青藏高原中部NE向其香错断裂全新世左旋走滑速率及其构造意义

HOLOCENE SLIP RATE ALONG THE NE-TRENDING QIXIANG CO FAULT IN THE CENTRAL TIBETAN PLATEAU AND ITS TECTONIC IMPLICATIONS

青藏高原中部NE向断裂滑动习性的研究缺失制约着我们对青藏高原中部变形模型的理解。文中选取In SAR结果为右旋走滑的NE向其香错断裂为研究对象,通过Google Earth卫星影像解译,选取了1个典型断错地貌点,利用无人机航拍结合RTK-GPS地面控制点测量获取了高精度、高分辨率的DEM,利用La Di Caoz_v2. 1软件自动提取的T2地貌面上最大冲沟的水平左旋位错为(21. 3±7. 1) m,跨断层陡坎剖面揭示了T2地貌面的垂直位错量为(0. 9±0. 1) m。在T2地貌面上采集的2个U系测年样品的年龄分别为(4. 98±0. 17) ka和(5. 98±0. 07) ka。上述数据约束了其香错断裂全新世左旋走滑速率约为(3. 56±1. 19) mm/a,垂向滑动速率约为(0. 15±0. 02) mm/a。其香错断裂左旋走滑带有倾向分量的运动学特征与青藏高原中部地壳物质向E运移的特征相符合,其运动速率与其共轭断裂(格仁错断裂)基本一致,显示出青藏高原中部变形样式符合共轭走滑断裂模式。

The two mainstream deformation models of the Tibet plateau are continental escape model and crustal thickening model,the former suggests that the NW-trending Karakoram Fault,Gyaring Co Fault,Beng Co Fault and the Jiali Fault as the Karakoram-Jiali fault zone is the southern border belt and that the dextral strike-slip rate is estimated as up to 10~20mm/yr.However,research results in recent years show that the slip rates along those faults are significantly less than earlier estimates.Taylor et al.(2003)suggest that the conjugate strike-slip faults control the active deformation in the central Tibet.The lack of research on the slip behavior of the NE-trending faults in the central Tibet Plateau constrains our understanding of the central Tibet deformation model.Thus,we choose the NE-direction Qixiang Co Fault located at the north of the Gyaring Co Fault as research object.Based on the interpretation of satellite images,we found several faulted geomorphic sites.Using RTK-GPS ground control point and unmanned aerial vehicle(UAV)topographic surveying,we obtained less than 10cm/pix-resolution digital elevation model(DEM)in the Yaqu town site.We used the LaDiCaoz_v2.1 software to automatically extract the left-lateral offset of the largest gully on the terrace T 2 surface,which is(21.3±7.1)m,and the vertical dislocation of the scarp on the terrace T 2 surface,which is(0.9±0.1)m.The age of both U-series dating samples on the terrace T 2 is(4.98±0.17)ka and(5.98±0.07)ka,respectively.The Holocene left-lateral slip rate along Qixiang Co Fault is(3.56±1.19)mm/a and the vertical slip rate is(0.15±0.02)mm/a.The kinematic characteristics of the sinistral strike-slip with normal slip coincide with the eastward motion of the central Tibet plateau,and its magnitude is in agreement with its conjugate Gyaring Co Fault,suggesting that the deformation pattern of the central Tibetan plateau complies with the conjugate strike-slip faults mode.