【摘要】：大別造山帶分布有大量NNE走向的巖脈,其巖石類型多樣,包括石英正長斑巖、花崗斑巖、石英閃長巖以及輝綠巖等。區(qū)內(nèi)廣泛發(fā)育中生代巖漿巖,以中酸性為主,伴有少量的基性巖。巖脈切穿區(qū)內(nèi)廣泛發(fā)育的巖漿巖,為燕山期巖漿活動最晚的產(chǎn)物。通過鋯石LA-ICPMS定年方法得到石英正長斑巖、石英閃長巖和花崗斑巖3種類型的四件巖脈樣品的年齡分別為127.1±4.5 Ma、127.5±1.9 Ma、127.4±2.5 Ma和127.9±2.1 Ma,這些巖脈的形成時代較為集中,其形成時代為早白堊世,代表了大別造山帶中生代巖漿活動幕的結(jié)束。巖脈群是郯廬斷裂帶左行走滑動力學體制下,巖漿沿剪張裂隙侵入形成,巖脈的形成時代指示郯廬斷裂帶南段中生代第三次左行走滑可能發(fā)生在127 Ma左右。大別造山帶中生代石英二長巖和二長巖體中暗色包體廣泛發(fā)育。這些暗色包體具有典型的巖漿結(jié)構(gòu),與寄主巖有著相似的礦物組合,但礦物粒度更細,暗色礦物含量更高,巖性主要為閃長巖質(zhì)。部分包體中發(fā)育鉀長石斑晶和眼球狀的石英,以及針狀磷灰石。三個包體和一個寄主巖的鋯石U-Pb定年表明,暗色包體的形成年齡主要為133~129 Ma,石英二長巖為130 Ma左右,表明包體與寄主巖的形成時代在誤差范圍內(nèi)一致,都為早白堊世。單礦物的電子探針分析得到,二者礦物化學組分相似,形成的溫壓條件相仿,且包體中存在地幔物質(zhì)的加入。在地球化學方面,包體和寄主巖的主量元素組成在Hacker圖解中呈現(xiàn)出明顯的線性關(guān)系。二者都較富集輕稀土元素和大離子親石元素,虧損高場強元素,稀土元素配分圖和微量元素蛛網(wǎng)圖的配分模式表現(xiàn)出相似的特點,說明包體和寄主巖之間存在成因聯(lián)系。綜合包體和寄主巖的巖石學礦物學特點、鋯石U-Pb年齡和相關(guān)地球化學特征,本文認為大別地區(qū)發(fā)育的暗色包體是巖漿混合作用的結(jié)果。早白堊世幔源巖漿底侵,誘發(fā)下地殼物質(zhì)的部分熔融,進而發(fā)生鐵鎂質(zhì)巖漿和長英質(zhì)巖漿的混合作用。
[Abstract]:The Dabie orogenic belt has a large number of veins with NNE strike, and its rock types include quartz syenite porphyry, granitic porphyry, quartz diorite and diabase. Mesozoic magmatic rocks are widely developed in the area, mainly intermediate acid with a small amount of basic rocks. The magmatic rocks widely developed in the area are the latest product of Yanshanian magmatic activity. Through zircon LA-ICPMS dating method, the ages of four types of quartz syenite porphyry, quartz diorite and granitic porphyry are 127.1 鹵4.5 Ma,127.5 鹵1.9 Ma,127.4 鹵2.5 Ma and 127.9 鹵2.1 Ma, respectively. The age of their formation is early Cretaceous. It represents the end of the Mesozoic magmatic activity curtain in the Dabie orogenic belt. Under the dynamic regime of left strike-slip in the Tanlu fault zone, the magma intruded along the shear-tensional fissure. The formation age of the vein indicates that the third left strike-slip occurred in the southern part of the Tan-Lu fault zone at about 127 Ma. Dark inclusions are widely developed in Mesozoic quartz monzonitic rocks and erzhang rocks in the Dabie orogenic belt. These dark inclusion bodies have typical magmatic structure and have similar mineral assemblages with host rocks, but the mineral granularity is finer, the dark mineral content is higher, and the lithology is mainly diorite. Potassium feldspar porphyry and eyeball quartz, as well as needle-like apatite, were found in some of the inclusions. The zircon U-Pb dating of three xenoliths and one host rock indicates that the age of dark xenoliths is about 130 Ma, which indicates that the ages of formation of the xenoliths and the host rocks are consistent within the range of errors and belong to the early Cretaceous. Electron probe analysis of single mineral shows that the chemical components of the two minerals are similar, the temperature and pressure conditions are similar, and the inclusion of mantle material exists in the inclusion. In terms of geochemistry, the principal element compositions of the xenoliths and host rocks show an obvious linear relationship in the Hacker diagram. Both of them are relatively rich in light rare earth elements and large ion lithophile elements, and are depleted of high field strength elements. The distribution patterns of rare earth elements and trace element cobwebs show similar characteristics, indicating the genetic relationship between the xenoliths and host rocks. Based on the petrological and mineralogical characteristics of the xenoliths and host rocks, zircon U-Pb age and related geochemical characteristics, it is considered that the dark inclusion developed in the Dabie area is the result of magmatic mixing. In the early Cretaceous mantle magma submergence induced partial melting of lower crust materials and then the mixing of ferromagnesian magma and felsic magma occurred.
【學位授予單位】：合肥工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P597.3;P587

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