长白山天池火山千年大喷发2期空降浮岩对比

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王禹钦, 于红梅, 许建东, 陈正全, 赵波. 长白山天池火山千年大喷发2期空降浮岩对比[J]. 地震地质, 2019,41(1): 208-224.
WANG Yu-qin, YU Hong-mei, XU Jian-dong, CHEN Zheng-quan, ZHAO Bo. A COMPARATIVE STUDY ON THE CHARACTERISTICS OF TWO STAGES OF FALLOUT PUMICES DEPOSITS FROM THE MILLENNIUM ERUPTION OF TIANCHI VOLCANO IN CHANGBAISHAN AREA[J]. SEISMOLOGY AND GEOLOGY, 2019,41(1): 208-224. 复制到剪切板

DOI:10.3969/j.issn.0253-4967.2019.01.014
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长白山天池火山千年大喷发2期空降浮岩对比

王禹钦, 于红梅^*, 许建东, 陈正全, 赵波

中国地震局地质研究所, 活动构造与火山重点实验室, 北京 100029

*通讯作者: 于红梅, 女, 副研究员, E-mail: yuhongmei@ies.ac.cn。

〔作者简介〕王禹钦, 男, 1993年生, 2018年于中国地震局地质研究所获构造地质学专业硕士学位, 主要研究方向为火山地质, 电话: 010-62009012, E-mail: 782027230@qq.com。

收稿日期: 2018-05-23

基金项目: 国家自然科学基金(41502314)资助

摘要

长白山天池火山的喷发历史和喷出物层序一直以来是人们关注的焦点。目前, 对于千年大喷发以来空降堆积物, 尤其是灰白色空降浮岩层之上的粗面质杂色空降浮岩的地层划分仍具有较大争议。文中通过对野外地层的详细观察, 对2层空降浮岩层进行对比研究, 发现两者之间没有沉积间隔, 认为2期空降浮岩均应划分为千年大喷发的喷发物。下部赤峰期灰白色空降浮岩成分较为均一, 呈棱角状, 正粒序, 分选较好; 上部圆池期喷发为脉动式喷发, 岩性为富土黄色浮岩和富黑色浮岩颗粒互层, 浮岩呈棱角状, 粒序不明显, 分选较好。2期浮岩粒度呈正态分布, 在中值和分选系数图中均投点于空降堆积区内。浮岩内斑晶以长石和辉石为主, 但圆池期黑色浮岩内斑晶含量略高。赤峰期空降浮岩为灰白色碱流质, 气孔较大, 连续贯通, 气孔壁薄。圆池期土黄色空降浮岩为粗面质, 气孔连通, 气孔壁略厚; 黑色浮岩颗粒成分虽然也投点为粗面质, 但SiO₂含量明显较低, 气孔度低, 气孔壁厚。圆池期喷发强度较赤峰期喷发强度弱。多种岩浆成分说明长白山天池火山下具有复杂的岩浆系统, 多种岩浆可能以分层的形式存在, 赤峰期仅喷出了上部的碱流岩, 圆池期的脉动式喷发喷出了不同层位的岩浆。

关键词: 空降浮岩; 粒度; 气孔结构; 成分; 千年大喷发; 天池火山

中图分类号:P317.3 文献标志码:A 文章编号:0253-4967(2019)01-0208-17

A COMPARATIVE STUDY ON THE CHARACTERISTICS OF TWO STAGES OF FALLOUT PUMICES DEPOSITS FROM THE MILLENNIUM ERUPTION OF TIANCHI VOLCANO IN CHANGBAISHAN AREA

WANG Yu-qin, YU Hong-mei, XU Jian-dong, CHEN Zheng-quan, ZHAO Bo

Key Laboratory of Active Tectonics and Volcano, Institute of Geology,China Earthquake Administration, Beijing 100029, China

Abstract

Tianchi volcano in Changbaishan area is located at the border between China and Democratic People’s Republic of Korea, and is one of the most dangerous volcanoes in China. It has experienced several explosive eruptions in late Pleistocene and Holocene, i.e. 50000a BP eruption, 946 AD eruption, 1668 AD eruption, 1702 AD eruption, 1903 AD eruption. Especially, the 946 AD eruption(also known as “Millennium eruption”)of this volcano is considered to be one of the largest volcanic eruptions in the world in the past 2000a. The eruption history and strata sequence of Tianchi volcano have long been the focus of attention. The stratigraphic unit division of fallout deposits in the past millennium is controversial, especially for the heterogeneous trachytic pumices(erupted from the Yuanchi stage)above the off-white pumices(erupted from the Chifeng stage).

In this paper, through the detailed field exploration and strata comparation, it was found that there was no depositional interval between the two stage eruptions, or the interval was not long, and thus, it is believed that two stages of fallout pumice should be classified into the Millennium eruption. The off-white fallout pumices in Chifeng stage are relatively homogeneous, with angular shape, normal grading and good sorting. The median size( Md_Φ)and the sorting coefficient( σ_Φ)of Chifeng pumice are in the range of -4.25~-1.3 and 0.93~1.53, respectively. The eruption of Yuanchi stage is in pulsing pattern, and the strata show interbedding of rich khaki pumice layer and rich black pumice layer. The pumices with angular shape show inconspicuous grain grading and good sorting. The median size( Md_Φ)and the sorting coefficient( σ_Φ)of Yuanchi pumice are in the range of -2.55~-0.6 and 1~1.68, respectively. Both the granularities of the pumice particles from two stages are normally distributed and fall into the air-fall field in the median diameter versus sorting diagram. The pumices from 50000a BP and pyroclastic flow of Millennium eruption were also shown in the diagram.

Phenocrysts in pumices are mainly feldspar and pyroxene, but the phenocrysts with obvious resorbed characteristic in Yuanchi black pumice are bigger, and the phenocryst contents are a little higher than those in others. Feldspar content in off-white pumice in Chifeng stage was 0.24%~1.77%, that in khaki pumice in Yuanchi stage was 0.2%~7.5%, and that in black pumice in Yuanchi stage was 3.02%~8.0%. The phenocrysts in Chifeng pumice are broken, which represents more violent explosion. The vesicles inside the pumice also reflect the intensity of the eruption. The Chifeng pumices have large, continuous vesicles and thin vesicle walls. The Yuanchi khaki pumices have continuous vesicles but thicker vesicle wall than the Chifeng pumices. The vesicularity is the lowest and the vesicle walls are the thickest in the black pumices in Yuanchi stage, indicating the eruption strength become weaker from Chifeng stage to Yuanchi stage.

The Chifeng pumices with SiO₂ content of 69.12~72.71wt%, K₂O content of 4.33~4.52wt%, Na₂O content of 5.26~5.39wt%, Al₂O₃ content of 10.32~11.99wt%, CaO content of 0.29~0.95wt%, MgO content of 0.11~0.51wt%, TiO₂ content of 0.23~0.43wt% are comendite in composition. The pumices from 50000a BP eruption are comendite in composition, and their SiO₂ content(65.56~68.28wt%)is slightly lower than Chifeng pumices. The Yuanchi khaki pumices with SiO₂ content of 62.14~63.29wt%, K₂O content of 5.35~5.7wt%, Na₂O content of 5.35~5.62wt%, Al₂O₃ content of 15.00~15.59wt%, CaO content of 1.06~1.61wt%, MgO content of 0.25~0.57wt%, TiO₂ content of 0.4~0.64wt% belong to trachyte in composition, and are close to the composition of the black pumices on the Tianwen Peak. The Yuanchi black pumices are also trachyte in composition, but have obviously lower SiO₂(59.51~60.59wt%), K₂O(4.39~4.84wt%), and Na₂O(4.94~5.08wt%)content, and higher Al₂O₃(15.81~16.42wt%), CaO(2.78~3.66wt%), MgO(1.43~1.9wt%), TiO₂(1.04~1.4wt%)content than the khaki pumices.

