大兴安岭中段塔尔气地区中侏罗世花岗岩岩石成因及构造背景
发布时间：2018-08-06 17:09
【摘要】：本文以大兴安岭中段塔尔气地区中侏罗世花岗岩为研究对象，对该地区的中侏罗世花岗岩进行了岩石学、年代学、地球化学及Hf同位素等方面的研究，厘定了花岗岩的形成时代，确定了大兴安岭中段塔尔气地区中侏罗世花岗岩的岩石成因以及与其有关的地球动力学背景。本文的研究结果不仅使塔尔气地区的地质资料获得进一步完善，同时也为大兴安岭地区中侏罗世岩浆—构造的演化历史提供了科学依据。 在研究区内，我们选择了4件花岗岩样品进行了LA-ICP-MS锆石U-Pb同位素分析，锆石均发育结构清晰的振荡生长环带，并且具有较高的Th/U比值，暗示其为典型岩浆成因锆石，可以反映岩石的形成时代。经测试分析，样品的206Pb/238U年龄分别为173±1.3Ma、169.4±1.6Ma、166.3±1.2Ma、166.7±0.8Ma，显示大兴安岭中段塔尔气地区的花岗岩形成于中侏罗世。 此外，大兴安岭中段塔尔气地区的中侏罗世花岗岩具有富硅、富碱以及贫钙、镁的特点，ACNK值多集中在0.9～1.1之间，，为弱过铝质高钾钙碱性花岗岩。样品的稀土元素表现出轻稀土元素富集，重稀土元素相对亏损的特征，并且具有明显的Eu负异常。此外大离子亲石元素元素Rb、Th、U相对富集，Nb、Ta、Ti等高场强元素以及Sr、Ba相对亏损。上述这些地球化学特征均显示大兴安岭中段塔尔气地区中侏罗世花岗属于I型花岗岩。而且，在Harker图解中花岗岩样品表现出明显的线性变化趋势，同样指示着I型花岗岩的岩石特征。此外，样品在判别图解中落在高分异I型和A型花岗岩区域，但是研究区内的花岗质岩石的Zr元素含量大多小于A型花岗岩的最低值，平均锆石饱和温度低于典型A型花岗岩的形成温度，显示了高分异I型花岗岩的特征。 大兴安岭中段塔尔气地区中侏罗世花岗的εHf（t）值和二阶段地幔模式年龄与兴蒙造山带东段的典型花岗质岩石具有相似的特点，指示研究区内花岗质岩浆来源于显生宙期间新增生的年轻地壳物质的部分熔融。同时结合岩石学，年代学以及地球化学研究，认为研究区内中侏罗世花岗岩的形成可能与蒙古-鄂霍茨克洋演化过程中的伸展作用有关，而该拉张环境为加厚岩石圈拆沉引起的软流圈地幔物质上涌所致。
[Abstract]:In this paper, the middle Jurassic granites in the Tal gas region of the middle part of Daxing'an Mountains are studied in petrology, geochronology, geochemistry and HF isotopes. The formation age of granites is determined and the petrogenesis and geodynamic background of the Middle Jurassic granites in the Tal gas region of the central part of the Daxing'an Mountains are determined. The results of this paper not only further improve the geological data of Tal gas area, but also provide a scientific basis for the evolution history of the Middle Jurassic magmatic tectonics in the Daxing'anling area. In the study area, we selected four granite samples for LA-ICP-MS zircon U-Pb isotopic analysis. The zircons all developed a clear oscillatory growth ring zone with a high Th/U ratio, suggesting that they are typical magmatic zircon. It can reflect the age of rock formation. The 206Pb/238U ages of the samples are 173 卤1.3 Ma, 169.4 卤1.6 Ma, 166.3 卤1.2 Ma, 166.7 卤0.8 Ma, respectively, indicating that the granites in the Tal gas area of the middle part of the Daxing'an Mountains were formed in the Middle Jurassic. In addition, the Middle Jurassic granites in the Tal gas area of the middle part of the Daxing'anling Mountains are rich in silicon, alkali and calcium, and the characteristics of magnesium are mainly between 0.9 and 1.1, which are weak peraluminous high-potassium calc-alkaline granites. The rare earth elements of the samples show the characteristics of light REE enrichment, relative depletion of heavy REE elements, and obvious EU negative anomalies. In addition, the large ion lipophilic element RbHU is relatively enriched with high field strength elements, such as NbTa-Ta-Ti, and the relative depletion of Sr ~ (2 +) Ba. These geochemical characteristics indicate that the Middle Jurassic granitic granites belong to I-type granites in the Tal gas area of the middle part of the Daxing'anling Mountains. Moreover, the granite samples show a linear variation trend in the Harker diagram, which also indicates the rock characteristics of the I-type granite. In addition, the samples fall in the high grade I type and A type granite areas in the discriminant diagram, but the Zr element content of the granitic rocks in the study area is mostly less than the minimum value of the A type granite. The average zircon saturation temperature is lower than the formation temperature of typical A-type granites, which shows the characteristics of high-grade iso-I-type granites. The 蔚 Hf (t) values of the Middle Jurassic granitic rocks and the age of the two-stage mantle model are similar to the typical granitic rocks in the eastern part of the Xingmeng orogenic belt in the Tal gas region of the central part of the Daxing'anling Mountains. It is indicated that the granitic magma in the study area originated from the partial melting of newly proliferated young crustal materials during the Phanerozoic period. In combination with petrology, geochronology and geochemistry, it is considered that the formation of the Middle Jurassic granites in the study area may be related to the extensional process in the evolution of the Mongolia-Okhotsk Ocean. The extensional environment is caused by the upwelling of the asthenospheric mantle caused by the delamination of the thickened lithosphere.
