The lithospheric structure of the lower Yangtze Craton and its adjacent regions by S receiver function imaging

The lower Yangtze Craton, Located at the triple junction area of the Eurasian Plate, Pacific Plate, and Philippine Sea Plate, has undergone intensive extension and magmatic activities ever since the Mesozoic. The lithospheric structure and property of the lower Yangtze Craton and its adjacent regions could throw new insight into the tectonic evolution and dynamic process of the South China Block or even the whole eastern China in the Phanerozoic. In this paper, the authors collected data from the NCISP-Ⅲ arrays deployed by the Institute of Geology and Geophysics, Chinese Academy of Sciences, and used the wave equation-based migration technique of S-receiver function to image the lithospheric structure. The results show that the Moho depth and lithosphere-asthenosphere boundary (LAB) depth along the profile is~32-42 km and~84-112 km, respectively. Both of the discontinuities deepen from east to west, and the variation of them corresponds well to the tectonic features. The results support the argument that the lower Yangtze Craton and its adjacent regions may have undergone extensive lithospheric modification and thinning since the Mesozoic:The Hefei Basin of the southern NCC is characterized by a complicated Moho and thick lithosphere, indicating that the modification in this region is of less extent. The lower Yangtze Craton and the Cathysia Block may have behaved coherently in the Mesozoic modification, because the lithospheric structures of this two blocks are alike, only characterized by subtle undulation of the velocity discontinuities beneath the Jiangnan Orogen. Combined with the magnetotelluric results in the southern part of this profile, the authors propose a similar mantle flow model as in the NCC to explain the modification in the lower Yangtze Craton and its adjacent regions. The lithosphere beneath the Tanlu Fault and the Jiangnan Orogen is mechanically weak, and may act as the upwelling channel of the asthenospheric material under the subduction of the Pacific Plate to facilitate the modification.