本文選題：揚子陸塊北緣 + 畢機(jī)溝釩鈦磁鐵礦��； 參考：《長安大學(xué)》2015年碩士論文

【摘要】：畢機(jī)溝大型釩鈦磁鐵礦床位于揚子陸塊北緣漢南-米倉山構(gòu)造帶最北部,從大地構(gòu)造位置上看,位于揚子陸塊北緣和南秦嶺構(gòu)造帶相交接部位,有利于成礦元素富集。該構(gòu)造帶區(qū)域上呈NE-SW向展布有一條寬約60km、長約180km的巖漿巖帶,其中前人將該巖漿巖帶中分布于漢中南部的巖漿巖統(tǒng)稱漢南雜巖,前人雖然對該雜巖帶中典型巖體進(jìn)行了大量研究,但對于揚子陸塊北緣新元古代時期構(gòu)造環(huán)境仍存在分歧。本文主要通過研究畢機(jī)溝堆晶雜巖體的野外產(chǎn)出特征及規(guī)模,巖相組合及分帶特征,典型造巖礦物及金屬礦物特征,全巖主微量及稀土元素地球化學(xué),鋯石U-Pb年代學(xué)及Hf同位素特征,查明了畢機(jī)溝巖礦體巖漿演化特征、成礦時代、礦床成因以及巖漿源區(qū)特征。通過畢機(jī)溝釩鈦磁鐵礦床成巖成礦構(gòu)造背景的研究對揚子陸塊北緣新元古代構(gòu)造演化提供約束,并在該巖漿巖帶中尋找類似于畢機(jī)溝釩鈦磁鐵礦的巖體進(jìn)行成礦潛力分析。主要取得了一下幾點成果和認(rèn)識:(1)畢機(jī)溝巖體主要由下部斜長橄欖巖相帶;中下部輝長巖相帶、中上部異剝輝長巖相帶;上部閃長巖相帶三個巖相帶組成。巖石類型有橄欖巖、斜長橄欖巖、橄長巖、橄欖輝長巖、輝長巖、輝長閃長巖、閃長巖等。主要造巖礦物有橄欖石、斜方輝石、單斜輝石、斜長石和角閃石。礦石礦物主要以磁鐵礦和鈦鐵礦為主,賦礦層位主要分布于中上部異剝輝長巖相帶。(2)地球化學(xué)研究表明:畢機(jī)溝輝長巖具有拉斑玄武巖系列特征,貧Si,富Al、Ca,中等的Fe和Mg,低K、Na,在稀土元素球粒隕石標(biāo)準(zhǔn)化曲線顯示出“右傾型”的平緩形式,Eu正異常,輕稀土略富集重稀土相對虧損;微量元素蛛網(wǎng)圖中顯示出富集大離子親石元素(LILE),虧損Nb、Ta、Zr、Hf等高場強(qiáng)元素(HFSE),Th、U負(fù)異常以及Sr正異常特征。說明該巖體在巖漿演化過程中經(jīng)歷了明顯的結(jié)晶分異作用,顯示出了大陸邊緣弧的地球化學(xué)特征。(3)對畢機(jī)溝巖體的主要巖石類型輝長巖、圍巖花崗巖進(jìn)行了鋯石U-Pb測年,獲得了輝長巖成巖年齡為766.9±4.5Ma;圍巖花崗巖形成時代分別為784.2±3.6Ma和788.6±4.3Ma;同時獲得穿插于良心河含鈦磁鐵礦基性巖體內(nèi)部花崗脈巖年齡為760.2±2.9Ma。從而厘定了畢機(jī)溝地區(qū)在新元古代存在三期巖漿事件活動,畢機(jī)溝基性巖體中鋯石Hf同位素研究表明巖漿源區(qū)為虧損地幔且經(jīng)過地殼物質(zhì)混染。
[Abstract]:Bijigou large scale vanadium titanomagnetite deposit is located in the northern margin of Yangtze block Hannan-Micangshan tectonic belt. From the geotectonic position, it is located at the junction of the northern margin of Yangtze block and the southern Qinling tectonic belt, which is favorable for the enrichment of metallogenic elements. There is a magmatic belt with a width of about 60km and a length of about 180km in the NE-SW direction. The magmatic rocks distributed in the zone in the southern part of Hanzhong are called Hannan complex by their predecessors. Although many researches have been done on the typical rock mass in the complex, there are still differences on the Neoproterozoic tectonic environment in the northern margin of the Yangtze block. In this paper, the characteristics of field production and scale, lithofacies assemblage and zoning, typical rock-forming minerals and metal minerals, main trace and REE geochemistry of the whole rock are studied. Zircon U-Pb chronology and HF isotopic characteristics have been used to identify the characteristics of magma evolution, metallogenic epoch, ore genesis and magmatic source area of the Bijingou ore body. Based on the study of diagenetic and metallogenic tectonic setting of the Bijigou vanadium titanomagnetite deposit, the Neoproterozoic tectonic evolution of the northern margin of the Yangtze block is constrained, and the ore-forming potential of the rock body similar to that of the Bijigou vanadium titanomagnetite is analyzed in this magmatic belt. The Bijigou rock body is mainly composed of three lithofacies zones: lower oblique peridotite facies belt, middle and lower gabbro facies belt, middle and upper heteropyroxene facies belt, and upper diorite facies belt. Rock types include peridotite, peridotite, olivine gabbro, gabbro, pyrodiorite, diorite, etc. The main rock-forming minerals are olivine, clinopyroxene, clinopyroxene, plagioclase and amphibole. The ore minerals are mainly magnetite and ilmenite, and the ore-bearing strata are mainly distributed in the middle and upper heteropyroxene facies belt. The geochemical study shows that the Bijigou gabbro has the characteristics of tholeiite series. Si-poor, Al-Ca-rich, medium Fe and Mg-rich, low Ka-Na. The normalized curves of chondrites show a positive anomaly of EU in the "right-dip" flat form, and a slight enrichment of heavy rare earths. The trace element cobweb shows the negative anomalies and the positive Sr anomalies of high field strength elements such as high field strength, such as the enrichment of large ion lithophile element Lilei, and the depletion of high field strength elements, such as NbBX, Tazo-ZrHf, and so on. The results show that the rock mass has undergone obvious crystallization differentiation during magmatic evolution, showing the geochemical characteristics of continental margin arc. The zircon U-Pb dating of the main rock types of the Bijigou rock body, gabbro and surrounding rock granites, has been carried out. The diagenetic age of gabbro is 766.9 鹵4.5 Ma, the age of formation of surrounding rock granites is 784.2 鹵3.6Ma and 788.6 鹵4.3 Ma.The age of granitic dikes interspersed in the basic rocks of ilmenite bearing ilmenite is 760.2 鹵2.9 Ma. It is concluded that there are three magmatic events in the Neoproterozoic in the Bijigou area. The HF isotopic study of zircon in the Bijigou basic rock body shows that the magmatic source area is a depleted mantle and is contaminated by crustal materials.
【學(xué)位授予單位】：長安大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：P618.2

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