长白山天池火山天文峰期黄色浮岩成因研究  

Formation mechanism of yellow pumice in the deposition of Tianwenfeng eruption at Changbaishan-Tianchi volcano

作　　者：潘波[1,2] 程滔[3] 徐丹 刘松军 PAN Bo;CHENG Tao;XU Dan;LIU SongJun(National Observation and Research Station of Jilin Changbaishan Volcano,Institute of Geology,China Earthquake Administration,Beijing 100029,China;State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,Beijing 100029,China;National Geomatics Center of China,Beijing 100830,China)

机构地区：[1]中国地震局地质研究所,吉林长白山火山国家野外科学观测研究站,北京100029 [2]中国地震局地质研究所,地震动力学国家重点实验室,北京100029 [3]国家基础地理信息中心,北京100830

出　　处：《岩石学报》2020年第7期2067-2080,共14页Acta Petrologica Sinica

基　　金：中国地震局地质研究所地震动力学国家重点实验室开放基金(LED2018B02)资助。

摘　　要：长白山天池火口北侧天文峰之上,一套醒目的黄色浮岩引起广泛的关注,其颜色成因问题更是讨论的热点。本文通过野外地质调查、显微形貌和地球化学分析等方法,探索了黄色浮岩的颜色成因问题,并对此次喷发活动(天文峰期喷发)有了更进一步的认识。黄色浮岩与其下部灰白色浮岩应为同一期喷发所形成,两者成分一致且特征相似。黄色浮岩初始颜色为灰白色,后期受所处环境(降水丰富)与本身气孔特征的影响,浮岩内发生了元素析出和元素沉淀的过程。首先,浮岩内Si与H2O结合形成弱硅酸(H2SiO3),而大气中CO2与H2O结合形成弱碳酸(H2CO3),在弱酸环境下火山玻璃逐渐析出Si、K、Al、Ca和Fe等阳离子,而析出的元素易溶于水的部分被流水带走,难溶于水的Fe与Al富集并粘附在火山玻璃壁上,同时由于Fe可与H2O络合形成黄色的Fe的水合物(Fe2O3·nH2O),而Al与H2O络合形成凝胶状白色水合物(Al2O3·nH2O),两者混合形成了黄色胶状物粘附在火山玻璃壁上,改变了浮岩原本的灰白色,形成了黄色浮岩。因此,天文峰期浮岩的黄色是由于后期风化淋滤作用所造成,属于次生色。本研究提高了对火山喷发堆积物风化淋滤作用过程的认识,也为其他地区相似颜色变化问题的讨论提供了借鉴。One thick pumice deposition with yellow color,located on the north slope of Tianchi caldera,has attracted widespread attention,meanwhile,the formation mechanism of its yellow color become a hot topic.Through detailed field observations,micromorphology,and geochemical determination,we unveiled the formation mechanism and processes for the yellow color of pumice,and also improved the understanding for the Tianwenfeng eruption.Based on the same geochemical composition of volcanic glass and micromorphological characteristics of pumice,the upper yellow pumice and lower grey pumice at Tianwenfeng section are identified as the same eruption with different color,and the initial color of yellow pumice also should be grey.The changing from grey to yellow has experienced the elemental separation from glass and elemental concentration on the wall of glass due to the environment with rich rainfall and snowfall at Changbaishan-Tianchi volcano area.In the vesicle of pumice with water,the Si from glass can combine with H2O and formed the silicic acid(H2SiO3),and the CO2 from atmosphere can combine with H2O and form the carbonic acid(H2CO3).In the weak acid environment,the elements such as Si,K,Al,Ca and Fe will slowly separate from volcanic glass.Meanwhile,some of elements such as Si,Na,and K are easily dissolved in the water and taken away by flowing water from vesicle,but some of elements such as Al and Fe are hardly dissolved in water and remained on the wall of glass.In addition,the complexing of Fe and H2O can form the yellow iron hydrate(Fe2O3·nH2O),and the complexing of Al and H2O can form the white gel-like aluminum hydrate(Al2O3·nH2O).The mixing of Fe and Al hydrate adheres to the wall of glass,and causes the original grey pumice gradually change to the yellow pumice.This study will improve the understanding of the weathering and leaching process for pumice deposits,and also provides a reference for the topic of color changing in other regions.

关 键 词：长白山天池火山 天文峰期喷发 风化淋滤 析出与沉淀 铁铝水合物 黄色浮岩 

分 类 号：P317.3[天文地球—固体地球物理学]