Wedge tectonics in south china: constraints from new seismic data

Collisional orogens are locations where continental terranes amalgamate and are potential sites of weakness that facilitate subsequent continental breakup. Therefore, the lithospheric architecture of collision zones provides key information for evaluating the long-term evolution of the continental interior: for example, the South China Block (SCB), where the tectonic history is severely obscured by extensive surface deformation, magmatism, and metamorphism. Using new passive-source seismic models, we show a contrasting seismic architecture across the SCB, with three prominent crustal dipping structures across the Jiangnan Orogen. Based on multi-disciplinary constraints from regional geophysical datasets, these pronounced dipping patterns are attributed to relict wedge-like lithospheric deformation zones initiated in the fossil collisions that assembled the Yangtze Block and the SCB. The overall trend of these tectonic wedges implies successive crustal growth along paleo-continental margins and is indicative of northward subduction and docking of accretional terranes. In contrast, no such dipping structures are preserved in the Cathaysia Block, indicating a weak and reorganized lithosphere. The variations in the deformation responses across the SCB reflect the long-term modifications of the lithosphere caused by prolonged collision and extension events throughout the tectonic history of the SCB. The deep lithospheric constraints from the SCB demonstrate the critical roles that suture zones played in the successive growth and evolution of the continental lithosphere.