【摘要】：西藏雅魯藏布江縫合帶西段南北亞帶間的仲巴微地體是近年來的研究熱點(diǎn),其成因及演化歷史爭(zhēng)議較大。仲巴微地體作為雅魯藏布江縫合帶西段的重要組成部分,明確其定義和邊界,厘定地層格架,查明沉積與構(gòu)造屬性及其演化,不僅對(duì)雅江縫合帶的構(gòu)造演化和特提斯洋東部的古地理研究具有重要的參考意義,同時(shí)對(duì)岡瓦納大陸北緣已經(jīng)裂解出的各地體的古地理重建也可提供重要的參考信息。公珠錯(cuò)花崗巖體位于仲巴微地體雅魯藏布江縫合帶南亞帶一側(cè),其主要巖性為二云母花崗巖。巖體北側(cè)二云母花崗巖礦物主要由石英(40%)、斜長(zhǎng)石(35%)、白云母(10%)、黑云母(7%)、鉀長(zhǎng)石(5%)及副礦物鋯石、磷灰石、石榴石、榍石等(3%)組成,西側(cè)二云母花崗巖轉(zhuǎn)石與北側(cè)二云母花崗巖具有幾乎一樣的巖石學(xué)特征。北側(cè)二云母花崗巖樣品的鋯石U-Pb年齡變化于439-470Ma,表明這些花崗巖類侵位于中-晚奧陶世。巖體北側(cè)二云母花崗巖的K2O/Na2O比值大于1,鋁飽和指數(shù)(A/CNK)為1.47~1.82,屬于高鉀鈣堿性過鋁質(zhì)花崗巖,巖石總體上富集大離子親石元素(Rb、K等),虧損高場(chǎng)強(qiáng)元素(Nb、Ta、Zr、Ti等)。明顯富集親稀土元素[(La/Yb)N=4.79~19.37],顯示輕微的負(fù)Eu異常(δEu=0.72~0.84)。地球化學(xué)特征指示公珠錯(cuò)二云母花崗巖為S型花崗巖,主要源于古老地殼物質(zhì)(如砂屑質(zhì)巖石)的高溫重熔。樣品的微量元素標(biāo)準(zhǔn)化蛛網(wǎng)圖、巖石組合R1-R2圖解、Rb-(Y+Nb)和Nb-Y圖解均指示公珠錯(cuò)花崗巖形成的構(gòu)造環(huán)境為洋陸俯沖之后的同碰撞構(gòu)造環(huán)境。公珠錯(cuò)花崗巖體與出露于青藏高原南部各地體的早古生代火山巖存在一定的相關(guān)性,可能是原特提斯洋巖石圈俯沖之后仲巴微地體拼貼到岡瓦納大陸北緣形成的大陸碰撞花崗巖。
[Abstract]:The Zhongba microbody between the northern and southern subzones of the western section of the Yalu Zangbo suture belt in Tibet has been a hot research topic in recent years, and its origin and evolution history is controversial. As an important part of the western section of the Yalu Zangbo River suture belt, the Zhongba micro-terrane defines its definition and boundary, determines the stratigraphic framework, and ascertains the sedimentary and tectonic attributes and their evolution. It not only has important reference significance for the tectonic evolution of the Yagang suture zone and the paleogeography study in the eastern Tethys ocean, but also provides important reference information for the paleogeographic reconstruction of the cracked bodies in the northern margin of Gondwana continent. The Gongzhu dislocation granite body is located in the south Asia side of the Yalu Zangbujiang suture belt of Zhongba micro-terrane, and its lithology is mainly dimica granite. In the northern side of the mica granite, the minerals are mainly composed of quartz (40%), plagioclase (35%), Muscovite (10%), biotite (7%), potassium feldspar (5%), zircon, apatite, garnet and sphene (3%). There are almost the same petrological characteristics between the two mica granites in the west and in the north. The zircon U-Pb age of the two mica granite samples on the northern side varied from 439-470 Ma, indicating that the granitic transgressions occurred in the Middle-Late Ordovician. The K2O/Na2O ratio of the dimite granites on the northern side of the rock mass is greater than 1, and the aluminum saturation index (A/CNK) is 1.47 ~ 1.82, which belongs to the high-potassium calc-alkaline peraluminous granites. The rocks are generally rich in large ion lithophile elements (Rb,K et al) and depleted in high field strength elements (Nb,Ta,Zr,Ti et al.). The enrichment of REE [(La/Yb) N _ (4.79) ~ (19.37)] shows a slight negative Eu anomaly (未 Eu=0.72~0.84). The geochemical characteristics indicate that the Gongzhu dislocation mica granite is S-type granite, which is mainly derived from the high temperature remelting of ancient crustal materials (such as sandy rocks). The trace element standardized cobweb diagram, R1-R2 diagram of rock assemblage, Rb- (Y Nb) and Nb-Y diagram all indicate that the tectonic environment of Gongzhu fault granite is the same collision tectonic environment after oceanic subduction. There is a certain correlation between the Gongzhuso granite body and the early Paleozoic volcanic rocks exposed in various parts of the southern Qinghai-Xizang Plateau. It may be the continental collisional granite formed by the assemblage of the Zhongba micro-terrane to the northern margin of Gondwana after the subduction of the original Tethys oceanic lithosphere.
【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】：2017
【分類號(hào)】：P59;P588.121
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本文編號(hào)：2258468