本文選題：柴北緣 + 北祁連��； 參考：《中國(guó)科學(xué)技術(shù)大學(xué)》2016年博士論文

【摘要】：對(duì)板塊俯沖變質(zhì)帶中榴輝巖的研究可以揭示高壓／超高壓變質(zhì)作用和俯沖之前區(qū)域構(gòu)造的信息。榴輝巖可以在大洋俯沖帶或者大陸俯沖帶形成,兩類榴輝巖都具有不同的來(lái)源和復(fù)雜的地球化學(xué)組成。由于陸殼俯沖是由洋殼俯沖牽引的,在大陸俯沖變質(zhì)帶洋殼榴輝巖可能和陸殼巖石共存,記錄了從洋殼俯沖到陸殼俯沖的構(gòu)造轉(zhuǎn)換。位于青藏高原東北緣的祁連造山帶是一個(gè)由其北部的北祁連洋殼高壓變質(zhì)帶和南部的柴北緣陸殼超高壓變質(zhì)帶組成的復(fù)合型造山帶。本文對(duì)北祁連和柴北緣榴輝巖分別進(jìn)行了全巖地球化學(xué)和鋯石學(xué)研究,結(jié)果揭示了洋殼和陸殼榴輝巖原巖的多樣性,并利用地球化學(xué)手段區(qū)分了柴北緣變質(zhì)帶的洋殼和陸殼榴輝巖,同時(shí)也對(duì)大陸超高壓變質(zhì)帶從洋殼俯沖到陸殼俯沖的構(gòu)造演化提供了制約。另外,對(duì)柴北緣錫鐵山地區(qū)長(zhǎng)英質(zhì)脈體及其圍巖的巖石學(xué)和地球化學(xué)研究則系統(tǒng)探討了不同巖性陸殼巖石深熔作用的熔融結(jié)構(gòu)、時(shí)限、機(jī)制和地球化學(xué)演化等。對(duì)北祁連低溫高壓洋殼榴輝巖和基性藍(lán)片巖進(jìn)行了全巖地球化學(xué)、單礦物O同位素和鋯石學(xué)的綜合研究。結(jié)果表明,這些洋殼榴輝巖和藍(lán)片巖的原巖是弧后盆地基性巖,而非通常認(rèn)為的洋中脊玄武巖(MORB)型基性巖。這些變基性巖具有不均一的主量和微量元素組成,在微量元素圖解上它們從類似于島弧玄武巖(IAB)、MORB變化到類似于洋島玄武巖(0IB)。這種變化多樣的成分特征和弧后盆地中不同階段發(fā)育的玄武巖類似。變基性巖成分的差別是從原巖繼承來(lái)的,全巖Nd同位素組成表明,弧后盆地地幔源區(qū)中存在不同比例沉積物衍生熔體。礦物之間的O同位素分餾多處于不平衡狀態(tài)。石榴石的O同位素組成表明,全巖的δ18O值高于或低于正常地幔值,這是繼承自不同溫度下海水熱液蝕變修正的弧后盆地基性巖。殘留的巖漿鋯石保留振蕩環(huán)帶,具有高的Th和U含量、高的Th/U比值,陡峭的重稀土配分形式并伴有顯著的Eu負(fù)異常,U-Pb定年揭示變基性巖的原巖年齡為496-486Ma。相比于殘留巖漿鋯石,變質(zhì)鋯石含有綠輝石、金紅石和多硅白云母等礦物包裹體,具有低的Th、U和HREE等含量,低的Th/U比值,U-Pb定年給出榴輝巖相變質(zhì)年齡為463±10 Ma。鋯石具有虧損的Hf同位素組成,其Hf模式年齡稍微或顯著老于原巖年齡,表明變基性巖原巖源區(qū)中有地殼組分加入。多數(shù)鋯石的δ18O值都不同于正常地幔值,并且不同樣品中鋯石δδ180值高低與石榴石δ18O值保持一致,表明在變質(zhì)過(guò)程中流體活動(dòng)是內(nèi)部緩沖的�？傊�,具有不同成分的變質(zhì)基性巖是來(lái)自早古生代弧后盆地的不同玄武質(zhì)巖石,弧后盆地在形成后轉(zhuǎn)變?yōu)檠髿じ_帶并發(fā)生了榴輝巖相變質(zhì)作用。為了限定柴北緣榴輝巖的原巖性質(zhì)和變質(zhì)演化,我們對(duì)其進(jìn)行了詳細(xì)的全巖主微量元素、Sr-Nd同位素、礦物O同位素,以及鋯石U-Pb年齡、微量元素、礦物包裹體和O-Hf同位素研究。結(jié)果被用來(lái)區(qū)分洋殼和陸殼榴輝巖、制約造山帶從洋殼俯沖到陸殼俯沖的構(gòu)造轉(zhuǎn)換。暗色CL鋯石區(qū)域具有高的Th和U等微量元素含量,高的Th/U比值,陡峭的重稀土配分形式并伴有顯著的Eu負(fù)異常,表明它們是經(jīng)歷過(guò)不同程度變質(zhì)改造的殘留原巖巖漿鋯石。對(duì)這些殘留原巖鋯石的分析揭示了兩類榴輝巖：第一類榴輝巖具有～830 Ma的原巖年齡和850--1100 Ma的Hf模式年齡,而第二類榴輝巖具有-500 Ma的原巖年齡和500～650 Ma的Hf模式年齡。占主體的第一類榴輝巖具有類似于來(lái)自不同地幔源區(qū)的大陸裂谷玄武巖的地球化學(xué)特征,如過(guò)渡型微量元素組成、大體正的εNd(t)值和正常地幔的δ18O值。這類榴輝巖是由新元古代羅迪尼亞超大陸裂解過(guò)程中產(chǎn)生的基性巖變質(zhì)而來(lái)的陸殼榴輝巖。第二類榴輝巖僅有少量分布.它們具有從類似于IAB變化到類似于MORB和OIB的微量元素配分形式,正的εNN(t)值和低的δ18O值。這類榴輝巖是由經(jīng)歷過(guò)海底高溫?zé)嵋何g變的弧后盆地輝長(zhǎng)巖轉(zhuǎn)變而來(lái)的洋殼榴輝巖。相比于殘留原巖鋯石,淺色CL鋯石區(qū)域含有石榴石、綠輝石和金紅石等礦物包裹體,具有低的Th和U等微量元素含量,低的Th/U比值,平坦的重稀土配分形式并沒(méi)有Eu的負(fù)異常。因此,這些鋯石是在榴輝巖相變質(zhì)條件下生長(zhǎng)的變質(zhì)鋯石;然而不論采樣地點(diǎn)和原巖性質(zhì),這些變質(zhì)鋯石給出了一致的433-440 Ma榴輝巖相變質(zhì)年齡。對(duì)兩個(gè)片麻巖中鋯石的分析也得到了427～439 Ma類似的榴輝巖相變質(zhì)年齡,而且其中一個(gè)片麻巖的鋯石中還發(fā)現(xiàn)了柯石英包裹體。洋殼榴輝巖和陸殼榴輝巖及片麻巖相同的榴輝巖相變質(zhì)年齡表明,洋殼榴輝巖可能原先位于洋陸轉(zhuǎn)換帶附近,因此與陸殼巖石具有相同的俯沖帶變質(zhì)演化。總之,洋殼榴輝巖和陸殼榴輝巖的共存記錄了柴北緣超高壓變質(zhì)帶從洋殼俯沖到陸殼俯沖的構(gòu)造轉(zhuǎn)換。另外,柴北緣和北祁連洋殼變基性巖具有相似的原巖年齡和弧后盆地基性巖化學(xué)成分,表明北祁連和柴北緣可能代表了一個(gè)從洋殼俯沖演化到陸殼俯沖的復(fù)合造山帶,它們與祁連地塊一起構(gòu)成祁連造山帶。對(duì)柴北緣錫鐵山地區(qū)的長(zhǎng)英質(zhì)脈體及其圍巖片麻巖和變基性巖進(jìn)行了綜合的巖石學(xué)、年代學(xué)和地球化學(xué)研究,結(jié)果揭示了深俯沖陸殼折返時(shí)的部分熔融。巖相學(xué)證據(jù)表明,片麻巖和變基性巖都發(fā)生了部分熔融。