A STUDY ON THE STRUCTURAL EVOLUTION CHARACTERISTICS OF THE BURIED HILL IN THE EASTERN PART OF YIHEZHUANG

The buried hill in the eastern part of Yihezhuang has a southern high and northern low morphology, which has undergone three stages of tectonic movements: Indosinian thrust compression in rows, Yanshan sinistral strike slip zoning, and Himalayan dextral strike slip tension finalization, forming a checkerboard shaped fault block and displaying a complex structural feature.

The thrust fault of the buried hill in the eastern part of Yihezhuang was formed in the late Triassic, during which the northern part of the North China plate was restricted by the Xingmeng Orogenic belt that had been formed in the late Paleozoic, and the southern part was collided by the Yangtze plate, resulting in a regional stress field of NE-SW compression. Luoxi fault and Luoxi No. 1 and No. 2 secondary large faults were formed in the eastern part of Yihezhuang buried hill, dividing the eastern part of Yihezhuang buried hill into three rows, forming three buried hill belts in the south, middle and north.

Yanshan movement began in the Jurassic period. The early NWW thrust fault began to extend under the effect of the tension component, and a negative reversal occurred. The reverse degree of the thrust fault is different. A small number of high level faults are completely reversed, which is now characterized by normal faults. At the same time, the formation of the Paleozoic is high in the south and low in the north. The reverse degree of most low level faults is low. Under the left-handed shear stress field, a large strike slip Fracture zone was formed, generating near NE-SW secondary extension, and a series of NNE leftward translational faults appeared.

In the Paleogene, the NWW Thrust fault formed in the early stage basically stopped its activity. The main faults formed during the left lateral strike slip period of Yidong in the buried hill belt in the northeast of Yihezhuang continued to operate during the Himalayan period. The fault shifted from left lateral strike slip to right lateral strike slip, accompanied by strong tension, forming the current Yidong Fracture zone, and deriving the NNE and NS plume type secondary faults. At the end of Himalayan period, the basin was uplifted as a whole, and the high buried hill was denuded, entering Neogene Quaternary, dominated by depression, and the overall fault activity was reduced.