An approach to diagnose the structure of lithospheric keel beneath eastern North China Craton

The North China Craton (NCC), formed in the Archean, is one of the oldest continental craton in the world. The eastern part of the North China Craton (ENCC) is featured by low seismic velocity at lithospheric depths, which is distinct from all the other cratons around world. Since the Mesozoic, the craton has undergone massive extension, which is likely caused by its interaction with subducting to the east - a situation similar to what has occurred in the western United States during the Cenozoic. While various mechanisms have been proposed on the observed lithospheric thinning beneath ENCC, it is critically important to know whether part of the old cratonic mantle lithosphere is still present beneath the Moho.

To test the possibility of discerning pre-existing cratonic relics under ENCC, we performed a 2-D synthetic forward modeling test based on the 3D velocity model derived from the full wave tomography study of Tao et al. (2018). The model space is 600 km in length and 200 km in depth with a grid spacing of 5 km. The thinned lithospheric mantle is assumed to be 60 km thick, which is overlaid by a 30 km thick crust. In model 1, the 60-km mantle lithosphere composes a newly formed thermal boundary layer (TBL), while in model 2 it is composed of a 40 km thick cratonic relic and an underlying 20-km TBL. Rayleigh waves computed from the two models showed distinct difference, especially at long periods. In the following study, we plan to conduct full wave inversion with ambient noise data recorded by a broadband array in the study area, together with forward modeling of teleseismic receiver function data to constrain seismic velocity structure of the mantle lithosphere beneath the ENCC. The seismic model will be used to determine whether the Archean mantle lithosphere has been completely lost or not during the lithospheric thinning process.