【摘要】 三危山断裂为阿尔金断裂带东段的重要分支,位于青藏高原北缘北向扩展的前缘位置,为一条左旋走滑兼逆冲的活动断裂。通过卫片解译和野外实际调查,发现三危山主断裂穿过鸣沙山后,向西至党河水库及阳关镇附近以断层陡坎的形式出露地表。由阳关镇段向西至党河水库段,穿过鸣沙山至三危山主断裂,断层陡坎的形态由复杂变简单,落差基本集中于2～6m,但呈现逐渐减小的趋势,水平位移量也逐渐变小,反映了断裂活动强度由西向东逐渐减弱的特点。探槽和剖面解译结果显示,该段断裂错断下更新统玉门组(Qp~1)砂岩和砾岩、中更新统酒泉组(Qp~2)砂砾石层以及上更新统(Qp~3)冲洪积砂砾石层。卫片解译、野外实地调查和深部大地电磁(MT)剖面的解译结果表明,南截山断裂向西在莫高窟南侧与三危山断裂交汇,二者在深部向阿尔金断裂收敛,上述三条断裂共同构成区域挤压性非对称半正花状构造。高原北缘的扩展是通过一系列北东-南西向走滑断裂活动及其所夹地块向北东运动和挤压实现。更多还原

【Abstract】 The Sanweishan fault, an important branch of the eastern segment of the Altyn Tagh fault and located in the leading edge of the northwestern Tibet Plateau is a left-lateral strike-slip and thrusting activity. Field investigation and satellite image interpretation reveals that the main fault, after crossing through Mingsha Mountain, continues to extend westward and finally crops out in Danghe water reservoir segment(DHRS) and Yangguan County in the form of fault escarpment. The length of DHRS is almost 16 km, strikes near 90°. Morphology of the fault escarpment changes from simple to complicated with the fault crossing Yangguan County westward to DHRS and from Mingsha Mountain to Sanwei Mountain. The difference of the escarpment ranges from 2 to 6 m, but it tends to decrease and horizontal displacement also reduces. All of these phenomena reflect that the intensity of fault activity weakens gradually from west to east. The results of trenching and section interpretation show that the fault offsets the Lower Pleistocene sandstone and conglomerate(Yumen Formation, Qp~1), the Middle Pleistocene gravel layers(Jiuquan Formation) and the Upper Pleistocene alluvial gravels. Satellite image interpretation, field investigation and magnetotelluric profiles indicate that the Nanjieshan fault intersects with the Sanweishan fault on the south side of the Mogao Grottoes, and the two faults merge to the Altyn Tagh fault at depth. The above three faults constitute an asymmetric positive half-flower structure with regional compression. The extension of the northern margin of the plateau may result from the activities of an array of NE-SW strike-slip faults and the northeast movement of the blocks between those faults.更多还原