Crust and uppermost mantle S-wave velocity structure of the Wudalianchi volcanic belt from direct surface-wave tomography

The Wudalianchi volcanic belt is located at the junction among the Greater Xing’an range, the Lesser Xing’an range, and the Songliao basin. Investigation of detailed crustal velocity structure under the Wudalianchi volcanic belt is of great significance to better understand the deep geodynamics of Northeast Asia. Applying the direct surface-wave tomography method to ambient noise records of our newly deployed dense WAVESArray stations from 2015 to 2019, we aim to determine a high-resolution three-dimensional (3-D) S-wave velocity (Vs) model of the crust and uppermost mantle down to 45 km depth beneath the Wudalianchi volcanic belt and surrounding areas. The WAVESArray stations have good azimuthal coverage around the Wudalianchi volcano. Our high-resolution tomographic model reveals low-Vs anomalies in the upper crust and the uppermost mantle beneath the Wudalianchi volcano and high-Vs anomalies in the mid-lower crust, indicating the presence of hot mantle upwelling and lower crust cooling solidification. This upwelling process is related to the complex dynamics of the big mantle wedge that has developed above the subducted Pacific slab that is stagnant in the mantle transition zone beneath East Asia. In addition, low-Vs anomalies are visible beneath the Erkeshan, Wudalianchi, Keluo, and Xunke volcanoes in the upper crust and they are connected with a low-Vs layer in the mid-lower crust, which provides a new piece of seismological evidence for the homology of these volcanoes, suggesting that there might be exchanges of material and energy between these volcanoes.