Control of stepwise subduction and slab breakoff on volcanism and uplift in the Tibetan Plateau

The Tibetan Plateau plays a crucial role in Asian and global geomorphology and climate change, yet how it grew and how its deep geodynamic processes control surface systems remains unclear. We present a novel model to explain this by multistage bilateral subduction, lithospheric breakoff, and subsequent foundering. Modelling based on a global tomography method reveals four distinct stepwise high-velocity anomalies in the mantle. The high-resolution seismic velocity model was inverted using >16 million arrival times of P, Pn, pP, PP, PKP, and PKiKP phases from the International Seismological Center and EHB bulletins and ~3 million arrival times of P, PP, and PcP phases from the 1,034 China Seismic stations in Tibet. We also collected hundreds of volcanic rocks to analyze their spatio-temporal distribution in the Tibetan Plateau since 60 Ma. The locations and morphology of the remanent slabs associated with the subducted/subducting Neo-Tethyan Ocean, Greater Indian plate, and Asian lithosphere have been constrained using plate reconstruction and the surface igneous rock data. We find that discrete episodic surface volcanism and plate uplift at 56-44 Ma, 44-28 Ma, 28-18 Ma, and 18-0 Ma in the Tibetan Plateau coincide with the four-stage stepwise lithosphere processes. We observe paired slab-like anomalies during the second and third steps, indicating the simultaneous detachment of subducting lithosphere from opposing directions. Building upon this observation, we propose a two-sided breakoff model, where bilateral subduction and lithospheric gravitational subsidence triggered extensive volcanism and episodic uplift of the plateau. This model indicates that subsidence from both past and present lithospheric break-offs of the Indian and Asian plates spawned extensive volcanism that had a significant impact on climate patterns. By shedding new light on the deep-seated geodynamic mechanisms at play, our study establishes a systematic framework linking lithospheric processes and surface phenomena in Tibet.