The structure and subduction relicts of the Changchun–Yanji suture, NE China: new evidence from deep seismic reflection profiling

The Changchun–Yanji suture is the key position of the superposition and transformation of the Paleo-Asian Ocean and Paleo-Pacific domain in the NE China. It is the best laboratory to understand the end of Paleo-Asian Ocean subduction and the start of Paleo-Pacific subduction. To reveal the details of lithospheric fine structure and tectonic deformation, especially the structural characteristics of the crust and upper mantle, we carried out a deep seismic reflection profile, namely the Yantongshan–Liaoyuan section (YLS), which was laid across the Changchun–Yanji suture zone and covered 55 km in the direction of NE to SW. The results show that the discontinuous strong reflection around TWT (Two-Way Travel time) 5 s divides the crust into upper and lower layers, and it is speculated as a large-scale detachment structure layer. The upper crust is dominated by arc-shaped short reflection and disorderly weak reflection, and the continuous layered reflection is locally developed in the shallow TWT 0–3 s. The lower crust is characterized by a large number of strong southward dipping reflections that extend to the upper mantle and cut by Moho. At the southernmost of the YLS, the lower crust is densely developed with strong near-horizontal reflection, extending downward to mantle reflection M. In the YLS, Moho reflection is clear and continuous, which occurs between TWT 10.1–10.8 s. The Moho interface fluctuates a little, and the middle part is slightly deeper. Southerly dipping mantle reflectors are identified in the profile, which may represent fossil subduction relics. Based on the deep seismic reflection profile in combination with geological evidence, we suggest that the Changchun–Yanji suture zone is located in the south of the Yantongshan area, and is the low angle southward dipping subduction zone of 15–20°.