Sharpness of the Midlithospheric Discontinuities and Craton Evolution in North China

The lithospheric layering and evolution of Archean cratons can be effectively constrained by seismic properties. We present fine-scale lithospheric discontinuity images of the North China Craton (NCC) using the seismic daylight imaging (SDI) technique, which is also known as the autocorrelogram method. With the aid of large-scale surface-wave velocity models, the characters of autocorrelograms related to lithospheric discontinuities in the NCC are investigated. Spatial variation in discontinuity characteristics is revealed across the craton. In the modified/destroyed eastern NCC, both the midlithospheric discontinuity (MLD) and the lithosphere-asthenosphere boundary (LAB) are rather sharp (~2 km). Various dynamic processes, including juvenile underplating, asthenospheric upwelling, and corner flow induced by paleo-Pacific Plate subduction, may contribute to such sharp interfaces. In the stable western NCC, P wave reflections cannot easily reveal the LAB, suggesting a diffuse (thicker than 30 km) lithosphere-asthenosphere transition (LAT). Multiple MLDs are also found that may have arisen during craton formation and multiple phases of rejuvenation of the cratonic lithosphere as evidenced by the petrological results. The use of higher-frequency data enables us to distinguish among the lithospheric discontinuity styles and favor multiple origins of the MLDs and LAB in the cratonic lithosphere.