【作者】 赵波；

【导师】 许建东；

【作者基本信息】 中国地震局地质研究所 ， 构造地质学， 2010， 博士

【摘要】 长白山天池火山千年大喷发火山碎屑流分布范围广泛,是国内火山碎屑流领域重要的研究对象。前人研究表明:(1)长白山天池火山千年大喷发火山碎屑流搬运堆积机制复杂,且火山碎屑流近源、中源部分一般分布在人迹罕至尚未开发的地方,火山碎屑流相模式尚未系统建立;(2)火山碎屑流是长白山地区主要灾害类型,尚未有专题的灾害区划图;(3)早期粒度分析主要采用人工法测试,精度低,误差大,大量微米级碎屑的动力学信息流失。针对上述问题,本文开展了长白山天池火山千年大喷发火山碎屑流研究工作。1.研究内容(1)建立火山碎屑流纵向厚度分布图,分析其平面分布形态特征,探讨分布形态与天池原始地貌之间的关系;(2)通过野外地质调查,分别建立近源、中源和远源地层堆积构造组合特征,对火山碎屑流的流体性质及搬运方式进行探讨;(3)通过岩石学和地球化学数据分析,分别建立近源、中源和远源的岩相特征,探讨不同阶段火山碎屑流的流体性质;(4)建立中源、远源纵向和垂向粒度分布剖面对比图,研究粒度(<64mm)的碎屑粒度、成分和形貌分布规律,并对细火山灰直方图分布特征进行研究,探讨粒度分布与火山碎屑流流体性质之间的关系;(5)以白西林场火山碎屑流的地浪堆积地层为研究对象,分析其成因、探讨其搬运堆积模式;(6)以天池火山地貌TIN和DEM图为基础,选取火山碎屑流搬运的物理模型和数学计算模型,计算不同规模喷发碎屑流动距离,建立火山碎屑流灾害区划图。2.研究思路和方法(1)确定研究对象,在野外寻找一套完整的现象明显的火山碎屑流;(2)系统研究火山碎屑流地质特征、采集样品和获取第一手数据,其中地质特征包括空间分布、岩相特征、地层构造特征、矿物学特征、岩石化学特征等,建立火山碎屑流相模式;(3)室内分析碎屑粒度特征(区分出浮岩、岩屑、晶屑),对比研究各种碎屑的分布特征。用SEM方法研究对应碎屑显微形貌特征及其形成机制。对两者结果进行对比,并得出结论;(4)研究火山碎屑流地层有规律的堆积构造特征;(5)在以上研究基础上,研究天池火山火山碎屑流灾害区划。在以上研究中,主要用到岩石学、地球化学、地层学和沉积学的研究方法,具体包括薄片分析、全岩分析、粒度分析、统计学分析、显微形貌特征分析和形态分析等方法。3.主要结论及认识本篇论文主要从分布形态、地层堆积构造、岩石学、地球化学、火山碎屑特征和搬运堆积模式六个方面对长白山天池火山千年大喷发火山碎屑流进行研究,并在此基础上建立了天池火山碎屑流灾害区划图。本次研究主要得到以下九点结论:(1)天池火山千年大喷发火山碎屑流分布形态严格受到天池火山原始地貌的影响:以十二道白河为例,在大概0~10km范围内,在火山锥体峡谷底部堆积,厚度在1-4m;大概10-20km范围内,为峡谷堆积,厚度在10-40m;20-50km为扇状堆积。根据形态和厚度分布特征,天池火山碎屑流分布形态为火山碎屑裙,厚度一般小于10m。(2)近源火山碎屑流地层堆积构造组合有斑杂构造、类熔岩构造等;中源火山碎屑流地层堆积构造组合有柱状节理、块状构造(垮塌成因)、强熔结条带、底部岩屑富集带、浮岩富集带等,此外发育逃气孔、峰从等构造;远源火山碎屑流地层堆积构造组合有粗尾粒序层理、爬升地层和地浪堆积地层等,次生改造程度高。(3)近源岩石一般为碱性粗面质熔结凝灰岩;中源岩性为碱性粗面质熔结凝灰岩;远源为碱流质浮岩松散堆积。(4)近源、中源黑色浮岩为粗面岩;远源灰白色浮岩为碱流岩。(5)中源和远源松散堆积的小于64mm的碎屑,随着与火口距离的增加,纵向上火山碎屑中值有变大的趋势,随着剖面深度的增加,火山碎屑中值变小的趋势;随着与火口距离的增加,随着与火口距离的增加,4-8mm火山碎屑的球形度整体变化趋势是增大,但增势较缓,反映了近源火山碎屑流流体密度高;随着与火口距离的增加,岩屑含量减少,反映了重力分异作用,一定程度上揭示了流体密度的降低。(6)火山碎屑粒度越小,碎屑棱边改造越少,碎屑形态越丰富,火山碎屑搬运机制越趋于单一化;细火山分布特征具有相似性,呈单峰态负偏态分布。(7)灰云浪和地浪直方图特征相似,向细粒集中,反映流体密度低。火山碎屑流流动单元直方图分布呈多峰态,反映搬运方式复杂。(8)天池火山西坡白西林场千年大喷发火山碎屑流在搬运过程中有水作用参与。(9)以天池火山为中心,喷发柱高度为10km,灾害区划最大半径为13.69km;喷发柱高度为20km,灾害区划最大半径为35.42km;喷发柱高度为30km,灾害区划最大半径为57.8km。以千年喷发火山碎屑流分布格局为参考,根据天池火山周边地区地貌特征制作出天池火山火山碎屑流不同规模喷发灾害区划图。4.创新点在研究过程,主要有以下四点创新:(1)本篇论文首次通过长白山天池火山火山碎屑流分布形态、地层堆积构造、岩石学、地球化学、粒度分析和地浪地层搬运模式的研究,采用了扫描电镜、形态分析和激光粒度仪等实验分析方法,建立了长白山天池千年大喷发火山碎屑流相模式,提出近源火山碎屑流流体密度高,搬运能力强,堆积厚度薄,岩相特征为碱性粗面质熔结凝灰岩;中源火山碎屑流流体密度有所减弱,重力分异作用明显,堆积厚度巨大,岩相特征为碱性粗面质熔结凝灰岩;远源火山碎屑流流体密度最低,湍流和地浪等流体化作用明显,堆积厚度薄,岩相特征为碱流岩。(2)本文首次对火山碎屑流和火山碎屑涌流细火山灰(小于62.5μm)粒度分布特征进行了研究,主要有以下两个发现:发现了火山碎屑流细火山灰直方图具有一定相似性,呈单峰态、负偏态分布特征;发现了火山碎屑涌流在0.1μm-1μm之间仍有碎屑分布,而火山碎屑流基本上无小于1μm的碎屑,从粒度分析角度证明了射汽岩浆爆破式喷发作用导致的碎屑破碎化程度要高于岩浆爆破式喷发作用。(3)本文通过地层分析、扫描电镜分析和粒度分析等方法对长白山地区天池火山白西林场地层进行系统研究,提出了白西林场火山碎屑流有水作用参与,并建立了白西林场火山碎屑流搬运堆积模式,初步划分为碎屑淬火、蒸汽膨胀和堆积三个阶段。(4)国内首次运用滑块模型对天池火山火山碎屑流流动距离进行计算。更多还原

【Abstract】 Changbaishan Tianchi volcano is the largest composite volcano, which is located in the northeast of China, at the boundary between China and North Korea. In 1215(±15), there was a large plinian eruption in Tianchi volcano which is called millennium eruption. Millennium eruption produced widespread pryolcatic-flow deposits. According to the previous study, there are three problems about the pyroclastic-flow deposits. First, there is no systematic facies about that pyroclastic-flow. Most of the pyroclastic flow deposited in the wild place which is undeveloped. Second, there is no hazard zonation for pyroclasitc-flow which is a major disaster in Changbaishan area. Third, grain-size analysis has not reached