混合巖化片麻巖中保留了熔體存在的顯微結(jié)構(gòu),如具有不同輪廓的花崗質(zhì)礦物集合體,礦物邊界具有小的二面角的礦物顆粒以及具有巖漿習(xí)性的長(zhǎng)石顆粒等。片麻巖和退變榴輝巖中的長(zhǎng)英質(zhì)脈體都顯示良好的熔體結(jié)晶結(jié)構(gòu),表明它們是深熔熔體結(jié)晶的產(chǎn)物。脈體和圍巖的Sr-Nd同位素分析表明,片麻巖中脈體結(jié)晶自片麻巖深熔產(chǎn)生的熔體,而變基性巖中脈體的物質(zhì)來(lái)源既有變基性巖的貢獻(xiàn)也有片麻巖的貢獻(xiàn)。在An-Ab-Or圖解上,片麻巖中的脈體具有與類似條件下產(chǎn)生的實(shí)驗(yàn)熔體相似的化學(xué)成分。另外,片麻巖中的脈體具有與片麻巖大體平行的微量元素配分型式,但是它們的微量元素含量較片麻巖低并且具有輕微的Sr和Eu的正異常。片麻巖中脈體的地球化學(xué)特征受到部分熔融過(guò)程中特定礦物分解和殘留的控制。變基性巖中的長(zhǎng)英質(zhì)脈體富集石英或者斜長(zhǎng)石,幾乎不含鉀長(zhǎng)石。它們具有很低的微量元素含量,而且富長(zhǎng)石的脈體具有顯著的Eu和Sr的正異常�？紤]到一些脈體具有堆晶結(jié)構(gòu),推測(cè)這些脈體是從不同來(lái)源的深熔熔體中結(jié)晶的產(chǎn)物。但是,所有的脈體都具有一些共同的微量元素配分型式,如相對(duì)富集LILE和LREE并相對(duì)虧損HFSE和HREE。脈體和混合巖化片麻巖中的深熔鋯石給出了～420 Ma的年齡,小于附近的榴輝巖相變質(zhì)年齡,因此部分熔融發(fā)生在折返過(guò)程中。結(jié)合巖相學(xué)觀察、前人P-T軌跡和實(shí)驗(yàn)巖石學(xué)制約,推斷片麻巖經(jīng)歷了白云母脫水熔融而變基性巖的部分熔融是在外來(lái)流體參與下進(jìn)行的。不同成分的超高壓變質(zhì)巖在折返初期都經(jīng)歷了部分熔融,產(chǎn)生了具有不同微量元素特征但具有相似配分型式的深熔熔體。
[Abstract]:The study of Eclogite in the plate subduction metamorphic belt can reveal the information of high pressure / ultrahigh pressure metamorphism and regional tectonics before subduction. Eclogite can be formed in the oceanic subduction zone or the continental subduction zone. The two types of eclogites have different sources and complex geochemical formation. In the continental subduction metamorphic belt, the eclogite may coexist with the continental crust rocks, and the tectonic transition from subduction to continental subduction is recorded. The Qilian orogenic belt, located in the northeastern margin of the Qinghai Tibet Plateau, is a complex orogenic belt composed of the northern Qilian oceanic crust high pressure metamorphic belt and the Southern Chai Bei marginal continental crust ultrahigh pressure metamorphic belt. In this paper, the total rock geochemistry and zircon study of the Eclogite in northern Qilian and the northern Qaidam area were carried out respectively. The results revealed the diversity of the oceanic and crustal eclogites, and used geochemical methods to distinguish the oceanic crust and eclogite from the northern margin of the Qaidam metamorphic belt and the subduction of the continental ultrahigh pressure metamorphic belt from the oceanic crust to the continental subduction. In addition, the petrology and geochemistry of the long angled veins and its surrounding rock in the tin Tieshan area of the northern margin of the Qaidam area were studied, and the melting structure, time limit, mechanism and geochemical evolution of different lithologic continental crust rocks were discussed. The eclogite and the basic blue schist of the low temperature and high pressure oceanic crust in North Qilian were carried out. A comprehensive study of all rock geochemistry, single mineral O isotopes and zirconium studies. The results show that the original rocks of these oceanic eclogites and blue schist rocks are the