Lithospheric structure variations between the eastern and central North China Craton from S- and P-receiver function migration

Abstract

I imaged the lithospheric structure beneath the Bohai Bay Basin (BBB) in the eastern North China Craton (NCC) and the Taihang Mountains (TM) and areas further to the west in the central NCC by applying the wave equation migration technique to both the S- and P-receiver functions (RFs) collected in this region. The data images and synthetic modeling results indicate that S-RF imaging is more appropriate than P-RF imaging for mapping lithospheric discontinuities, especially the lithosphere-asthenosphere boundary (LAB) in various types of regions, even directly applicable to basin areas that are covered by thick sediments. The constructed S-RF images show that the lithospheric thickness of the study region is highly variable. The imaged LAB is on average ∼80 km beneath the BBB, and displays obvious undulations from ∼120 km under the TM to <90 km further west in the central NCC. A rapid change of ∼30 km in the LAB depth was detected at around the boundary between the BBB and the TM, roughly coincident with the distinct gravity decrease of more than 100 mGal that marks the North–South Gravity Lineament (NSGL) in the region. The S-RF images also revealed a generally thin crust (∼30 km) beneath the basin in the eastern NCC and a thicker one (>40 km) under the mountain areas in the central NCC, consistent with previous P-RF imaging results. The observed structural differences between the eastern and central NCC are likely associated with different lithospheric tectonics in these two regions. While widespread lithosphere reactivation and extension in the eastern NCC during the late Mesozoic time was plausibly responsible for both the thinned crust and lithosphere in the BBB, lithospheric thinning in the central NCC may be equally heterogeneous but less significant, and probably occurred mainly in Cenozoic. Such a process may have given rise to the highly variable present-day lithospheric thickness in this region. However, it probably did not noticeably affect the overlying crust that was reported to have thickened in response to the early magmatic underplating in the Mesozoic time. The different tectonic processes in the eastern and central NCC may have induced the formation of the NSGL, which likely serves as a major tectonic boundary separating the two regions of contrasting lithospheric structures at present.