The above results show that the eruptive intensity of the Yuanchi stage is weaker than that of the Chifeng stage and the several magmatic compositions of pumices from the Millennium eruption reveal a complex magma system under the Tianchi volcano. The magma layers with different compositions may exist in the magma chamber contemporaneously. At Chifeng stage, only the upper comendite magma erupted, but the magma below erupted in the pulsing pattern at the Yuanchi stage.

Keyword: fallout pumice; particle size; vesicle structure; composition; the Millennium eruption; Tianchi volcano

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0 引言

长白山天池火山位于吉林省东部中朝边境上, 是一座大型的复式活火山。该火山于(946± 3)AD发生了大规模的喷发(Xu et al., 2013), 对全球气候造成了巨大的影响, 被认为是世界上历史时期规模最大、影响最广的火山喷发之一(Machida et al., 1983), 也被称为 “ 千年大喷发” 。其年代较新, 野外喷发物保存较为完整, 因此, 其喷发年代、分布范围、灾害评估也受到广泛关注(杨清福等, 1996, 1998; 魏海泉等, 1997; 刘祥等, 2004; 刘祥, 2006; 于红梅等, 2012; Yu et al., 2013; Pan et al., 2017)。

刘嘉麒等(1982)对天池火山在新生代以来的火山活动及其特征进行了详细研究。汤德平等(1989)、刘若新等(1998a, b)、郑祥身等(1998)、李霓等(2004)、樊祺诚等(2007)、魏海泉(2010)等通过大量的岩石地球化学数据及岩浆通道的模拟, 反演了长白山火山岩浆的演化过程, 逐步建立了造盾、造锥到全新世的喷发属于粗面玄武岩— 玄武质粗安岩— 粗面岩— 碱流岩的演化系列。郭正府等(2005)通过测试斑晶包裹体与共存的玻璃基质之间的挥发份含量差, 获得了火山气体喷发含量, 得出天池火山所喷出的气体从早到晚的含量变化, 评测了其对环境的影响。许东满等(1993)划分了天池地区上新世以来的火山活动地层单元, 金伯禄等(1994)划分了新生代火山喷发的期次, 二者均把千年大喷发的灰白色碱流质浮岩命名为白云峰期, 将白云峰组之上的黑色粗面质浮岩命名为八卦庙期。杨清福等(1998)结合大量野外资料, 根据空降物粒度在天池近、中、远缘的变化, 分析了千年大喷发空降物的分布范围, 认为在风力影响下, 空降浮岩由NW向SE呈扇形分布。刘祥(2006)对千年大喷发的空降物以及碎屑流、泥石流进行了更为详细的野外探查, 认为千年大喷发包含2次间隔不长的普林尼式喷发, 并分别命名为赤峰期和圆池期(图1)。本次野外考察中也发现该区在千年大喷发的灰白色空降浮岩层之上存在一期空降层, 2层空降分别对应刘祥(2006)提出的赤峰期和圆池期喷发。潘波(2016)的最新研究显示该土黄色浮岩层与白云峰顶黑色粗面质浮岩(八卦庙期)为同期喷发物, 并否定了前人认为的千年大喷发与八卦庙期之间存在时间间隔的观点, 提出2期可能为连续喷发活动。

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	图1 天池火山千年喷发空降堆积物分布图(据刘祥, 2006和潘波, 2016修改)Fig. 1 Sketch map on the distribution of fallout tephra of the Millennium eruption of Tianchi volcano (after LIU Xiang, 2006; PAN Bo, 2016).

表1 天池火山千年喷发产物及期次划分汇总表(据Pan et al., 2017修改) Table1 Summery of the chronostratigraphy of the Millennium eruption of Tianchi volcano(after Pan et al., 2017)

关于 2 层空降物的喷发时代目前还存有较大的争议(表1), 并且上层空降物成分较复杂, 以土黄色浮岩为主, 夹杂黑色浮岩、岩屑和晶屑。本次研究以千年大喷发产生的2层空降浮岩堆积(沿用刘祥(2006)的命名方式, 分别称其为赤峰期和圆池期)为研究对象, 进行了详细的野外地层观测, 采集了大量碎屑样品, 进行碎屑粒度、岩相学和成分的测试及对比分析, 获取2次空降喷发之间的关系、喷发特征和岩浆成分的变化特征。

1 野外地层堆积特征

赤峰期的灰白色空降浮岩沿火口呈SEE向分布。这一期空降物在圆池— 钓鱼台一带现象非常一致, 层理清晰, 成分均一。略微有所不同的是, 因地势高低不同, 其上所覆盖的灰白色浮岩的碎屑流有所差异。圆池期的土黄色和黑色空降浮岩颗粒主要沿火口正东向分布, 在火口NE的东方红林场区域、正东方向的圆池一带以及NNE向的黑石沟— 老房子小山一带都有广泛分布(图1)。但是各处的空降堆积层序有很大的差异。具有代表性的剖面主要有4处, 分别是圆池剖面、黑石沟剖面、老房子小山剖面和东方红大桥剖面。其中, 圆池剖面和黑石沟剖面的地层最为详实地记录了火山喷发的过程。

1.1 圆池剖面

圆池剖面位于天池火口正东方向约30km, 因此地现存圆池湖而命名。千年大喷发堆积物位于近地表腐殖质之下约20cm, 可观测到总厚度约90cm的空降浮岩, 剖面层序如下(图2):

①富集土黄色浮岩层。此层厚度6~9cm。粒径较大, 0.5~1.5cm, 混杂少量黑色浮岩颗粒、晶屑和岩屑。顶部约2cm富集黑色浮岩颗粒, 夹少量土黄色浮岩, 黑色浮岩含量高, > 80% , 与地表土壤植被根系接触。

②黑色与土黄色浮岩颗粒混杂层。厚9cm, 下部4cm为土黄色浮岩夹少量黑色浮岩、晶屑、岩屑, 中间层厚2cm, 土黄色浮岩含量显著增加; 上层3cm为土黄色浮岩混杂黑色浮岩、晶屑和岩屑。此层中的土黄色浮岩颗粒粒径较小, 大多约0.5cm, 不超过0.7cm。

③碎屑泥沙层。厚7cm, 以晶屑、岩屑和火山灰为主, 夹杂灰白色浮岩颗粒, 浮岩粒径普遍较小, 仅约1cm。

④赤峰期灰白色正粒序千年大喷发空降浮岩。厚45cm, 下部粒度较大, 粒径可达1.7cm左右, 中部0.7cm左右, 上部0.2cm左右。

在圆池附近, 向E至钓鱼台的其他区域, 地势较高, 赤峰期的灰白色空降浮岩有着广泛的分布, 但是除了圆池剖面外没有发现任何土黄色空降浮岩层。因此, 第2次普林尼式喷发时的风向可能更偏SW-NE方向。

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	图2 圆池剖面野外照片及剖面地层图Fig. 2 Field photo and strata sequence of Yuanchi profile.

1.2 黑石沟剖面

黑石沟位于天池火山东15km, 为发育自火口东缘的一条大型冲沟, 因沟内无长流水, 故被当地人称为干沟。该处堆积了巨厚的火山碎屑, 并在顶部堆积了圆池期土黄色浮岩和黑色浮岩。因修建公路, 在黑石沟— 老房子小山沿线都可以观测到不同层厚、不同层序的圆池期空降物。黑石沟剖面总体厚约50cm, 剖面特征如下(图3):

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	图3 黑石沟剖面野外照片及剖面地层图Fig. 3 Field photo and strata sequence of Heishigou profile.

