發(fā)布時(shí)間：2018-04-16 20:26

  本文選題：羌塘 + 片巖　； 參考：《中國(guó)地質(zhì)大學(xué)(北京)》2015年碩士論文

【摘要】：一直以來(lái)羌塘地區(qū)都是研究古特提斯洋演化和岡瓦納大陸構(gòu)造演化的重要場(chǎng)所,在近幾年的研究中,南羌塘地區(qū)不斷有前寒武紀(jì)的碎屑鋯石和巖漿鋯石年齡的出現(xiàn),這些數(shù)據(jù)都反映了南羌塘可能存在元古代結(jié)晶基底。而在本次西藏榮瑪鄉(xiāng)1:5區(qū)域地質(zhì)礦產(chǎn)調(diào)查項(xiàng)目研究區(qū)西部的亞丹地區(qū),發(fā)現(xiàn)了高角閃巖相的角閃石榴云母片巖以及一系列的低綠片巖相的片巖組合,與整個(gè)研究區(qū)內(nèi)的低級(jí)變質(zhì)巖相比,亞丹片巖的變質(zhì)相明顯更高。研究表明,此片巖經(jīng)歷了兩期變質(zhì)作用的影響,前一期為高角閃巖相的峰期變質(zhì)作用,后一期為影響的的低綠片巖相變質(zhì)作用。這兩期變質(zhì)作用,產(chǎn)生了不同的變質(zhì)礦物組合,高角閃巖相的變質(zhì)礦物組合為:夕線石+石榴石+黑云母+石英+斜長(zhǎng)石;角閃石+鐵鋁榴石+斜長(zhǎng)石,后期疊加低綠片巖相變質(zhì)作用,產(chǎn)生的變質(zhì)礦物組合為白云母+石英+斜長(zhǎng)石+石榴子石;陽(yáng)起石+綠泥石+鈉長(zhǎng)石+方解石。整體片巖的變形特點(diǎn)顯示為:北西-南東向的韌性剪切,形成礦物的定向分布,剪切同構(gòu)造的石英脈,形成S1面理。東西向的擠壓應(yīng)力影響S1片理面產(chǎn)生褶皺,沿片理面形成小的彎滑褶皺,構(gòu)成S2面理。S3面理形成于新生代的時(shí)期區(qū)域上的南北向推覆作用,影響巖層形成一系列尖棱褶皺的軸面等。而亞丹片巖稀土、微量元素的北美頁(yè)巖標(biāo)準(zhǔn)化圖上,輕稀土富集,重稀土平坦,部分大粒子親石元素虧損,Ce和Eu輕微虧損,兼具沉積巖與基性巖的原巖特點(diǎn)。通過(guò)圖解進(jìn)行原巖恢復(fù),結(jié)果顯示偏向基性巖的樣品,為一套亞堿性或堿性玄武質(zhì)巖石,而另外一部分樣品則是偏向于泥質(zhì)粉砂巖、雜砂巖類。其基性原巖的構(gòu)造環(huán)境為大陸或大陸裂谷環(huán)境,而泥質(zhì)原巖的構(gòu)造環(huán)境為大陸島弧環(huán)境,并且可能繼承了物源的構(gòu)造環(huán)境特征。片巖的圍巖為一套基性的侵入巖,其LA-ICP-MS U-Pb測(cè)年數(shù)據(jù)顯示,峰值年齡段為711.5~758.6Ma,峰值年齡段的加權(quán)平均年齡為746.3±3.7Ma,顯示為新元古代的羅迪尼亞大陸裂解的時(shí)間,整體測(cè)年結(jié)果中,最老的為一顆碎屑鋯石年齡為3107.4±28.72Ma,記錄了中太古代的構(gòu)造熱事件。最年輕的一顆巖漿鋯石年齡為660±17.02 Ma,沒(méi)有記錄到泛非事件,較拉薩地塊,羌塘中部,喜馬拉雅地區(qū)的泛非性質(zhì)的基底尚不能形成有效的對(duì)比,但可以作為羌塘基底存在的重要證據(jù)。
[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.

【學(xué)位授予單位】：中國(guó)地質(zhì)大學(xué)(北京)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：P588.344

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