base rocks of the back arc basin, but not the commonly considered basalt (MORB) base rocks of the mid ocean ridge. These metamorphic rocks are composed of inhomogeneous principal and trace elements, and they are diagrammed in trace elements. From similar to island arc basalts (IAB), MORB changes to similar Yu Yang island basalt (0IB). This variety of components is similar to the basalts developed at different stages in the back arc basin. The variation of basic rock components is inherited from the original rock, the whole rock Nd isotope composition table shows that there are different proportions in the mantle source area of the back arc basin. The O isotopic fractionation between minerals is mostly in unbalanced state. The O isotopic composition of garnet indicates that the delta 18O value of the whole rock is higher or lower than the normal mantle value. This is the base rock of the back arc basin that inherited the alteration of the hydrothermal alteration under different temperatures. The residual magmatic zircon retained the oscillating belt, which has a high Th and U content. High Th/U ratio, steep rare-earth distribution form and significant Eu negative anomaly. U-Pb dating shows that the original rock age of the metamorphic rocks is 496-486Ma. compared to the residual magma zircon. The metamorphic zircon contains mineral inclusions such as omroxene, Jin Hongshi and polysilicon muscovite, with low Th, U and HREE content, low Th/U ratio, U-Pb dating. The metamorphic age of the eclogite facies is 463 + 10 Ma. zircon with a loss of Hf isotopes, and its Hf mode age is slightly or significantly older than the original rock age, indicating that there are crustal components in the basic lithic source area. The delta 18O values of most of the zircon are different from that of the normal mantle, and the values of the delta delta 180 of zircon in different samples and the garnet Delta 18O The value remains consistent, indicating that fluid activity is internal buffer during the process of metamorphism. In a word, the metamorphic base rocks with different components are different basaltic rocks from the early Paleozoic back arc basin. After formation, the back arc basin changed into the oceanic subduction zone and the eclogite phase transformation of the eclogite occurred. In order to limit the original lithology of the Eclogite in the northern margin of the Qaidam Basin Qualitative and metamorphic evolution, we have carried out a detailed total rock main trace elements, Sr-Nd isotopes, mineral O isotopes, and zircon U-Pb age, trace elements, mineral inclusions and O-Hf isotopes. The results were used to distinguish Oceanic and crustal eclogites from the tectonic transformation of the orogenic belt from the oceanic subduction to the continental subduction. The dark CL zircon The region has a high content of trace elements such as