①富土黄色浮岩层。厚约6cm, 为土黄色浮岩中夹杂黑色浮岩颗粒, 成分混杂, 土黄色空降浮岩粒径更大, 约2cm, 与地表接触。

②黑色浮岩颗粒富集层。厚约3cm。

③富土黄色空降浮岩层。厚约2cm, 夹杂大量的黑色浮岩颗粒, 成分混杂, 土黄色空降浮岩的粒径为1~2cm。

④黑色浮岩富集层。厚约6cm, 黑色浮岩颗粒粒径< 0.2cm。

⑤富土黄色空降浮岩层。厚约18cm, 粒度较大, 此层中土黄色浮岩粒径为1~1.7cm, 同样夹杂了大量的黑色浮岩颗粒。

⑥富土黄色空降浮岩层。厚18cm, 粒度较小, 粒径在0.3~0.6cm之间, 夹杂大量的黑色浮岩颗粒, 成分混杂。

⑦火山碎屑流。可见厚度1m, 夹杂大量千年大喷发的灰白色颗粒, 火山灰支撑。

1.3 老房子小山剖面

老房子小山剖面位于天池火口NE方向约17km, 黑石沟NW约5km。该处以旧林场保护站和保护站旁边的小山而得名。小山实际为玄武岩采石场, 在采石过程中, 出露完整的圆池期空降浮岩剖面。该处地势较高, 难以形成小规模积水, 有利于空降物堆积, 且空降物层面也很少受到碎屑流的侵蚀, 因此, 在该处发现了互层现象最清晰明显的原生空降剖面。

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	图 4 老房子小山剖面野外照片及剖面地层图Fig. 4 Field photo and strata sequence of Laofangzi Xiaoshan profile.

富土黄色空降浮岩和富黑色浮岩互层, 共计约72cm(图4), 肉眼可见二者至少有9层:

①黑色浮岩颗粒。厚约10cm。

②土黄色空降浮岩。厚约4cm, 成分混杂。

③黑色浮岩颗粒。厚约7cm。

④土黄色空降浮岩和黑色浮岩颗粒互层(4~6层)。共厚约20cm, 每个空降序列厚2~4cm。

⑤黑色浮岩颗粒。厚约9cm。

⑥土黄色空降浮岩。厚约18cm。粒度较大, 最大粒径可达7cm。

⑦火山碎屑流。可见厚度> 1m, 夹杂千年大喷发的灰白色颗粒, 火山灰支撑。

底部的黑色颗粒层和土黄色浮岩层厚度较大, 中间层和顶部层厚度较薄。底部厚层的土黄色空降粒度也明显较中间粗。这表明喷发的初始阶段规模较大, 喷出物较多, 能量也更大, 较大颗粒的浮岩可以落到更远的区域, 因此底部层面物质多、粒度大。

1.4 东方红水泥桥剖面

东方红大桥位于天池火口NE 27km, 东方红林场内。自林场大桥SE废弃的营地至东方红大桥北1km, 沿线8km的区域, 圆池期空降物和赤峰期碎屑流层序较为稳定, 剖面特征较为一致。下部为赤峰期巨厚的火山泥石流, 其中夹杂着赤峰期灰白色大块浮岩, 粒径最大可达十几甚至20cm, 厚1至数m不等。上部为圆池期空降沉积, 土黄色浮岩、少量黑色浮岩与岩屑混杂, 厚8~18cm不等, 在距离火口更近的林场桥南废弃营地, 圆池期空降层厚度仅有8cm, 成分以黑色浮岩为主, 在距离火口更远的东方红水泥桥北, 圆池期空降层厚度达到了18cm, 成分以土黄色浮岩为主, 顶部为一层厚约2cm的黑色浮岩颗粒层(图5)。

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	图5 东方红水泥桥剖面野外照片 a 火山碎屑流; b 圆池期空降堆积Fig. 5 Field photo of Dongfanghong Bridge profile.

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	图6 天池火山代表性浮岩碎屑粒度分布图Fig. 6 Particle size distribution of representative pumices from Tianchi volcano.

2 碎屑粒度分析

通过粒度分布特征来判断堆积物的分选性和成因类型是火山碎屑研究的一种基础手段。杨清福等(2007)、赵波等(2010)和Zhao等(2013)曾对天池火山区不同成因类型的浮岩碎屑进行过粒度分析, 但是未曾区分圆池期和赤峰期浮岩。利用德国莱驰AS200自动筛分仪, 对采样区域中的44件空降浮岩和火山碎屑流样品进行了筛分, 得到了样品的粒度分布(图6), 计算粒度中值Md_Φ和分选系数σ _Φ(Φ =-log₂d, d为碎屑粒度), 并进行碎屑成因投图(图7)。潘波(2016)在黑石沟内千年大喷发空降碎屑之下发现了50ka前喷发的空降浮岩, 本研究对此处的样品也进行了分析。对圆池期土黄色浮岩和黑色浮岩颗粒未进行区分。

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	图 7 浮岩碎屑成因投图(Walker, 1983)Fig. 7 Median diameter(Md_Φ)versus sorting(σ _Φ)diagram(after Walker, 1983).

空降浮岩粒度分布图均显示正态分布特征, 赤峰期空降浮岩粒度中值Md_Φ为-4.25~-1.3(d为1.69~18mm), 分选系数σ _Φ为0.93~1.53。圆池期空降浮岩粒度中值Md_Φ为-2.55~0.6(d为0.36~6.5mm), 分选系数σ _Φ为1~1.68。在Md_Φ和σ _Φ关系图中均投点在空降浮岩区域。50ka年前喷发的浅黄色浮岩粒度中值Md_Φ为-2.55~-2.4, 分选系数σ _Φ为1.65~1.68。几个碎屑流样品的σ _Φ值很高(3.25~4.23), 投点落入火山碎屑流区域。

3 岩相学特征

对2期喷发的浮岩进行了详细的岩相学观察。对于圆池期空降浮岩, 挑选出土黄色浮岩颗粒和黑色浮岩颗粒, 分别磨制了薄片。黑色浮岩颗粒较小, 置于水中并不能像其他浮岩一样浮在水面, 而会直接沉到水底, 有的研究者称之为黑色粗安岩角砾(樊祺诚等, 2005)。但是在光学显微镜下和扫描电镜下可以观测到其明显的气孔结构(图8, 9), 因此本文称之为黑色浮岩。3种浮岩在光学显微镜及扫描电镜下显示出不同的特征。

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图 8 天池火山浮岩光学显微镜照片
a 黑色浮岩中的气孔(单偏光); b 灰白色浮岩中的拉长气孔(单偏光); c 黑色浮岩中保存完好的长石聚片双晶(正交); d 黑色浮岩内熔蚀的长石(单偏光); e 灰白色浮岩中自形的长石(正交); f 灰白色浮岩中的破碎长石(单偏光); g 土黄色浮岩中熔蚀的长石(单偏光); h 土黄色浮岩中的辉石和长石(单偏光)。 V气孔; Fld长石; Px辉石Fig. 8 Microphotographs of pumices from Tianchi volcano.

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	图 9 扫描电子显微镜下火山浮岩的背散射电子图像从左到右分别为灰白色(左)、土黄色(中)、黑色(右)浮岩在80倍(上)、 200倍(中)、 500倍(下)放大倍数下的图像Fig. 9 Backscatter electron images of pumices.

