关键词: 活断层, 褶皱变形, 青藏高原, 大通断裂, 西宁盆地

Abstract: Datong Fault belt is a northwest trending fault in the north of Qinghai-Tibet plateau which controls the boundary of Xining Basin and Datong Basin.It consists of the Maziying-Miaogou(F₁)Fault and the Laoye mountain-Nanmenxia Fault(F₂).There is obvious displacement in vertical direction along the fault belt.The field investigation results show that this belt has long-term activity.There are several meters-long crushed zone and veins along the fault side in the basement rock.In the visible profile of fault,the Cambria system thrusts to the red brick Quaternary gravel,and there are several centimeters-thick fault gouges along the fault side.ESR dating of the fault gouge in the fault profile shows an age of(610?61)ka.The covering deluvial loess is not offset,and the OSL result is(14.6?1.5)ka.So it can be concluded that the fault belt was active in middle Pleistocene but not in later Pleistocene according to the age data and geomorphologic feature.Interior stratum of the Datong Basin is mainly featured with fold with the major axis in northwest direction.According to the relation of fault and fold deformation,Datong Fault is a transversal tear,which is due to uneven compression of the folds in different parts and the NNE-oriented regional compressional stress.It is common among the NE-trending faults in northeastern Qinghai-Tibet plateau.These NE-trending faults aren't large,and most are located in the active plate.They are all nearly vertical to the axis of the folds and compressive basins.

Key words: active fault, the deformation of folds, Qinghai-Tibet plateau, Datong Fault, Xining Basins