华北克拉通边界带区域深部结构的特征差异性及其构造意义

Contrasting Structural Features at Different Boundary Areas of the North China Craton and Its Tectonic Implications

华北克拉通的显生宙破坏在空间上是高度不均匀的。克拉通自身岩石圈性质的横向差异及其周边块体的构造运动和相互作用,造成克拉通不同地区构造变形特征具有显著差异性。而这种差异性必然会在深部结构上留下印迹。因此,详细的深部结构信息能够为研究华北克拉通破坏的方式和动力学机制提供重要约束。对近年来基于华北内部结构计划（NCISP）密集流动地震台阵资料获得的华北克拉通边界带区域的深部结构图像进行介绍,并对比分析地壳、岩石圈结构和上地幔变形特征的区域变化,进而对克拉通破坏的空间差异性以及破坏的方式和过程做初步探讨。研究结果显示,华北克拉通东部的郯庐断裂带作为华北和扬子边界的构造薄弱带,具有克拉通全区最薄的岩石圈（~60 km）和明显减薄的地壳（〈35 km）,是克拉通东部岩石圈整体性减薄和破坏最强烈的区域;东北部燕山地区和西北部鄂尔多斯北边界区域都表现出厚、薄岩石圈共存和壳幔结构显著变化的特征,反映了这些地区岩石圈减薄和改造的空间不均匀性。燕山地区尖锐的Moho面、岩石圈结构和上地幔变形特征的小尺度变化可能是中生代多期挤压和晚中生代—新生代区域伸展共同作用的结果;而鄂尔多斯北边界附近稳定克拉通地区与新生代裂陷区壳幔结构的强烈差异和裂陷区的岩石圈减薄,则可能与克拉通本身的结构横向不均匀性以及长期构造演化过程中多次热—构造事件的影响有关。

The destruction of the North China Craton（NCC） during the Phanerozoic is highly spatially uneven.The inherent heterogeneity of the cratonic lithosphere and the tectonics of interactions among the sourrounding blocks may be responsible for the distinctly different tectonic processes and deformation patterns in the different parts of the NCC.The tectonic diversity certainly would have left significant imprints on the deep structure beneath different geological domains of the craton.A detailed knowledge of the deep structure of the NCC therefore can provide important constrains on the dynamic process and mechanism of the Phanerozoic craton destruction.In this paper,we present the deep structural images of the different boundary zones of the NCC.These images were constructed from the data recently collected by the dense broadband seismic arrays of the North China Interior Structure Project（NCISP）.Considering the contrasting features of the crustal and lithospheric structure as well as the upper mantle deformation pattern between these boundary zones,we discuss the spatial heterogeneity and possible tectonic processes of the craton destruction.Our results show that as a mechanically weak zone along the eastern margin of the NCC,the Tanlu Fault Zone has the thinnest lithosphere（-60 km） and obviously attenuated crust（〈35 km） at the present time,indicating that this fault zone may have been the most significantly affected during the whole-sale lithospheric destruction and thinning in the eastern NCC.On the other hand,both the Yanshan belt and the northern Ordos block around the northeastern and northwestern boundaries of the NCC,respectively,are characterized by the coexistence of both thinned and thick lithosphere and sharp changes in the crustal and upper mantle structure,suggesting an uneven lithopsheric remobilization and thinning in these regions.The sharp Moho and fine-scale variations in both the lithospheric structure and upper mantle deformation pattern beneath the Yanshan belt probably resulted from the joint influence of the multiple phases of compressional deformation in the Mesozoic and intense regional extension from Late Mesozoic to Cenozoic.Striking structural contrasts are even more pronounced between the stable interior of the Ordos block and the surrounding Cenozoic rift areas near the northwestern boundry of the NCC.This as well as the localized lithospheric thinning observed in the rift areas may be attributed to the pre-existing structural heterogeneity and repeated thermo-tectonic reactivation during the long term evolution of the craton.