The Crust and Upper Mantle Structures in Regions Between the Yangtze Block and North China Craton

Abstract:

The Yangtze Block and North China Craton collided in Triassic. In the Mesozoic, the eastern parts of these two blocks experienced widespread lithospheric reactivation and magmatism under the extensional environment. In this study, we applied the P-wave receiver function and shear-wave splitting methods to the data recorded by the broadband temporary seismic array. The crustal thickness is in the range of 29–36km. From the NW part of the Jiangnan fault to the North China Craton, the Moho becomes deeper gradually. The common conversion point stacking result shows that the 410-km discontinuity is relatively flat while the 660-km discontinuity is deeper to the north of ~29°N than the south. Combined with seismic tomography studies, the results suggest that the base of the MTZ is influenced by the cold temperature environment of the ancient stagnant slabs to the north of ~29°N. The MTZ thickness under the Yangtze Block is larger relative to the IASP91 model. The fast polarization directions are NE-SW in Cathaysia Block, NW-SE and NEE-SWW in Yangtze block and NWW-SEE in eastern North China Craton. The Fresnel zone analysis indicates that the anisotropy in the relatively shallow depth varies significantly from the Cathaysia Block to the Yangtze block, indicating the significantly different lithospheric structures of them. The Jiangnan fault is revealed as an important boundary within the Yangtze block.