本文選題：巖漿作用　切入點：郯廬斷裂帶　出處：《中國科學技術大學》2016年博士論文　論文類型：學位論文

【摘要】：巖漿作用是地球內(nèi)部各圈層之間能量及物質(zhì)交換的重要途徑和媒介,在陸殼形成、生長和演化中具有重要作用。同時,作為來自深部地球的樣品,巖漿巖可以作為探視地球深部結構、組成以及了解深部過程的天然探針。巖漿巖成分、時代分布、空間展布特征及其演化可以為大地構造變遷、深部巖漿房形成和演化等提供重要的信息。此外,巖漿過程中的同位素(分餾)行為是穩(wěn)定同位素地球化學的基礎問題,這關系到穩(wěn)定同位素作為地質(zhì)過程的示蹤劑等基礎應用。鎂同位素是新近發(fā)展起來的新型同位素地質(zhì)示蹤劑,已經(jīng)在示蹤沉積物循環(huán)以及碳循環(huán)上得到了一定的應用。但是,目前對于高硅巖漿體系(如花崗巖)的鎂同位素體系了解很有限,對花崗質(zhì)巖漿過程中的鎂同位素行為也尚不清楚�；谏鲜龅恼J識,本博士論文工作主要包括兩個方面的內(nèi)容：1)利用中酸性巖漿巖這一類“深部探針”來窺探華北克拉通破壞的深部過程及啟動機制；2)對酸性巖漿(主要是花崗巖)開展鎂同位素地球化學研究,嘗試理解鎂同位素在地殼巖漿活動中的同位素行為。本博士論文第一個研究內(nèi)容是郯廬斷裂帶兩側分布的中生代巖漿巖進行了元素地球化學、地質(zhì)年代學和氧同位素的分析調(diào)查,來限定和理解克拉通巖石圈減薄、郯廬斷裂帶的大規(guī)模走滑活動和大量的巖漿作用間的聯(lián)系和深部過程。針對該區(qū)域內(nèi)的中生代巖漿巖進行了分析結果顯示沿郯廬斷裂走向分布的高鎂埃達克巖的侵入年齡都集中在在130-134Ma之問,這種時間和空間分布上的特征表明這些高鎂埃達克質(zhì)巖的形成和郯廬斷裂在中生代的大規(guī)模走滑(156-162Ma)活動具有明顯的成因上的聯(lián)系。此外,蘇魯造山帶內(nèi)的低鎂埃達克質(zhì)巖(120-127Ma)整體上形成于稍晚于高鎂埃達克質(zhì)巖形成的時代,這一結果同樣稍晚于大別造山帶低鎂埃達克質(zhì)巖的形成時代(129-143Ma)。綜合上述結果,顯示郯廬斷裂帶中生代的切穿巖石圈的走滑活動可能是華北克拉通東南緣的巖石圈減薄的啟動機制：斷裂帶大規(guī)模的走滑可能引發(fā)了斷裂附近加厚下地殼局部破碎而形成一些比重比較大的下地殼碎片,這些碎片沉入較輕的軟流圈和橄欖巖反應而顯著提高熔體的Mg#而形成年齡稍老的高鎂埃達克質(zhì)巖；另外,斷裂的活動也同時使蘇魯造山帶下方的下地殼的重力不穩(wěn)定的程度增加,進而引發(fā)蘇魯造山帶的大規(guī)模的去山根過程,形成低鎂埃達克質(zhì)巖和一些普通花崗巖。此外,對此地區(qū)中生代巖漿巖的鎂同位素的初步研究表明鎂同位素可能不是示蹤“拆離的下地殼物質(zhì)與地幔相互作用進而形成高鎂達克質(zhì)巖巖”這一地質(zhì)過程的有效手段,從而無法通過鎂同位素有效區(qū)分高、低鎂埃達克質(zhì)巖。而低鎂埃達克質(zhì)巖均一的鎂同位素組成也折射本地區(qū)下地殼的鎂同位素組成相對均一,并接近地幔值。極少數(shù)普通花崗巖的鎂同位素偏重,表明極少部分地區(qū)存在小規(guī)模的沉積物循環(huán)加入。本博士論文另一個研究內(nèi)容是系統(tǒng)分析蚌埠隆起區(qū)晚侏羅紀巖漿作用的代表巖體—荊山花崗巖(其巖漿物質(zhì)來源為深俯沖過程中楔入華北東南緣的華南片麻巖的部分熔融)的各類主要巖性的巖石樣品(主體花崗巖、細晶巖及殘留體)以及單礦物(石榴子石和黑云母)的主-微量元素化學及鎂同位素組成,解析了此巖體形成和演化過程可能發(fā)生的鎂同位素分餾,進而對陸殼深俯沖過程中的鎂同位素循環(huán)及陸殼部分熔融過程中的鎂同位素分餾提供了啟示和限定。荊山花崗巖代表性的淡色花崗巖樣品和相關的殘留體的全巖鎂同位素數(shù)據(jù)表明,荊山花崗巖具有非常特殊的輕鎂同位素特征。綜合該巖體的氧同位素特征,其源區(qū)應具有典型低氧-高鎂的同位素特征。結合周邊各主要巖石類型的氧-鎂同位素特征及二元混合模擬計算,只有在其巖漿源區(qū)加入一定比例的輕鎂-重氧的碳酸巖的混熔才有可能形成具有該巖體的低氧高鎂的同位素特征。這一結果揭示了俯沖帶及周邊地區(qū)碳酸巖可能進入深部地球巖漿循環(huán),對了解地球深部碳循環(huán)過程具有重要的意義。對單礦物的調(diào)查結果表明,荊山花崗巖中黑云母與石榴子石間普遍存在大于1‰的鎂同位素分餾。這一分餾對于理解部分熔融過程中可能發(fā)生的同位素分餾具有重要的啟示作用。轉熔石榴子石是殼內(nèi)部分熔融的重要富鎂礦物,對其的鎂同位素組成及共生富鎂礦物的調(diào)查可以直接對殼內(nèi)部分熔融過程中的鎂同位素分餾進行直接限定。我們的結果表明,轉熔石榴子石和黑云母間存在著顯著的分餾,隨著石榴子石對鎂體系的控制能力的提高(如更多的黑云母分解轉換為石榴子石或者石榴子石中鎂含量的提高),部分熔融反應過程中產(chǎn)生的熔體的鎂同位素會顯著的向重鎂同位素方向發(fā)生分餾。這一推論表明在地殼部分熔融過程(特別是普遍具有轉熔石榴子石參與部分熔融的S型花崗巖的形成)很可能會發(fā)生顯著的同位素分餾,對解釋大陸地殼的鎂同位素特征和演化具有重要的意義。
[Abstract]:Magmatic activity is between the various spheres of the earth's internal energy and material exchange in an important way and the media, formed in the continental crust, which plays an important role in the growth and evolution. At the same time, as the sample from the deep earth, magmatite can visit as deep earth structure, natural probe as well as the understanding of the deep process of magmatite. Composition, age distribution, distribution characteristics and evolution of space for tectonic evolution, deep magma chamber formation and evolution provide important information. In addition, in the process of magma (isotope fractionation) behavior is a basic problem of stable isotope geochemistry, which relates to the stable isotope tracers as geological processes and other basic applications. Is a new type of isotopic tracer magnesium isotope newly developed, has been in circulation as well as the carbon cycle