[S-GC37] Volatiles in the Earth - from Surface to Deep Mantle

[SGC37-08] The diverging subduction of tearing slab controls the deep carbon recycling efficiency: Geochemical evidence from the SE Tibetan Plateau

*Yingchun Wang¹、Xiaocheng Zhou²、Jiao Tian²、Bingyu Yao³、Chunhui Cao⁴、Hikaru Iwamori⁵ (1.Chengdu University of Technology、2.Institute of Earthquake Forecasting, China Earthquake Administration、3.China University of Geosciences, Beijing、4.Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences、5.Earthquake Research Institute, The University of Tokyo)

キーワード：hot spring degassing, He-CO2 systemics, slab tearing, carbon recycling efficiency, southeast Tibetan Plateau

The spatial variations of helium isotopic ratios at tectonic belt and regional scales play a crucial role in tracing crust-mantle interactions, as well as the transfer of heat and volatiles from the Earth’s interior. This study presents gas geochemical data from 26 thermal springs (54 new data) and compiled 854 samples (350 sites) along the Xianshuihe fault and Red River fault zones on the southeast Tibetan Plateau. Systematic helium anomalies and varying proportions of recycled carbon from altered oceanic crust (AOC) have been identified based on the ³He/⁴He and δ¹³C−CO₂ characteristics as well as a revised helium-carbon coupling model. The δ¹³C-CO₂ and CO₂/³He values show significant differences between the northwest and southeast sides of the helium boundary zone (HBZ) and the average mantle helium-3 flux on the northwest side is 1.7×10⁴ atoms m⁻² s⁻¹, while on the southeast side it is 1.04×10⁴ atoms m⁻² s⁻¹. This are highly consistent with the results of geophysical observations as the presence of a slab tear in the Indian slab south of the Lijiang-Xiaojinhe fault (LXF). Moreover, a decarbonation demarcation caused by the subducting slab was identified as recycled carbon to the northwest (~31%) is higher than that of the southeast (~22%) around the HBZ (~26°N). This variation is related to the different subduction depth and angle resulted from the tearing of the Indian slab. The study emphasizes the significant impact of diverging subduction on the control of the efficiency of deep carbon recycling and its’ variation along convergent plate boundary.