Tectonic Geomorphology And Active Tectonics In The Center Of The North China Block

The study area is located in the center of the North China Craton which was affected by the three global domains:the Paleo-Asian, the Paleo-Pacific and the Tethys tectonic domains. Since the Mesozoic, the North China Craton has been active. A large number of NE-trending thrust faults and folds developed in the Mesozoic. In the Cenozoic, the North China Craton was under destruction, the Bohai Bay Basin and the Fenwei Graben developed. Until now, the faulting is still active, and cause lots of intra-continental earthquakes. Therefore, it is very significant to study the active tectonics and the tectonic geomorphology in the center of the North China Craton. Combined with previous studies, field investigations, DEM, earthquake distribution, geochronology and the relations among faults with different strikes, uplift history of mountains and subsidence depocenter migration of basins are intergated for understanding the active tectonism as follows.The active faults in the study area include the Zhangjiakou-Penglai Belt, the Taihang Mountain Belt, the Southern Border Fault of the North China Block and the Fenwei Graben. The NE-trending faults are subdivided into the NNE-trending and NEE-trending faults, the slip component of the NNE-trending fault is larger than those of the NEE-trending faults, and being much larger in the Quaternary. The NW-trending and EW-trending faults which cut across the NE-trending faults are sinistral strike-slipping one.The sedimentation rates of the Shanxi grabens have being larger since the grabens were formed since the Miocene. In the Quaternary, different trending grabens show different rates. The sedimentation rates of the NNE-trending grabens are larger than those of the NE-trending grabens. The subsidence center of some grabens migrated to the subsidence region that are controlled by the NEE-trending faults.In the Miocene, the Qinghai-Tibet Plateau and the uplifting mountains in the North China Block in the same period. Considering the structural features of the faults and the grabens in the Quaternary, this paper deduces that the active tectonics in the center of the North China Block since the Miocene is mainly influenced by the extrusion resulting from the collision of the Indian Plate and the Eurasian Plate. The extrusion causes the NE-trending dextral shearing and the NWW-trending sinistral shearing that play role in the center of the North China Block. The joint role of those shearings results in the destruction in the north and south parts of the North China Block in the Miocene. The acceleration of the Qinghai-Tibet Plateau uplifting causes the two shearing events had different amplitudes, the joint force also switched from the NW-trending extension to the NNW-trending extension, and transferred its influence to the east and north parts of the study area, resulting in the development of grabens, the variation of activity of faults with different strikes, and the migration of the subsidence and deposit centers since the Pliocene.