海拉尔北部八大关地区花岗岩的年代、地球化学特征与成因研究

发布时间：2018-01-02 16:01

  本文关键词：海拉尔北部八大关地区花岗岩的年代、地球化学特征与成因研究　出处：《吉林大学》2017年硕士论文　论文类型：学位论文

  更多相关文章： 花岗岩 锆石U-Pb测年 Hf同位素 地球化学 岩石成因 八大关

【摘要】：海拉尔北部八大关地区位于中俄两国交界处,大地构造位置属于额尔古纳地块,处在著名的德尔布干构造带上。额尔古纳地块北侧为蒙古-鄂霍茨克褶皱带,南缘被南蒙晚古生代古海洋沉积物所覆盖,是古亚洲洋构造域、环太平洋构造域与蒙古鄂霍茨克构造域强烈叠加、复合、转换部位,构造形迹极其复杂,对研究东北地区构造演化起着重要作用。近年来,诸多学者对额尔古纳地块北部花岗岩时代、地球化学特征与岩石成因进行了详细研究,积累了一大批高精度锆石U-Pb和40Ar/39Ar同位素年龄与地球化学资料,然而对其西缘即八大关地区的花岗岩年代学和地球化学特征的研究相对薄弱,尤其是Hf同位素的研究更为少见,前人主要是依据花岗岩与地层之间的接触关系、变质程度、变形特征与K-Ar定年结果,但是由于八大关地区构造形迹复杂,花岗岩大部分都经过后期改造,破坏了样品中原有的同位素体系,因此这些花岗岩年龄不能反应八大关地区花岗岩的岩浆侵位年龄,而地化数据缺失制约了对其成因的深入理解。鉴于此,本文对八大关地区的花岗岩进行了年代学与地球化学及锆石Hf同位素研究,精准地界定了花岗岩的具体形成时期,探讨了其形成机制以及所产生的构造环境,为东北地区区域构造演化提供了新的依据。1.花岗岩的组合类型及形成时代八大关地区花岗岩由正长花岗岩和二长花岗岩组成。锆石U-Pb同位素测年结果显示,正长花岗岩年龄为216~226Ma,二长花岗岩年龄为212~220Ma,总体来看,八大关地区花岗岩的形成时代非常接近,均为晚三叠世。2.花岗岩的地球化学特征正长花岗岩SiO_2含量较高,w(SiO_2)=71.34%~76.41%,铝弱过饱和,w(Al_2O_3)=10.86%~15.61%,A/CNK比值为1.02~1.10(分子数),全碱含量较高,w(K_2O)+w(N_2O)=7.37%~10.00%,K_2O/Na_2O=1.12~1.35,相对富钾,镁钙含量较低,w(MgO)=0.08%~0.31%,w(CaO)=0.33%~0.44%,花岗岩分异程度较高(DI=92.48~95.80),稀土配分曲线呈右倾型,稀土总量∑REE=112.37×10~(-6)~193.13×10~(-6),具有中等的负铕异常(δEu=0.51~0.71),微量元素富集大离子亲石元素Zr、Hf、Rb、Th、K,亏损高场强元素P、Ti、Nb、Ta等。二长花岗岩主量元素分析结果显示,w(SiO_2)=75.86%~77.75%,w(Al_2O_3)=10.99%~11.78%,A/CNK比值介于1.01~1.10之间,为弱过铝质,w(MgO)=0.27%~0.31%,w(CaO)=0.33%~0.62%,含量偏低,全碱含量高w(K_2O)+w(N_2O)=6.59%~8.01%,花岗岩分异指数介于93.35~94.14之间。稀土总量(∑REE)为141.66×10~(-6)~164.75×10~(-6),在其配分曲线中显示为轻稀土富集的右倾型特征,铕为中等负异常型(δEu=0.56~0.65),微量元素上,Rb、Th、K等大离子亲石元素(LILE)较为富集,Nb、Ta、P、Ti等高场强元素(HFSE)较为亏损。综上所述,八大关地区花岗岩具有相似的主、微量元素特征和变化规律,如均富硅、高碱、贫镁钙,均为弱过铝质花岗岩,其稀土配分曲线均为右倾型,分异指数均较高(DI90)等,根据地球化学特征,判断其八大关地区的正长花岗岩和二长花岗岩均为高分异的I型花岗岩。3.花岗岩的岩石成因及构造背景八大关地区花岗岩锆石Hf同位素数据显示:正长花岗岩和二长花岗岩εHf(t)均为正值,介于4.50~10.45,两种花岗岩在t-εHf(t)图解上均落入球粒陨石演化线之上并且比较集中,二阶段Hf模式年龄较为年轻,为新元古代(0.59~0.97 Ga)。结合地球化学特征及区域构造演化等方面成果,认为花岗岩浆来源于蒙古鄂霍茨克洋板块向南俯冲背景下新元古代新增生的基性地壳物质部分熔融。
[Abstract]:Ba Da Guan in northern Hailar area is located in the Sino Russian border, tectonically belongs to the Eergu'Na block, in the famous Del cloth dry tectonic belt of Eergu'Na block. On the north side of the Mongolia Okhotsk fold belt, southern margin of the late Paleozoic marine sediments were Nanmeng covered, is the paleo Asian Ocean, circum Pacific tectonic domain and Mongolia the Okhotsk tectonic domain strongly superimposed composite conversion parts, structural feature is extremely complex, to study the tectonic evolution of Northeast China plays an important role. In recent years, many scholars of the northern part of the Eergu'Na massif granite age, geochemical characteristics and petrogenesis are studied in detail, the accumulation of a large number of high precision zircon U-Pb and 40Ar/39Ar isotopic age with the geochemical data, however on the west edge of Ba Da Guan area granite geochronology and geochemistry of the study on the weak, especially The Hf isotope study is more rare, the former is mainly based on the contact relationship between the granite and strata metamorphism, deformation features and K-Ar dating results, but because of the Ba Da Guan area with complex structural features of granite mostly after transformation, destroyed the original isotopic system in the sample, so these granite granite age can not be the reaction in the Ba Da Guan area of magmatic emplacement age, and lack of data restricts the understanding of its causes. In view of this, this paper study on geochronology and isotope geochemistry and zircon Hf on the Ba Da Guan area of granite, precise definition of the specific formation period of granite, discusses its formation mechanism and tectonic environment produced the.1. provides a new basis for the combination types of granite granite formation and age of the Ba Da Guan area as the regional tectonic evolution of Northeast China By syenogranite monzogranite and two zircon U-Pb isotopic dating results show that syenogranite ages 216~226Ma, two granite ages 212~220Ma, overall, formation age is very close to the Ba Da Guan area are granite, geochemical characteristics of Late Triassic Granites is three.2. long high granite content of SiO_2, w (SiO_2) =71.34%~76.41%, weakly peraluminous and saturated w (Al_2O_3) =10.86%~15.61%, A/CNK = 1.02~1.10 (number of molecules), total alkali content is higher, w (K_2O) +w (N_2O) =7.37%~10.00%, K_2O/Na_2O=1.12~1.35, relatively rich in potassium, calcium and magnesium content is low, w (MgO) =0.08%~0.31%, w (CaO) =0.33%~0.44%. Granite high degree of differentiation (DI=92.48~95.80), REE distribution curve right type, the total rare earth Sigma REE=112.37 * 10~ (-6) ~193.13 * 10~ (-6), with moderate negative Eu anomaly (delta Eu=0.51~0.71), trace element enrichment in large ion lithophile elements Zr, H f,Rb,Th,K,浜忔崯楂樺満寮哄厓绱燩,Ti,Nb,Ta绛，

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