本文選題：長(zhǎng)白山天池火山 + 成因　； 參考：《吉林大學(xué)》2016年博士論文

【摘要】：長(zhǎng)白山天池火山由于遠(yuǎn)離俯沖帶板塊邊界/海溝,位于平臥的俯沖板塊(西太平洋板塊)上方約600 km左右,顯然成因不同于傳統(tǒng)的俯沖帶火山,應(yīng)該屬于內(nèi)陸火山成因的一種。目前對(duì)于這種遠(yuǎn)離板塊邊界/海溝的陸內(nèi)火山成因,尚不是十分清楚。由于地震層析成像等技術(shù)的支持,俯沖板塊深部脫水導(dǎo)致上覆地幔部分熔融進(jìn)而產(chǎn)生巖漿作用,引起越來(lái)越多的關(guān)注。目前,俯沖板塊深部脫水導(dǎo)致上覆地幔部分熔融進(jìn)而產(chǎn)生巖漿作用的成因機(jī)制研究主要是通過(guò)數(shù)值模擬計(jì)算或者通過(guò)地震層析成像等數(shù)據(jù)進(jìn)行推測(cè),但是直接證據(jù),特別是巖石地球化學(xué)方面的證據(jù)還較少。本次研究的內(nèi)容主要分為地球動(dòng)力學(xué)數(shù)值模擬和巖石地球化學(xué)分析兩部分。根據(jù)地球動(dòng)力學(xué)數(shù)值模擬的結(jié)果,結(jié)合巖石地球化學(xué)的分析結(jié)果,最終對(duì)長(zhǎng)白山天池火山的成因給出合理的、定量的解答。為了從地球動(dòng)力學(xué)角度分析太平洋板塊俯沖對(duì)長(zhǎng)白山天池火山成因的影響,建立了一個(gè)二維的熱力學(xué)耦合數(shù)值模型對(duì)太平洋板塊水化、俯沖、脫水(深部脫水)、部分熔融產(chǎn)生、熔融物質(zhì)上升、以及陸內(nèi)火山/巖漿作用形成的整個(gè)地球動(dòng)力學(xué)過(guò)程進(jìn)行了模擬。研究?jī)?nèi)容主要包括板塊的深部脫水過(guò)程以及弧后盆地的演化過(guò)程。前者是說(shuō)明水分可以被俯沖板塊帶到深部(~600 km)并最終釋放出來(lái),引起上覆地幔楔部分熔融,形成陸內(nèi)巖漿房,最終在陸內(nèi)形成火山作用的整個(gè)動(dòng)力過(guò)程。后者是說(shuō)明板塊俯沖可以形成寬廣的弧后盆地(寬度大于1000 km),從而使得大陸板塊前緣可以遠(yuǎn)離俯沖帶板塊邊界/海溝1000 km。巖石地球化學(xué)分析主要利用野外地質(zhì)調(diào)查、巖石地球化學(xué)分析、年齡測(cè)定等手段,與地球動(dòng)力學(xué)數(shù)值模擬的結(jié)果進(jìn)行比對(duì),進(jìn)一步的研究長(zhǎng)白山陸內(nèi)火山/巖漿的成因。經(jīng)過(guò)本次研究主要得到了以下結(jié)論:(1)模擬結(jié)果說(shuō)明俯沖板塊有能力將水分帶入到~660 km的相變面并釋放出來(lái),俯沖板塊深部脫水所釋放的水分隨著時(shí)間的推移逐漸增多并向上覆的地幔楔運(yùn)移。水分的存在使得地幔楔物質(zhì)的熔融點(diǎn)降低,從而導(dǎo)致了地幔楔中發(fā)生部分熔融。這些部分熔融物質(zhì)可以運(yùn)移到大陸板塊下方形成巖漿房,從而引發(fā)陸內(nèi)的火山/巖漿作用。(2)板塊深部脫水及深部地幔楔部分熔融是一個(gè)十分復(fù)雜的地球動(dòng)力學(xué)過(guò)程,具有眾多的影響因素:最大控制因素是地幔楔中巖石熔融點(diǎn)的變化特性,因?yàn)槠渲苯涌刂浦蒯Ｎ镔|(zhì)是否可以發(fā)生部分熔融;產(chǎn)生大量的深部部分熔融需要一個(gè)很長(zhǎng)的模型演化時(shí)間,因此板塊的俯沖演化時(shí)間也是深部熔融的一個(gè)重要影響因素;在模型演化過(guò)程中觀察到板塊會(huì)在不同的時(shí)間或者部位發(fā)生拆沉,板塊的拆沉影響了板塊深部脫水及深部地幔楔部分熔融的過(guò)程,以及最終部分熔融發(fā)生以及上升的位置;地幔楔的溫-壓條件由于在整個(gè)俯沖過(guò)程中變化不大,因此對(duì)板塊深部脫水的影響不大。(3)本文運(yùn)用數(shù)值模擬技術(shù)分析了俯沖帶弧后盆地?cái)U(kuò)展的四個(gè)階段,并歸納了3個(gè)弧后盆地?cái)U(kuò)展的主要模式,并得到了俯沖板塊如果擁有合適的地球物理參數(shù)是有能力形成~1000 km的弧后盆地的結(jié)論。另外,系統(tǒng)討論了弧后伸展的影響因素,認(rèn)為當(dāng)板塊年齡適中(120 Ma),且具有合適的板塊間耦合力(合適的λfluid andλmelt值,如0.05),以及較慢的匯聚速率時(shí),板塊的地球物理性質(zhì)使其可以產(chǎn)生寬廣的弧后擴(kuò)展區(qū)。(4)分析長(zhǎng)白山天池火山二道白河流域玄武巖主量元素、微量元素、稀土元素Sr-Nd同位素特征,表明二道白河流域玄武質(zhì)巖石來(lái)源于同一地幔源區(qū),具有似原始地幔的特征,靠近原始地幔且有略向EM1富集地幔偏移的趨勢(shì),是在地幔條件下經(jīng)橄欖石、輝石和基性斜長(zhǎng)石結(jié)晶分異后形成的巖漿,玄武巖保留部分熔融趨勢(shì),其形成與俯沖板片的部分熔融有關(guān),且?guī)r漿在上升的過(guò)程中遭受了殼源物質(zhì)的同化混染。本文首次結(jié)合地球動(dòng)力學(xué)數(shù)值模擬技術(shù)和地球巖石化學(xué)分析對(duì)長(zhǎng)白山火山這一遠(yuǎn)離海溝的陸內(nèi)火山成因進(jìn)行了探討,并給出了一個(gè)較為合理的解釋。這一結(jié)果(1)將對(duì)研究板塊俯沖及火山巖漿形成的動(dòng)力學(xué)機(jī)制提供重要的依據(jù);(2)對(duì)區(qū)域新生代火山巖及巖漿形成演化機(jī)制的研究提供基礎(chǔ)資料;(3)為探討區(qū)域玄武巖巖漿來(lái)源、巖漿性質(zhì)和成因、構(gòu)造環(huán)境提供新的論據(jù);(4)為進(jìn)一步研究該地區(qū)火山的活動(dòng)性、噴發(fā)機(jī)制、預(yù)測(cè)方法等提供定量化的基礎(chǔ)資料;(5)為東亞遠(yuǎn)離海溝的陸內(nèi)弧后火山的形成,提供定量化的、可視化的深部地球動(dòng)力學(xué)背景;(6)為火山災(zāi)害監(jiān)測(cè)與預(yù)防等提供一定參考,具有重要的現(xiàn)實(shí)意義。
