Geometry And Kinematics Of The Eastern End Of The Altyn Tagh Fault

The sinistral strike-slip Altyn Tagh Fault(ATF) is characterized by intensive activity since the Cenozoic,and it plays an important role in the tectonic evolution of the northern Qinghai-Tibet Plateau. As the boundary of northward growing front of the Qinghai-Tibet Plateau, the eastern end of the ATF is dramatically influenced by the interaction between the Tarim block, the Qinghai-Tibet Plateau, and the Gobi-Alashan block. Hence it is of great significance to understand the detailed geometric structure of the Altyn Tagh Fault and to reveal the northern Qinghai-Tibet Plateau deformation processes and their relationship to the adjacent blocks.In this paper, the author carried out a quantitative slip rate research of the eastern end of the ATF. Meanwhile, a compilation of previous rates and sedimentary basin analysis work, especially the Cenozoic crustal shortening rate of the Jiuxi basin, was performed in order to obtain the ATF slip velocity distribution and the tectonic conversion relationship of the study area. Combined with the crustal shortening rate of the interior Jiuxi basin, the deformation pattern of the east Altyn Tagh Fault and northern Qinghai-Tibet plateau were discussed. The main conclusions are as follows:The eastern end of the Altyn Tagh Fault refers to the fault segment from the east of the Shule river mouth to the southwest of the Kuantan Mountain with a total length of 70 km. Based on satellite imagery interpretation, field geological investigation, geochronology methods, and high-precision topography aerial image measurement, the quantitative study of the fault activity was achieved. The result indicates that the slip rate near the Shule river mouth area is > 1.58 mm/yr and it decreases to 1.00-1.50 mm/yr at the ATF-2. To the west of the Hongliuxia, a rate of 0.58-0.72mm/yr is obtain near ATF-3. The rate further decreases without obvious horizontal displacement to the east of the Hongliuxia and only thrust features were observed. In terms of vertical slip rate, the whole segment showed northward thrusting and the vertical slip rate decreased towards the east with most measurements between 0.1 and 0.3mm/yr.Based on the previous research results, the Chijinxia segment of the Dengdengshan fault, easternmost end of the Altyn Tagh fault is a southwest thrust fault. The estimated thrust fault slip rate is < 0.1mm/yr on the basis of the geomorphic surface exposure ages. Study along another branch fault of the Altyn Tagh Fault, i.e. the Heishan fault, the northern border of the Jiuxi basin in western Hexi corridor, indicated that the thrust slip rate since the late Pleistocene is 0.26 ± 0.06 mm/yr.Integrated with previous researches concerning the quantitative estimations of north-west faults in the Jiuxi basin, western Hexi corridor, this paper concludes that the shortening rate of a series of thrust faults and folds of western Hexi corridor is 1.4-2.4 mm/yr in a parallel direction of the Altyn Tagh Fault, equal to the 1-2 mm/yr rate of the eastern Altyn Tagh Fault. Therefore, the sinistral strike-slip of eastern Altyn Tagh fault is inferred to be absorbed and transferred by the active thrust fault and the Cenozoic crustal shortening. The horizontal slip rate of the eastern Altyn Tagh Fault gradually decreased eastward and it eventually ends near the Chijinbao, Kuantan Mountain, eastern Hexi corridor. Thus together with the Dengdengshan fault and the Jintananshan fault, the Heishan fault of northern Jiuxi basin, western Hexi corridor constitute the northeast front of the Qinghai-Tibet Plateau.