Seismic evidence of subduction during assembly of the North China Craton from multimodal dispersion inversion

The Precambrain basement of the North China Craton (NCC) was formed through the merger of micro-continental blocks, the amalgamation mode of which has remained debated. To provide further insights and better understand the underground structures, we construct a more detailed shear wave velocity model of crust and uppermost mantle in the central and western NCC using multimodal ambient noise tomography. The multimodal Rayleigh wave dispersion curves are obtained through the Frequency-Bessel transform, utilizing seismic records from 548 stations in the ChinArray-Himalaya project. Subsequently, we employ the quasi-Newton method to invert the shear wave velocity model to a depth of 60 km. The results reveal a southward low-velocity subduction-like feature in the upper-middle crust south of the Solonker Suture Zone to the Inner Mongolia Suture Zone. This feature likely represents the subduction remnants associated with the southward subducted Paleo-Asian Ocean slab. Additionally, the model highlights a westward intra-crustal low-velocity downthrust body beneath the Trans-North China Orogen, potentially indicating relics of subduction from the Paleoproterozoic amalgamation of the NCC. Moreover, we observe a widely distributed low-velocity layer within the lower crust of the Ordos Block, which may indicate a felsic-dominated lower crust, likely formed during the prolonged tectonic stability following the ancient subduction-collision processes of the NCC.