tracing of sediments has been used. However, in order for high silicon The magmatic system (such as granite) magnesium isotopic system understanding is limited, the magnesium isotope behavior of granitic magma in the process is not clear. Based on the above understanding, this dissertation mainly includes two aspects: 1) deep process and mechanism to start to see the destruction of the North China Craton using acidic magma this kind of "deep rock probe"; 2) of acidic magma (mainly granite) to carry out research on magnesium isotope geochemistry, try to understand the isotope behavior in the earth's crust in magmatic activity. The magnesium isotope doctoral thesis first research content is the Mesozoic magmatite of Tanlu fault zone on both sides of the distribution of elements in the earth chemical analysis, investigation of geochronology and isotope, to define and understand the cratonic lithosphere, the Tanlu fault zone of large-scale strike slip movement and a large number of magmatism between contact and deep Part of the process are analyzed. Aiming at the Mesozoic magmatite region shows the intrusive age along Tanlu fault strike high Mg adakitic rocks distribution are concentrated in the 130-134Ma in question, characteristics of the time and space distribution showed that these high Mg adakitic rocks and the formation of the Tanlu fault in Mesozoic large-scale strike slip (156-162Ma) activity has obvious genetic relationship. In addition, the low Mg adakitic rocks in the Su Lu Orogen (120-127Ma) on the whole formed in the later formation of high Mg adakitic rocks of the era, the results are also slightly later than the low Mg adakitic rocks in the Dabie orogenic belt forming era (129-143Ma). The above results, show the strike slip movement of the Mesozoic lithosphere in cutting of the Tanlu fault zone may be the southeast margin of the North China Craton lithosphere of the starting mechanism of thin: large-scale strike slip fault zone may lead The fault in the vicinity of thickened lower crust fracture formed some relatively large proportion of the lower crustal fragments, these fragments into the asthenosphere and peridotite reaction lighter and significantly improve the melt Mg# and the formation of the old age a little high Mg adakitic rock; in addition, the activity of the fault at the same time the Su Lu orogenic belt below the lower crust of gravitational instability degree increases, causing the Su Lu orogenic belt scale to root process, the formation of low Mg adakitic rocks and some common granite. In addition, this area of the Mesozoic magmatite magnesium isotope preliminary research shows that magnesium isotopic tracer may not be removed from the "crust and mantle interaction the role of effective means and the formation of the geological process of high rock rock" Mei Da Ke, which can not effectively distinguish by magnesium isotopes, low Mg adakitic rocks. While the low Mg adakitic rocks The region also reflected magnesium isotopic composition of lower crust is relatively uniform composition of magnesium isotope uniform, and close to the mantle. A handful of magnesium isotope value of common granite emphasis, indicate the existence of small scale