The Analysis Of The Developmental Characteristics And Activty About Fault Zone Of Longxian-Baoji

Longxian-Baoji fault zone is located in the transition area of the middle and the northern section of the famous north-south seismic zone,northeast of the northern Tibetan Plateau margin block,arc of the southwest margin of the Ordos fault the southern section of the beam, is also the transition zone of huge tectonic belt from East-west and north-south, it is very complicated in geological structure. Following the Wenchuan earthquake, This fault seismic activity has been much more attentioned by the geologists.In this paper, Using the following methods:satellite image interpretation, field surveys and trenching to expose and so on, for the first time on the Longxian-Baoji development characteristics and fault activity carried out systematic research and new knowledge gained as follows:1,The Geomorphological features of fault zone:Longxian-Baoji fault zone composed by the four faults:the Taoyuan-Guichuan Temple fault, Guguan-Guo town fault, Qianyang-Biao jiao fault and Longxian-Qishan-Ma zhao fault, the overall NW trend of narrowing the north, extending gradually to the cast of the southeast, arrived in the west of Weihe River basin, and ends near the Qinling Mountains. Ryuji landscape to form a bend of the structural framework.2,The fault characteristics of the faults and activities of the fault development characteristics:①Taoyuan-Guichuan Temple faults:outcrop length of 65km, the fault to 310～340°, tend to the North East, angle45～80°, the fault plane trace was slightly convex curved north east. Cretaceous metamorphic rocks under the front plate is, volcanic rocks and granite, gravel on the disk is Liupanshan group. Since there are no active faults since the Middle Pleistocene.②Guguan-Guozhen faults:outcrop length of 110km, the fault to 300～340°, inclination Nancy,angle 55～88°, the lower plate of the former Cretaceous, on the plate for the Liupanshan group. Fault outcrop rich Badu-Gaozhuang fault scarp geomorphology clear village section, but also shows the movement of left-lateral strike-slip features, such as the Song Mountains and other places can see, the Longwei-Guozhen section covered by Quaternary is buried state. No activity since the late Pleistocene.③Qianyang-Biaojiao fault:fault strikes 130°, inclination NE, stretching from the southern section of the Weihe River basin, the surface mostly covered by Quaternary loose deposits, the fault was concealed state.④Long xian-Qishan-Mazhao fault:the exposed length of 138km, the fault plane trace was slightly convex arc to the southwest, into a new set of Sichuan-Longxian section, Longxian-Qishan section and Qishan-Mazhao segments. New set of Sichuan-Longxian segment to 290-300°, inclination NE, angle 45～85°; Longxian-Qishan section to 280～320°, inclination SW, angle 55～85°; Qishan-Mazhao segment to 310～330°, inclination NE. Plane distribution of the fault was the right order echelon form, in large DU ditch, Yao field squeezing rock bridge area such as the formation, in wangjiawan, Yanjiawan to form the extension rocks area. Rich fault outcrop, the fault is Late Pleistocene fault.3,The Fault tectonic evolution:fault zone formed in early Paleozoic, before the late Jurassic, by the strong compression. Early Cretaceous, the formation of a strong left-lateral strike-slip tension environment, the formation of "one Ryuji bend" landscape. Cretaceous, the late performance of right-lateral strike-slip fault zone and the movement of the thrust characteristics of extrusion, after long-term uplift. In the late Pleistocene by Eastern Liupanshan sinistral strike-slip extrusion, Ordos block counterclockwise rotation, to the north and south of Weihe fault basin expansion and other effects,fault zone is characterized by a positive dip slip.4,Fault construction stress features:The deep fault zone is in the extrusion environment, characterized by NE extensional tectonic stress field; Shallow in the extensional environment, characterized by SSE extensional tectonic stress field. Among them, the main features of deep are tectonic stress field which NE to the extrusion, SSE to the extensional,and this is just the opposite of shallow.