【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
本文编号：2168397
[Abstract]:In this paper, the middle Jurassic granites in the Tal gas region of the middle part of Daxing'an Mountains are studied in petrology, geochronology, geochemistry and HF isotopes. The formation age of granites is determined and the petrogenesis and geodynamic background of the Middle Jurassic granites in the Tal gas region of the central part of the Daxing'an Mountains are determined. The results of this paper not only further improve the geological data of Tal gas area, but also provide a scientific basis for the evolution history of the Middle Jurassic magmatic tectonics in the Daxing'anling area. In the study area, we selected four granite samples for LA-ICP-MS zircon U-Pb isotopic analysis. The zircons all developed a clear oscillatory growth ring zone with a high Th/U ratio, suggesting that they are typical magmatic zircon. It can reflect the age of rock formation. The 206Pb/238U ages of the samples are 173 卤1.3 Ma, 169.4 卤1.6 Ma, 166.3 卤1.2 Ma, 166.7 卤0.8 Ma, respectively, indicating that the granites in the Tal gas area of the middle part of the Daxing'an Mountains were formed in the Middle Jurassic. In addition, the Middle Jurassic granites in the Tal gas area of the middle part of the Daxing'anling Mountains are rich in silicon, alkali and calcium, and the characteristics of magnesium are mainly between 0.9 and 1.1, which are weak peraluminous high-potassium calc-alkaline granites. The rare earth elements of the samples show the characteristics of light REE enrichment, relative depletion of heavy REE elements, and obvious EU negative anomalies. In addition, the large ion lipophilic element RbHU is relatively enriched with high field strength elements, such as NbTa-Ta-Ti, and the relative depletion of Sr ~ (2 +) Ba. These geochemical characteristics indicate that the Middle Jurassic granitic granites belong to I-type granites in the Tal gas area of the middle part of the Daxing'anling Mountains. Moreover, the granite samples show a linear variation trend in the Harker diagram, which also indicates the rock characteristics of the I-type granite. In addition, the samples fall in the high grade I type and A type granite areas in the discriminant diagram, but the Zr element content of the granitic rocks in the study area is mostly less than the minimum value of the A type granite. The average zircon saturation temperature is lower than the formation temperature of typical A-type granites, which shows the characteristics of high-grade iso-I-type granites. The 蔚 Hf (t) values of the Middle Jurassic granitic rocks and the age of the two-stage mantle model are similar to the typical granitic rocks in the eastern part of the Xingmeng orogenic belt in the Tal gas region of the central part of the Daxing'anling Mountains. It is indicated that the granitic magma in the study area originated from the partial melting of newly proliferated young crustal materials during the Phanerozoic period. In combination with petrology, geochronology and geochemistry, it is considered that the formation of the Middle Jurassic granites in the study area may be related to the extensional process in the evolution of the Mongolia-Okhotsk Ocean. The extensional environment is caused by the upwelling of the asthenospheric mantle caused by the delamination of the thickened lithosphere.
【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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