Continuous nonthermal slab gap formed by progressive tearing beneath Northeast Asia

Slab gaps in subducted plates are widely hypothesized to channel hot mantle upwellings, yet their formation and thermal state remain enigmatic. Here we image a continuous ~1000 km-long arcuate slab gap in the mantle transition zone beneath Northeast Asia with no evidence of anomalous heat. By integrating dense-array teleseismic tomography, 3-D waveform modeling, and a joint inversion of seismic velocities with transition-zone thickness, we constrain the fine-scale geometry and thermal structure of the gap. Sharp lateral boundaries are consistent with a mechanical opening within the stagnant slab, and gap temperatures are comparable to ambient upper‑mantle values and >200 °C lower than plume‑like temperatures. The planform of the gap aligns with the path of a migrating triple junction, suggesting formation through progressive slab tearing during plate-boundary reorganization. These observations demonstrate that a slab gap can persist without hot upwelling, consistent with the diffuse intraplate volcanism above the region.