Seismic evidence for collisional tectonics of the North China and Yangtze blocks in the Tongbai-Dabie orogenic belt.

• The North China Block subducted southward beneath the Tongbai-Dabie orogenic belt in the Jurassic. • The broken-off Paleo-Tethyan Oceanic slab is imaged as a high-velocity anomaly at depths of 300–400 km beneath the Tongbai-Dabie orogenic belt. • A two-stage subduction model is proposed about the Yangtze Block and North China Block subductions. The Tongbai-Dabie orogenic belt was formed in the Middle to Late Triassic through continental collision between the North China Block and the Yangtze Block. To reveal the collisional tectonics of the two blocks, we apply teleseismic tomography to study the 3-D P-wave velocity structure down to 400 km depth beneath the Tongbai-Dabie orogenic belt using 37,251 first P-wave arrival times of 1423 teleseismic events recorded at 99 seismic stations in the study region. Our tomography reveals three obvious high-velocity anomalies. One is dipping southward beneath the Tongbai-Dabie orogenic belt, reflecting the southward subduction of the North China Block. The second is visible down to 100 km depth beneath the eastern Tongbai-Dabie orogenic belt, which reflects the Yangtze Block. The third appears at depths of 300–400 km, which is interpreted as the retained broke-off paleo-Tethyan oceanic slab. On the basis of our tomographic results and previous findings, we propose a two-stage subduction model showing that the Yangtze Block subducted northward in the Triassic, and then the North China Block subducted southward in the Jurassic beneath the Tongbai-Dabie orogenic belt. [ABSTRACT FROM AUTHOR]