关键词: 阿尔金断裂带, 走滑断层, 断错地貌, 滑动速率

Abstract: As the northern boundary of the Tibet Plateau,the Altun Fault runs more than 1500km from Lazhuglung,Tibet Autonomous Region to Kuantanshan,Gansu Province,separating the Tibet Plateau from the Tarim Basin.The fault is one of the longest strike-slip faults in China,and the research of it may provide important information about the formation and evolution processes of the Tibet Plateau. The displacement and slip-rate of the Altun Fault is a topic full of disputation.Because of its significance to the formation and evolution of the Tibet Plateau,different estimates of slip-rates and displacement on the Altun Fault have been proposed in various models of the evolution of the Tibet Plateau. This paper focuses on the late Quaternary slip-rate on the Altun Fault west to the Qarqan River.On the basis of the analysis of SPOT images of this region,three typical sites including Koramlik,Aqqan pasture and Dalakuansayi were chosen for field investigation.To calculate the slip-rate of the fault,displacement of terraces were measured on SPOT satellite images or in-situ during the fieldwork,and the ages were dated by thermo-luminescence method.To get the ages of terraces,samples of sand were collected from the uppermost sand beds just beneath the loess.The method of calculating the slip-rate of a fault is to divide the displacement of a ridge lies between two neighboring terraces of one river by the age of the lower terrace.The displacements of rivers are not considered in this study because of its uncertainty. At Koramlik,the slip-rate of the Altun Fault since6.02?0.47ka BP is11.6?2.6mm/yr,and since15.76?1.19ka BP is9.6?2.6mm/yr. At Aqqan pasture about30km to the west of Koramlik,the slip-rate of the fault since2.06?0.16ka BP is12.1?1.9mm/yr. At Dalakuansayi,the slip-rate of the fault since4.91?0.39ka BP is12.2?3.0mm/yr. The average slip-rate of all above is11.4?2.5mm/yr,which is the average slip-rate of the western segment of the Altun Fault since Holocene.This result is close to the latest results from GPS research.

Key words: Altun Fault zone, strike-slip fault, offset landform, slip-rates