The nature of the Late Syn-rift Sag Basin (LSSB)

The "steer's head" geometry and saucer-shaped architecture in rift basins are generally regarded as a direct consequence of thermal subsidence and post-rift evolution. However, these definitions can be problematic due to the widespread coexistence of synchronous wedge-shaped and saucer-shaped geometries in many rift basins and rifted margins globally. Although the Late Syn-rift Sag Basins (LSSBs) at rifted margins provide an alternative model for the discrepancy, their nature remains enigmatic. Using high-resolution 3D seismic data in the Hailar Rift, for the first time, our study deciphers the 3D architecture and strain behaviour of the LSSB. We identify four types of architectures which suggest that the strain behaviour within the LSSB is dominated by sagging, with varying degree of the mixing of faulting and sagging. The LSSB is considered to be the shallow response to the ductile deformation of lower crust, accompanied by the increase in heat flow.