关键词: 阿尔金断裂带, 走滑断层, 断错地貌, 滑动速率

Abstract: As northern boundary of the Tibet Plateau, the Altyn Tagh Fault attracts the attention of lots of geo scientists from different parts of the world. The offset and slip-rate of the Altyn Tagh Fault are a topic full of disputation. To make clear the slip-rate of the Altyn Tagh Fault is important for understanding the coupling relationship between the uplift and strike-slip on the northern Tibet Plateau. On the eastern Altyn Tagh Fault, to the west of the outlet of the Shulehe River, the late Quaternary terraces and alluvial fans are offset by the fault. There are some typical offset landforms in this region, and by investigating these geomorphological features, slip-rate of the Altyn Tagh Fault can be evaluated. To the West of Shulehe River, three sites, Erjiatai, Niuyagou gully and Bagexia were surveyed for obtaining the slip-rate on this part of the Altyn Tagh Fault. The range of fieldwork region for this study is about from 94°24′E to 94°37′E. At Erjiatai, offset of the lowest terrace T₁ cannot be identified because of its absence near the fault. The offsets of T₂, T₃ and T₄ terraces are 40m, 100m and 220m, respectively, and the TL ages of T₁, T₂ and T₃ terraces are 7.82ka BP, 22.53ka BP and 53.26ka BP. According to these data, we can calculate the average slip-rates of the fault in different periods since late Quaternary. The slip-rate of the fault at this site is about 4～4 5mm/yr since 50ka BP. At Niuyagou, the fault offset all the terraces but T₁. The offsets of T₂, T₃ and T₄ terraces are 6.4m, 40m and 120m, respectively, and the TL ages of T₁, T₂ and T₃ terraces are 6.97ka BP, 10.06ka BP and 28.81ka BP. So the slip-rate of the fault here is about 4～4.2mm/yr since 30ka BP. At Bagexia, the lowest terrace T₁ is not offset by the fault but the other terraces above T₁ are offset by the fault. Here the slip-rate of the fault is a little higher than the other two sites described above. Here the slip-rate of the fault since 20ka BP is about 4.7mm/yr. Based on the above mentioned data the following conclusion can be drawn: The slip-rate of the eastern Altyn Tagh Fault to the west of Shulehe River since 20ka BP is about 4～5mm/yr and the slip-rate become a little higher westward. Regarding the strike of the Altyn Tagh Fault in this region is about N73°E, we may estimate that the strike-slip on the eastern Altyn Tagh Fault assimilates the north-south shortening of the Tibetan Plateau at a rate of 1.5mm/yr at maximum.

Key words: Altyn Tagh Fault, strike-slip fault, offset geomorphologic feature, slip-rate