【摘要】：本文以大興安嶺中段塔爾氣地區(qū)中侏羅世花崗巖為研究對象，對該地區(qū)的中侏羅世花崗巖進行了巖石學、年代學、地球化學及Hf同位素等方面的研究，厘定了花崗巖的形成時代，確定了大興安嶺中段塔爾氣地區(qū)中侏羅世花崗巖的巖石成因以及與其有關的地球動力學背景。本文的研究結(jié)果不僅使塔爾氣地區(qū)的地質(zhì)資料獲得進一步完善，同時也為大興安嶺地區(qū)中侏羅世巖漿—構(gòu)造的演化歷史提供了科學依據(jù)。 在研究區(qū)內(nèi)，我們選擇了4件花崗巖樣品進行了LA-ICP-MS鋯石U-Pb同位素分析，鋯石均發(fā)育結(jié)構(gòu)清晰的振蕩生長環(huán)帶，并且具有較高的Th/U比值，暗示其為典型巖漿成因鋯石，可以反映巖石的形成時代。經(jīng)測試分析，樣品的206Pb/238U年齡分別為173±1.3Ma、169.4±1.6Ma、166.3±1.2Ma、166.7±0.8Ma，顯示大興安嶺中段塔爾氣地區(qū)的花崗巖形成于中侏羅世。 此外，大興安嶺中段塔爾氣地區(qū)的中侏羅世花崗巖具有富硅、富堿以及貧鈣、鎂的特點，ACNK值多集中在0.9～1.1之間，，為弱過鋁質(zhì)高鉀鈣堿性花崗巖。樣品的稀土元素表現(xiàn)出輕稀土元素富集，重稀土元素相對虧損的特征，并且具有明顯的Eu負異常。此外大離子親石元素元素Rb、Th、U相對富集，Nb、Ta、Ti等高場強元素以及Sr、Ba相對虧損。上述這些地球化學特征均顯示大興安嶺中段塔爾氣地區(qū)中侏羅世花崗屬于I型花崗巖。而且，在Harker圖解中花崗巖樣品表現(xiàn)出明顯的線性變化趨勢，同樣指示著I型花崗巖的巖石特征。此外，樣品在判別圖解中落在高分異I型和A型花崗巖區(qū)域，但是研究區(qū)內(nèi)的花崗質(zhì)巖石的Zr元素含量大多小于A型花崗巖的最低值，平均鋯石飽和溫度低于典型A型花崗巖的形成溫度，顯示了高分異I型花崗巖的特征。 大興安嶺中段塔爾氣地區(qū)中侏羅世花崗的εHf（t）值和二階段地幔模式年齡與興蒙造山帶東段的典型花崗質(zhì)巖石具有相似的特點，指示研究區(qū)內(nèi)花崗質(zhì)巖漿來源于顯生宙期間新增生的年輕地殼物質(zhì)的部分熔融。同時結(jié)合巖石學，年代學以及地球化學研究，認為研究區(qū)內(nèi)中侏羅世花崗巖的形成可能與蒙古-鄂霍茨克洋演化過程中的伸展作用有關，而該拉張環(huán)境為加厚巖石圈拆沉引起的軟流圈地幔物質(zhì)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 鹵1.3 Ma, 169.4 鹵1.6 Ma, 166.3 鹵1.2 Ma, 166.7 鹵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.
【學位授予單位】：吉林大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：P588.121

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