Radial Anisotropy of the Crust and Uppermost Mantle Beneath the Central North China Craton From Joint Inversion of Surface Wave Dispersion Curves and Ellipticity: Implications for the Mechanisms of Differential Rifting and Uplift

The central North China Craton (NCC) acts as a transition zone between the stable western and reworked eastern NCC. It is characterized by high seismic activity and experienced volcanic activity with small magma volumes. To assess the dynamic processes of the central NCC, particularly in a zone marked by intense differential tectonic deformation, we have obtained a 3-D radial anisotropic model of crust and uppermost mantle via joint inversion of Love- and Rayleigh-wave dispersion curves and ellipticity measurements. Compared to models without Rayleigh-wave ellipticity, our new model shows improved accuracy in crustal radial anisotropy. This refined model reveals two noteworthy geological features: (a) Most of the Shanxi Rift has pronounced positive radial anisotropy in the crust except for Linfen and Xinding Basins, as critical earthquake-prone areas, which are characterized by weak positive to negative anisotropy with much thinner sediments. This observation suggests that differential rifting processes with uneven sedimentation and crustal deformation occur in these Cenozoic basins due to right-lateral strike slip motion. (b) The crust in the Lvliang Mountains shows weak positive or negative anisotropy with a lower crustal low-velocity layer beneath the northern parts, whereas the crust in the Taihang Mountains exhibits positive anisotropy. This implies that the Lvliang Mountains experienced uplift under compressional environments since the Yanshanion Orogeny. Furthermore, the magmatic underplating in the crust accelerated the uplift of the northern Lvliang Mountains. In contrast, the Taihang Mountains underwent relative uplift under extensional environments, along with the subsidence of the Bohai Bay Basin during the Cenozoic.