Direct surface-wave tomography under Northeast China: New insights into 3-D crustal S-wave velocity structure and dynamics of intraplate volcanism

A new three-dimensional shear-wave velocity structure of the crust beneath Northeast China is constructed by inversion of phase velocity dispersion curves between 5 and 40 s using the direct surface-wave ambient noise tomography method. In addition to 127 NECESSArray (NorthEast China Extended SeiSmic Array) seismic stations, 19 SCVDSZ (Study of Changbai Volcanoes and Deep Subduction Zone) plus 3 CDSN (China Digital Seismograph Network) stations are added in the data collection. The addition of these data greatly improves the ray path coverage and imaging results around the Zhangguangcai range and the Changbaishan mountain. Our results show an obvious low-velocity anomaly extending from the surface down to uppermost mantle under the Changbaishan, suggesting that the volcano formation could be related to mantle upwelling. One more striking feature is a widely distributed mid-lower crustal low-velocity layer under the entire Northeast China, which is connected to those in the upper crust under the volcanoes, indicating that these volcanoes could have exchanges of material and energy in the mid-lower crust. In addition, under the Shuangliao and Erke volcanoes, lowvelocity anomalies are visible in the upper and middle crust but high-velocity anomalies in the lower crust, whereas under the Abaga and Halaha volcanic groups, the low-velocity anomalies extend from the crust down to uppermost mantle, suggesting their continuous mantle magma provision. Integrating with previous global and regional body-wave tomographic models, our results suggest that the volcanoes in Northeast China could be related to hot and wet mantle upwelling in the big mantle wedge caused by the deep subduction of the subducted Pacific slab in the mantle transition zone.