Intralithospheric mantle structures recorded continental subduction

摘要

We investigated the intralithospheric mantle (ILM) structures beneath the North China Craton (NCC) by the seismic imaging with over 16,000 high-quality receiver functions from 255 broadband stations. These images were created for six profiles spanning different tectonic units in the NCC.Initially,we inferred the crustal velocity model using an integrated receiver function imaging technique.Subsequently,we performed a series of synthetic tests of common conversion point (CCP) stacking images to distinguish between the multiple waves generated by the crustal structure and the velocity discontinuities in the ILM. The ILM structures were constructed by waveform inversion on the basis of these analyses.Our imaging results reveal (1) a homogenous lithospheric mantle in the western NCC,(2) intermittent and juxtaposed velocity interfaces in the ILM beneath the southern NCC,and (3) local high-velocity and lower-velocity volumes in the ILM beneath the eastern NCC. In addition,the lower crust beneath the southern NCC is thin,and the Moho dips northward,which present evidence of the Yangtze craton subduction beneath the NCC.The imaged high-velocity volumes in the ILM beneath the southern NCC were interpreted as a subduction remnant in the uppermost mantle,which reveal a flat subduction channel resulting from the continent-continent collision between the NCC and the Yangtze craton.The homogeneous ILM beneath a Paleoproterozoic amalgamation zone in the NCC implies that the remnants of the lithosphere that were subducted before 1.8 Ga might have sunk into the deeper mantle.