to the micron level.In order to answer these problems, some research works have been developed in this paper.1. Main contents and research methodologMain contents for research are:(1) to establish vertical thickness map of pyroclastic-flow in one valley, analysis shape characteristics, and discuss the relationship between shapes of pyroclastic-flow and prime topography before that eruption;(2) to separately establish the stratum characteristics for the proximal, medial and distal pyroclastic-flow, and discuss the transportation of pyroclastic-flow ;(3) to separately establish the litofacies characteristics for the proximal, medial and distal pyroclastic- flow by analyses of micro structure and major element, and discuss the fluid nature of pyroclastic-flow in different stages;(4) to establish the grain-size distribution for the medial and distal pyroclastic-flow, study fine ash distribution, and discuss the relationship between grain-size and pyroclastic- flow transportation;(5) to describe pyroclastic flow stratums at the distal part of the pyroclastic-flow in Baixi, analysis the genetic classification of the stratum, and discuss the transportation and deposition processes.(6).to establish the hazard zonation for pyroclastic-flow which is based on the slide-block model and analyses of DEM&TIN in Tianchi volcano. Research methodologies are :(1) to find a complete pyroclastic-flow in the Tianchi volocano , and determine the object of this study; (2)to study the stratum、litho and geochemistry by analysis of micro structure, major element and Scanning Electron Microscope (SEM); (3) to study the grain-size distribution by sieve instrument (Easy Sieve) and some of them by manual sieve ; (4) to describe the shape of grain-size from the median and distal pyroclastic-flow by analysis of SEM and morphological instrument (Camerasizer);(5) to analyses the fine ash distribution by laser grain-size analyzer.2. Main conclusionsThis paper has studied the shape, strata, litho, geochemistry, grain-size and transportation of ground–surge from pyroclasitc-flow of millennium eruption in Tianchi volcano. The main conclusions which have been got are as follows:(1) The shape of pyroclastic-flow in millennium eruption is strictly affected by the prime topography of Tianchi volcano. About in 0~10 km in the cone, pyroclastic-flow deposited in the valley, and the thickness is at about 1~4m. About in 10~20 km in the shield, pyoclastic-flow deposited in the valley, and the thickness is at about 10~40m. About in 20~42km, pyroclastic-flow deposited in the lava table, and the thickness is less than 10m.(2) The proximal strata of pyroclastic-flow are combined with the eutaxite structures and lava-like structures. The median strata are combined with massive beds、pumice-rich layers、litchis-richer layers and welded zones which are representative of the transportation processes for gravitational differentiation. And columnar joints and block structures are also developed which are representative of the deposition processes for cooling. The distal strata are combined with coarse-tail beds, ground surge beds and climbing beds. There are also some altered beds because of flood. The distal pyroclastic-flow strata have some fluidized characteristics.