表2 天池火山空降浮岩主量元素分析结果(单位: wt%) Table2 Major element composition of pumices from Tianchi volcano

	样品编号	SiO₂	Al₂O₃	TiO₂	Fe₂O₃	FeO	CaO	MgO	K₂O	Na₂O	MnO	P₂O₅	H₂O⁺	H₂O^-	灼失量	总和
圆池期黑色浮岩	16CBS-7a-B	59.51	16.42	1.3	1.83	4.43	3.56	1.9	4.57	5	0.121	0.278	0.87	0.24	0.9	99.82
	16CBS-7b-B	59.32	16.42	1.4	1.7	4.74	3.66	1.88	4.47	4.92	0.122	0.29	0.67	0.18	0.92	99.83
	16CBS-7c-B	60.53	15.81	1.05	2.04	3.99	2.88	1.67	4.71	5.08	0.124	0.23	1.56	0.35	1.73	99.85
	16CBS-8a-B	59.37	16.33	1.29	1.58	4.65	3.33	1.67	4.77	5.08	0.123	0.268	0.68	0.31	1.38	99.85
	16CBS-10a-B	60.56	15.96	1.04	1.96	4.1	2.82	1.43	4.77	5.08	0.13	0.231	1.28	0.53	1.79	99.85
	16CBS-15-B	59.61	16.05	1.2	2.02	4.43	3.28	1.88	4.39	4.94	0.13	0.277	0.86	0.43	1.61	99.83
	HSG-1-B	60.59	15.89	1.11	1.91	4.33	2.78	1.51	4.84	4.96	0.128	0.243	1.2	0.28	1.57	99.86
圆池期土黄色浮岩	16CBS-7a-H	63.29	15.48	0.58	1.68	3.51	1.47	0.44	5.7	5.35	0.136	0.104	1.69	0.49	2.18	99.91
	16CBS-7b-H	63.16	15.29	0.57	1.52	3.66	1.45	0.43	5.6	5.35	0.136	0.1	2.21	0.55	2.65	99.91
	16CBS-7c-H	63.6	15	0.5	1.69	3.37	1.32	0.34	5.61	5.43	0.134	0.08	2.56	0.61	2.84	99.91
	16CBS-8a-H	62.14	15.44	0.64	1.58	3.8	1.61	0.57	5.56	5.33	0.136	0.125	1.49	0.68	2.97	99.9
	16CBS-7d	65.41	14.25	0.4	1.76	3.13	1.06	0.25	5.35	5.62	0.127	0.048	1.97	0.45	2.49	99.89
	HSG-1-H	63.27	15.15	0.53	1.78	3.51	1.38	0.39	5.44	5.37	0.139	0.091	1.94	0.65	2.88	99.91
	16CBS-10a	62.83	15.43	0.54	1.52	3.8	1.36	0.39	5.46	5.33	0.142	0.102	1.69	0.81	3	99.91
	16CBS-15a	63.09	15.59	0.53	1.72	3.57	1.33	0.35	5.53	5.36	0.148	0.097	1.44	0.82	2.59	99.91
	16CBS-16a	63.06	15.4	0.54	1.88	3.49	1.37	0.4	5.43	5.41	0.145	0.101	1.31	0.76	2.68	99.9
天文峰顶黑色浮岩	16TWF-1	64.61	15.56	0.49	2.47	2.54	1.29	0.32	5.8	5.68	0.13	0.079	0.7	0.22	0.96	99.91
	16TWF-2	64.71	15.49	0.46	1.91	3.01	1.23	0.29	5.86	5.78	0.129	0.07	0.68	0.18	0.97	99.92
	16TWF-3	65.07	15.3	0.45	1.57	3.27	1.19	0.3	5.67	5.64	0.127	0.069	1.08	0.23	1.26	99.91
赤峰期灰白色浮岩	16CBS-15e	72.07	10.54	0.26	1.87	2.5	0.4	0.18	4.37	5.32	0.082	0.017	1.62	0.78	2.21	99.82
	16CBS-16c	70.96	10.84	0.31	1.84	2.74	0.57	0.25	4.34	5.26	0.091	0.034	1.37	0.7	2.58	99.82
	16CBS-20	72.71	10.32	0.23	2.06	2.26	0.29	0.11	4.33	5.39	0.08	0.011	1.23	0.61	2.06	99.82
	16CBS-22	69.12	11.99	0.43	2.17	2.59	0.95	0.51	4.52	5.28	0.092	0.057	1.65	0.39	2.12	99.83
50ka 前浅黄色浮岩	HSG-2	68.28	10.13	0.29	4.37	2.72	0.40	0.17	4.13	4.83	0.153	0.022	3.79	1.43	4.26	99.75
	HSG-3a	65.56	11.78	0.35	5.23	2.54	0.52	0.29	3.87	4.20	0.186	0.049	4.46	1.95	5.15	99.74
	HSG-3b	66.05	11.43	0.34	5.06	2.64	0.46	0.27	3.87	4.29	0.184	0.042	4.35	2.05	5.11	99.74
	16TWF-4	68.18	11.78	0.33	5.02	0.50	0.56	0.12	4.71	5.80	0.119	0.016	2.31	0.62	2.70	99.82

表2 天池火山空降浮岩主量元素分析结果(单位: wt%) Table2 Major element composition of pumices from Tianchi volcano

浮岩斑晶以长石和辉石为主, 由于2期浮岩具有较大的气孔度, 斑晶百分含量较低。在显微镜下以线统计法统计2期浮岩中的长石斑晶含量, 得到赤峰期灰白色浮岩中的长石含量为0.24%~1.77%, 圆池期土黄色浮岩中的长石含量为0.2%~7.5%, 圆池期黑色浮岩中的长石含量为3.02%~8%。从气孔形态上看, 灰白色及土黄色样品气孔度高, 气孔普遍存在拉长变形, 反映了强烈的喷发动力学特征。相较而言, 黑色浮岩在光学显微镜下显得非常致密, 不仅气孔度大大低于前者, 而且气孔的拉长变形并不明显, 其喷发动力远远不如前两者。从晶体特征上看, 赤峰期和圆池期的长石斑晶都受到了一定程度的熔蚀破坏, 但是圆池期长石熔蚀得更明显(图8d, g), 而赤峰期斑晶出现较多的破碎现象(图8f)。

从背散射图像上看, 在高放大倍数的2D图像中, 3种浮岩的气孔具有更显著的区别(图9), 灰白色与土黄色浮岩中的气孔大多呈现贯通的形态, 黑色浮岩中的气孔大多独立存在, 灰白色以及土黄色浮岩的气孔度远远大于黑色浮岩。灰白色浮岩的气孔壁很薄, 远远低于气孔孔径, 土黄色浮岩的气孔壁大约是孔径的一半左右, 黑色浮岩的气孔壁大约是孔径的2~3倍。

4 浮岩主量元素成分分析

对采集的样品进行了全岩主量元素分析, 结果见表2。分析单位为河北省区域地质矿产调查研究所实验室, 分析仪器为X荧光光谱仪。

结果显示, 圆池期2种颜色的浮岩成分明显不同, 土黄色浮岩SiO₂的含量为62.14~63.29wt%, K₂O 的含量为5.35~5.7wt%, Na₂O 的含量为5.35~5.62wt%, Al₂O₃的含量为15.00~15.59wt%, CaO的含量为1.06~1.61wt%, MgO的含量为0.25~0.57wt%, TiO₂的含量为0.4~0.64wt%, 为粗面质, 与山顶八卦庙期(潘波, 2016)的成分基本相同; 而黑色浮岩SiO₂的含量为59.51~60.59wt%, 远远低于土黄色浮岩, K₂O的含量为4.39~4.84wt%, Na₂O 的含量为4.94~5.08wt%, CaO的含量为2.78~3.66wt%, Al₂O₃的含量为15.81~16.42wt%, MgO的含量为1.43~1.90wt%, TiO₂的含量为1.04~1.4wt%, 在TAS图解中虽然也投点于粗面岩, 但偏向粗安岩。2种成分明显投点在2个集中区, 中间不连续。赤峰期的灰白色浮岩成分在TAS图中投点为碱流岩(图10), 与前人的数据范围基本一致, SiO₂含量高(69.12~72.71wt%), 更偏酸性, K₂O 的含量为 4.33~4.52wt%, Na₂O的含量为5.26~5.39wt%, Al₂O₃的含量为10.32~11.99wt%, CaO的含量为 0.29~0.95wt%, MgO的含量为0.11~0.51wt%, TiO₂的含量为0.23~0.43wt%, 岩浆的演化程度较高。50ka前的黄色浮岩SiO₂的含量为65.56~68.28wt%, 比赤峰期灰白色浮岩略低, 投点为碱流岩。

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	图10 天池火山空降浮岩TAS图解(据Le Maitre et al., 1989修改)Fig. 10 TAS diagram of pumices from Tianchi volcano(after Le Maitre et al., 1989).

