Sedimentary and crustal velocity structure of Trans-North China Orogen from joint inversion of Rayleigh wave phase velocity and ellipticity and some implication for Syn-rift volcanism

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

“…Moreover, prominent low-velocity perturbations can be found beneath the Datong volcano (Figures7 and S1). This low-velocity anomaly extends slightly northwest (Figure7c,d), which is also observed by the corresponding low S-wave velocity[20,27]. The low-velocity anomalies beneath the northeastern margin of the Tibetan plateau are obvious but not continuous.…”

“…For example, the low-velocity anomalies of the asthenosphere revealed by Xu et al [16], related to the lithospheric thinning, are segmented by irregular high-velocity anomalies in the eastern NCC, which are obviously inconsistent with the results obtained by full-waveform tomography [23], indicating that the eastern NCC is dominated by extremely low velocities. The upwelling of hot material beneath the Datong volcano is indicated by low-velocity anomalies in previous results [20,21,25,27], but its origin and mechanism are still under debate. Huang et al [27] proposed that the asthenospheric upwelling came from the northeastern margin of the Ordos block.…”

“…The upwelling of hot material beneath the Datong volcano is indicated by low-velocity anomalies in previous results [20,21,25,27], but its origin and mechanism are still under debate. Huang et al [27] proposed that the asthenospheric upwelling came from the northeastern margin of the Ordos block. Yao et al [20] confirmed this hypothesis and attributed it to lithospheric stretching.…”

“…The azimuthal anisotropy of the Rayleigh wave phase velocity around the Ordos block in the crustal and mantle lithosphere, corresponding to the periods of 15-40 s (Figure 7a-d), is quite consistent with the proposed model of rotation. The low Rayleigh wave phase velocity (Figure 7a,b) as well as the S-wave velocity [27] anomalies along the periphery of the Ordos block are the manifestation of the weak crustal structure that is more likely to produce the transtensional shear deformation inside the crust of the extensional grabens. Our results seem to support the previous hypothesis that the eastward extrusion of the Tibetan plateau and the subduction of the Paleo-Pacific plate caused the shortening rate as high as 3.0 mm/yr in the Liupan thrustfold belt and extensional rate of 1.3-1.7 mm/yr across the Weihe and Fenhe grabens [69], respectively, and jointly contributed to the rotation of the Ordos block [20][21][22].…”

“…Recently, many studies revealed the velocity structure and seismic anisotropy beneath the crust and upper mantle of the NCC [23,[25][26][27]. However, these results on understanding the lithospheric thinning and deformation of the NCC are still controversial.…”