中国松潘甘孜地块通天河流域碎屑锆石U-Pb年代学和Hf同位素研究

发布时间：2018-12-11 21:57

【摘要】：河流碎屑沉积物碎屑锆石U-Pb定年、Lu-Hf分析和微量元素等微区分析,已经成为探索大陆地壳起源和演化最重要的方法,本文采用河流碎屑锆石方法来探讨通天河河流沉积物代表的岩浆事件发生时间,评估岩浆事件中新生地壳的信息,判断河流的物源比。共采集通天河河流沉积物样品21件,并以河流南支、北支、干流划分进行讨论,得到如下认识:(1)南支、北支河流样品SiO_2含量均60%,主量元素总体一致,但干流偏低,基本表现出河流沉积物样品的均一性;样品的REE分布型式和上地壳基本一致;微量元素显示上地壳的典型特征。(2)通天河河流的南部,沉积物经历了长期的搬运,镁铁质组分的含量较低;北部和东部的沉积物距源区较近,搬运的距离短,镁铁质的比例含量较高。(3)通天河河流沉积物锆石U-Pb年龄主要分布为:古元古代(1600~2500 Ma)、新元古代(541~1000 Ma)的锆石年龄比例较大,约占到26%、24%;其次为早古生代和晚古生代;古近纪锆石集中在南段。所有样品中差别主要表现在白垩纪、侏罗纪年龄的缺失,与松潘-甘孜地块普遍缺失侏罗纪、白垩纪地层有关,楚玛尔河源头附近存在古老基底。(4)Hf同位素的TDM2的范围是0.38~4.36 Ga,存在3个明显的年龄峰值,分别为0.9~1.5 Ga,1.5~2.3 Ga,2.3~3.2 Ga,说明至少存在三次比较明显的地壳增生事件。(5)松潘-甘孜地块、北羌塘地块和东昆仑地块为通天河河流提供的物源比为5:3:2,0~800 Ma和2000~3000 Ma阶段,北羌塘可能提供更多物质,800~2000 Ma的年龄阶段,松潘甘孜地块可能提供了较多物质。
[Abstract]:The U-Pb dating, Lu-Hf analysis and trace element analysis of zircon from river detrital sediments have become the most important methods to explore the origin and evolution of continental crust. In this paper, the river detrital zircon method is used to study the occurrence time of magmatic events represented by the sediments of the Tongtian River, to evaluate the information of the new crust in the magmatic events, and to judge the material source ratio of the rivers. A total of 21 samples of Tongtian River sediment were collected and discussed by dividing the south branch, north branch and main stream. The following conclusions were obtained: (1) the SiO_2 content of the southern branch and the northern branch of the river were all 60 and the main elements were consistent. But the main stream is on the low side, which shows the homogeneity of the river sediment samples. The REE distribution pattern of the samples is basically consistent with that of the upper crust, and the trace elements show the typical characteristics of the upper crust. (2) in the southern part of the Tongtian River, the sediment has undergone a long period of transport, and the content of magnesium and iron components is relatively low; The sediments in the north and east are close to the source region, and the transport distance is short, and the proportion of magnesium and iron is higher. (3) the U-Pb age of zircon in the sediments of the Tongtian River is mainly distributed in Paleoproterozoic (1600 ~ 2500 Ma),). The zircon age of Neoproterozoic (541 ~ 1 000 Ma) is relatively large, accounting for 26 ~ 24% of the zircon age. The early Paleozoic and the late Paleozoic, and the Paleogene zircon concentrated in the southern segment. The differences in all samples are mainly related to the Cretaceous, the absence of Jurassic age, and the general absence of Jurassic and Cretaceous strata in the Songpan-Ganzi massif. There is an ancient basement near the source of the Chumar River. (4) the range of TDM2 of the Hf isotope is 0.38 ~ 4.36 Ga,. There are three obvious age peaks, respectively, of 0.9 ~ (1.5) Ga,1.5~2.3 Ga,2.3~3.2 Ga,. The results show that there are at least three obvious crustal accretion events. (5) the ratio of material sources provided by the Songpan-Ganzi block, the northern Qiangtang block and the East Kunlun block to the Tongtian River is 5: 3: 2 0800 Ma and 20003 000 Ma. The North Qiangtang may provide more material, and the 800 Ma age period, the Songpan Ganzi block, may provide more material.
【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】：P597

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