Th and U, high Th/U ratio, steep rare-earth distribution and significant negative Eu abnormality, indicating that they are remnant primary magmatic zircon from varying degrees of metamorphism. The analysis of these residual zircon reveals two types of eclogite: the first type of eclogite has 830 Ma. The age of the original rock and the Hf pattern age of 850--1100 Ma, and the second type eclogite with -500 Ma of the original rock age and the Hf mode age of 500~650 Ma. The first type of eclogite, which is the main body, is similar to the geochemical characteristics of the continental rift Xuan Wuyan from different mantle sources, such as the composition of the transitional trace elements, and the gross positive e Nd (T) values. The delta 18O value of the normal mantle. This type of eclogite is a terrestrial eclogite from the metamorphic base rocks of the Neoproterozoic ultralonian supercontinent. The second types of eclogites have only a small number of eclogites. They have the distribution form of the trace elements similar to IAB to MORB and OIB, the positive value of the NN (T) and the low delta 18O value. The eclogite is the oceanic eclogite that has changed from the gabbro in the back arc basin of the seabed high temperature hydrothermal alteration. Compared with the residual zircon, the light color CL zircon region contains the mineral inclusions of garnet, omyroxene and Jin Hongshi, with low content of trace elements such as Th and U, low Th/U ratio, and flat rare-earth distribution form. There is no negative anomaly of Eu. Therefore, these zircons are metamorphic zircons grown under the metamorphic condition of the eclogite facies. However, the metamorphic zircon gives the consistent 433-440 Ma eclogite facies metamorphic age regardless of the sampling sites and the original rock properties. The analysis of zircon in two gneiss has also obtained 427~439 Ma similar eclogite phase transition years. The COO quartz inclusions are also found in one of the gneiss zircon. The same eclogite metamorphic age of the pomegranate Hui Yan and Lu Keliu Hui Yan and the gneiss indicates that the pomegranate Hui Yan may have been originally located near the oceanic transition zone, so that the continental crust rocks have the same subduction zone metamorphic evolution. The coexistence of the eclogite records the tectonic transition from subduction to continental subduction in the UHP metamorphic belt of the northern margin of the Qaidam Basin. In addition, the metamorphic base rocks of the northern margin of the Qaidam and Northern Qilian oceanic crust have similar proto rock age and the chemical composition of the base rocks in the back arc basin, indicating that the northern Qilian and the Qaidam basin may represent a subduction from the oceanic crust to Lu Kefu. The compound orogenic belt, which is formed by the Qilian massif, constitutes