Tomography Images of Crustal and Upper Mantle Structure beneath Sulu Orogenic Belt

The Sulu Triassic collision zone between the North China block and the Yangtze block contains the largest ultrahigh-pressure (UHP) metamorphic belt in the world. It has become a hot spot in the research of plate convergence, subduction, and collision. We determined a detailed three-dimensional P-wave velocity structure of the crust and upper mantle beneath the Sulu orogenic belt by applying 10 922 arrival times from 1 079 local and regional earthquakes, and 11 931 data from 251 teleseismic events, which were recorded by 64 seismic stations in our study region. Our tomographic imaging shows that prominent low velocity anomalies are imaged beneath Shandong Peninsula and the middle and lower Yangtze River metallogenic belt, which may represent the asthenosphere upwelling.A high velocity anomaly which may represent the subducted Paleo-Tethyan oceanic slab is imaged clearly in the east of Tanlu fault beneath the depth of over 300 km. The crustal and mantle velocity structure of the Sulu orogenic belt formed by the collision of the North China block and the Yangtze block is mainly characterized by high velocity anomalies. The north subduction of the Yangtze block is not obviously, and the North China block is characterized by the southeastward subdction of the high velocity anomalies. The subduction of the north China block can be divided into two subduction styles bounded by 35° N. In the north of the 35°N, the southeastward subduction of North China block is not obvious and is stopped in the west of Tanlu fault. In the south of the 35° N, North China block southeastward subducted under the Sulu orogenic belt.