银川盆地东南缘面子山—清水营断裂活动性

Activity of the Mianzishan-Qingshuiying fault in the southeast margin of the Yinchuan basin

研究银川盆地的构造活动特征对于认识青藏、鄂尔多斯和阿拉善3大地块的相互作用具有重要意义。银川盆地东南缘的面子山—猪头岭一带地形高差显著,影像上线性明显,可能发育一条未知的活动断裂。本文沿面子山—清水营一线开展了野外地质调查、探槽开挖和地层年代测试等工作,结果表明:银川盆地东南缘发育面子山—清水营断裂,全长50 km,以猪头岭北为界,分为面子山断层和清水营断层两段。面子山断层以高角度正断为主,断层擦痕显示具有左旋走滑运动,走向北东,跨断层数条冲沟显示具有左旋扭动特征;而清水营断层则表现为逆断层,走向北东东,发育陡坎地貌。该断裂断错了(23.65±1.17) ka BP和(33.16±1.82) ka BP的沉积地层,表明断裂最新活动时代为晚更新世晚期。该断层的发现表明,鄂尔多斯地块的西北边界复杂,构造变形带较宽,且不严格的受控于断陷盆地的边界断裂,其构造变形已扩张到地块一侧,这可能与青藏高原持续向东北向的推挤扩展有关。

Studying the tectonic activity characteristics of the Yinchuan basin is of great significance for understanding the interaction among the three major blocks of Qinghai Tibet,Ordos and Alxa.The terrain elevation difference in the Mianzishan-Zhutouling area on the southeastern margin of the Yinchuan basin is significant,and the linear trace on satellite image is obvious,indicating the development of an unknown active fault.This article conducted field geological surveys,trench excavation and stratigraphic dating along the Mianzishan-Qingshuiying line.The results showed that the linear trace along the Mianzishan-Qingshuiying line had been dominated by fault,which was developed on the southeastern margin of the Yinchuan basin with a total length of 50 km.It is divided into two segments,the Mianzishan fault and the Qingshuiying fault.The Mianzishan fault is mainly characterized by high angle normal faults,the scratches on the fault surface show a sinistral strike slip motion,heading northeast,several gullies across the fault layer display left-handed twisting characteristics.The Qingshuiying fault,on the other hand,exhibits a reverse fault trending NEE,developing steep slope landforms.The fault has displaced sedimentary strata deposited at(23.65±1.17)ka BP and(33.16±1.82)ka BP,indicating its latest activity was postdated by Late Pleistocene.The discovery of this fault indicates that the boundary of the northwestern Ordos block is a complex zone associated with a wide structural deformation zone.This zone is not strictly controlled by the boundary faults of Yinchuan basin,but expanded to interior of the Ordos block,which may be related to the continuous northeast pushing and expansion of the Qinghai Tibet Plateau.