Seismic Tomography On 3D Velocity Structure Of The Crust And Upper Mantle Beneath Ne Asia And Its Deep Dynamics

Northeast Asia(NE Asia)is located in the northeastern part of Eurasia and east to the Pacific sea and geological composed by Sino-Korean Craton in south,Siberian Craton in north and the orogenic belts between them.During the Paleozoic,NE Asia was mainly controlled by the evolution of the Paleo-Asian Ocean tectonic system between Siberia Craton and the Sino Korean Craton,which was dominated by the amalgamation of multiple microcontinental massifs and the closure of the Paleo-Asian Ocean.Since the Mesozoic,NE Asia has also experienced the overprinting of the MesoCenozoic circum-Pacific and the Mesozoic Mongol-Okhotsk tectonic systems.The tectonic evolution of the NE Asian subcontinent is mainly influenced by the large-scale multi-phase and multi-angle subduction of the Pacific plate to the Eurasian lithosphere during the Meso-Cenozoic.Therefore,it is of great significance to obtain the fine velocity structure of the crust and upper mantle in the Northeast Asia in order to discuss the tectonic cause and the geodynamic mechanism of the region.Seismic tomography is the most effective way to obtain the velocity structure inside the earth at present.A high-resolution model of 3-D P-wave velocity structure beneath Northeast Asia and adjacent regions is determined by using 244,180 arrival times of 14,163 local and regional earthquakes and 319,857 relative travel-time residuals of 9988 teleseismic events recorded at ?2100 seismic stations in the study region.Our tomographic results reveal the subducting Pacific slab clearly as a prominent high-velocity anomaly from the Japan Trench to the North-South Gravity lineament(NSGL)in East China.The NSGL is roughly coincident with the western edge of the stagnant Pacific slab in the mantle transition zone(MTZ).The subducting Pacific slab has partly sunk into the lower mantle beneath Northeast China,but under the Sino-Korean Craton the slab lies horizontally in the MTZ.The NSGL,as an important tectonic line in Mainland China,is marked by sharp differences in the surface topography,gravity anomaly,crustal and lithospheric thickness and mantle seismic velocity from the east to the west.These features of the NSGL and large-scale hot and wet upwelling in the big mantle wedge(BMW)in the east of the NSGL are all related to the subduction processes of the Western Pacific plate,where the hot mantle materials rise to the shallow mantle,resulting in the positive gravity anomalies in the east of the NSGL.The Changbai intraplate volcanic group is underlain by a striking low-velocity anomaly from the upper MTZ and the BMW up to the surface,and deep earthquakes(410–650?km depths)occur actively in the subducting Pacific slab to the east of the Changbai volcano.We propose that the Changbai volcanic group is caused by upwelling of hot and wet asthenosphere materials and active convection in the BMW.The formation of other volcanic groups in the east of the NSGL is also associated with the subduction-driven corner flow in the BMW.