Slab tearing controlling divergent volatile fluxes at convergent plate boundaries, southern Tibetan Plateau

The morphology and characteristics of subducting slabs play a critical role in controlling the formation and release of volatiles at plate boundaries. However, this control mechanism remains unclear in orogenic belts, such as the Tibetan Plateau. This study compiles helium and carbon data from 116 hot springs (132 samples) across three rift systems in southern Tibet—Pumqu-Xianza Rift, Yadong-Gulu Rift, and Cuona-Woka Rift—and employs a revised helium‑carbon coupling model, along with Monte Carlo simulation. The results reveal a transitional zone between the previously defined helium boundary (“mantle suture”) and newly identified carbon boundary (“tear boundary”), indicating a 200-km-wide transitional zone between the pre-established helium boundary and the newly identified carbon boundary, showing northward displacement of the carbon boundary relative to the helium boundary. Calculated ³He fluxes demonstrate spatial variations: 8.8 × 10³ atoms/m²/s south of the helium boundary, 3.3 × 10⁴ atoms/m²/s within the transitional zone, and 2.1 × 10⁵ atoms/m²/s north of the carbon boundary. Slab tearing appears to between YGR and PXR (∼89°E), resulting in significant differences in mantle volatile distribution. The mantle carbon is <1 % south of the helium boundary, ranges from 1 % and 2 % in the transition zone, while higher than 2 % north of the carbon boundary (with a mean of 4.6 %). V-type slab tearing west of YGR facilitates asthenospheric upwelling under ongoing north-south compression, generating E-W crustal extension that ultimately forms the rift system. These findings highlight the critical impact of slab tearing on the mantle-crust interactions, the regulation of volatile migration, and the geodynamic processes influencing habitability in the collision zone.