(3) The proximal ignimbrite is alkaline trachytic welded tuff. The median ignimbrite is also alkaline trachytic welded tuff. And the distal ignimbrite is alkaline rhyolite. The welded tuff is weaker from the proximal to the distal. (4) The proximal and median black pumice is trachyte. And the distal gray pumice is rhyolite.(5) The median diameters of pumice which is less than 64mm from the median and distal strata have an increasing tendency with the distance increasing from the crater. And the median diameters become smaller with the depth increasing from the top of strata. The Sphericity (Spht) has an increasing tendency with the distance increasing from the crater. And the contents of lithoclasts in number percentage decrease with the distance increasing from the crater which reveals gravitational differentiation.(6) With the pumice becoming smaller, there are more angles, richer irregular shapes and simpler transportation. The grain-size distributions of fine ash are similar and have a single peak which is close to the fines.(7) The histograms of ahs cloud and ground surge have a similar characteristic which is ladder-like and close to the fines. And the histograms of pyroclastic- flow have many peaks which are representative of the composite transportation.(8) There was hydration at the distal part of pyroclastic-flow, and the ground surge came from pyroclastic-flow and water interaction in Baixi.(9) According to computation, with 10km column height, the maxim radius of pyroclastic-low hazard zonation is 13.69km; with 20km column height, the maxim radius of pyroclastic-flow hazard zonation is 35.42km; with 30km column height, the maxim radius of pyroclastic-flow hazard zonation is 57.8km. Base on the pyroclasti -flow zonation in millennium eruption and topography of Tianchi volcano, the map of pyroclastic-flow hazard zonation has been established for different column heights which are representative of eruption scale.3. InnovationIn the course of study, four innovations have been discovered as follows:(1)In this paper, through research of shapes, strata, lithofaices, geochemistry, grain-size, transportation and deposition processes, using SEM, Camerasizer and Laser grain-size analyzer, it is firstly proposed the facies of pyoclastic flow in millennium eruption in Tianchi volcano, Changbaishan. (2)It is first to discovery that the grain-size distributions of fine ash are similar and have a single peak which is close to the fines in the pyroclastic-flow strata from median to distal. Compared with the fine ashes in pyroclastic-surge in Longquanlongwan volcano, Longgang volcanic cluster, it is found some differences between pyroclastic-flow and pyroclastic-surge. The grain-size of fine ashes in pyroclastic-surge can reach to 0.1μm, and the grain-size of fine ashes in pyroclastic-flow only reach to 1μm. The pyroclastic-surge which is produced by phreat-magma explosive eruption has more fine fragments than pyroclastic-flow which is produced by magma explosive eruption.(3) Through the analysis of SEM, stratum and grain-size, it is found that there was hydration at the distal part of pyroclastic-flow and the ground surge came from pyroclastic-flow and water interaction in Baixi.(4) In this paper, it is first to use the sliding block model computing the distance of pumice transportation.更多还原