTM digital elevation model (www.earthexplorer.usgs.gov). Numbers represent hydrothermal fields from which bubbling gas samples were collected for geochemical analysis, with carbon and helium isotope data shown in Fig. 3a, b.