Crustal structure of the eastern Qinling orogenic belt and implication for reactivation since the Cretaceous

- High resolution crustal model of Qinling is obtained by joint analysis of surface wave, receiver function, and gravity.
- Crustal low velocity and low Vp/Vs ratio of the Qinling indicates a felsic crust with the removal of mafic lower crust.
- A ~ 10 km high-velocity and -density layer beneath the central NCC with high Vp/Vs ratio suggests mafic underplating.

A high resolution crustal model of the eastern Qinling belt and central North China Craton (central NCC) is obtained along a N-S trending profile (corridor) by joint inversion of surface wave and receiver function. The NCC is one of the oldest cratons on Earth and the Qinling belt is the suture zone between the NCC and South China block (SCB). The Qinling belt is characterized by low crustal velocity (< 3.6 km/s) as well as low bulk Vp/Vs ratio (1.66-1.8), suggesting that the mid- to lower crust is predominantly felsic in composition, which could be the consequence of removal of mafic root by delamination in the past. The quartz-rich hence mechanically weak crust beneath the Qinling belt could be responsible for the strain focusing and significant reactivation since the Cretaceous. Beneath the central NCC, a ~ 10 km thick high-velocity layer (3.9-4.1 km/s) is observed just above the Moho, consistent with the regional high bulk Vp/Vs ratio (> 1.8). The forward gravity modeling supports the presence of a high-density layer (3.05 g/cm3) at the base of the crust beneath the central NCC. We propose that the high velocity in the lowermost crust beneath the central NCC is most likely due to the repeated mafic underplating, which also results in high crustal Vp/Vs ratio and is responsible for the rapid crustal uplift during the late Mesozoic.