5 讨论

5.1 地层对比

横向对比圆池剖面、黑石沟剖面、老房子小山剖面和东方红大桥剖面, 圆池剖面中圆池期空降浮岩降落在赤峰期灰白色空降浮岩之上, 其他剖面降落在赤峰期火山碎屑流之上, 几处的圆池期空降应为同一期喷发。虽然圆池剖面中圆池期空降浮岩和赤峰期灰白色空降浮岩中间存在泥沙层, 但该泥沙层以晶屑、岩屑和火山灰为主, 应该为火山喷发物二次堆积的产物。所以, 圆池期空降直接覆盖在赤峰期之上, 中间没有沉积间隔, 证明赤峰期跟圆池期空降堆积过程连续, 二者的喷发之间不足以形成沉积间隔, 2期空降浮岩均应划分为千年大喷发的喷发物。

但是几处地层层理并不一致, 老房子小山剖面的互层现象更明显, 层理更多, 更加明确地展示了脉动式喷发的过程。层理的变化应该与喷发强度、扩散过程中风速、风向的变化以及距火山口的距离有关。

5.2 千年大喷发的强度变化

从喷发物堆积厚度来看(图2), 同一地点圆池期空降厚度小于赤峰期空降浮岩厚度。从粒度分析看(图7), 赤峰期浮岩粒度更大, 分选更好, 代表更强的爆炸强度。浮岩内部气孔的大小和数量也反映了喷发的强度(于红梅等, 2012), 赤峰期的浮岩气孔更大, 拉长更明显, 气孔数量较多, 气孔壁更薄, 也说明喷发的强度更大。故千年大喷发在赤峰期后强度变弱。

千年大喷发爆发指数(VEI)达到了7, 喷发柱高达35km(刘若新等, 1998b)。1980年美国圣海伦斯火山喷发(VEI=5), 喷发物SiO₂的含量为66~80wt%, 喷发柱的高度为25km(Carey et al., 2009); 1991年菲律宾皮纳图博火山喷发(VEI=6), 喷发物SiO₂的含量为68~77wt%, 喷发柱的高度达到了40km(Koyaguchi et al., 1996)。可见一般布里尼式喷发多为酸性岩浆。但是中性岩浆也可以产生大规模的爆炸式喷发, 例如意大利维苏威火山于79AD喷发(VEI=5), 喷发物中SiO₂的含量为54~61wt%, 喷发柱的高度最高达到了33km。所以, 虽然圆池期喷发的强度有所减弱, 但并不能否认将来再次发生大规模爆炸式喷发的可能。

5.3 岩浆成分的复杂性

成分测试显示圆池期的浮岩较赤峰期更偏基性, 属于粗面岩。潘波(2016)、 Pan等(2017)测试圆池期空降物与天文峰顶部的黑色浮岩成分和斑晶成分一致, 认为其为同一期产物, 并统称为 “ 八卦庙期” 。但本研究显示圆池期空降浮岩成分复杂, 含有2种颜色的浮岩, 其中土黄色浮岩成分与天文峰顶部黑色浮岩成分相近, SiO₂的含量为62~66wt%, 而圆池期黑色浮岩成分中SiO₂的含量低(59~60.6wt%), 两者的其他氧化物含量也具有明显的区别。另外, 土黄色浮岩的灼失量明显高于黑色浮岩。野外地层显示圆池期喷发为脉动式, 2种颜色的浮岩混杂在一起, 甚至有些颗粒内部有2种颜色的岩浆混合存在, 所以其与天文峰顶部黑色浮岩是否为同一期喷发产物还有待进一步的研究。

史兰斌等(2005)认为流纹质和粗面质浮岩均来自地壳岩浆房, 为岩浆房内不同分异演化阶段的产物, 并认为岩浆房具有分带性, 不同性质的岩浆存在混合作用。2种粗面岩浆成分的存在说明长白山火山下岩浆系统远比潘波(2016)和Pan等(2017)给出的岩浆系统演化模式要复杂得多, 可能粗面岩浆内部也存在成分分层, 而脉动式的喷发喷出了不同层位的岩浆。

6 结论

通过对长白山天池火山千年大喷发以来的2层空降堆积地层和室内浮岩碎屑的详细分析, 得到以下初步结论:

(1)赤峰期灰白色空降浮岩受风力作用广泛分布于天池火山东南侧, 其浮岩为棱角状, 正粒序, 分选较好, 成分较为均一。圆池期喷发为脉动式喷发, 该层浮岩为棱角状, 粒序不明显, 分选较好, 主要为土黄色浮岩和黑色浮岩颗粒互层。

(2)2期浮岩粒度均投点于空降堆积区内, 2层空降喷发中间没有沉积间隔, 时间间隔不长, 2期空降浮岩均应划分为千年大喷发的喷发物。

(3)赤峰期空降浮岩为灰白色碱流质, 气孔较大, 连续贯通, 气孔壁薄, 喷发强度较大。圆池期土黄色空降浮岩为粗面质, 气孔贯通, 气孔壁略厚, 而黑色浮岩颗粒成分虽也为粗面质, 但SiO₂含量明显较低, 气孔不连续贯通, 喷发强度较赤峰期弱。

(4)多种岩浆成分说明天池火山下复杂的岩浆系统可能以分层的形式存在, 脉动式的喷发喷出了不同层位的岩浆。

The authors have declared that no competing interests exist.

参考文献

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2005

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樊祺诚, 隋建立, 孙谦, 等. 2005. 天池火山千年大喷发的岩浆混合作用与喷发机制初步探讨[J]. 岩石学报, 21(6): 1703—1708.

FAN

Qi-cheng

, SUI

Jian-li

, SUN

Qian

, et al. 2005. Preliminary research of magma mixing and explosive mechanism of the Millennium eruption of Tianchi volcano[J]. Acta Petrologica Sinica, 21(6): 1703—1708(in Chinese).

Studies on magma evolution and on geophysical observations indicate that there are two magma chambers beneath Tianchi volcano. Continuous basaltic magma influx from mantle chamber to crust chamber are essential to the keep Tianchi volcano active over a million years, and are also important to interpret the magma evolution of Tianchi volcano. In this paper, we present evidence of magma influx and magma mixing from the gray pumice of the Millennium eruption of Tianchi volcano. The breccias in the gray pumice and the banded structures indicate the occurrence of magma mixing. The petrological, mineralogical and chemical studies of these samples reveal the story of magma influx and mixing, which may trigger the Millennium eruption of Tianchi volcano.

根据岩浆演化和地球物理深部探测，天池火山之下存在地壳和地幔双层岩浆房。地幔玄武质岩浆向地壳岩浆房的补给，保持了天池火山逾百万年持续不断的喷发活动。本文从天池火山千年大喷发浮岩中的玄武质粗安岩一粗安岩角砾和条带状岩浆的岩相学、矿物学和岩石化学研究，提出地幔的粗面玄武质岩浆向地壳岩浆房的注入，触发千年大喷发，初步探讨了天池火山千年大喷发的岩浆混合作用与喷发机制。

... 黑色浮岩颗粒较小, 置于水中并不能像其他浮岩一样浮在水面, 而会直接沉到水底, 有的研究者称之为黑色粗安岩角砾(樊祺诚等, 2005) ...

2007

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... 汤德平等(1989)、刘若新等(1998a, b)、郑祥身等(1998)、李霓等(2004)、樊祺诚等(2007)、魏海泉(2010)等通过大量的岩石地球化学数据及岩浆通道的模拟, 反演了长白山火山岩浆的演化过程, 逐步建立了造盾、造锥到全新世的喷发属于粗面玄武岩#cod#x02014 ...

