柴达木盆地西南缘狮子沟断裂晚第四纪构造变形分析

Analysis on Late Quaternary Tectonic Deformation of the Shizigou Fault,Southwestern Margin of the Qaidam Basin

狮子沟断裂位于柴达木盆地西南缘英雄岭背斜南翼。对狮子沟断裂晚第四纪构造变形进行分析,有助于理解该区长期的构造演化和地震地质灾害的评价。通过对该断裂带构造地貌调查、断层剖面和探槽研究,得到以下认识:狮子沟断裂是一条向SW方向逆冲的全新世活动断裂,断裂的逆冲活动一部分沿着山前分支断层,该分支错断了全新世早中期的冲洪相地层,晚更新世中期以来的最小垂直活动速率为0.12~0.15 mm/a;另一部分沿着盆地内隐伏分支断层活动,形成次级褶皱隆起,最近主要的一期构造活动发生在(97.93±7.98)^(59.43±3.42)ka间。这些晚第四纪构造变形单元分布在基岩山前以南约750 m的范围内,因此,在该区进行地震地质灾害评价时应考虑此类构造变形。

The Shizigou fault situates at the south limb of Yingxiongling uplift in the Southwestern Margin of Qaidam Basin. It is significant to analyze late quaternary tectonic deformation of the fault for hazard mitigation and understanding tectonic deformation in this zone. By investigating the Shizigou anticline frontal tectonic geomorphology,we have cleared a fault profile on the west side of the Shizigou No. Ⅱgully mouth,and excavated four trenches in the southwest limb of the small anticline in the frontal basin. Based on these data,we focus on analyzing the late quaternary tectonic deformation of the fault zone. The results show that the Shizigou fault is a Holocene active fault with southwest-verging reverse motion. The slip of the Shizigou fault can be divided to two parts. One part expresses along the boundary between basin and Shizigou anticline which offsets early-middle Holocene formation. The minimum of vertical slip rate of this branch of fault is about 0. 12 ～ 0. 15 mm/a since middle period of late Pleistocene. And the other part transports into basin which produce some small monoclines and small anticlines southwest of the Shizigou fault. The most recent one-stage stick-slip event likely occurred between（ 97. 93 ± 7. 98） ka and（ 59. 43 ± 3. 42） ka. These tectonic deformation units display about 750 m south of the Shizigou fault and should be taken into consideration when seismic safety evaluation is carried out in this area.