Crustal structure of the southeastern margin of the Ordos Block

We use a profile made up of teleseismic receiver functions to study the crustal thickness and structure of the southeastern margin of the Ordos Block. The Mohorovičić discontinuity(Moho) has been identified beneath all stations. Its depth gradually decreases towards the southeast, from about 43 km in the Ordos Block to ∼30 km near the northern margin of the Qinling Orogen. Our results show clear lateral variations in the structure of the crust and the features of the Moho. Accordingly, the study region can be divided into four parts: (1) Beneath the Ordos Block, the Moho is visible and flat at a depth of ∼40 km. The crustal structure is best characterized by stable cratonic crust. (2) In the Weihe-Shanxi Graben, the Moho is uplifted by about 3 km, which may be the result of upwelling of upper mantle materials. (3) Under the Xionger-Funiu Mountains, the Moho is flat at a depth between 36 and 33 km, but becomes shallower towards the southeast. (4) In the Hehuai Basin, adjacent to the northern margin of the Qinling Orogen, the Moho shows strong lateral variations with a mean depth of ∼31 km. The crustal structure here is complex, which may indicate a complicated tectonic environment. Additionally, the Moho is clearly interrupted at two locations (beneath stations st11 and st18) near major tectonic boundaries. These results suggest that the structure of the deep crust along the southeastern margin of the Ordos Block has great lateral variability, which strongly affects the complex geological features on the surface. Furthermore, these results can help us understand the interrelationships of different parts of the southeastern margin of the Ordos Block.