2005

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1994

0.0

... 许东满等(1993)划分了天池地区上新世以来的火山活动地层单元, 金伯禄等(1994)划分了新生代火山喷发的期次, 二者均把千年大喷发的灰白色碱流质浮岩命名为白云峰期, 将白云峰组之上的黑色粗面质浮岩命名为八卦庙期 ...

2000

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2004

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李霓, 樊祺诚, 孙谦, 等. 2004. 长白山天池火山岩浆演化: 来自主矿物成分的证据[J]. 岩石学报, 20(3): 575—582.

, FAN

Qi-cheng

, SUN

Qian

, et al. 2004. Magma evolution of Changbaishan Tianchi volcano: Evidence from the main phenocrystal minerals[J]. Acta Petrologica Sinica, 20(3): 575—582(in Chinese).

The main phenocrysts of Changbaishan Tianchi volcanic rocks were olivines, pyroxenes, feldspars and Ti-Fe oxides,which had clear characteristics of components evolution by electron microprobe analysis. From shield-forming stage, cone-forming stageto Holocene eruptions, the content of iron in olivines kept increasing till it almost reached the end-member of fayalite; iron and sodiumcontents also increased in clinopyroxene. In the meantime, feldspars evolved from labradorite to anorthoclase and sanidine which hadmore potassium and sodium, and the contents of Fe-Ti oxides in rocks were reduced cleary. The evolution of phenocrysts in threestages of Tianchi volcanic rocks reflected the complete series of Tianchi magma evolution in 2 Ma, which was in conformity with theevolution tide of fractional crystallization.

长白山天池火山岩的主要矿物成分为橄榄石、辉石、长石和铁钛氧化物，经电子探针测试，其成分变化特征明显，自造盾阶段一造锥阶段一全新世喷发，橄榄石中铁含量增加，一直达到铁橄榄石的端元组分；单斜辉石中铁质和钠质含量增加；长石则从基性的拉长石向含钾、钠渐高的歪长石和透长石演化；铁钛氧化物含量则明显减少。三阶段斑晶矿物成分的变化反映了天池火山近200万年来岩浆演化的完整系列，符合分离结晶作用的演化趋势。

1982

0.0

刘嘉麒, 王松山. 1982. 长白山火山与天池的形成时代[J]. 科学通报, 27(21): 1312—1315.

LIU

Jia-qi

, WANG

Song-shan

. 1982. Age of Changbaishan volcano and Tianchi lake[J]. Chinese Science Bulletin, 27(21): 1312—1315(in Chinese).

连接中朝两国的长白山是三江(鸭绿江、图们江、松花江)之源,是我国著名的年轻火山,山

... 刘嘉麒等(1982)对天池火山在新生代以来的火山活动及其特征进行了详细研究 ...

1998

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1996

0.0

2006

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刘祥. 2006. 长白山火山历史上最大火山爆发火山碎屑物层序与分布[J]. 吉林大学学报(地球科学版), 36(3): 313—318.

LIU

Xiang

. 2006. Sequence and distribution of the pyroclastic deposits of the greatest eruption of Changbaishan volcano during the period of history[J]. Journal of Jilin University(Earth Science Edition), 36(3): 313—318(in Chinese).

The recorded 1199~1200 A.D. eruption is the largest among all the Changbaishan volcano eruptions in history. It can be subdivided into two phases of Plinian eruption, the first is named the Chifeng phase and the second the Yuanchi phase. The eruptive pattern of the Chifeng phase is: Plinian column (the Chifeng pumice fall deposits) → pyroclastic flow (the Changbai pyroclastic flow deposits) → lahar (the Erdaobaihe lahar deposits) mainly triggerd by pyroclastic flow. The eruptive pattern of the Yuanchi phase is from Plinian column (the Yuanchi pumice and ash fall deposits) → pyroclastic flow (the Bingchang pyroclastic flow deposits). The total volume of both the first and the second Plinian falls has been estimated at about 120 km 3 . The bulk volume of the Changbai pyroclastic flow deposits was estimated about 8 km 3 ; that of the Bingchang pyroclastic flow deposits about 0.5 km 3 and of the Erdaobaihe lahar deposit about 2 km 3 . The author deals with mainly the sequence and distribution of the pyroclastic deposits of the 800 a.B.P. eruptions.

College of Earth Sciences, Jilin University, Changchun 130061, China

长白山火山历史时期规模最大的火山喷发发生在1199~1200年。这次大爆发分为两次普林尼（Plinian）式喷发:第一次（早期）喷发称赤峰期，第二次（晚期）喷发称园池期。赤峰期喷发模式为：普林尼式喷发柱（赤峰空落浮岩层）—火山碎屑流（长白火山碎屑流层）—火山泥流（二道白河火山泥流层），主要由火山碎屑流诱发火山泥流；园池期火山喷发模式为：普林尼式喷发柱（园池空落浮岩火山灰层）—火山碎屑流（冰场火山碎屑流层）。两次普林尼式喷发空落火山碎屑物总量约120 km 3 ，长白火山碎屑流层总量约8 km 3 ，冰场火山碎屑流层总量约0.5 km 3 ，火山泥流堆积总量约为2 km 3 。主要论述了这次大爆发的火山喷发碎屑堆积物的层序和分布。

... 刘祥, 2006 ...

2004

0.0

刘祥, 隋维国, 向天元, 等. 2004. 长白山天池地区全新世以来火山活动及其特征[J]. 第四纪研究, 24(6): 638—644.

LIU

Xiang

, SUI

Wei-guo

, XIANG

Tian-yuan

, et al. 2004. Holocene volcanic activities and their features in Tianchi area, Changbaishan Mountains[J]. Quaternary Sciences, 24(6): 638—644(in Chinese).

The Changbaishan Volcano, a stratovolcano or a gigantic polygenetic volcanic cone, is located at the border between China and North Korea.The historically recorded 1199-1200A.D. eruption is the largest Changbaishan Volcano eruption during the period of Holocene. It can be subdivided into two phases of Plinian eruption; the first is named Chifeng phase and the second Yuanchi phase. The total volume of both the first Plinian fall and the second Plinian fall has been estimated more than 120km3.The eruptive pattern of the Chifeng phase is Plinian column (Chifeng pumice fall deposit)-pyroclastic flow (Changbai pyro-clastic flow deposit)-lahar (Erdaobaihe lahar deposit) which was mainly triggered by pyroclastic flow deposit. The Chifeng pumice fall deposit is characterized by light colour, fine grains and very good sorting. The deposit was spread towards SE direction as a tephra fan whose apex is at the summit of volcano. The Changbai pyroclastic flow deposit is distributed around the volcano as far as 50km from the vent and the area of deposit is about 2 100km2 and the bulk volume of deposit can be estimated over 8km3. The pumice flow deposit is of poor sorting, massive structure, developed graded structure, and gas escaping structure. The Erdaobaihe lahar deposit was accumulated along the Erdaobaihe River and the Songhua River and extended over 300km from the volcano.The eruptive pattern of the Yuanchi phase is Plinian column (Yuanchi pumice and ash fall deposits)-pyroclastic flow ( Bingchang pyroclastic flow deposits) . The Yuanchi pumice and ash fall deposit was blown towards east by the west unidirection wind and the apex of the tephra fan is at the summit of volcano. The deposit with yellow colour is mainly of alternative pumice and ash deposition. The Bingchang pyroclastic flow deposit filled the gorges around the volcano. This kind of deposit can be observed inside the caldera and on the top of the volcano in some places. The bulk volume of the deposit is about 0.5km3. The Bingchang pyroclastic flow deposit appears to be welded tuff, welded breccia and agglutinate with black to purple colour.The Qixiangzhan pantellerite is covered by the airfall tephra produced in this 800aB. P. eruption of the Changbaishan Volcano and the Qixiangzhan pantellerite is reported to be formed in Late Pleistocene-Early Holocene according to the geological occurrence of volcanic rocks and age dating. The view that the airfall tephra produced in 800aB. P. eruption of the Changbaishan Volcano was covered by the Qixiangzhan pantellerite and the Qixiangzhan patellerite was formed in Holocene suggested by Xu Dongman, Zheng Xiangshen and Xu Xiangxi is incorrect.