[Abstract]:The Tianchi volcano, in Changbai Mountain, is about 600 km above the subducted plate boundary / trench above the subduction plate (the Western Pacific plate). It is obviously different from the traditional subduction zone volcano. It should be one of the inland volcanoes. At present, the origin of the intracontinental volcanism far away from the plate boundary / trench is not yet very much. It is clear that the deep dewatering of the subducted plate leads to the partial melting of the overlying mantle and then the magmatism due to the support of seismic tomography and other techniques. At present, the mechanism of the cause of the partial melting of the overlying mantle resulting in partial melting of the overlying mantle and resulting in the magmatism is mainly calculated by numerical simulation or There are few evidence for direct evidence, especially in rock geochemistry. The main contents of this study are divided into two parts: geodynamic numerical simulation and rock geochemical analysis. Based on the results of geodynamic numerical simulation, the results of geochemistry analysis are combined with the results of rock geochemical analysis. In order to analyze the influence of the Pacific plate subduction on the genesis of the Changbai Mountain Tianchi volcano from the geodynamic point of view, a two-dimensional thermodynamic coupling numerical model was established for the hydration, subduction, dehydration (deep dehydration), partial melting and melting of the Pacific plate, in order to analyze the influence of the subduction of the Pacific plate on the genesis of the volcano in Changbai Mountain Tianchi volcano. Material rise, and the whole geodynamic process of the intracontinental volcano / magmatism, mainly include the deep dehydration of the plates and the evolution of the back arc basin. The former shows that the water can be carried to the deep (~600 km) and eventually released, resulting in the partial melting of the overlying mantle wedge. It forms an intracontinental magma chamber that eventually forms the entire dynamic process of volcanic activity within the continent. The latter indicates that the plate subduction can form a broad back arc basin (the width is more than 1000 km), so that the front edge of the continental plate can be far away from the plate boundary of the subduction zone / the 1000 km. rock geochemical analysis of the trench, mainly using the field geological survey. Geochemical analysis, age measurement and other means, compared with the results of geodynamic numerical simulation, further study the genesis of the Changbai Mountain intracontinental volcano / magma. (1) the simulation results show that the subduction plate has the ability to bring water into the phase transition surface of ~660 km and release the subduction plate. The water released by the deep dehydration of the block increases with time and moves to the overlying mantle wedge. The presence of water reduces the melting point of the mantle wedge, resulting in partial melting of the mantle wedge. These partial molten materials can be moved to the magma chamber under the continental plate, thus causing the volcano in the land. Magmatism. (2) deep dehydration of the plate and deep mantle wedge partial melting is a very complicated geodynamic process, which has a great number of influencing factors: the maximum control factor is the change in the melting point of the rock in the mantle wedge, because it directly controls the partial melting of the mantle material and