本文選題：混合巖 + 巖石類(lèi)型��； 參考：《合肥工業(yè)大學(xué)》2017年碩士論文

【摘要】：在大陸深俯沖和碰撞形成造山帶過(guò)程中,地殼普遍存在的深熔作用可影響造山帶內(nèi)地殼的熱力學(xué)和流變學(xué)性質(zhì),進(jìn)而可能會(huì)導(dǎo)致造山帶最終垮塌。造山帶中的混合巖主要由深熔作用形成,所以混合巖研究對(duì)于理解部分熔融、變質(zhì)演化和造山過(guò)程的相互關(guān)系具有重要意義。大別造山帶的北大別構(gòu)造單元廣泛發(fā)育混合巖。前人對(duì)北大別混合巖的命名和分類(lèi)比較混亂,缺乏系統(tǒng)的觀察和分類(lèi);對(duì)于北大別混合巖的成因機(jī)制各個(gè)學(xué)者觀點(diǎn)不一,且對(duì)于混合巖形成的確切時(shí)代依然存有爭(zhēng)議。選擇羅田和岳西穹隆中混合巖開(kāi)展了野外觀察、巖相學(xué)、礦物化學(xué)、巖石化學(xué)和鋯石LA-ICP-MS U-Pb定年等系統(tǒng)工作,發(fā)現(xiàn)北大別混合巖主要分為疊層狀和膨脹結(jié)構(gòu)中等深熔混合巖以及眼球狀和析離體狀高度深熔混合巖兩種類(lèi)型。疊層狀淺色體、淺色脈體和花崗巖顯著虧損Fe_2O_3、MgO、MnO、TiO_2和CaO,高度深熔淺色體則稍微富集這些元素。疊層狀淺色體的全巖主量元素組成分為花崗質(zhì)和英云閃長(zhǎng)質(zhì),淺色脈體為花崗質(zhì)。高度深熔淺色體的全巖主量元素組成與片麻巖相似,為花崗閃長(zhǎng)質(zhì)。淺色體和花崗巖表現(xiàn)為L(zhǎng)REE以及不相容元素Ba、Th和U的富集,而Nb和Ti顯著虧損。疊層狀淺色體具有強(qiáng)烈的Eu正異常,花崗質(zhì)淺色脈體和花崗巖則表現(xiàn)為Eu負(fù)異常,高度深熔淺色體無(wú)明顯Eu異常。這些都指示高度深熔淺色體、疊層狀淺色體和花崗質(zhì)淺色脈體具有成因聯(lián)系,分別結(jié)晶于不同演化程度的熔體。鋯石U-Pb同位素定年結(jié)果表明,北大別混合巖的原巖主要為來(lái)自新元古代的巖石、另有少量的古元古代地殼。混合巖化作用從145 Ma持續(xù)到124 Ma。斜長(zhǎng)石-角閃石溫壓計(jì)估算結(jié)果顯示,混合巖形成的溫壓條件為723-768°C和3.7-5.2 kbar,對(duì)應(yīng)于中上地殼環(huán)境�；旌蠋r的成因機(jī)制以長(zhǎng)英質(zhì)片麻巖水飽和條件下的富水熔融為主。其反應(yīng)為:黑云母+石英+斜長(zhǎng)石+水=角閃石+斜長(zhǎng)石(殘留)+花崗質(zhì)熔體。少數(shù)混合巖的成因機(jī)制為角閃片麻巖中角閃石的脫水熔融。其反應(yīng)為:角閃石+斜長(zhǎng)石+石英=單斜輝石+富水熔體。
[Abstract]:During the process of continental deep subduction and collision forming orogenic belt, the deep melting in the crust can affect the thermodynamic and rheological properties of the crust of the orogenic belt, which may lead to the eventual collapse of the orogenic belt.The migmatite in the orogenic belt is mainly formed by deep melting, so the study of migmatite is of great significance in understanding the relationship between partial melting, metamorphic evolution and orogenic process.Migmatite is widely developed in the Beidabie tectonic unit of the Dabie orogenic belt.Previous scholars have confused the naming and classification of Peking University migmatite, lack of systematic observation and classification, different scholars have different views on the genetic mechanism of Peking University migmatite, and there are still disputes about the exact age of the formation of migmatite.Luotian and Yuexi dome migmatists were selected to carry out systematic work such as field observation, petrography, mineral chemistry, petrochemistry and zircon LA-ICP-MS U-Pb dating.It is found that the Beidabie migmatite is mainly divided into two types: laminated migmatite and expandable structure medium deep melt migmatite and eyeball and exfoliated high deep melt migmatite.Laminated light-colored bodies, light-colored veins and granites are significantly depleted of Fes _ 2O _ 3MgO _ 2O _ (mn) O _ (2) TiO _ 2 and CaO _ 2, and are slightly enriched in these elements by the highly deep-melt light-colored bodies.The main element compositions of the laminated light-colored bodies are granitic and diorite, while the light-colored veins are granitic.The main element composition of the whole rock is similar to that of gneiss and is granodiorite.The light-colored bodies and granites are characterized by enrichment of LREE and incompatible elements Ba-Th and U, while NB and Ti are significantly depleted.There are strong positive EU anomalies in laminated light-colored bodies, negative EU anomalies in granitic light-colored veins and granites, and no obvious EU anomalies in highly submersible light-colored bodies.All of these indicate that there is a genetic relationship between the laminated light-colored bodies and granitic light-colored veins, and they are crystallized in melts with different degrees of evolution.The results of zircon U-Pb isotopic dating show that the primary rocks of the Beidabie migmatite are mainly from Neoproterozoic rocks and a small amount of Paleoproterozoic crust.The migmatization lasted from 145 Ma to 124 Ma.The temperature and pressure conditions of the mixed rocks are 723-768 擄C and 3.7-5.2 kbar. which correspond to the middle and upper crustal environment.The genetic mechanism of migmatite is water-rich melting of felsic gneiss under water saturation.The reaction was: biotite quartz plagioclase water = amphibole plagioclase (residual) granitic melt.The genetic mechanism of a few mixed rocks is dehydration and melting of amphibole in hornblende gneiss.The reaction is: amphibole plagioclase quartz = clinopyroxene rich water melt.
【學(xué)位授予單位】：合肥工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：P588.36

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