中国西南三江河流碎屑锆石U-Pb年代学和Hf同位素研究及其地质意义

发布时间：2018-02-27 08:17

本文关键词： 河流碎屑锆石中国西南青藏高原 U-Pb年龄 Hf同位素　出处：《中国地质大学(北京)》2015年硕士论文　论文类型：学位论文

【摘要】：目前,地质学的一个热点课题即探讨大陆地壳的形成机制及其演化过程。近年来,越来越多的地质工作者致力于分析河流碎屑锆石,从而探讨大陆地壳的形成机制与演化过程。青藏高原位居全球之巅,国内外学者都非常重视它是如何形成,又具有怎样的演化历程。中国西南三江分别是:金沙江、澜沧江、怒江。三条江沿着三条缝合带流淌,分别是:班公湖-怒江缝合带、龙木错-双湖-澜沧江缝合带和西金乌兰-金沙江缝合带。三条缝合带是松潘-甘孜地块、北羌塘-昌都地块、南羌塘-保山地块及拉萨地块之间的界限。我们通过对金沙江、澜沧江、怒江河流沉积物锆石的U-Pb年龄结果来探讨三条江可能的源区,源区重大地质事件发生的时间,相邻地块的碰撞拼贴时间,以及古特提斯洋的形成演化历史;通过对金沙江、澜沧江、怒江河流碎屑锆石的Hf同位素研究来探讨源区新生地壳的产生时间,及形成历史演化。本文获得的认识有下面4点:1)金沙江河流沉积物U-Pb年龄分为5个阶段:98Ma,175~355 Ma,402~639 Ma,730~1200 Ma和1409~3160Ma。主要年龄峰值为229 Ma,832 Ma,1722和2487Ma。澜沧江河流沉积物U-Pb年龄分为5个阶段:177 Ma,201~418 Ma,428~544 Ma,581~1189 Ma和1406~2533 Ma。主要年龄峰值为260 Ma,788 Ma,1827 Ma和2474 Ma。怒江河流沉积物U-Pb年龄分为6个阶段:50~74 Ma,84~235 Ma,275~413 Ma,451~569 Ma,657~1429Ma,1602~3436 Ma。主要峰值年龄为65 Ma,110 Ma,500 Ma和900 Ma。2)金沙江和澜沧江河流碎屑锆石的源区可能都是北羌塘地块,怒江河流碎屑锆石的源区主要是中拉萨地块,北拉萨地块可能为其提供了很少的物质。3)金沙江洋盆于早石炭世打开,并于石炭纪持续扩张,二叠纪进入消减阶段,早、中三叠世羌塘地块与松潘-甘孜地块碰撞拼贴,大洋闭合的时间是晚三叠世。澜沧江洋盆的开裂时间为泥盆纪-早石炭世,发展到最大面积是在早二叠世,经历了俯冲消减之后,南、北羌塘地块碰撞拼贴,洋盆最终于晚三叠世末封闭。怒江洋盆于三叠纪形成并和拉萨地块碰撞,早白垩世俯冲结束,拉萨地块与羌塘地块连接在一起。4)金沙江和澜沧江河流碎屑锆石的Hf二阶段模式年龄可以共同限定北羌塘地块的形成演化历史。新太古代-中元古代,是北羌塘地块从亏损地幔物质增生到地壳的持续生长阶段,此阶段增生的地壳物质构成现今北羌塘地块全部地壳物质的70%以上。中拉萨地块东段的形成与演化历史由怒江河流碎屑锆石Hf二阶段模式年龄得出,地壳最为快速的增生时期是在2.0~1.2 Ga之间。
[Abstract]:At present, a hot topic in geology is to study the formation mechanism and evolution process of continental crust. In recent years, more and more geologists have devoted themselves to the analysis of river detrital zircon. Therefore, the formation mechanism and evolution process of the continental crust are discussed. The Qinghai-Tibet Plateau is at the top of the world, and scholars at home and abroad attach great importance to its formation and evolution. The three rivers in southwest China are the Jinsha River and the Lancang River, respectively. Nujiang River. The three rivers flow along three suture zones, namely, the Bangonghu and Nujiang suture zones, the Longmuco-Shuanghu-Lancang River suture zone and the Xijin Wu Lan Jinsha River suture zone. The three suture zones are the Songpan-Ganzi block. The boundary between the northern Qiangtang Changdu block, the southern Qiangtang Baoshan block and the Lhasa block. The U-Pb age results of zircon from sediments of Jinsha, Lancang and Nujiang rivers are used to study the possible source regions of the three rivers. The time of major geological events in the source area, the time of collision and collage of adjacent blocks, and the history of the formation and evolution of the ancient Tethys ocean. HF isotopic study of detrital zircon from the Nujiang River to study the time of the birth of the new crust in the source region, The U-Pb age of Jinsha River sediment is divided into five stages: 9: 1) the U-Pb age of Jinsha River sediment is divided into five stages: 9: 98 Ma, 175,355 Ma-402U 639 Ma, 7301200Ma and 1409 Ma, 3160 Ma. The main age peaks are 229 Ma, 832 Ma, 1722 and 2487 Ma. the U-Pb age of the sediments of the Jinsha River is divided into five stages. The U-Pb age of the sediments of the Jinsha River is divided into five stages. The U-Pb age of the sediments of the Jinsha River is divided into 5. The main age peaks are 260 Ma, 788 Ma, 1827 Ma and 2474 Ma. The U-Pb age of the Nujiang River sediment is divided into six stages, the U-Pb age of the Nujiang River is divided into 6 stages, namely, the U-Pb age of the Nujiang River, consisting of 6 stages, namely, the U-Pb age of 275413 Ma451 569 Ma 657 1429 Ma 1602N 3436. The main peak age is 65 Ma110 Mai 500 Ma and 900 Ma.2) the Jinsha River and Lancang rivers. The source region of the detrital zircon may be the northern Qiangtang block. The source region of the detrital zircon of the Nujiang River is mainly the Middle Lhasa block, and the northern Lhasa block may have provided it with very little material .3) the Jinsha River ocean basin opened in the early Carboniferous and continued to expand during the Carboniferous, and the Permian period entered the stage of subduction. The middle Triassic Qiangtang block collided with the Songpan-Ganzi block, and the time of ocean closure was the late Triassic. The cracking time of the Lancang River ocean basin was Devonian and early Carboniferous, and the largest area developed in the early Permian. After subduction, the southern and northern Qiangtang blocks collide and collage, and the ocean basin is finally closed at the end of the late Triassic. The Nujiang ocean basin formed in the Triassic and collided with the Lhasa block, and the early Cretaceous subduction ended. The HF two-stage age of zircon from the Jinsha and Lancang rivers can jointly define the formation and evolution history of the northern Qiangtang massif. It is a stage of sustained growth from depleted mantle material to crustal growth in the northern Qiangtang block. The formation and evolution history of the eastern segment of the Middle Lhasa block is derived from the age of detrital zircon HF model of the Nujiang River. The fastest period of crustal growth is between 2.0 and 1.2 Ga.
【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】：P597.3;P588.21

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