肃北野马河北侧断裂地貌特征及其晚第四纪活动性

GEOMORPHOLOGIC CHARACTER AND QUATERNARY ACTIVITY OF THE NORTH OF YEMAHE FAULT IN SUBEI

阿尔金活动断裂带东段的滑动速率由西向东逐渐减小,而肃北是阿尔金断裂东段滑动速率的"突变点"之一。在肃北以东分布多条分支断裂,野马河北侧断裂便是其中的一条。野马河北侧断裂长约30km,总体走向NEE,该断裂沿野马河盆地北侧山前洪积扇延伸,沿断裂具有大量的左旋走滑和逆冲等地貌现象,多处冲沟出露有断层剖面。野外调查结果表明该断裂是一条左旋走滑兼逆冲断裂,错断了晚更新世时期形成的洪积扇或冲沟阶地。通过实测得到地貌面左旋、垂直错动数据,并采集样品测试相关地貌面的年龄,估算该断裂晚更新世以来的平均水平滑动速率为(1.27±0.18)mm/a,平均逆冲速率为(0.4±0.07)mm/a,该断裂分解了阿尔金断裂东段的部分运动量。

The slip rate decreased at Subei,Shibaocheng and Shulehe regions on the eastern segment of Altyn Fault,the regions called as ＂singularity points＂. Subei is one of ＂singularity points＂ on the eastern segment of Altyn Fault,and the north of Yemahe Fault in the northeast of Subei is the fault we study in this paper. The fault is located in the northeast of Yemahe Basin. It starts at Erdaogou gully in the east and ends at Niujuan gully, extending along the Yema mountain front and parallel to the Altyn Fault in the direction of NEE on the whole. It separates Sinian from Quaternary gravel layer. There are plenty of left-lateral slip-strike and thrusting geomorphologic phenomena and exposed stratigraphic sections on the sides of gullies. Ridges and gullies are dislocated synchronously. Through more than one month investigation, we obtained the distribution and the geological and geomorphologic characteristics of the fault, measured a series of left-lateral slip gullies, ridges and thrust scarps and got the relevant data. Some samples are also collected. The left-lateral slip of gullies is distributed from 1.3m to 175m,and the height of thrust scarps is from 0.95m to 8.53m. The horizontal averaged slip rate of the fault is calculated to be 1.27±0. 18mm/a,and the averaged thrusting rate is 0. 4±0. 07mm/a. This fault,together with the Danghenanshan thrust fault at its south,resolved part of the movement components of the eastern segment of Ahyn Fault.