produces a large amount of deep partial melting. Thawing requires a long model evolution time, so the subduction evolution time of the plate is also an important factor of deep melting. During the evolution of the model, the plate will be deformed at different time or part, and the disintegration of the plate affects the process of deep dehydration of the plate and the partial melting of the deep mantle wedge. The temperature pressure condition of the mantle wedge has little influence on the deep dehydration of the plate. (3) in this paper, the four stages of the expansion of the subducting basin were analyzed by numerical simulation technology, and the main modes of the expansion of 3 back arc basins were classified and obtained. The subduction plate, if having the appropriate geophysical parameters, is a conclusion that has the ability to form a back arc basin of ~1000 km. In addition, the system discussed the influence factors of the post arc extension, considering that when the plate age is moderate (120 Ma), and with appropriate coupling force between the plates (a suitable fluid and [and] melt value, such as 0.05), and a slower convergence rate, The geophysical properties of the plates make it possible to produce broad post arc expansion areas. (4) analysis of the main elements, trace elements and Sr-Nd isotopes of the basalt in the two Dao of the Tianchi volcano, Tianchi volcano, Changbai Mountain, indicates that the basaltic rocks of the two Dao River Basin are derived from the same mantle source and have the characteristics of primitive mantle, close to the original site. The trend of mantle migration to the EM1 enriched mantle is the magma formed by the crystallization of olivine, pyroxene and basic plagioclase under the mantle condition, and the basalt has a tendency to retain partial melting, which is related to the partial melting of the subduction plate, and the magma has been assimilated and dyed with the shell source in the process of rising. The geodynamic numerical simulation technique and the geochemistry analysis of the earth petrochemistry have discussed the genesis of the intracontinental volcanism of the Changbai Mountain volcano, a far away trench, and gave a more reasonable explanation. This result (1) will provide an important basis for the study of the dynamic mechanism of plate subduction and the formation of volcanic magma; (2) to the Cenozoic in the region The research on the formation and evolution of volcanic rocks and magma provides basic information; (3) it provides a new basis for exploring the source of magma, magmatic properties and genesis and tectonic environment of regional basalt; (4) providing quantitative basic data for further study of the activity, eruption mechanism and prediction methods of the volcanoes in this area; (5) it is the interior of the East Asia far away from the trench. The formation of post arc volcanoes provides quantitative and visual deep geodynamic background; (6) it is of great practical significance to provide some reference for monitoring and prevention of volcanic disasters.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：P317

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