Crustal structure in western Qinling tectonic belt and its adjacent regions deduced from receiver functions

Seismic waveform data from 117 broadband seismic stations in the western Qinling tectonic belt and its adjacent regions were used to compute crustal thickness and velocity ratio (v_P/v_S) by the H-k stacking method of receiver functions. Crustal structures were studied by analyzing the crustal thicknesses, velocity ratios and their relationship, as well as the receiver function images calculated with the common conversion point stacking method. The results show strong lateral variations and transitional features of crustal structures in this area. The crust thins from southwest to northeast. The crustal thickness varies from 72 km in the Qiangtang block to 39 km near the Weihe basin. The crustal thickness in western Qinling tectonic belt is 42—56 km, and NS-trending Moho depth shows little change. The average velocity ratio v_P/v_S is 1.74 in the study area and 1.72 in western Qinling tectonic belt. Lower velocity ratios mainly distribute in western Qinling tectonic belt, Qilian block, northern Songpan--Garze block and Xiangshan--Tianjingshan fault zone. Lower velocity ratios in this area are probably due to the thickened upper crust of the felsic acid rock composition. The lack of ultrahigh velocity ratios indicates that there is little possibility of magma underplating beneath the lower crust and significant partial melting in the upper crust. Crustal structures in the western Qinling tectonic belt and its adjacent regions are mainly caused by the crustal tectonic deformation occurred during continuous uplifting and northeastward spreading of the Tibetan Plateau as blocked by surrounding terrane. The characteristics of Moho interfaces and velocity ratios in the western Qinling tectonic belt are correlated with underwent extension and strike-slip movement after the collision orogeny and crustal thickening.