喜马拉雅造山带中段亚东地区片麻岩的早古生代岩浆作用与新生代变质作用

发布时间：2018-08-02 13:09

【摘要】：亚东地区位于喜马拉雅造山带中段,这里出露的高喜马拉雅结晶岩系主要由泥质片岩、长英质片麻岩以及少量石英岩、大理岩、镁铁质岩和钙硅酸盐岩构成,这些岩石被大面积的淡色花岗岩侵入。本文对该地区的正片麻岩进行了岩石学以及锆石年代学研究。所研究的正片麻岩分为两类,第一类为暗色片麻岩,矿物组成主要为石英(30%~35%)、斜长石(30%~35%)、钾长石(20%~25%)、黑云母(3%~5%),含或不含少量白云母和角闪岩,岩石化学分析结果显示,3个暗色片麻岩的Si O2在68.50 wt.%~76.55 wt.%之间,Al2O3在13.22 wt.%~14.97 wt.%之间,Ca O在1.21 wt.%~3.45 wt.%之间,全碱含量(Na2O+K2O)在5.64 wt.%~7.64 wt.%之间,A/CNK在1.06~1.14之间,均为过铝质。3个样品具有较高的REE总量,富集Rb、K等大离子亲石元素和Th、Ta等高场强元素,贫Ba、Sr等大离子亲石元素和Nb、Ti等高场强元素;第二类为浅色片麻岩,矿物组成主要为石英(30%~35%)、斜长石(25%~30%)、钾长石(25%~30%)、黑云母(3%~5%),或含少量夕线石。2个浅色片麻岩的Si O2分别为77.83 wt.%和75.19wt.%,Al2O3分别为13.47 wt.%和14.15 wt.%,Ca O分别为0.31 wt.%和0.60 wt.%,全碱含量(Na2O+K2O)分别为7.01 wt.%和7.78 wt.%,A/CNK值分别为1.84和1.48,均为过铝质;2个样品的REE总量较低,富集Rb、K等大离子亲石元素,亏损Ba和Sr等大离子亲石元素以及Th、Nb、Ti等高场强元素。片麻岩中锆石多具核-边结构,由一个岩浆核和一个窄的变质边组成,少量锆石不具核-边结构,为单颗粒变质锆石。锆石核部具有明显的振荡环带,REE配分模式以富HREE,Eu负异常为特点;锆石的变质边和单颗粒变质锆石具有相对低的REE含量,负Eu异常。锆石U-Pb年代学分析表明,5个样品的锆石岩浆核部给出478±14Ma~507±40Ma的加权平均年龄,代表片麻岩的早古生代原岩年龄。锆石变质域给出了20.8±1.8 Ma~22.8±5.5 Ma的新生代年龄。暗色片麻岩呢锆石Hf同位素分析显示,锆石核部的εHf(t)值分别为 8.1~+0.1、 5.9~ 2.1和 4.8~+6.7,TDM2年龄分别为1.44~1.96 Ga、1.59~1.83 Ga和1.03~1.76 Ga,远大于样品结晶年龄。这表明它们起源于古老陆壳物质的部分熔融。上述资料表明,所研究的暗色片麻岩是早古生代花岗岩经历新生代变质作用的产物,而浅色片麻岩是早古生代花岗岩在新生代发生深熔作用所形成的淡色花岗岩变形作用的产物。本研究表明,喜马拉雅造山带中的正片麻岩具有早古生代造山作用的记录,即为原特提斯洋向冈瓦纳大陆北缘俯冲导致的安第斯型造山作用。同时,这些正片麻岩也记录了新生代变质和深熔事件,为印度-亚欧板块碰撞造山作用的反映。
[Abstract]:The Yadong region is located in the middle part of the Himalayan orogenic belt, where the high Himalayan crystalline series is mainly composed of shaly schist, felsic gneiss and a small amount of quartzite, marble, mafic rock and calcium silicate. These rocks were invaded by large areas of pale granite. The petrology and zircon chronology of normal gneiss in this area have been studied in this paper. The normal gneiss studied is divided into two categories: the first is dark gneiss, the mineral composition is mainly quartz (30%), plagioclase (30%), potassium feldspar (20%), biotite (3 5%), and contains or does not contain a small amount of Muscovite and hornblende, and is mainly composed of quartz (30%), plagioclase (30%), potassium feldspar (20%), biotite (3%), and amphibolite. The results of petrochemical analysis showed that the Sio _ 2 content of the three dark gneisses was between 68.50 wt.%~76.55 wt.% and 13.22 wt.%~14.97 wt.%, and the total alkali content (Na2O K _ 2O) was between 5.64 wt.%~7.64 wt.% and 1.061.14, respectively. All of them are peraluminous. The three samples have high total REE content, rich in large ion lithophile elements such as RB ~ (+) K and high field strength elements such as Th ~ (3 +) Ta, and are poor in large ion lithophile elements, such as Ba-Sr and NB ~ (+) Ti, and in light-colored gneiss, the second is light-colored gneiss, and the other is light-colored gneiss. The mineral composition is mainly quartz (300.35%), plagioclase (2530%), potash feldspar (2530%), biotite (30.5%), or small amount of sillimanite. The Sio _ 2 content of the two light-colored gneiss is 77.83 wt.% and 75.19 wt.Al _ 2O _ 3 are 13.47 wt.% and 14.15 wt.t.The Cao is 0.31 wt.% and 0.60 wt. respectively, and the total alkali content (Na2O K2O) is 0.60 wt. The CNK values of 7.01 wt.% and 7.78 wt.% were 1.84 and 1.48, respectively, which were peraluminous, the total REE of the two samples was lower, It is rich in large ion lithophile elements such as RbBK, depleted in large ion lithophile elements such as Ba and Sr, and in high field strength elements such as Thn NbPTi. The zircon in the gneiss is mainly composed of a magmatic core and a narrow metamorphic edge. A small amount of zircon has no core-edge structure and is a single grain metamorphic zircon. The REE partition model in the core of zircon is characterized by the negative anomaly of rich HREE EU, and the metamorphic edge of zircon and the single grain metamorphic zircon have relatively low REE content and negative EU anomaly. The U-Pb chronological analysis of zircon shows that the weighted mean age of 478 卤14Ma~507 卤40Ma in the magmatic core of the five samples represents the early Paleozoic age of the gneiss. A Cenozoic age of 20.8 卤1.8 Ma~22.8 卤5.5 Ma has been obtained in the zircon metamorphic domain. The zircon HF isotopic analysis of the dark gneiss shows that the 蔚 Hf (t) values of the zircon core are 8.1 ~ 0.1, 5.9- and 4.86.7TDM2 respectively, and the ages of 1.441.96Ga 1.591.83 Ga and 1.03U 1.76Ga are much larger than the crystallization age of the sample. This indicates that they originated from partial melting of ancient continental crust material. The above data indicate that the studied dark gneiss is the product of the Cenozoic metamorphism of the early Paleozoic granite. The light-colored gneiss is the product of the deformation of the paleozoic granites formed by the deep melting of the early Paleozoic granites in the Cenozoic. This study shows that the norneiss in the Himalayan orogenic belt has a record of early Paleozoic orogeny, that is, the proto-Tethys ocean subducted to the northern margin of Gondwana continent. These normal gneisses also recorded Cenozoic metamorphic and deep melting events reflecting the collision orogeny of the Indo-Eurasian plate.
【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】：2016
【分类号】：P588.3

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