西藏羌塘荣玛地区亚丹片岩变形变质特征及地质意义

发布时间：2018-04-16 20:26

本文选题：羌塘 + 片岩　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：一直以来羌塘地区都是研究古特提斯洋演化和冈瓦纳大陆构造演化的重要场所,在近几年的研究中,南羌塘地区不断有前寒武纪的碎屑锆石和岩浆锆石年龄的出现,这些数据都反映了南羌塘可能存在元古代结晶基底。而在本次西藏荣玛乡1:5区域地质矿产调查项目研究区西部的亚丹地区,发现了高角闪岩相的角闪石榴云母片岩以及一系列的低绿片岩相的片岩组合,与整个研究区内的低级变质岩相比,亚丹片岩的变质相明显更高。研究表明,此片岩经历了两期变质作用的影响,前一期为高角闪岩相的峰期变质作用,后一期为影响的的低绿片岩相变质作用。这两期变质作用,产生了不同的变质矿物组合,高角闪岩相的变质矿物组合为:夕线石+石榴石+黑云母+石英+斜长石;角闪石+铁铝榴石+斜长石,后期叠加低绿片岩相变质作用,产生的变质矿物组合为白云母+石英+斜长石+石榴子石;阳起石+绿泥石+钠长石+方解石。整体片岩的变形特点显示为:北西-南东向的韧性剪切,形成矿物的定向分布,剪切同构造的石英脉,形成S1面理。东西向的挤压应力影响S1片理面产生褶皱,沿片理面形成小的弯滑褶皱,构成S2面理。S3面理形成于新生代的时期区域上的南北向推覆作用,影响岩层形成一系列尖棱褶皱的轴面等。而亚丹片岩稀土、微量元素的北美页岩标准化图上,轻稀土富集,重稀土平坦,部分大粒子亲石元素亏损,Ce和Eu轻微亏损,兼具沉积岩与基性岩的原岩特点。通过图解进行原岩恢复,结果显示偏向基性岩的样品,为一套亚碱性或碱性玄武质岩石,而另外一部分样品则是偏向于泥质粉砂岩、杂砂岩类。其基性原岩的构造环境为大陆或大陆裂谷环境,而泥质原岩的构造环境为大陆岛弧环境,并且可能继承了物源的构造环境特征。片岩的围岩为一套基性的侵入岩,其LA-ICP-MS U-Pb测年数据显示,峰值年龄段为711.5~758.6Ma,峰值年龄段的加权平均年龄为746.3±3.7Ma,显示为新元古代的罗迪尼亚大陆裂解的时间,整体测年结果中,最老的为一颗碎屑锆石年龄为3107.4±28.72Ma,记录了中太古代的构造热事件。最年轻的一颗岩浆锆石年龄为660±17.02 Ma,没有记录到泛非事件,较拉萨地块,羌塘中部,喜马拉雅地区的泛非性质的基底尚不能形成有效的对比,但可以作为羌塘基底存在的重要证据。
[Abstract]:Since the Qiangtang area is an important place to study Gut Tis ocean evolution and Gondwana continental tectonic evolution, research in recent years, with emergence of Precambrian detrital zircon and magmatic zircon ages in South Qiangtang area, these data are reflected in the southern Qiangtang may exist in Proterozoic crystalline basement. In the study area of Western Tibet Rong Ma Xiang 1:5 regional geological survey project of the Yadan region, found high amphibolite facies garnet mica schist and amphibolite greenschist facies series of schist combination, compared with the study of low-grade metamorphic zone, Yadan schist metamorphic facies was significantly higher. The results show that the effects of these rocks have undergone metamorphism, before a period of peak period of high amphibolite facies metamorphism, for after a period of low greenschist facies metamorphism. The two have different metamorphism. The metamorphic mineral assemblage, high amphibolite facies metamorphic mineral assemblage: sillimanite + garnet + biotite + quartz + hornblende + plagioclase; Almandite + plagioclase, superimposed low greenschist facies metamorphism, metamorphic mineral assemblage of Muscovite + plagioclase + quartz + garnet actinolite + Zi Shi; chlorite + albite + calcite. The deformation characteristics of whole schist display: the NW-SE trending ductile shear, the formation of directional distribution of minerals, quartz vein shear syntectonic, forming S1 foliation. E-W extrusion stress on S1 foliation fold, formed along the foliation small flexural slip fold S2.S3, a foliation foliation formed in the region of Cenozoic period of N-S thrusting and the axial plane of a series of angularfold effects of rock formation. While Yadan map of the North American shale rare earth schist, standard trace elements, LREE enrichment, hree Flat, part of the large particle lithophile element loss, Ce and slight depletion of Eu, both the original rock characteristics of sedimentary rocks and mafic rocks. To restore the original rock through the diagram shows bias rocks samples into a set of sub alkaline or alkaline basaltic rocks, while the other part of the sample is biased in favor of argillaceous siltstone, graywacke. Its tectonic environment mafic protolith is continental or continental rift environment, and tectonic environment of argillaceous protoliths for continental arc environment, characteristics of tectonic environment and may inherit the source. The surrounding rock schist is a set of mafic intrusive rocks, the LA-ICP-MS U-Pb dating data show that the peak age is 711.5~758.6Ma, the weighted average age peak age was 746.3 + 3.7Ma, display the Neoproterozoic Rodinia splitting time, the overall dating results, the oldest is a detrital zircon age was 3107.4 + 28.72Ma, recording The Archean tectonic thermal events. The youngest a magmatic zircon age of 660 + 17.02 Ma, there is no record to a Pan African event, Lhasa block, central Qiangtang, form an effective comparison of basal properties in Himalaya area of the Pan African is not important, but evidence exists as the Qiangtang basement.

【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】：P588.344

【参考文献】