Pn anisotropic tomography of Northeast China and its implications to mantle dynamics

Abstract

In this study, we manually pick a total of 9197 high-quality Pn arrival-time data from seismograms of 457 events recorded at 271 provincial seismic stations and 69 NECESSArray portable seismic stations in Northeast (NE) China. Using these Pn arrivals, having much better crosscrissing coverage of ray-paths in the uppermost mantle, we determine a new high-resolution anisotropic tomographic model. Our new model shows distinct lateral heterogeneities in both velocity and anisotropy, which are closely related to surface geology. Obvious high Pn velocities are imaged under the Songliao, Hailar, and Erlian stable basins. Prominent low Pn velocities are observed under the Changbaishan, Jingpohu, Longgang, Wudalianchi, and Datong volcanic areas as well as the Halaha and Abaga volcanic groups. Furthermore, some low Pn velocities are well connected or they are separated by high Pn velocities but connected by the fast directions of Pn propagation. These results suggest the existence of some correlations among these volcanoes in the present day or the traces preserved in the past tectonic evolution history. We propose a possible dynamic model that illustrates the material and energy exchange among the volcanoes, which could be caused by a complicated rather than simple E-W horizontal flow of mantle convection in the big mantle wedge due to the stagnancy and dehydration of the western Pacific slab in the mantle transition zone. These results provide new insights into the mechanism of genesis of active volcanoes and complex mantle dynamics of NE China.