阴山西段河流阶地发育的年代序列及其对构造隆升的指示意义

摘要

阴山位于河套断陷带北部,晚新生代以来,构造运动非常活跃,阴山持续不断隆起,河套随之不断下陷,作为地貌响应之一,阴山河谷中发育了一系列河流阶地.本文通过详细的野外地质调查,结合地貌学、沉积学及年代学方面的研究,厘定了阴山西段河谷普遍发育的4～5级河流阶地;并利用光释光(OSL)测年方法,恢复了其堆积-下切历史,建立了河流阶地年代框架:T4、T3、T2、T1级阶地大致形成时间分别为58.00 ka BP、46.25 kaBP、32.19ka BP、15.79ka BP之后;分析了本区河流阶地的成因:阴山的构造隆升为本区河流下切提供动力基础,是形成河流阶地的主要驱动力,气候变化通过改变水流流量与沉积物通量的比率影响阶地的堆积-下切行为的转换,是河流阶地形成的重要影响因素;进而利用河流侵蚀速率差异性讨论了晚更新世以来阴山西段的构造隆升模式:51.61～41.28 ka BP之间,阴山西段隆升以中部高于东西部的穹窿式差异性隆升为主,23.22 ka BP之后,阴山西段的隆升区段差异性减小,趋向于整体隆升.%Located at the northern part of the Hetao fault basin,Yinshan Mountains had uplift and Hetao basin subsided intermittenty since late Cenozoic.As an important geomorphology response to the tectonic,the river terraces developed well in this area.Based on a detailed field geological survey and the optically stimulated luminescence (OSL) dating,we designated 4～5 fluvial terraces in the transverse drainage of the western Yinshan mountains,and the terraces T4 through T1 experienced four intermittent aggradation stages during the periods of approximately 79.65～58.00,51.61～46.25,41.28～32.19,and 23.22～15.79 ka BP respectively,and incision stages during the periods of 58.00～51.61,46.25～41.28,32.19～23.22,and 15.79 ka BP～ the present,respectively.We also discussed the mechanism of the river terraces,which formed by the combined actions of climatic shifts and tectonic uplift.Tectonic uplift was a driving force for river downcutting,and the climate change was an important fact or influencing the aggradation of the terraces.And we analysed the uplift mode by the river incision rates:the Yinshan Mountains uplift higher in the middle section than the eastern and western section during the period of 58.00～41.28 ka BP,and after about 32.19 ka BP,the western Yinshan tended to up lifte overall with uplift difference decroased.