藏南亚东帕里盆地的沉积演化及其构造意义

发布时间：2018-01-31 04:42

本文关键词： 晚新生代近南北向裂谷帕里盆地沉积演化构造意义　出处：《中国地质大学(北京)》2017年硕士论文　论文类型：学位论文

【摘要】：帕里盆地位于亚东-谷露裂谷最南端,是藏南近南北向裂谷系中少有的出露较好晚新生代沉积地层的盆地,该盆地的沉积地层记录了亚东-谷露裂谷构造演化过程,能够在一定程度上反映藏南近南北向裂谷系的发展演化以及高原的隆升特征。本文对帕里盆地晚新生代地层进行了详细的沉积特征分析和沉积相划分,同时对地层进行了古地磁年代学研究,在此基础上划分出了盆地的沉积演化阶段,并对其构造意义进行了分析。本文取得的主要认识如下:1.在盆地中出露的海拔较低的砂-泥层与海拔较高的砂-砾石层的新老问题上,本文通过野外详细地质调查,发现海拔较低的砂-泥层顶部与海拔较高的砂-砾石层底部都为一层浅黄色的胶结不好的砂质层,且两者产状基本一致,都微向北倾,说明海拔较低的砂-泥层下伏于海拔较高的砂-砾石层。2.通过对出露地层岩性特征及其组合、沉积构造等进行综合分析,共识别出湖泊相、湖泊扇三角洲相、冲积扇相三种沉积相。其中湖泊相主要发育于出露地层下部;湖泊扇三角洲相发育于中部,包括水退型与水进型湖泊扇三角洲相;冲积扇相发育于出露地层的顶部。3.通过古地磁年代学研究,发现出露地层主要为晚中新世-早更新世沉积,沉积时代为7.5-2.5 Ma。由于出露地层未见底,说明帕里湖盆发育于7.5 Ma之前。约2.5 Ma盆地开始发育一套厚度100m的冲积扇相砾岩,标志湖盆的消亡。4.根据盆地出露地层沉积特征以及古地磁年代结果,帕里湖盆沉积演化可以划分为5个沉积阶段,分别为盆地初始形成阶段(约13 Ma)、湖泊扩张阶段(7 Ma)、湖泊收缩阶段(7-3.5 Ma)、湖泊再次扩张阶段(3.5-2.5 Ma)以及湖泊消亡阶段(2.5Ma)。5.通过帕里盆地的沉积演化分析,结合高原隆升与近南北向裂谷系相关资料,本文认为:约13 Ma是藏南裂谷系形成和发育的高峰期,同时也是高原快速隆升期;7.5-7Ma,帕里盆地处于构造平静期,区域上没有强烈的构造运动;7-3.5 Ma帕里盆地以及周边孔错-当惹雍措裂谷、错那-沃卡裂谷、定结-申扎裂谷都处于构造活动状态,是藏南近南北向裂谷系进一步发育的时期;约2.5 Ma帕里湖盆沉积格局的极大变化,说明盆地受到强烈构造运动,联系到高原在约3 Ma气候明显变化,说明2.5-3 Ma是高原强烈隆升期,且隆升幅度较大,并隆升到了影响气候的高度。
[Abstract]:The Pali basin is located at the southernmost end of the Yadong-Gulu rift. It is a basin with relatively good late Cenozoic sedimentary strata which is rare in the south-to-north rift system of southern Tibet. The sedimentary strata of the basin record the tectonic evolution of the Yadong-Gulu rift. To a certain extent, it can reflect the evolution of the NNW rift system and the uplift characteristics of the plateau. In this paper, the late Cenozoic strata in the Pali Basin are analyzed and the sedimentary facies are classified in detail. At the same time, the paleomagnetic chronology of the strata is studied, and the sedimentary evolution stage of the basin is divided on this basis. The main understanding of this paper is as follows: 1. The new and old problems of sand-mud bed with lower elevation and sand-gravel bed with higher elevation are exposed in the basin. Through the detailed geological investigation in the field, it is found that the top of the sand and mud layer at lower altitude and the bottom of the sand gravel layer at higher altitude are both a layer of light yellow sand layer with poor cementation, and the occurrence of the two layers is basically the same. It is indicated that the sand-mud bed with lower altitude is located in the sand-gravel bed at higher altitude. 2. The lacustrine facies are identified by comprehensive analysis of lithologic characteristics of exposed strata and their assemblages, sedimentary structures and so on. The lacustrine fan delta facies and alluvial fan facies are three sedimentary facies. The lacustrine fan delta facies is developed in the middle, including the receding and advancing lake fan delta facies. The alluvial fan facies developed at the top of the outcrop. Through paleomagnetic chronological study, it was found that the exposed strata were mainly late Miocene and early Pleistocene deposits. The sedimentary age is 7.5-2.5 Ma. The results show that the Pali lake basin developed before 7.5 Ma and developed a set of alluvial fan facies conglomerates 100 m thick in about 2.5 Ma basin. According to the sedimentary characteristics of outcrop strata and paleomagnetic age, the sedimentary evolution of Pali lake basin can be divided into five sedimentary stages. They are the initial formation stage of the basin (about 13 Ma), the lacustrine extension stage (7 Ma), and the lake contraction stage (7-3.5 Ma). Lake re-spreading stage 3.5-2.5 Ma) and lake dying stage 2.5 Ma.5.The sedimentary evolution of the Pali basin is analyzed. Based on the data of the uplift of the plateau and the near-South-North rift system, this paper holds that about 13 Ma is the peak period of the formation and development of the southern Tibetan rift system, and it is also the period of rapid uplift of the plateau; 7.5-7 Ma, the Pali basin is in the period of structural calm, there is no strong tectonic movement in the region; The 7-3.5 Ma Pali basin and its surrounding hole fault-the Yayongcuo rift, the Thona-Woca rift and the Dingzhen-Shenza rift are all in the tectonic active state, which is the period of further development of the NNW rift system in the south of Tibet; The great variation of sedimentary pattern in the Pali lake basin at about 2.5 Ma indicates that the basin was strongly tectonic, and the climate of the plateau changed obviously at about 3 Ma. It is suggested that 2.5-3 Ma is a strong uplift period in the plateau, and the uplift is relatively large, and the uplift reaches the height that affects the climate.
【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】：2017
【分类号】：P512.2;P548

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