Heat flow constraints on the subduction limits of the Indian and Asian lithospheres in central Tibet

The India-Asia convergence dynamics beneath Tibet remain debated, particularly regarding the northern extent of Indian lithosphere subduction and potential southward subduction of Asian lithosphere. These uncertainties primarily stem from ambiguous seismic interpretations, where tomographic images struggle to differentiate subducted Indian lithosphere from thickened Tibetan lithosphere. Here we provide crucial new thermal constraints to address this controversy. Based on newly measured temperature profiles, rock thermal conductivity, crustal stratigraphy, and heat production rates, we show that the Qiangtang Terrane has exceptionally high surface heat flow (86 ± 32 mW/m²) with a pronounced south-to-north increase (62 ± 17 mW/m² to 89 ± 23 mW/m²). Lithospheric thermal structure further reveals that northern Qiangtang (mantle heat flow: 39 mW/m²) and the Bangong-Nujiang suture zone (41 mW/m²) have higher mantle heat flow than southern Qiangtang (23 mW/m²). However, unlike the thick lithosphere observed in the Bangong-Nujiang suture zone (thermal lithospheric thickness: 137 km) and southern Qiangtang (137 km), northern Qiangtang (61 km) shows a much thinner thermal lithosphere. Together, these patterns indicate intense deep thermal input beneath northern Qiangtang and Bangong-Nujiang suture. Integrating these thermal constraints with previous geophysical and geochemical observations, we suggest that the observed thermal regime is consistent with a double subduction scenario in which the Indian lithosphere subducts beneath the Bangong-Nujiang suture, whereas the Asian lithosphere subducts southward below northern Qiangtang, where it undergoes slab breakoff.