S‐Velocity Mantle Structure of East Asia From Teleseismic Traveltime Tomography: Inferred Mechanisms for the Cenozoic Intraplate Volcanoes

Abstract

Abstract Clusters of Cenozoic volcanoes are found in Korea and Northeast China away from plate boundaries, but the mechanisms responsible for their formation is still unknown. To resolve this issue, we derive an S‐wave velocity model of the upper mantle structure beneath East Asia using 131,947 S‐wave relative traveltimes from 974 earthquakes recorded at 1,948 seismic stations in China, Korea, Taiwan, and Japan. Our results show that low‐velocity anomalies beneath Mt. Baekdu (Changbaishan) and Jeju Island extend to the bottom of the mantle transition zone (MTZ) through slab gaps in the stagnant Pacific slab. On the other hand, low‐velocity anomalies beneath the Datong volcanic field are observed to connect to the edge of the stagnant Pacific slab, which may be attributed to subduction‐triggered upwelling or deep dehydration from the hydrous MTZ perturbed by subducting slabs. Furthermore, tilted high‐velocity anomalies are found all the way down to the MTZ beneath the Great Xing'an Range and the Songliao basin, which may indicate delaminated lithosphere. The intraplate volcanoes north of the Songliao basin, such as the Wudalianchi and Halaha volcanoes, are located just above the delaminated bodies, thereby implying that decompression melting after delamination may be responsible for the intraplate volcanoes. Therefore, the dominant origin of intraplate volcanoes in East Asia may be subduction‐related hot upwelling, complemented by shallow origins such as edge‐driven convection and lithospheric delamination.