The Research Of Fault Gouge From Main Active Fault Zone And Its Engineering Significance In Bailongjiang Basin

Bailongjiang Basin is located in southeast of Gansu province which is in the north of Sichuan province.The area develops plenty of active faults which is one of the high incidence parts of geological hazards and earthquakes in China.The research object of this paper is Diebu-Bailongjiang fault zone and Guanggaishan-Dieshan south fault zone.Through field investigation and laboratory testing,combined with the results of luminescence and optically stimulated luminescence dating,the thesis researches the characteristic of micro-shape of quartz and clay minerals in fault gouge of mainly active fault deeply,analyzes the date of the fault activity and motion mode of main faults,discusses the engineering significance of fault gouge research primarily.In Bailongjiang Basin,there are clear tectonic landforms and obvious signs of activity of the main active faults.There are newborn secondary faults cutting terraces,offset and turning of water and ridges and earthquake wedges and ancient earthquake filling along the faults.The micro-shape of quartz in fault gouge is mainly dissolved micro-shape in this area.And stress micro-shape of quartz is happened by accident.The combination of the quartz micro-shape is complex including orange peel-like to pot-hole.It reflects that the main active faults have multi-stage activities and stick-slip and creep-slip motion mode.The type of quartz micro-shape are mainly of Ic and ?,secondly Ib and ? and rarely la in the fault gouge of Diebu-Bailongjiang fault zone.It reflects that the activity of fault begins in the Pliocene,strongly acts in the Early Pleistocene and weaks in the Late Pleistocene.The activity of fault is mainly manifested as older in the west and newer in the east.The activity of fault zone has the evolutionary trend from west to east.Every part of Guanggaishan-Dieshan south fault zone has different types of quartz micro-shape and different activity.The peak activity time of the fault zone from west to east are as follows:Pliocene to initial Early Pleistocene-Early Pleistocene-late Early Pleistocene-Early Pleistocene to Late Pleistocene.The eastern part also actives in Holocene.Guanggaishan-Dieshan south fault zone also has the evolutionary trend from west to east.The clay minerals in active fault gouges are composed of illite,illite-smectite layer-mixed minerals,chlorite and kaolinite which have the content of 10-40%.The content of the clay minerals in different sections of the same fracture and different fractures vary a lot which indicate that their activity are different.The analysis of the clay minerals can not exclude the possibility of fracture stick-slip motion.Based on the active time,active stages and motion mode that the characteristic of quartz micro-shape and clay minerals in fault gouges determined,combined with the studies of seismic activity,it can guide the engineering evaluation of active fault and provide the geological basis for site planning of major projects in the study area.The current activities of fault have a tight connecting with the formation,development and resurrection of geological disasters in particular fracture zone landslide.Carrying out futher study about fault gouges of fracture zone landslide is necessary to understand the formation mechanism and set up disaster mode of fracture zone landslide.