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三关口-牛首山断裂的运动学特征对认识青藏高原东北缘弧形构造带的扩展具有重要意义.在野外调查的基础上,通过大比例地质填图、典型地貌测量和沉积地层年代测定等方法,确定该断裂是一条具有明显右旋走滑特征的断裂,而非前人认为的左旋走滑断裂.研究发现,形成于古生代、中生代、新生代的地质界线均被断层右旋错动,断错位移相近,消除地形效应后确定的断裂最大走滑位移为(961±6)m.断裂北段的三关口断裂具有明显的新活动特征,一系列小冲沟跨断裂发生了同步右旋扭动,获得的断裂晚第四纪以来平均水平滑动速率约0.35mm/a.而形成于上新世末的先存褶皱构造被断裂错断异位,表明断裂的右旋走滑不早于上新世末.利用最大位移和平均滑动速率估算的断裂起始右旋走滑时间在2.7Ma之后.结合前人对高原东北缘扩展的认识,根据褶皱变形和断裂活动的先后关系分析,在上新世末(~2.7Ma),青藏高原的北东扩展到达三关口-牛首山一带,导致该区域地层发生广泛的褶曲变形和区域性抬升;到第四纪初,受青藏高原东北向推挤和鄂尔多斯地块逆时针旋转的联合作用,三关口-牛首山断裂开始右旋走滑活动,形成了青藏高原东北缘弧形构造带扩展的最前缘边界.
The kinematic characteristics of the Sanmenkou-Niuoshoushan fault are of great significance for understanding the extension of the arc structural zone in the northeastern margin of the Qinghai-Tibet Plateau.Based on the field surveys, through the methods of large-scale geological mapping, typical geomorphologic measurements and dating of sedimentary strata , It is determined that the fault was a fault with obvious dextral strike-slip feature rather than the left-lateral strike-slip fault believed by predecessors.It is found that the geological boundaries formed in Paleozoic, Mesozoic and Cenozoic are all dextralized by faults The maximal strike-slip displacement of the fault was (961 ± 6) m after the relief effect was eliminated. The Sanjuankou fault in the northern segment of the fault had obvious new activity features. A series of small strike-slip dextral torsion The average horizontal slip rate since the Late Quaternary was about 0.35mm / a. The precession fold formed at the end of the Pliocene was fractured and ectopic, indicating that the dextral strike-slip of the fracture was not earlier than that of the upper The Late Pleistocene strike-slip time estimated by the maximum displacement and average slip rate after 2.7 Ma, combined with the previous understanding of the extension of the northeastern margin of the plateau, according to the order of fold deformation and fault activity Analysis shows that at the end of the Pliocene (~ 2.7 Ma), the northeastern extension of the Qinghai-Tibet Plateau reached the area of San Guan Kou - Niushou Mountain, resulting in extensive fold deformation and regional uplift in this area. By the early Quaternary, Northeastward thrust and anticlockwise rotation of the Ordos block, the right-lateral strike-slip event begins at the Sanmenkou-Niuoshoushan fault, forming the forefront boundary of the extension of the arc structural zone in the northeastern margin of the Qinghai-Tibet Plateau.