Study on Crust‐Mantle Transitional zone in West Margin of Zhangjiakou‐Bohai Fault Belt

Abstract

AbstractUsing the complexity coefficient, frequency spectrum analysis and wavelet transformation, we have processed Pm waveform data of the deep seismic sounding profile cross the west margin of the Zhangjiakou‐Bohai fault belt. Our purpose is to investigate the parameter features of the crust‐mantle transitional zone and their implications for lithospheric evolution. Our results show that different tectonic units have distinct complexity coefficients and frequency spectrum features. Beneath the Mongolia platform, the complexity coefficient is small and the Moho interface is of the first order discontinuity. Below the Huai'an‐Zhangbei area, west margin of the Zhangjiakou‐Bohai fault belt, the complexity coefficient of Pm wave is large, the frequency spectrum has many extremes and the Moho is a complicated crust‐mantle transitional zone. In terms of wavelet analysis and synthetic seismograms of reflectivity, it is revealed that the crust‐mantle transitional zone beneath the study area consists of 2~3 layers, with a total thickness about 6~9km, which is thickest below the Huai'an basin. It is inferred that this transitional zone was resulted from underplating during continental rifting, and its layering feature is associated with many times of magma activities in Mesozoic and Cenozoic times.