满洲里东部嵯岗白云母花岗岩地球化学特征及岩石成因

发布时间：2018-03-31 19:28

  本文选题：满洲里东部　切入点：白云母花岗岩　出处：《吉林大学》2017年硕士论文

【摘要】：众多研究显示,白云母花岗岩有其特殊的岩石成因及构造意义,与白云母花岗岩分布非常较广、研究程度较高的我国华南地区相比,在被誉为“花岗岩海”的大、小兴安岭地区却鲜有白云母花岗岩出露,因而相关研究也很少。幸运的是,我们在大兴安岭中部的满洲里东部发现了石榴石白云母花岗岩,本文对其进行详细的岩相学、锆石U-Pb年代学、地球化学以及锆石Hf同位素的研究,讨论了其岩石成因和形成的构造背景。所研究的石榴石白云母花岗岩出露于满洲里东部的嵯岗镇北部,包括中粒石榴石二云母花岗岩和细粒石榴石白云母花岗岩两类,后者呈脉状侵入到前者中。锆石U-Pb测年结果显示中粒二云母花岗岩形成于236±3Ma的中三叠世,细粒白云母花岗岩形成于130±2Ma的早白垩世。中粒二云母花岗岩和细粒白云母花岗岩都具有高硅(SiO2=74.65%-78.12%)富碱(Na2O+K2O=7.74%-8.35%)、贫镁(Mg#=0.14-0.35)低铁(TFe2O3=0.34%-1.03%)的地球化学特征,均属于过铝质的高钾钙碱性系列。它们的稀土元素总含量都非常低(∑REE=17.73×10-6-73.52×10-6),相对富集轻稀土元素亏损重稀土元素,具有明显负Eu异常(δEu=0.19-0.51);相对富集Rb、Th、K等大离子亲石元素,而亏损Sr和Ba,亏损Nb、Zr、P、Ti等高场强元素,相对富集Ta。这两类花岗岩的锆石初始Hf同位素成分εHf(t)值分别为10.34-16.63和12.07-16.17,两阶段模式年龄(TDM2)分别为606-203Ma和413-138Ma。中粒二云母花岗岩和细粒白云母花岗岩的Zr含量(15.5×10-6-99.7×10-6)和(Zr+Nb+Ce+Y)含量(78.4×10-6-166.9×10-6)明显低于典型的A型花岗岩的最小值250×10-6和350×10-6,且A/NK比值(1.17-1.24)大于A型花岗岩的平均值(1.05),结合分异指数(DI=92.60-95.75)及相关微量元素判别图解,表明它们均是高分异的I型花岗岩。中粒二云母花岗岩显示出低Sr高Yb的地球化学特征,属于南岭型花岗岩;细粒白云母花岗岩具有低Sr低Yb的地球化学特征,属于喜马拉雅型花岗岩。本文认为这两类花岗岩均起源于新增生的基性下地壳的部分熔融,但相比之下,细粒白云母花岗岩的岩浆源区更深。中三叠世中粒二云母花岗岩形成于与蒙古-鄂霍茨克构造域有关的活动大陆边缘环境,而早白垩世细粒白云母花岗岩形成于加厚岩石圈的伸展环境。
[Abstract]:Many studies have shown that Muscovite granite has its special petrogenetic and tectonic significance. Compared with Muscovite granite, which is widely distributed in South China, it is called "Granite Sea". However, there are few Muscovite granite exposed in Xiaoxinganling area, so there are few related studies. Fortunately, we found garnet Muscovite granite in the eastern part of Manzhouli in the central part of Daxing'an Mountains. Zircon U-Pb chronology, geochemistry and zircon HF isotopes are studied in this paper. The petrogenesis and tectonic setting of the zircon are discussed. The garnet Muscovite granites are exposed to the northern part of Sagangzhen, east of Manzhouli. There are two types of medium-grained garnet dimica granites and fine-grained garnet Muscovite granites, the latter being veined into the former. The zircon U-Pb dating results show that the medium-grained dimica granites were formed in the Middle Triassic of 236 卤3Ma. The fine-grained Muscovite granites were formed in the early Cretaceous of 130 卤2Ma. Both the medium-grained dimica granites and the fine-grained Muscovite granites have geochemical characteristics of high SiO2O2-74.65-78.12) alkali-rich Na2OK2O-7.74-8.35m, Mg#0.14-0.35) low Fe _ 2O _ 3- 0.34-1.03T). They all belong to peraluminous calc-alkaline series. The total contents of rare earth elements in them are very low (鈭，

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