Lithospheric structure of Northeast China from dense array receiver functions: Insight into two-side subduction of the Paleo-Asian Ocean plate

Abstract

A northwest-southeast trending high-density seismic array was deployed in the southern Xing’an-Mongolian Orogenic Belt, spanning the Songliao basin, the North-South gravity gradient lineament, the Great Xing’an Mountains, and the Erlian basin. The high-density seismic array included 1000 stations with an interval of ∼0.5 km. We image the lithospheric structure using the teleseismic receiver function method. Our results show that the Moho depth gradually increases from ∼35 km beneath the Songliao basin to ∼40 km beneath the Great Xing’an Mountains. In the vicinity of the North-South gravity lineament, the Moho is slightly inclined with a continuous depth of ∼5 km, which forms a transition zone from the basin to the orogenic belt. A middle crustal discontinuity, or the Conrad discontinuity, is imaged beneath the Songliao-Xilinhot block and the northern margin of the North China Craton. The Conrad and Moho discontinuities beneath the suture zones show traces of bidirectional subduction of the Paleo-Asian Ocean plate. Meanwhile, we find subtle changes in the receiver functions due to variations in the sedimentary layer thickness. The sedimentary layer beneath the southern Songliao basin is estimated to be ∼1.2 km thick and it thins toward its edge. Moreover, we find a middle lithospheric discontinuity below the Moho under the Songliao-Xilinhot block. Combining with previous findings, we deem that the middle lithospheric discontinuity reflects a high-temperature layer in the upper lithosphere mantle associated with hot and wet upwelling flows in the big mantle wedge under NE China.