Faculty of Earth Sciences, Jilin University, Changchun 130061

长白山火山全新世规模最大的喷发活动发生在公元1199-1200年,即800年前的大爆发,被确定为普林尼或布里尼(Plinian)式喷发。这次大爆发形成体积巨大的、分布广泛的以空中降落堆积物为主的火山喷发碎屑堆积物,在长白山火山周围,远至日本都留下了地质记录。文章辨认并划分了这次大爆发火山碎屑物的成因类型:火山喷发空中降落堆积物(airfalltephra)、火山碎屑流(pyroclasticflow)状堆积物和火山泥流(lahar)堆积物,并且点、面结合,近、远和国内、国外兼顾,分析了这些火山碎屑物的主要特征、分布和相互关系,进而确定这些火山碎屑物分别属于两次普林尼式爆发。第1次(早期)普林尼式爆发称赤峰期,火山喷发模式为:普林尼式喷发柱(赤峰空落浮岩层)-火山碎屑流(长白山火山碎屑流层),随即主要由火山碎屑流诱发火山泥流(二道白河火山泥流层);第2次(晚期)普林尼式爆发称园池期,喷发模式为:普林尼式喷发柱(园池空落浮岩火山灰层)-火山碎屑流(冰场火山碎屑流层)。在层序上将气象站期碱流岩置于800年前大爆发火山碎屑物之下是正确的,其时代为晚更新世-全新世早期。

... 刘祥等, 2004 ...

2016

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... 64wt%, 为粗面质, 与山顶八卦庙期(潘波, 2016)的成分基本相同 ...

2005

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史兰斌, 陈孝德, 杨清福, 等. 2005. 长白山天池火山千年大喷发不同颜色浮岩的岩石化学特征[J]. 地震地质, 27(1): 73—82.

SHI

Lan-bin

, CHEN

Xiao-de

, YANG

Qing-fu

, et al. 2005. Petrochemistry of pumices of various colors produced by the eruption of Changbaishan Tianchi volcano at 1000 years ago[J]. Seismology and Geology, 27(1): 73—82(in Chinese).

The Changbaishan Tianchi volcano is the most dangerous volcano in China. The volcano has erupted for several times since Holocene,and especially the violent Plinian-type eruption at about 1000 years ago had produced volcanic fallouts that had been carried as far as to Japan,and ignimbrite deposit within the range of 50 km around the volcanic crater. The ignimbrite deposit can be divided into two types: the valley-pond ignimbrite and ignimbrite sheet. The valley-pond ignimbrites are distributed mainly in Fushilin (Pumice Forest) and the valleys of the Jingjiang,Heishihe and Yalujiang Rivers,having a thickness of 20~60m. The ignimbrite sheets are distributed mainly in Guangming,Xinghuo,Dongfanghong and Weidong Forestry Centers,having a thickness of less than 10m. The ignimbrite deposits consist mainly of volcanic ash and pumice,associated with small amount of crystal and lithic fragments. It was commonly accepted in previous works that the pumice from ignimbrite deposit is grayish white in color and belongs to comendite. However,our field investigation has revealed that in addition to grayish white pumice,a small amount of black,gray and other colored pumices are also widely distributed. The samples of pumices of various colors have been collected during field investigation,and their chemical composition has been analyzed in the lab for comparison. The results show that the grayish white and black pumices belong respectively to comendite and trachyte,while the gray pumice belongs to trachyte but closer to comendite end member. The pumices of various colors came from the same crustal magma chamber,and were the products of different evolution stages of magma within the chamber. The simultaneous extrusion of these pumices indicates the zonation of the magma chamber and the mingling of magmas of various compositions.

1. Institute of Geology, China Earthquake Administration, Beijing 100029, China; 2. Earthquake Administration of Jilin Province, Changchun 130022, China

长白山天池火山大约1000年前的大喷发,形成了巨厚的火山碎屑流堆积层,其主要组成是浮岩与火山灰。以往的研究普遍认为其中的浮岩为灰白色,属流纹质。笔者在考察中发现了不少黑色及少量其它颜色的浮岩,系统地采集了各色样品作浮岩化学成分分析,结果表明,灰白色浮岩与黑色浮岩分别为流纹质和粗面质,灰色浮岩属于粗面质但靠近流纹质端元。它们都来源于地壳岩浆房,是岩浆房内不同分异演化阶段的产物,它们同时喷出说明岩浆房内具有分带性及不同性质岩浆的混合。

... 史兰斌等(2005)认为流纹质和粗面质浮岩均来自地壳岩浆房, 为岩浆房内不同分异演化阶段的产物, 并认为岩浆房具有分带性, 不同性质的岩浆存在混合作用 ...

1989

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2010

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1997

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... 魏海泉等, 1997 ...

1993

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许东满, 郑祥身, 许湘希. 1993. 长白山天池地区全新世以来火山活动及其特征[J]. 第四纪研究, 13(1): 85—94.

Dong-man

, ZHENG

Xiang-shen

, XU

Xiang-xi

. 1993. Holocene volcanic activities and their features in Tianchi area, Changbaishan Mountains[J]. Quaternary Sciences, 13(1): 85—94(in Chinese).

Volcanic calamity would have a great impact on the mankind and the environment. There have been frequent and intense Cenozoic volcanic activities in Changbaishan region, which is a part of the Circum-Pacific volcanic belt. Recent investigations on the Baitoushan volcano, Tianchi area of Changbaishan region provide many new information about Holocene volcanic activities in this region. Before Holocene, intense and frequent eruptions of basaltic lavas constructed the base of the Baitoushan volcano in Tianchi area. The shield base of the Baitoushan volcano was constructed by the Junjianshan basalt in Late Pliocene. Recent information from volcanologic and volcano calamity investigations had shown that since the beginning of Holocene the Baitoushan volcano had gradually entered another hightide of activities. At least six eruption stages in Tianchi area have been distinguished based on the residual materials on land surface, geological relationship and some chronological datings. The basaltic lavas and scorias of Laohudong stage had constructed several small cones which are scattered on the slope of the Baitoushan volcano. New discovery of the basaltic rocks in Holocene shows that the volcanic activities and the magmatic evolution process might be more complex than that discussed before. Pyroclastic Pumice Flow of Baiyunfeng stage began with an intensive explosion of gasified magma, which broke through the Tianchi crater and produced a very high and huge explosion column. Alkali trachytic clastic rocks of Baguamiao stage outcropped on the inner side of the crater, hillside of cone and valleys were erupted from the Tianchi crater. The Qixiangzhan pantelleritic lavas have been determined with some new investigations, that is, the forming age of the pantelleritic lavas and breccia is Holocene instead of Pleistocene suggested by Liu Xiang (1989). The Tianchi Weather Observatory is located just at the center of a small crater which was blocked by Pantellerites. New geological datings show that tuff breccia of Nangou stage is probably the products of several limited intermittent eruptions. Some black coke-like cinder and soil scattered in the ditches nearby the sixth boundary tablet between China and Korea (Liuhaojie), might be the relict of another limited volcanic activity. Based on the above information it can be seen that in Holocene, the most important ac- tivities in Changbaishan region are the strong explosions of Baiyunfeng and Baguamiao stages, which caused pyroclastic flows and brought great suffering to this area. Another limited eruption in Holocene also shows the potential dangers in Tianchi arta in the near future. People should pay close attention to the possibility of short term volcanic hazard.