sediment circulation with very few parts of this dissertation. Another research content is the system analysis of Bengbu uplift in late Jurassic magmatism on behalf of the rock - Jingshan granite (the magma origin is wedged into the deep subduction process of the southeastern margin of North Southern China gneiss partial melting) all kinds of main lithology rock samples (the main granite aplite and residue) and minerals (garnet and biotite) of the main trace elements and magnesium isotopic composition, isotopic fractionation analysis of the magnesium rock formation and evolution may occur, and then melting of continental subduction in the process of magnesium isotope cycle and continental Department Provide inspiration and limit the magnesium isotopic fractionation process. Jingshan granite representative granite samples and related residues of the whole rock mg isotopic data suggest that Jingshan granite has light magnesium isotopic characteristics of very special. The comprehensive oxygen isotopic characteristics of the rock mass and isotopic characteristics of typical hypoxia - high magnesium should be the area surrounding the source. Combined with the main rock types of the oxygen isotope characteristics of magnesium and two yuan hybrid simulation, only the light magnesium carbonate rock - added at the magma source region of a certain proportion of the heavy oxygen mixing can be formed with the isotopic characteristics of the rock mass of high magnesium. The hypoxia results revealed carbonate rocks in subduction zones and the surrounding areas may enter the earth deep magmatic cycle, has important significance for understanding the earth's deep carbon cycle process. According to survey results of single minerals, Jingshan biotite granite Common magnesium isotopic fractionation is greater than 1% of the existing parent and garnet. This fractionation has important implications for understanding possible isotopic fractionation during partial melting. The peritectic garnet is an important part of magnesium rich mineral melting within the crust, the magnesium isotopic composition and magnesium rich mineral intergrowth the investigation can be directly on the magnesium isotopic fractionation during partial melting of the crust are directly limited. Our results show that peritectic garnet and biotite have significant fractionation, with the ability to control the garnet system of magnesium increased (such as more biotite garnet or decomposed into the increase of the content of magnesium garnet), magnesium isotopic melt generated partial melting during the reaction will be to the direction of significant heavy magnesium isotopic fractionation occurs. This shows that in the process of partial melting of the crust. (special It is possible that significant isotopic fractionation is likely to take place in the formation of S granites, which is generally involved in the melting of garnet and partial melting. It is of great significance to explain the characteristics and evolution of magnesium isotopes in the continental crust.

【學位授予單位】：中國科學技術大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：P588.11;P597

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本文編號：1585825