Crustal structure characteristics beneath the Weiyuan area,Sichuan revealed by receiver functions
The Weiyuan area is located in the southwest of the Sichuan basin,in which the Weiyuan anticline is the main surface tectonic unit.Based on the teleseismic waveform data recorded by 40 three-component broadband stations in the Weiyuan area,the P-wave receiver functions(RFs)are extracted.Clearly Moho Ps phase can be found in RFs,and positive phase C1 and negative phase C2 also exit in 1～4 s.After the synthetic testing,we believe that the C2 phase indicates the sedimentary PpSs+PsPs phase.Firstly,we pick up the C2 phases and compare them with the modeling synthesis RFs to obtain the sedimentary thickness of each station.And C1 phase may indicate the sedimentary PpPs phase or the Ps phase of the Conrad interface.For the former phase,the arrival time of C1 decreases with increasing ray parameters,which means this phase shows a negative slope.However,the Conrad Ps phase shows a positive slope.Based on this character,we calculate the slope of the C1 phase at each station and infer the existence of the Conrad interface in areas outside the Weiyuan anticline because of its positive slope.Then the crustal thickness and the VP/VS ratio are estimated by H-κ stacking.The Common Conversion Point(CCP)stacking method is used to reveal the Moho and Conrad interfaces.The results show that the sedimentary thickness ranges from 3.0 to 7.0 km,and the sedimentary layer of the Weiyuan Anticline is thin,while the sedimentary layer of the Zigong sag is thick.The crustal thickness in the study area is about 40.9～49.2 km,with an average of 44.1 km.The crustal thickness is characterized by thick beneath the anticline core and thin beneath the syncline.The Conrad interface depth is about 19 km outside the Weiyuan anticline.According to the depth of the sedimentary basement,the Moho,and the Conrad interface,we speculate that the uplift of the Weiyuan anticline is caused by the thickening of both the upper and lower crust under the compressional environment.However after the uplift,the top of the upper crust has suffered erosion,and the lower crust has been preserved relatively intact.The VP/VS ratio varies from 1.71 to 1.92 with an average of 1.79 in the study area,which is the same as the average value of the global continent.There are two high-value regions in the study area.There may be a small-scale upwelling of mantle material at the intersection of the eastern Weiyuan anticline and the Lijiachang fold.While the Zigong sag is affected by the thick sedimentary at the top of the upper crust,and meanwhile,the middle-lower crust may be affected by the high-temperature material originating from the Sichuan-Yunnan block.The crustal composition of the Weiyuan anticline and southeast artesian anticline is mainly felsic or intermediate rocks,because of the lower VP/VS ratio.
万方数据
维普
