祁连山昌马断裂晚更新世滑动速率

STUDY ON THE SLIP RATE OF CHANGMA FAULT IN QILIAN MOUNTAINS SINCE LATE PLEISTOCENE

河西走廊-祁连断裂系、阿尔金断裂和海原断裂共同控制着青藏高原的东北边界及其变形模式。昌马断裂为河西走廊-祁连断裂系中一条活动强烈的走滑断裂带,其连接着阿尔金断裂和海原断裂。基于昌马断裂的活动特征和几何分布将其分为4段,并获取了其中3段的左旋滑动速率,分别为西段(1.33±0.39)mm/a、中西段(3.11±0.31)mm/a、中东段(3.68±0.41)mm/a,以及西段的缩短速率(0.70±0.20)mm/a。结果显示,昌马断裂的左旋滑动速率由西向东具有明显增大的趋势。昌马断裂的活动调节了阿尔金断裂约30%滑动速率减小量。研究证实了昌马断裂与祁连山西段其他次级断裂的左旋滑动、地壳缩短和盆地内部变形共同承担着阿尔金断裂东段多数的左旋位移,这种构造转换模式支持青藏高原东北缘是具有侧向挤出的地壳持续增厚模式。

The Hexi Corridor-Qilian Fault systems,the Ahyn Tagh Fault and the Haiyuan Fault jointly control the north boundary and deformation of the Qinghai-Tibet plateau.The Changma Fault,as one of the Hexi Corridor-Qilian Fault systems,is a highly active strike-slip fault,and connects the Ahyn Tagh Fault and the Haiyuan Fault.Based on the active characteristics and geometrical distribution,this fault is divided into four segments.We obtain the left-lateral strike-slip rates of three segments,which are 1.33±0.39mm/yr at the west segment,3.11 ±0.31mm/yr at the middle-west segment,and 3.68±0.41mm/ya at the middle-east segment,respectively,and the shortening rate at the west segment （0.70±0.20mm/yr）.The result shows that the sinistral slip rate of the fault is significantly increased from west segment to east segment.The activity of Changma Fault accommodates ～ 30％ reduction of Altyn Tagh Fault slip rate.The studies in this paper confirm that the sinistral slip and shortening of Changma Fault and other secondary faults in accompany with deformation inside the basin absorb most of displacement of east segment of Altyn Tagh Fault,and this structural change mode supports the hypotheses that the northeastern margin of Qinghai-Tibet plateau has a continuous crust thickening mode with lateral displacement.