西藏阿里公珠错花岗岩锆石U-Pb年代学、地球化学特征及其地质意义
发布时间：2018-10-09 07:25
【摘要】：西藏雅鲁藏布江缝合带西段南北亚带间的仲巴微地体是近年来的研究热点,其成因及演化历史争议较大。仲巴微地体作为雅鲁藏布江缝合带西段的重要组成部分,明确其定义和边界,厘定地层格架,查明沉积与构造属性及其演化,不仅对雅江缝合带的构造演化和特提斯洋东部的古地理研究具有重要的参考意义,同时对冈瓦纳大陆北缘已经裂解出的各地体的古地理重建也可提供重要的参考信息。公珠错花岗岩体位于仲巴微地体雅鲁藏布江缝合带南亚带一侧,其主要岩性为二云母花岗岩。岩体北侧二云母花岗岩矿物主要由石英(40%)、斜长石(35%)、白云母(10%)、黑云母(7%)、钾长石(5%)及副矿物锆石、磷灰石、石榴石、榍石等(3%)组成,西侧二云母花岗岩转石与北侧二云母花岗岩具有几乎一样的岩石学特征。北侧二云母花岗岩样品的锆石U-Pb年龄变化于439-470Ma,表明这些花岗岩类侵位于中-晚奥陶世。岩体北侧二云母花岗岩的K2O/Na2O比值大于1,铝饱和指数(A/CNK)为1.47~1.82,属于高钾钙碱性过铝质花岗岩,岩石总体上富集大离子亲石元素(Rb、K等),亏损高场强元素(Nb、Ta、Zr、Ti等)。明显富集亲稀土元素[(La/Yb)N=4.79~19.37],显示轻微的负Eu异常(δEu=0.72~0.84)。地球化学特征指示公珠错二云母花岗岩为S型花岗岩,主要源于古老地壳物质(如砂屑质岩石)的高温重熔。样品的微量元素标准化蛛网图、岩石组合R1-R2图解、Rb-(Y+Nb)和Nb-Y图解均指示公珠错花岗岩形成的构造环境为洋陆俯冲之后的同碰撞构造环境。公珠错花岗岩体与出露于青藏高原南部各地体的早古生代火山岩存在一定的相关性,可能是原特提斯洋岩石圈俯冲之后仲巴微地体拼贴到冈瓦纳大陆北缘形成的大陆碰撞花岗岩。
[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.
【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】：P59;P588.121
，
本文编号：2258468
[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.
【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】：P59;P588.121
，
本文编号：2258468
本文链接：https://www.wllwen.com/shoufeilunwen/benkebiyelunwen/2258468.html
