Abstract: The Changbaishan Tianchi volcano on the border between China and North Korea (42? N,128? E) is the most dangerous one with high destructive eruption potential in China. In the research of recent eruption history of the Tianchi volcano, a set of recent ejecta were recognized through field investigation, grain size analysis and petrochemistry analysis. The new ejecta were found on the northeast side of the Tianchi Lake. It is a set of multi-layered pyroclastic deposits of 9.2m thick overlying the 1668 AD airfall deposit. Grain size analysis shows that the ejecta are composed mainly of fall deposit with an interbed of surge deposit, and the type of eruption is phreatomagmatic. Fractal dimension value of the surge deposit is 2.7113, while that of the fall deposits ranges from 2.3028 to 2.4627, having an average value of 2.36. In the microscope, skeleton vitric fragments are observed but clay mineral is not found in the deposits, indicating that they are primary deposit produced by explosive eruption. Petrochemistry analysis of pumice component indicates that the magma can be assigned to trachytic magma. Based on historical records, stratigraphic correlation and features of the deposits, it is estimated that the ejecta are the product of 1903 AD eruption.

Key words: Holocene, pyroclastic deposit, Tianchi volcano

摘要： 长白山天池火山是中国最具有潜在灾害性喷发危险的活动火山。在开展长白山天池火山近代喷发历史的研究中,通过野外考察、粒度分析、岩石化学研究,识别出了一套新的火山喷发物。这套喷发物分布于天池水面东北侧,为一套灰色多层火山碎屑堆积,厚约9.2m。下伏公元1668年的火山空降堆积。粒度分析表明,天池火山最近一次喷发物以空降堆积为主,夹一层薄层涌浪堆积,火山喷发类型为射气岩浆型。涌浪堆积碎屑物的分数维值为2.71。空降堆积的分数维值小于涌浪堆积,综合投点求出的分数维值为2.36。显微镜下可观察到鸡骨架状玻屑,无黏土矿物,为原生火山爆发堆积。火山碎屑堆积物中的浮岩岩石化学分析结果表明岩浆成分为粗面质。根据历史记录、地层层序关系、堆积物特征的综合分析,推测堆积物的形成时间为公元1903年。

关键词: 全新世, 火山碎屑堆积, 天池火山