RESEARCH ON TECTONIC CHARACTERISTICS OF CICUN FAULT IN THE NORTH OF LUXI UPLIFT,NORTH CHINA CRATON

As a near-SN fault between Huimin Depression and Dongying Depression in the southeastern Bohai Bay Basin, Cicun Fault controls the sedimentary sand body and oil gas distribution in the depression. Predecessors thought that it was an extensional strike-slip fault since Late Mesozoic, but there is no research of the fault on early Mesozoic activity. Gravity and magnetic data show that Huidong fault is connected southward with Cicun fault of Luxi uplift. This paper mainly investigates the structural characteristics of Cicun fault by outcrops in the target area, which helps to reveal the development and evolution of Huidong fault. The Cicun fault consists of three faults from south to north and tilts eastward, with a dip angle of nearly 90° and right-lateral characteristics. The striation marks of 15°∠0° which occurred in the limestone strata of western wall of fault, indicating that the fault has left-lateral characteristics. Two groups of conjugate fractures with strikes of 203° and 143° can be seen in the Carboniferous siltstone in the west side of the Cicun fault, and the sharp angle points to 173°, indicating the north-south compression, corresponding to the stress field of the Indosinian period. These prove that the Cicun fault and the Tanlu fault zone were formed at the same time. Two groups of joints can also be seen in this formation, with the strikes of 110° and 187°, which indicating NW-SE compression, corresponding to the stress field of the early Yanshan period in Jurassic, early. In summary, aimed at the Cicun fault, this paper uses the method of field outcrop investigation and combines with the seismic data to conclude that the Cicun-Huidong fault was formed in the Indosinian period, mainly with left-lateral strike-slip, and then experienced the compression left-lateral strike-slip in the early Yanshan period. Due to the NE-SW extension was destroyed by the North China Craton in the Late Mesozoic. The Cenozoic has become the fault mainly with right-lateral extension strike-slip.