Geometry And Deformation Of The Fault Zone On North Boundary Of Yanghe Basin In North China

Research areas are located on Junction/composite parts of Zhangjiakou-Buohai tectonic zone that trending NWW and ShanXi fault zone that trending NE. It has complex characteristics about geological tectonic, activity structure and seismic activities. However, because of Various constraints factors, which make related investigation and research of this areas are still relatively weak, neither system nor depth, and scientific survey and research about neogenic structure is still a blank. This article research on the Geometry and deformation of fracture zone, it has important theoretical and practical significance about the analysis of tectonic geomorphology,the research about geometric structure and deformation characteristics and the discussion of tectonic transformation model of fracture zone.The fault zone on north boundary of Yanghe basin is the north margin of it, which distribution with zigzag. From the east to the west can be divided into four sections, namely: Zhangjiakou fault, Wanquan fault, Ximalin fault and the north margin fault of Huaian Basin. Its full-length above 140km, each paragraph has unique distribution and activities. On the whole, it is composted by three groups direction tectonic that trending NWW, NE and nearly EW, control ling the development and evolution of the basin.Based on detailed field investigations and electrical prospecting sections, this paper describes geometrical characteristics and tectonic activities of northern edge fault zone in Yanghe Basin. This research provides a more systematic basic data and tectonic transformation model for this area. The main results,conclusions and cognitions are as follows:①The fault zone on northern margin of Yanghe Basin is composed by a series of faults, trending NW-NWW, NE-NNE and NEE to nearly EW. Three groups direction of faults crossing, cutting and connection, from west to east in turn is the margin fault of Huaian basin, Ximalin fault, Wanquan fault and Zhangjiakou fault. The west,middle striking NWW, west striking nearly east to west, the former dipping north which is mainly reverse left-slip fault with high angle, the latter is normal fault with dipping south and has sinistral strike-slip component; Between the three is normal fault strikes NE, dips SE.②The northern margin of the Yanghe basin in geological fracture zone caused Stratum contact diametrically between Archean/Mesozoic and late Quaternary accumulation. Also cause terrain changes suddenly across the northern margin fracture zone of Yanghe Basin.On the whole, the fault with striking NWW is mainly Sinistral strike-slip fault, the fault with NNE-NE is mainly high angle normal fault. It sustained activities during the Quaternary period, the latest activities until the late Pleistocene or Holocene.Fracture geometry and spatial distribution and activity characteristics, show interaction and deformation conversion between Shanxi rift zone and Zhang Bo tectonic belt.③Zhangjiakou fault is tectonic boundaries between Shanxi rift zone and Yanshan fault block, controlling the northern border of Zhangjiakou-Xuanhua basin. The basin has complicated structure, effectting by composite role of Zhangjiakou-Bohai tectonic belt (trending NWW) and Shanxi rift zone (trending NNE). On the whole, the fracture zone, extending NWW in general with a length of 70km, and consisting of two sets of multiple secondary high-angle normal (or reverse) strike-slip faults striking NW and near EW, respectively, controlling the neotectonic movement of this region. Fracture zone is very wide, is the Late Pleistocene fault, a single fault average vertical velocity is greater than 0.07-0.30mm.④Wanquan fault is on northwestern margin of Wanquan town, controlling the northwest border of Wanquan basin, with a strike of 35°in general, dipping to south east at dip angle of 65°, 15km in length, and characterized with normal faulting. It divided into two segments:the South part since Zou village to Zhangguitun north, over 10km long; the North part staggered 2km to West, extended to the West of Wanquan town, about 5km long. The average vertical velocity of single fault is 0.04～0.20mm/a since late Pleistocene.Exploratory trench exposing Wanquan fault has occurred 3～4 times sudden activity near surface in Late Late Pleistocene, and has different Stagger (0.2～2m).⑤Ximalin fault which located in the northwest of Xuanhua basin. It is the northwest Segment of Ximalin-Shuiquan fault, with a strike of 320°, more than 10km in length, controlling development of landforms along fault or dislocation about mountain and basin plots, or constitute the basin boundary. It has rich geological phenomenon clear section and sliding structure,and characterized with or inverse, or normal, mainly strike-slip faulting, substantially cuts off the late Pleistocene loess.⑥The northern margin fault of Huaian Basin is located in the northwest of Huaian Basin, which is the tectonic boundary between mountain and basin and controlling landforms along fault. The fault overall length is about 50 km, which East segment strike 35-45°, Middle and Western segment Nearly EW. The two sides of fault has completely different Stratum, the north side is the Mashikou era granulite with weakly Migmatization and forming Mixed rock with banded in Local part; South is the alluvial fan, contacting to North mountains with Fault. Based on Satellite image and Geological survey, we found that the fault has rich geological phenomenon,clear Section and sliding structure and landforms of fault such as" steel cutting Bean curd ", also in everywhere we can found Fault scarp,triangles,characterized with normal faulting, and average vertical slip rate is about 0.21～0.22mm/a (Fang Zhongjing,1994).⑦By the tectonic stress field of the NEE-SWW extrusion and NNW-SSE tensional on this research area, which has Large-scale fault with striking NWW and activities is mainly Sinistral strike-slip, in tail of NWW striking fault, it turn to small scale tensile normal fault with striking NE, that is NE striking fault is the regulate conversion fault of NWW striking fault, so the stress constant release which formed by tectonic activity accumulate.