the Qilian orogenic belt together with the geo petrology, geochronology and geochemistry of the long angled veins and its surrounding rock gneiss and metamorphic rocks in the tin Tieshan area of the northern Qaidam border. The results reveal the partial melting of the reentry of the deep subducted continental crust. Petrographic evidence indicates that gneiss Partial melting has occurred in the metamorphic rocks. The microstructures of the melts are retained in the mixed rock gneiss, such as the granitic mineral aggregates with different outlines, mineral particles with small dihedral angles and feldspar particles with magma habits, and the feldspar veins in gneiss and degenerative eclogites all show The good crystalline structure of the melt indicates that they are the products of the crystallization of the deep melt melt. The Sr-Nd isotope analysis of the veins and surrounding rocks indicates that the veins in the gneiss are crystallized from the melts produced by the gneiss, and the material source of the veins in the metamorphic rocks has both the contribution of the metamorphic rock and the contribution of the gneiss. In the An-Ab-Or diagram, the gneiss The vein body is similar to the experimental melts produced under similar conditions. In addition, the veins in the gneiss have a distribution pattern of trace elements that are generally parallel to the gneiss, but their trace elements are lower than the gneiss and have a slight abnormal Sr and Eu. The geochemical characteristics of the veins in the gneiss are subject to the Department. The control of the decomposition and residue of specific minerals during the melting process. The feldspar veins in the metamorphic rocks are enriched with quartz or plagioclase, almost without potassium feldspar. They have a very low trace element content, and the rich feldspar veins have significant positive anomalies of Eu and Sr. The crystallization of the melts from different sources. However, all the veins have some common trace element distribution patterns, such as the relative enrichment of LILE and LREE, and the relative loss of HFSE and HREE. veins and the deep melting zircons in the mixed lithic gneiss. The age of ~ 420 Ma is less than the metamorphic age of the surrounding eclogite facies. The partial melting occurred during the process of exhumation. In combination with petrographic observation, the predecessors' P-T trajectory and experimental petrology have concluded that the gneiss experienced the dehydration and melting of the muscovite and the partial melting of the metamorphic rocks was carried out under the participation of foreign fluids. Deep melt melts with similar trace elements but similar distribution patterns.

【學(xué)位授予單位】：中國(guó)科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：P588.3
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本文編號(hào)：1803044