1. Seismology Office of Yanbian Korea Autonomous Prefecture; 2. Instisute of Geology, Chinese Academy of Sciences;

新生代以来,强烈而频繁的火山活动铸成了长白山火山的主体——白头山火山锥。近几年来,从火山学和火山灾害学角度在该区进行研究和调查所获得的资料发现,长白山天池地区在全新世至少有六期火山活动在地表留下了记录。除白云峰期和八卦庙期喷发出大量碱流岩质浮岩形成的火山碎屑流造成了严重的火山灾害之外,其他四次喷发的规模均较小、影响面不大。老虎洞期活动发生在浮岩喷发之前,主要产物为玄武质火山渣和熔岩;气象站期喷发可能是该火山近期活动的表现,以碱流岩喷溢为主。这些喷发活动证实,该区近代火山活动不仅从未停止过,相反,活动的频度却逐渐加大。

1996

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... 其年代较新, 野外喷发物保存较为完整, 因此, 其喷发年代、分布范围、灾害评估也受到广泛关注(杨清福等, 1996, 1998 ...

2007

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杨清福, 史兰斌, 张羽, 等. 2007. 长白山天池火山千年大喷发火山碎屑流堆积的粒度特征与地质意义[J]. 地震地质, 29(3): 480—491.

YANG

Qing-fu

, SHI

Lan-bin

, ZHANG

, et al. 2007. Grain-size characteristics of the Millennium pyroclastic flow deposits of Tianchi volcano and their geological implications[J]. Seismology and Geology, 29(3): 480—491(in Chinese).

Pyroclastic flow deposits have become a research topic of great interest in volcanology,because they may bring the humanity devastating hazards.This paper demonstrates the results of grain-size sieve analyses of the millennium pyroclastic flow deposits from Tianchi volcano.The result shows that the pyroclastic flow deposits are poorly sorted and the ash cloud surge deposits accompanied with pyroclastic flow are well sorted.The average greatest grain-sizes of lithic fragments and pumice fragments in pyroclastic flow deposits decrease with increasing distance from the crater,indicating that gravity sorting and mechanical wearing did occur during the transportation of the pyroclastic flow.In addition,fluidization also occurred during the transportation of pyroclastic flow.The rate of fluidization decreases with increasing distance from the crater,indicating the occurrence of degassing during the transportation process of the pyroclastic flow.This process might cause the increase of viscosity and yield strength of the pyroclastic flow,resulting in the deposition of the flow.The rate of fluidization,therefore,is an important factor controlling the transportation distance.The confluence of multi-channel pyroclastic flows at distal part may increase the rate of fluidization of the pyroclastic flow,as a result,the transportation distance becomes longer and the hazard area becomes greater.

1. Earthquake Administration of Jilin Province, Changchun 130022, China; 2. Institute of Geology, China Earthquake Administration, Beijing 100029, China

火山碎屑流堆积因其巨大的危害性而成为火山学研究的重要课题之一。文中对长白山区天池火山千年大喷发火山碎屑流堆积进行了粒度分析。分析结果表明,火山碎屑流堆积分选差,伴生的灰云浪堆积分选性好。火山碎屑流堆积中的岩屑和浮岩的平均最大粒度随着离开火山口距离的加大而减小,反映火山碎屑流搬运过程中存在重力分选和机械磨损作用。火山碎屑流在搬运过程中发生了流体化作用,离开火山口越远流体化速度越小,反映火山碎屑流在搬运过程中发生了流体化去气作用,这种作用使火山碎屑流的粘度和屈服强度增加而导致沉积。流体化速度是控制搬运距离的因素之一,远源多渠道火山碎屑流的汇合使流体化速度增大,搬运距离更远,造成的灾害范围也增大。

... 杨清福等(2007)、赵波等(2010)和Zhao等(2013)曾对天池火山区不同成因类型的浮岩碎屑进行过粒度分析, 但是未曾区分圆池期和赤峰期浮岩 ...

1998

0.0

... 其年代较新, 野外喷发物保存较为完整, 因此, 其喷发年代、分布范围、灾害评估也受到广泛关注(杨清福等, 1996, 1998 ...

2012

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... 于红梅等, 2012 ...

... 浮岩内部气孔的大小和数量也反映了喷发的强度(于红梅等, 2012), 赤峰期的浮岩气孔更大, 拉长更明显, 气孔数量较多, 气孔壁更薄, 也说明喷发的强度更大 ...

2010

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赵波, 许建东, 于红梅. 2010. 长白山地区火山碎屑粒度特征研究[J]. 地震地质, 32(2): 233—243. doi: DOI: 103969/j. issn. 0253-4967. 201002. 006.

ZHAO

, XU

Jian-dong

, YU

Hong-mei

. 2010. Grain-size characteristics of pyroclasts in Changbaishan Mountain area[J]. Seismology and Geology, 32(2): 233—243(in Chinese).

The pyroclastic deposits from tephra fall,pyroclastic-flow,base-surge,and lahar are well developed in Changbaishan Mountain area where volcanic activity is active in the Holocene.These different pyroclastic deposits are difficult to distinguish from each other in the field because of their similar physical and geological appearance.Through field investigation of pyroclastic deposit sections in the study area,we systematically collected different pyroclastic deposit samples at different sites,and then calculated the grain size parameters and plotted out the probability cumulative curves of all samples in the laboratory.Our results indicate that the pyroclastic samples from different origins can be distinguished by characteristic grain-size diagrams,e.g.median diameter(Md Ф )versus sorting(σ Ф ),F1 versus F2 diagram.In terms of texture,most pyroclastic deposits show similar characters.However,with the increase of distance from the volcano crater,grain size decreases correspondingly.Finally,Laser Particle Size analyzer is utilized at first time to analyze the subpopulation of fine ash(≤62.5μm)of our samples.On the basis of the fine ash subpopulation histogram distribution and weight cumulative curves,we found that the fine ashes with grain-size from 0.02μm to 62.5μm in pyroclastic-flow deposits and pyroclastic-surge deposits are significantly different due to their different formation origin and different transportation processes.

Institute of Geology, China Earthquake Administration, Beijing 100029, China

长白山地区全新世火山活动活跃,发育了良好的火山空降、火山碎屑流、火山涌流和火山泥石流堆积物。这些堆积物交错堆积,野外区分较为困难。在火山碎屑地层剖面调查基础上,系统采集了各种类型的火山碎屑堆积物样品。在实验室通过粒度参数和概率累积曲线分析,对堆积物成因类型进行了判别,讨论了火山空降堆积物和火山碎屑流堆积物随着与火口距离变化的规律。首次对研究区内粒度范围为62.5～0.02μm的细火山灰进行了粒度分析,对火山碎屑流和火山碎屑涌流中细火山灰端元分布特征和地质意义进行了分析和讨论。

... 杨清福等(2007)、赵波等(2010)和Zhao等(2013)曾对天池火山区不同成因类型的浮岩碎屑进行过粒度分析, 但是未曾区分圆池期和赤峰期浮岩 ...

1998

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2009

0.0

... 1980年美国圣海伦斯火山喷发(VEI=5), 喷发物SiO₂的含量为66~80wt%, 喷发柱的高度为25km(Carey et al ...

1996

0.0

... 1991年菲律宾皮纳图博火山喷发(VEI=6), 喷发物SiO₂的含量为68~77wt%, 喷发柱的高度达到了40km(Koyaguchi et al ...

1989

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1983

0.0

... , 2013), 对全球气候造成了巨大的影响, 被认为是世界上历史时期规模最大、影响最广的火山喷发之一(Machida et al ...

2017

0.0

... Pan et al ...

... 潘波(2016)、 Pan等(2017)测试圆池期空降物与天文峰顶部的黑色浮岩成分和斑晶成分一致, 认为其为同一期产物, 并统称为 #cod#x0201c ...

1983

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2013

0.0

... 3)AD发生了大规模的喷发(Xu et al ...

2013

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... Yu et al ...

2013

0.0