长白山天池火山成因研究

发布时间：2018-06-29 23:18

本文选题：长白山天池火山 + 成因　；参考：《吉林大学》2016年博士论文

【摘要】：长白山天池火山由于远离俯冲带板块边界/海沟,位于平卧的俯冲板块(西太平洋板块)上方约600 km左右,显然成因不同于传统的俯冲带火山,应该属于内陆火山成因的一种。目前对于这种远离板块边界/海沟的陆内火山成因,尚不是十分清楚。由于地震层析成像等技术的支持,俯冲板块深部脱水导致上覆地幔部分熔融进而产生岩浆作用,引起越来越多的关注。目前,俯冲板块深部脱水导致上覆地幔部分熔融进而产生岩浆作用的成因机制研究主要是通过数值模拟计算或者通过地震层析成像等数据进行推测,但是直接证据,特别是岩石地球化学方面的证据还较少。本次研究的内容主要分为地球动力学数值模拟和岩石地球化学分析两部分。根据地球动力学数值模拟的结果,结合岩石地球化学的分析结果,最终对长白山天池火山的成因给出合理的、定量的解答。为了从地球动力学角度分析太平洋板块俯冲对长白山天池火山成因的影响,建立了一个二维的热力学耦合数值模型对太平洋板块水化、俯冲、脱水(深部脱水)、部分熔融产生、熔融物质上升、以及陆内火山/岩浆作用形成的整个地球动力学过程进行了模拟。研究内容主要包括板块的深部脱水过程以及弧后盆地的演化过程。前者是说明水分可以被俯冲板块带到深部(~600 km)并最终释放出来,引起上覆地幔楔部分熔融,形成陆内岩浆房,最终在陆内形成火山作用的整个动力过程。后者是说明板块俯冲可以形成宽广的弧后盆地(宽度大于1000 km),从而使得大陆板块前缘可以远离俯冲带板块边界/海沟1000 km。岩石地球化学分析主要利用野外地质调查、岩石地球化学分析、年龄测定等手段,与地球动力学数值模拟的结果进行比对,进一步的研究长白山陆内火山/岩浆的成因。经过本次研究主要得到了以下结论:(1)模拟结果说明俯冲板块有能力将水分带入到~660 km的相变面并释放出来,俯冲板块深部脱水所释放的水分随着时间的推移逐渐增多并向上覆的地幔楔运移。水分的存在使得地幔楔物质的熔融点降低,从而导致了地幔楔中发生部分熔融。这些部分熔融物质可以运移到大陆板块下方形成岩浆房,从而引发陆内的火山/岩浆作用。(2)板块深部脱水及深部地幔楔部分熔融是一个十分复杂的地球动力学过程,具有众多的影响因素:最大控制因素是地幔楔中岩石熔融点的变化特性,因为其直接控制着地幔物质是否可以发生部分熔融;产生大量的深部部分熔融需要一个很长的模型演化时间,因此板块的俯冲演化时间也是深部熔融的一个重要影响因素;在模型演化过程中观察到板块会在不同的时间或者部位发生拆沉,板块的拆沉影响了板块深部脱水及深部地幔楔部分熔融的过程,以及最终部分熔融发生以及上升的位置;地幔楔的温-压条件由于在整个俯冲过程中变化不大,因此对板块深部脱水的影响不大。(3)本文运用数值模拟技术分析了俯冲带弧后盆地扩展的四个阶段,并归纳了3个弧后盆地扩展的主要模式,并得到了俯冲板块如果拥有合适的地球物理参数是有能力形成~1000 km的弧后盆地的结论。另外,系统讨论了弧后伸展的影响因素,认为当板块年龄适中(120 Ma),且具有合适的板块间耦合力(合适的λfluid andλmelt值,如0.05),以及较慢的汇聚速率时,板块的地球物理性质使其可以产生宽广的弧后扩展区。(4)分析长白山天池火山二道白河流域玄武岩主量元素、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质岩石来源于同一地幔源区,具有似原始地幔的特征,靠近原始地幔且有略向EM1富集地幔偏移的趋势,是在地幔条件下经橄榄石、辉石和基性斜长石结晶分异后形成的岩浆,玄武岩保留部分熔融趋势,其形成与俯冲板片的部分熔融有关,且岩浆在上升的过程中遭受了壳源物质的同化混染。本文首次结合地球动力学数值模拟技术和地球岩石化学分析对长白山火山这一远离海沟的陆内火山成因进行了探讨,并给出了一个较为合理的解释。这一结果(1)将对研究板块俯冲及火山岩浆形成的动力学机制提供重要的依据;(2)对区域新生代火山岩及岩浆形成演化机制的研究提供基础资料;(3)为探讨区域玄武岩岩浆来源、岩浆性质和成因、构造环境提供新的论据;(4)为进一步研究该地区火山的活动性、喷发机制、预测方法等提供定量化的基础资料;(5)为东亚远离海沟的陆内弧后火山的形成,提供定量化的、可视化的深部地球动力学背景;(6)为火山灾害监测与预防等提供一定参考,具有重要的现实意义。
[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.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P317

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