Mesozoic suture zone in the East China Sea: Evidence from wide-angle seismic profiles

Although the East China Sea (ECS) is widely accepted as the offshore extension of the South China Block (SCB), an alternate hypothesis is that the ECS basement is a buoyant allochthon that collided with Eurasia in the Cretaceous. In order to constrain the Mesozoic collision position, or the Mesozoic suture zone, wide-angle reflection/refraction seismic profiles (EC52017 and EC52019) were carried out in 2017 and 2019 to map the crustal structure of the ECS and clarify the possible Mesozoic suture zone. Crustal structures are generated by both a ray-tracing forward method (Raylnvr) and a travel time tomographic inversion (Tomo2D). The resulting velocity models show significant lateral variations along these two seismic profiles. An extended continental crust gradually decreases in thickness from 30 km in the Zhemin Volcanic Belt (ZMVB) to 15 km in the Continental Shelf Basin (CSB) with lateral velocity variations of 4.40-7.15 km/s and 4.30-6.90 km/s, respectively, indicating differences in crustal structure between the ZMVB and the CSB. A 50 km-wide high-velocity anomaly with high density and uplifted Moho is imaged between the ZMVB and the CSB. Combined with the Mesozoic subduction and collision zone of the exotic ECS basement by previous studies, we infer that the high-velocity anomaly marks the position of the Mesozoic suture zone, which is associated with magma intrusion due to upwelling molten through the detached slab with the rollback of the Paleo-Pacific subduction slab.