The Research Of Fault Gouge And It's Geochronology From Lintan-dangchang Fault Zone In Western Qinling

Southeast Gansu Province,located in the northeastern margin of the Tibetan Plateau,was in a unique position,which occurred in the North-South Seismic Belt and Kunlun-Qinling tectonic belt,as well as multiple sets of complex deep fault belts at their intersections,also at the intersections of three grade ?active tectonic blocks: Tibetan,South China and North China.As one of the mainly active faults,Lintan-Dangchang fault had strong activity,where happened earthquakes,landslide and debris flow and other geological disasters frequently.Taken Lintan-Dangchang fault as study object,with field survey and laboratory tests,this paper investigated the gauge quartz micro-morphology characteristic in the major active fault,and analyzed the gauge active features.Lintan-Dangchang fault is a transfer zone of East Kunlun fault belt and the West Qinling fault zone,also a thrust fault striking NW–SE with sinistral slip nature,diping NE.It is obvious tectonic landform,spreads slightly arcuate of North North-East.Earthquake occurred frequently in the fault belt and the surrounding,where still have strong activity since Holocene.The gouge quartz grains in the fault were mainly sub-angular,sub-rounded,rarely scratches,steps,broken cracks.Gouge quartz dissolved micro-morphology appeared mainly conchae,sub-conchoidal,orange peel-like,fish scale,and mossy,occasionally stalactitic,decay and cavernous,indicating that Lintan-Dangchang fault has undergone a few period of activity since Quaternary,peaked in the early-middle Pleistocene,continued until the late Pleistocene,and still had strong activity in partial section since Holocene.OSL dating results showed that the latest activities of Lintan-Dangchang happened between 6.2-135 ka.According to gouge quartz micro-morphology and OSL dating,both determined Lintan-Dangchang fault was still active in the Holocene,which also were confirmed by 5 earthquakes occurred during 2003-2013 along the fault belt.The quartz micro-morphology and OSL dating results also showed that the fault activity existed some differences in space.For example,the western part of the Hezuo fault wasn't active in Holocene,middle part Lintan area and eastern part Minxian to Dangchang area had partial strong activity in Holocene,and strong sections were at inflection point of the separate faults.The fault activity characteristics derived from gouge quartz micro-morphology were consistent with the earthquake distribution rules in this area.In comparison with the other two faults in the study area(Diebu-Bailong River fault,South Guanggaishan-Dieshan fault),it could be found that Diebu-Bailong River fault and South Guanggaishan-Dieshan fault were active in late Pleistocene,with fault activity mode of stick slip and nature of compression.While Lintan-Dangchang fault was active in Holocene,with fault activity mode of creep slip and nature of compresso-shearing.