河西走廊西段南北向左行逆冲活动断裂的发现及其意义

A SN-Trending Left-Slip Thrusting Active Fault in the Western Segment of Hexi Corridor,Gansu,NW China and It's Significance

在河西走廊西段酒西盆地中心偏北部的阴洼山西侧发现了南北走向的阴洼山西缘左行逆冲断裂。该断裂长约4km,近南北走向,倾向东,倾角中等,是发育于北西向阴洼山右行逆冲断裂近北西端部附近的一条次级活动断裂。沿该断裂奥陶系灰绿色浅变质砂岩逆冲于白垩系紫红色砂砾岩、新近系橘红色泥岩和晚第四纪上更新世末期松散坡积层(热释光年龄10.3ka)之上。在剖面上断裂表现为自东向西的逆冲作用,其最新一次新构造活动时间在全新世中晚期(距今3～5ka)。在平面上该断裂断错自东向西从阴洼山山体流水流向西侧低丘斜坡戈壁地带的小冲沟致使冲沟呈"S"形拐折,反映出断裂具有明显的左行走滑。该断裂沿断层面的左行斜冲总位移达3000m,其中垂向位移为1800m左右,与阴洼山断裂垂向位移及阴洼山隆升幅度相当。该断裂的形成是阴洼山断裂右行逆冲活动所引起的局部构造应力场作用的结果,也对阴洼山断裂右行逆冲所形成的巨大位移在短距离内起到了消减和平衡作用。

A SN-trending left-slip thrusting active fault has been found at the western Yinwashan margin in north of Jiuxi basin, western segment of Hexi corridor. The fault is about 4km long, extends SN-trending and dips to east at a middle angle. As a second-order active fault, the fault developed near the northwestern end of the NW-trending Yinwashan right-slip thrusting active fault, the grayish green Ordovician epimetamorphic fragmental rock has been thrusted along the fault up to the Cretaceous purplish red sandstone and conglomerate, Neogene tangerine mudstone and even upon the loose slop wash （TL dating is 10.3ka） of last stage of late Pleistocene. The fault shows a large trusting movement from the east to west in cross section and the last neo-structural activity occurred at the middle-late Holocene （about 3- 5ka BP）. It also offsets EW-trending gully from east Yinwashan Hill to west clinoform low hills or Gobi Desert and results in the gully curving as S-type in plane, which indicated the fault has an evident left-slip movement. The diagonal displacement along the fault plane is about 3000m and the vertical displacement is about 1800m, and the displacement is approximately equal to the vertical displacement of Yinwashan active fault or the uplifted height of Yinwashan Hill. The fault resulted from the partial structural stress field caused by the right-slip thrusting movement of the Yinwashan active fault. On the other hand, the large displacement of the Yinwashan active fault is balanced in a short distance by the right-slip thrusting movement of western Yinwashan SN-trending active fault.