Regional variations in crustal thickness and Vp/Vs ratio beneath the central-western North China Craton and adjacent regions

摘要

Using teleseismic waveform records from 363 broadband stations, we applied H-κ stacking of receiver functions to estimate crustal thickness (H) and average Vp/Vs ratio (κ) in the central and western North China Craton (NCC) and adjacent regions. Our results show that, except for thinning in the Cenozoic rifts and southern edge of the central NCC, H gradually thickens westward from ~30km at the easternmost edge of the central NCC to >60km near the northeastern margin of the Tibetan Plateau. κ exhibits complex variations, with locally high or low anomalies in the rifts, at the southern edge of the central NCC and at tectonic boundary zones. Low-density uppermost mantle and distinct N-S differences are observed in the Ordos, suggesting typical cratonic crust. Thickened crust and complex variations in κ at the southwestern boundary of the Ordos may be related to the formation of the Palaeozoic Qilian Block and late uplift of the Tibetan Plateau. Thinned crust and locally high κ are observed in and near the Cenozoic rifts, suggesting complex crustal modifications that may have been caused by repeated reactivation at pre-existing weak zones by successive thermal-tectonic events. Thin crust and low κ are found at the southern edge of the central NCC, suggesting crustal modifications such as delamination, especially in the lower crust, which may be related to collision of the NCC and Yangtze Block.