本文選題：吉爾孟巖體 + 花崗巖�。� 參考：《中國地質大學(北京)》2017年碩士論文

【摘要】：沿著柴北緣在南祁連一側出露有一系列早古生代的侵入巖,本文研究區(qū)在南祁連青海湖北部吉爾孟地區(qū),出露有花崗閃長巖、二長花崗巖和少量英云閃長巖等中酸性侵入巖,它們均侵位于早古生代地層,巖體年齡及成因對于南祁連地區(qū)早古生代的大地構造演化具有重要的意義。本文基于對該地區(qū)侵入巖體的野外調查、巖相學特征、鋯石U-Pb年代學、全巖地球化學及Hf同位素特征研究,揭示吉爾孟巖體的結晶年齡與巖石成因類型,探討了南祁連早古生代侵入巖的形成與大地構造演化之間的關系。利用高精度LA-ICP-MS鋯石U-Pb定年測得6個樣品的年齡,其中花崗閃長巖年齡為458Ma、439.6Ma、453.5Ma,二長花崗巖年齡為457.5Ma、455.8Ma,英云閃長巖年齡為448.4Ma,表明吉爾孟巖體形成于晚奧陶世-早志留世時期。地球化學特征顯示吉爾孟巖體屬于過鋁質-強過鋁質鈣堿性-高鉀鈣堿性系列的英云閃長巖到二長花崗巖,兼具有I型和S型花崗巖的特征,為I-S過渡型花崗巖;微量元素蛛網圖上富集大離子親石元素K、Th、U等,虧損高場強元素Nb、Ta、P、Sr、Ti等,具有島弧火山巖的特征;稀土元素球粒隕石標準化配分型式圖上,呈現(xiàn)出輕稀土富集、重稀土相對平坦的右傾“V”字型模式。通過對吉爾孟巖體的鋯石Hf同位素研究,獲得兩件花崗閃長巖樣品的εHf(t)值分別分布于-1.4~-12.0及-7.8~-11.8之間,兩階段模式年齡TDM C(Ma)變化范圍分別為1.50~2.17Ga(集中于1.70~2.17Ga)及1.92~2.17Ga。前者的Hf同位素組成變化范圍較大,暗示其有幔源巖漿的混入,而后者具有較穩(wěn)定的Hf同位素組成,暗示其來源于古老地殼基底的深熔。通過以上對南祁連吉爾孟巖體的研究,結合構造背景認為該地區(qū)花崗巖與南祁連洋向北俯沖消減具有密切的關系,巖漿來自于南祁連洋的俯沖到碰撞的構造體制轉換背景下古元古代地殼基底的部分熔融與地幔底侵物質的不均勻混合作用。因此,吉爾孟地區(qū)的花崗巖是處于同一俯沖帶內的不同時期形成于不同背景下的兩類花崗巖,揭示了450~460Ma之間南祁連洋仍然處于向北俯沖的構造背景之下,而439Ma時南祁連洋已經處于閉合階段,本文所研究的花崗巖形成于洋陸轉換階段。
[Abstract]:Along the northern margin of Qaidam, a series of early Paleozoic intrusive rocks were exposed on the side of South Qilian. In this study area, there are granodiorite, monzogranite and a small amount of dolomite and other intermediate-acid intrusive rocks in the Germeng area north of Qinghai Lake in South Qilian. Both of them are located in the early Paleozoic strata and the age and genesis of the rock mass are of great significance for the tectonic evolution of the early Paleozoic in the South Qilian area. Based on the field investigation, petrographic characteristics, zircon U-Pb chronology, whole rock geochemistry and HF isotopic characteristics of intrusive rock bodies in this area, this paper reveals the crystallization age and petrogenetic types of the Kilmeng rock mass. The relationship between the formation of early Paleozoic intrusive rocks and tectonic evolution in South Qilian is discussed. The age of 6 samples was determined by LA-ICP-MS zircon U-Pb dating with high accuracy. The age of granodiorite is 458 Ma-439.6Ma-453.5Ma., the age of monzogranite is 457.5 Ma-455.8Ma. the age of Yingyun diorite is 448.4 Ma. which indicates that the Gillmonite was formed in the late Ordovic-early Silurian period. The geochemical characteristics show that the Jilmeng rock body is a type of dolomite diorite to monzogranite of peralumina-strong peraluminous calc-alkaline high-potassium calc-alkaline series, which has the characteristics of both I-type and S-type granites, and is I-S transitional granite. The trace element cobwebs are enriched in large ion lithophile elements K _ (+) Thu and so on, and the depletion of high field strength elements, such as Nbtadao _ Ta-Ph _ (Sr) Ti and so on, are characterized by island arc volcanic rocks, and the normalized distribution pattern of chondrites of rare earth elements is characterized by light rare earth enrichment. Heavy rare earth relatively flat right-leaning "V" pattern. Based on the study of zircon HF isotopes of the Gillmund massif, the 蔚 HF ~ (t) values of two granodiorite samples are found to be between -1.4 ~ (-12.0) and -7.8 ~ 11.8, respectively, and the variation range of the two-stage model age TDM _ (C) Mais is 1.50 ~ 2.17Ga (concentrated at 1.702.17GaA) and 1.92kW _ (2.17Gaa), respectively. The HF isotopic composition of the former has a large variation range, which implies that it is mixed with mantle magma, while the latter has a more stable HF isotope composition, implying that it originated from the deep penetration of the basement of the ancient crust. Based on the above study of the South Qilian Gil Meng pluton and combined with the tectonic background, it is concluded that the granite in this area is closely related to the subduction of the South Qilian Ocean toward the north. The magma originated from the subduction to collision tectonic regime transformation of the South Qilian Ocean. The partial melting of the Gu Yuan ancient crustal basement and the inhomogeneous mixing of the mantle submersion material. Therefore, the granites in the Kilmeng area are two types of granites formed in different settings at different times in the same subduction zone, which reveals that the South Qilian Ocean between 450~460Ma is still in the tectonic setting of northward subduction. The South Qilian Ocean was already closed by 439Ma, and the granite studied in this paper was formed in the stage of oceanic transition.
【學位授予單位】：中國地質大學(北京)
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P597.3;P583
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本文編號：1959304