Stagnation and Tearing of the Subducting Northwest Pacific Slab

Despite numerous observational and geodynamic modeling studies, the presence of the northwest Pacific slab tear and its influence on mantle dynamics remain controversial. By imaging the mantle transition zone (MTZ) discontinuities beneath the Japan Sea and adjacent areas, we demonstrate an ESE-WNW elongated zone with significant MTZ thinning extending from central Honshu, Japan, to the Korean Peninsula, which provides additional supporting evidence for the existence and distribution of a large-scale slab tear. Our results, when combined with other geophysical and geochemical evidence, indicate that the hot mantle material oceanward of the slab may flow through the slab tear and contribute to surface volcanism. Substantial MTZ thickening is widely observed in the region south of the slab tear and suggests the existence of slab stagnation, possibly related to the strong resistance at the bottom of the MTZ.