六盘山东麓泾河上游河流阶地的形成年代及新构造运动意义

发布时间：2018-07-03 01:00

本文选题：六盘山 + 构造隆升　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：六盘山地区位于青藏块体东北部祁连断褶带与华北断块区西部鄂尔多斯块体之间的构造转换部位,是我国南北地震构造带北段的重要组成部分。六盘山由于受到青藏高原东北向侧向挤出作用的影响,发生强烈的构造隆升,并作为挤压应力支点推动鄂尔多斯地块发生逆时针旋转。六盘山是研究青藏高原东北缘隆升与构造变形的关键部位,其东麓泾河河流阶地是第四纪以来六盘山构造隆升的地貌载体。通过研究本文主要取得以下几点认识：(1)通过对泾河上游河流阶地的野外剖面实测,厘定了河流阶地的级序。泾河上游主要发育5级河流阶地T5-T1,不同地段阶地的形态类型不同,柳树沟T5、T4和T3为堆积阶地,T2和T1为基座阶地,高家山均为侵蚀或基座阶地。(2)利用光释光(OSL)、电子自旋共振(ESR)测年并与黄土-古土壤序列进行对比,建立了河流阶地的年代格架,T5-T1年代分别为541 ka B.P.、477 ka B.P.、 279 ka B.P.、60 ka B.P.和8 ka B.P。(3)通过对阶地的形态类型、形成年代与深海氧同位素气候曲线及黄土-古土壤序列的对应关系研究表明,气候变化可能控制河流堆积-切割行为的转换,构造运动控制侵蚀下切的幅度、为河流长期下切提供驱动力。(4)541～279ka B.P.柳树沟地区为堆积区,堆积速率为0.31m/ka,而位于柳树沟地区上游的高家山为构造隆升区,河流下切速率为0.37 m/ka,二者堆积速率与侵蚀速率基本一致,说明T5、T4和T3阶面上较厚的砾石层是六盘山隆升的相关沉积并共同为六盘山构造隆升速率进行了定量约束；279kaB.P.时期柳树沟隆升相对缓慢,接受六盘山隆升剥蚀的大量碎屑物质,处于沉积区,青藏高原继续向东挤压,六盘山向前扩展隆升,柳树沟地区转为隆升区,河流侵蚀作用加强,造成T2、T1平均下切速率增大为1.13 m/ka。因此,泾河柳树沟剖面的厚层砾石堆积正是对六盘山构造隆升的沉积响应,与之对应的高家山剖面在600～250ka B.P期间发生下切也是对六盘山隆升的响应,共同反映了此时六盘山扩展隆升过程。(5)计算陇西渭河与泾河上游阶地区域构造差异隆升速率,T5时期构造差异隆升速率△UT(max)、△UT(min)均为正值,说明六盘山西侧要比东侧隆升强烈,T4和T2阶段△UT(max)、△UT(min)均为负值,表明六盘山东侧比西侧隆升强烈。
[Abstract]:The Liupanshan area is located between the Qilian fault fold belt in the northeast of Qinghai-Tibet block and the Ordos block in the western part of the North China fault block, which is an important part of the northern segment of the north-south seismic tectonic belt in China. Due to the influence of lateral extrusion in northeast of Qinghai-Xizang Plateau, Liupanshan has a strong tectonic uplift, and as a fulcrum of compressive stress, the Ordos block rotates counterclockwise. Liupanshan is the key part to study the uplift and tectonic deformation of the northeastern margin of the Qinghai-Tibet Plateau, and its east foot Jinghe River terrace is the geomorphologic carrier of the Liupanshan tectonic uplift since the Quaternary. The main results of this paper are as follows: (1) the sequence of river terraces is determined by measuring the field profile of the river terraces in the upper reaches of Jinghe River. In the upper reaches of Jinghe River, there are mainly 5 grade river terraces T5-T1. The terraces in different sections are of different morphological types, and the accumulation terraces T2 and T1 are the base terraces in Liushugou, T5 T4 and T3, respectively. Gaojiashan is an erosion or pedestal terrace. (2) by means of optical luminescence (OSL) and electron spin resonance (ESR) dating and comparing with loess paleosol series, the chronological framework T5-T1 of the river terrace is 541 ka B.P., 477 ka B.P., 279 ka B.P.60 ka B.P. respectively. And 8ka B.P. (3) the relationship between the age of formation and the oxygen isotopic climate curve of deep sea and the loess paleosol sequence through the morphological types of terraces shows that climate change may control the transition of deposition and cutting behavior of rivers. Tectonic movement controls the extent of erosion undercutting, which provides a driving force for the long-term downcutting of rivers. (4) 541~279ka B.P. The accumulation rate is 0.31 m / ka in Liushugou area, and the tectonic uplift area is Gaojiashan in the upper reaches of Liushugou area, and the river cutting rate is 0.37 m / ka. The accumulation rate and erosion rate are basically the same. The results show that the thicker gravel layers on the T _ 5 / T _ 4 and T _ 3 terraces are the relative deposits of Liupanshan uplift, and the quantitative constraints for the uplift rate of Liupanshan tectonic are given in this paper at 279kaB.P. In this period, the Liushugou uplift was relatively slow, and a large amount of debris material, which accepted the denudation of Liupanshan uplift, was in the sedimentary area. The Qinghai-Xizang Plateau continued to squeeze eastward, Liupanshan extended and uplifted forward, the Liushugou area was transformed into a uplift area, and the river erosion was strengthened. As a result, the average down-cutting rate of T _ 2 T _ 1 was increased to 1.13 m / KA. Therefore, the thick gravel accumulation in the Liushugou section of Jinghe is the sedimentary response to the Liupanshan tectonic uplift, and the corresponding Gaojiashan section is also the response to the Liupanshan uplift during the 600~250ka B.P. It reflects the extended uplift process of Liupanshan Mountains at this time. (5) the differential uplift rate of UT (max), UT (min) of Weihe River and Jinghe upper terraces is positive in T5 period. It shows that the west side of Liupanshan is stronger than the east side of T4 and the UT (max), UT (min) of T2 stage is negative, which indicates that the east side of Liupanshan is stronger than the west side of Liupanshan.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P546;P931

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