CENO-MESOZOIC TECTONIC STRESS FIELD OF NORTH CHINA BASIN AND MECHANISM OF FORMATION AND DEVEELOPMENT OF BASIN

This paper discusses and probes the evolution of basin structrues, and analyses the mechnaism of basin subsidence, which depends on the fea-tures of geological structures, geophysics, and those of the deeper crust and the stress variation of the surrounding high land. The knowledge is achieved as follows: I. The both sides of the basin are bounded by the Tanlu Faulting Belt and Taihang Structure Belt whose structures have been complicated and are of large size with secular activities. Since Mesozoic, the two belts have mainly undergone three stages of the stress field evolution. Ⅱ. The three evolutional stages correspond to the three different types of structure mechanisms. 1) Early, Middle Yanshanian, the type of folding faulting basin on the background of intraplate uplift; 2)Late Yanshanian-Early Xishanian, the type of extensional graben-half graben basin under the con dition of intraplate subsidence; and 3)Late Xishanian, the type of de pressing of large scale. The first two types are closely related to the occurrence of oil and gas. Ⅲ. The values from the planar and the vertical basin stress fields are simulated by adopting a program of Limited Element Increment. The re-sults, in one respect,support the thesis that North China Basin has under-gone two different stages of stress fields and indicate: 1) the controll-ing factors of the previously existing faults on the basin; 2) the possible weak parts of rock deformation and damages in shallow strara of the crust; and 3) the critical factors of vertical force coming from deeper crust dur-ing the formation of the basin.