Deformation of the Crust and Upper Mantle beneath the North China Craton and Its Adjacent Areas Constrained by Rayleigh Wave Phase Velocity and Azimuthal Anisotropy

Abstract

The North China Craton (NCC) has experienced strong tectonic deformation and lithospheric thinning since the Cenozoic. To better constrain the geodynamic processes and mechanisms of the lithospheric deformation, we used a linear damped least squares method to invert simultaneously Rayleigh wave phase velocity and azimuthal anisotropy at periods of 10–80 s with teleseismic data recorded by 388 permanent stations in the NCC and its adjacent areas. The results reveal that the anomalies of Rayleigh wave phase velocity and azimuthal anisotropy are in good agreement with the tectonic domains in the study area. Low-phase velocities appear in the rift grabens and sedimentary basins at short periods. A rotation pattern of the fast axis direction of the Rayleigh wave together with a distinct low-velocity anomaly occurs around the Datong volcano. A NW–SE trending azimuthal anisotropy and a low-velocity anomaly at periods of 60–80 s are observed subparallel to the Zhangbo fault zone. The whole lithosphere domain of the Ordos block shows a high-phase velocity and counterclockwise rotated fast axis. The northeastern margin of the Tibetan plateau is dominated by a low-velocity and coherent NW–SE fast axis direction. We infer that the subduction of the Paleo-Pacific plate and eastward material escape of the Tibetan plateau mainly contribute to the deformation of the crust and upper mantle in the NCC.

Present-Day Three-Dimensional Deformation across the Ordos Block, China, Derived from InSAR, GPS, and Leveling Observations

“…The northeastern margin of the Ordos Block is a well-known distribution area for Datong Quaternary volcanoes. Previous studies on the crustal velocity structure and magnetotelluric imaging have suggested that mantle upwelling at the northeastern margin of the Ordos Block is still ongoing [28][29][30][31][32]. Our monitoring results indicate that the ground in the area is experiencing uplift and the strain rate shows tension, which further supports the upwelling of deep material beneath the northeastern margin of the Ordos Block (Figure 6).…”

“…Thus, we contend that the crustal deformation data do not support the occurrence of processes associated with the lower crustal flow beneath the Qinling Orogen. Other studies, based on velocity structure analysis, suggest the existence of an asthenospheric mantle flow channel with an eastward flow of material beneath the Qinling Orogenic Belt, located between the rigid blocks of the Ordos and Sichuan basins [28,[40][41][42][43][44]. These studies propose that the direction of the asthenospheric mantle flow may deviate from that of the overlying lithosphere.…”