青海沱沱河地区赛多浦岗日二长花岗岩岩石、矿物地球化学特征及地质意义

发布时间：2018-06-28 13:35

本文选题：青海省 + 赛多浦岗日　；参考：《吉林大学》2015年硕士论文

【摘要】：赛多浦岗日二长花岗岩体位于青海雁石坪西南约50km处，大地构造上位于拉竹龙－金沙江缝合带和班公错－怒江缝合带之间的羌塘地块北部，唐古拉边缘前陆盆地的雁石坪坳陷中。本文通过对赛多浦岗日二长花岗岩岩石学、岩石地球化学及矿物地球化学特征的研究，探讨了其形成的源区性质及大地构造背景。同时为建立该类花岗岩矿物学标型特征积累了数据资料。二长花岗岩岩石学研究表明，花岗岩中SiO2所占的比重大(70.89%~71.39%)，K2O含量高，略高于Na2O，显示准铝质-过铝质性质，常量元素的地化特征表明，该花岗岩为I型花岗岩。样品中轻重稀土分异明显。稀土配分为不对称向右陡倾的曲线，δEu值在0.56～0.68之间，为铕弱负异常，说明其源区有少量斜长石的残留或存在分离结晶作用。富集LREEs，亏损HREEs和HFSEs，Sr/Y比值介于72.47～83.48之间，大于40%，LaN/YbN比值介于53.06～107.36之间，大于20%等这些特点显示出埃达克岩的地球化学特征，说明该花岗岩为埃达克质岩石。通过讨论得出花岗岩形成于加厚的镁铁质下地壳部分熔融过程。锆石U-Pb法测年得出赛多浦岗日地区二长花岗岩的时代为古近纪中的古新世。斜长石成分测试表明，斜长石牌号较高，An介于24.83到31.66之间，属于更长石与中长石。斜长石环带从核部到外部An牌号依次为An31.66-An31.12-An24.84-An26.37-An25.23，显示为韵律环带，从核部-中间环带An牌号反而升高，出现斜长石的反环带可认为发生过岩浆混合作用，，也说明该花岗岩为新生代花岗岩。碱性长石矿物中，Or含量为67.78%-92.58%，Ab次之,为7.32%-31.44%， An分子含量很少都小于1，属于正长石。黑云母电子探针分析表明，黑云母为高铁镁云母。岩石地球化学测试数据反映在造山带演化的Y-Nb图上，样品投入到岛弧花岗岩区域，同时也投入到了同碰撞区域，在R1-R2图上，样品投入到了同碰撞区域，因此该区的地壳加厚过程可能是由板块碰撞导致的，说明本时代花岗岩可能是由于板块之间的碰撞导致了地壳变厚形成的。黑云母富镁、相对富铝以及缺少钛等特性表明，二长花岗岩形成于造山构造环境。上述研究表明，二长花岗岩岩石地球化学特征与矿物地球化学特征可以相互佐证，为利用矿物地球化学特征判断花岗岩岩石成因、物质来源及构造背景提供理论依据。
[Abstract]:The Xidopugang Erzhang granite body is located about 50km southwest of Yanshiping, Qinghai, and is located in the north of the Qiangtang block between the LazhulongJinshajiang suture belt and the Bangongcao-Nujiang suture belt. The Yanshiping depression in the Foreland basin of Tanggula margin. In this paper, the petrology, geochemistry and mineral geochemistry characteristics of the Xidopugang Erzhang granite are studied, and the origin properties and tectonic setting of the source region are discussed. At the same time, it accumulates data for the establishment of mineralogical typomorphic characteristics of this kind of granite. The petrological study shows that the content of K _ 2O is high (70.89%) and slightly higher than that of Na _ 2O, indicating that the granite is quasi-aluminum-peraluminous and characterized by geochemistry of the major elements, which indicates that the granite is I-type granite. The difference of light and light rare earth elements in the sample is obvious. The rare earth distribution can be divided into asymmetrical and steep right dip curves. The 未 EU value is between 0.56 and 0.68, which is a weak negative anomaly of europium, indicating that there is a small amount of plagioclase residue or separation and crystallization in its source region. LREEs-enriched, depleted HREEs and HFSEsN Sr-r-Y ratios between 72.47 and 83.48, larger than 40% LaN- / YbN ratios between 53.06 and 107.36, and more than 20% show the geochemical characteristics of the adakites, indicating that the granites are adakitic rocks. Through discussion, it is concluded that granite formed in the partial melting process of thickened magnesia-iron lower crust. Zircon U-Pb dating indicates that the age of the two feldspar granites in the Sedopu Gangri area is Paleogene in the Middle Paleogene. The composition test of plagioclase shows that the plagioclase grade is between 24.83 and 31.66, which belongs to the more feldspar and the meso-feldspar. The number of an of plagioclase is An31.66-An31.12-An24.84-An26.37-An25.23, which is a rhythmic ring, and the number of an from nuclear to middle annulus increases, and the anticlinal zone of plagioclase can be considered to have magmatic mixing. It also shows that the granite is a Cenozoic granite. In alkaline feldspar minerals, the content of Or is 67.78 -92.58% and the second is 7.32- 31.444.The content of an molecule is rarely less than 1, and belongs to orthoclase. The electron probe analysis of biotite shows that biotite is high-iron magnesium mica. The geochemistry data are reflected on Y-Nb diagram of orogenic belt evolution. Samples are input to island arc granite area, and also to the same collision area. In R1-R2 diagram, the sample is input into the same collision area. Therefore, the crustal thickening process in this area may be caused by plate collision, which suggests that the granite in the present age may have been thickened due to the collision between plates. The characteristics of biotite rich in magnesium, relatively rich in aluminum and lack of titanium indicate that the monzogranite was formed in the orogenic tectonic environment. The above results show that the geochemical characteristics of the rock and mineral geochemistry of the monzogranite can be mutually corroborated, which provides a theoretical basis for judging the genesis, material source and tectonic background of the granite by using the geochemical characteristics of the minerals.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.121

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