Lithospheric Deformation Mechanism from Northeastern Tibetan Plateau to Southeast Coast of China as Revealed by the SinoProbe Long Magnetotelluric Transect

The Chinese continent has underwent complex evolution history and result in diverse deformation patterns. However, the relationship between surface deformation and lithospheric structure is still not well known. In this contribution, we use a ~2400 km long Magnetotelluric (MT) transect finished by the SinoProbe project to investigate the lithospheric electrical structure across the major portion of Chinese continent and further infer the lithospheric deformation mechanism. The profile passes by the northeastern and eastern margins of the Tibetan Plateau and extends southeastward to the coast region of South China. 248 MT sites from the long transect was divided into 3 segments and inverted separately using the ModEM package with 3D NLCG algorithm. While inverting the profile of South China, distribution of seawater near the coast region was incorporated into the model based on bathymetry data. The inversion results reveal contrasting electrical features between the actively deformed Tibetan Plateau and the relatively stable South China block. Within the Tibetan Plateau, conductors are found to be pervasive in the lower crust and upper mantle, which implies continuous deformation dominated regime. In contrast, the lithosphere of South China is generally resistive with isolated conductors associated with paleo-suture or faults. In comparison, the conductors within the Cathaysia block are more developed. The isolated conductors in the Cathaysia block are mostly sub-vertical in their geometry. The electrical structure model is further compared with the overlapped deep seismic reflection profiles, which suggest generally good consistency. We further use the electrical resistivity to infer the rheology properties of the lithosphere, which suggests the Tibetan Plateau is dominated by continuum deformation, while the South China deforms more like rigid blocks.

* This Study is funded by project SinoProbe-02-04 and NSFC (41774087).