内蒙古狼山山前台地成因及其新构造运动意义

Genesis of Piedmont Terraces and Its Neotectonic Movement Significance in Langshan Mountain Area,Inner Mongolia

内蒙古狼山地处阴山造山带西段、河套断陷带的西北缘,晚新生代以来狼山山前断裂广泛发育、构造抬升强烈。研究晚更新世以来狼山的构造隆升对深入了解河套断陷带的形成演化机制及其隆升过程对河套盆地古地理格局的影响具有重要的意义。狼山山前翁格勒其格和乌兰敖包台地的沉积学、地貌学和年代学研究表明,T1台地形成于47.4kaB.P.,其沉积物为晚更新世河套古大湖沉积;T2台地形成于69 kaB.P.,其沉积物可能为黄河流经狼山山前的冲积物。台地特征的分析显示,狼山山前台地主要由构造抬升形成,两级台地记录了狼山晚更新世晚期(Qp3-2)以来的构造隆升过程。69 kaB.P.到47.4 kaB.P.翁格勒其格和乌兰敖包地区的隆升速率分别为1.34 m/ka和1.25 m/ka,47.4kaB.P.以来分别为0.81 m/ka和1.18 m/ka,狼山南段(翁格勒其格地区)构造抬升有减小的趋势。晚更新世晚期(Qp3-2)以来由于狼山的快速隆升,导致黄河河道不断东迁,河套平原的古河道是其迁移的证据。狼山山前湖岸阶地的研究进一步证实晚更新世晚期河套地区发育统一古大湖。

Langshan Mountain is located in the western segment of Yinshan orogenic belt and the northwestern margin of the Hetao rift zone in Inner Mongolia.Piedmont faults and tectonic uplifts in this region developed widely since the Late Cenozoic.The research on the tectonic uplift process of Langshan Mountain since the Late Pleistocene has significance in having a good knowledge of the formation and evolution mechanism of Hetao rift zone and the influence of the uplift process to the paleogeographic framework of Hetao basin.The sedimentologi-cal,geomorphological and geochronological study of the piedmont terraces in Wenggeleqige and Ulaan Ovoo,in-dicates that T1 terrace formed at 47.4 kaB.P. is characterized by lacustrine deposits from Hetao megalake,and T2 terrace developed at 69 kaB.P. is characterized by fluvial deposits which may be the products of the Yellow River when it flows through the pediment of Langshan Mountain.The analysis on characteristics of terraces shows that the two terraces are mainly tectonic genesis.Therefore,the two terraces recorded the rapid uplift process in Langshan Mountain after 69 kaB.P.Between 69 kaB.P. and 47.4 kaB.P. the time-averaged uplift rates in Wenggeleqige and Ulaan Ovoo were 1.34 m/ka and 1.25 m/ka,respectively,and the uplift rates were 0.81 m/ka and 1.1 8 m/ka during the past 47.4 kaB.P.,respectively suggesting that the uplift rate have a de-creasing trend in the southwest part of Langshan Mountain (Wenggeleqige region).Since the late Late Pleisto-cene (Qp3-2 ),the rapid uplift of the Langshan Mountain led to east moving of the Yellow River continuously by the evidence of the ancient channel on Hetao plain.The research on the lake terraces in Langshan Mountain fur-ther confirmed the existence of the Hetao megalake in Late Pleistocene.