青藏高原东北缘固关-虢镇断裂中段第四纪以来活动特征

固关-虢镇断裂是青藏高原东北缘、鄂尔多斯地块西南缘陇县-宝鸡断裂带中的一条主要断裂，该断裂的运动特征和活动性包含了青藏高原向东北方向扩展机制的重要信息。固关-虢镇断裂中段在卫星影像和DEM图上都显示出清晰的线性影像特征，地貌上表现为清楚的地貌陡坎，陡坎高80～100 m。通过卫星影像判读、野外调查、探槽开挖和年龄测试等方法的综合研究，结果认为固关-虢镇断裂中段第四纪早期有明显活动，并以左旋走滑运动为主，左旋走滑运动利用了早白垩世形成的正断层面；晚更新世以后固关-虢镇断裂停止了活动。造成断裂运动方式和活动性转变的原因是，第四纪以来印度-欧亚大陆碰撞的远程效应到达青藏高原东北缘之后，陇县-宝鸡断裂带周围的块体因为相互作用进行调整，形成了该断裂带局部构造应力以剪应力为主所致。

The active characteristics in the Quaternary period of the middle Guguan-Guozhen fault,northeast margin of Qinghai-Tibet Plateau

Guguan-Guozhen fault is one of the important faults of Longxian-Baoji fault zone, which marks the boundary of NE margin of the Tibetan Plateau and the SW margin of the Ordos block. The temporal and spatial patterns of the fault record vital information of the northeastward expansion of the plateau. The middle Guguan-Guozhen fault presents a clear linear feature on satellite and DEM images. On geomorphologic, the fault presents 80～100 m surface scarp. Multiple research methods including interpretation of satellite images, field investigation, trench excavations, and dating techniques are applied, the results show that the middle Guguan-Guozhen fault was active at the Early Quaternary and mainly conduct sinistral strike-slip faulting activity, which made use of the fault plane formed at the Early Cretaceous. After the Late Pleistocene, the fault stopped faulting activity. The cause of the transform of the fault behavior is that, the regional tectonic stress was changed because of the sub-blocks around the fault zone were adjusted for interactions after the remote effect of the Cenozoic India-Eurasia collision reached the NE margin of Tibetan Plateau, and the regional stress field of the study area turned into shearing stress since Quaternary.