张家口—渤海断裂带西缘壳幔过渡带研究

STUDY ON CRUST-MANTLE TRANSITIONAL ZONE IN WEST MARGIN OF ZHANGJIAKOU-BOHAI FAULT BELT

利用复杂性系数、频谱分析和小波变换方法处理了穿过张家口—渤海断裂带西缘的地震测深剖面的Pm波形资料 ,研究不同构造单元壳幔过渡带的多参数特征以及它们在岩石圈构造演化中的意义 .结果表明 :不同构造单元Pm波的复杂性系数和频谱特征有较大差异 ,内蒙地轴复杂性系数小 ,莫霍面具有明显的一级间断面特征 ,怀安—张北位于张家口—渤海断裂带的西缘 ,该区域Pm波复杂性系数大并且频谱为多极值 ,Moho面为复杂的壳幔过渡带 .利用小波分析和反射率理论地震图得到该壳幔过渡带由 2～ 3层组成 ,总厚度约为 6～ 9km ,最大厚度位于怀安盆地下方 .该壳幔过渡带是大陆裂谷环境中底侵作用的产物 ,壳幔过渡带的分层特征与该区域中新生代的多期岩浆活动有密切联系 .

In this paper complexity coefficient, frequency spectrum and wavelet teansform is used to process Pm wave from deep seismic sounding (DSS) profile passing through the west margin of Zhangjiakou-Bohai fault belt. The Moho heterogeneity characteristics in different tectonic units has been obtained. The results show that the complexity coefficients and frequency spectrums have larger variation in different tectonic units. The complexity coefficients in Inner Monggolia Platform are small. Its Moho has obvious the feature of first order discontinuous interface. Huai′an-Zhangbei region are the west margin of Zhangjiakou-Bohai fault belt, this region complexity coefficients are large and frequency spectrums have multi-peak feature. Its Moho reflects feature of crust-mantle transition zone. Using wavelet analysis and the synthetic seismogram with reflectivity, the tectonic form of the crust-mantle transition zone was obtained. It consists of 2～3 layers and about 6～9km thick. The largest thickness lies under Huai′an basin. The crust-mantle transition zone is the product of uderplating in continental rift environment. Its stratification is closely related with multiperiodic magmation during Meso-Cenozoic in this region.