Destruction of lithosphere within the north China craton inferred from surface wave tomography

The north China craton (NCC) is one of the oldest cratons in the world; however, the lithosphere of the craton was destructed during Phanerozoic tectonism and then became tectonically and seismically active. Because the lithospheric structure of this complex craton has not been well studied, the mechanism behind the thinning, transformation, and destruction of the lithosphere remains debated. Using an efficient and scalable 3-D surface wave tomography method, we obtain a high-resolution regional S wave velocity model that shows the three-dimensional lithospheric structure of the NCC. In addition, we convert the S wave structure to an estimated thermal structure using accepted relationships between S wave velocity and temperature. The model images a large upper mantle low-velocity body beneath the eastern NCC, especially beneath the seismically active zone from Tangshan to Xingtai. This body is interpreted to represent hot material or volatiles escaping from the slab edge in the transition zone between the upper and lower mantle. The low-velocity body is a key piece of evidence in demonstrating thermochemical bottomup erosion/transformation of the overlying cratonic lithosphere, thereby leading to destruction of the lithosphere, which may have occurred during the Cenozoic. This erosion mechanism appears to have had less influence in the western NCC (Ordos block); however, our results reveal a similar to 130-km-thick lithosphere beneath the present cratonic Ordos block, which is thinner than the similar to 200 km thickness of the NCC lithosphere during the Paleozoic, as determined from analyses of xenoliths.