Heating Stage Experimental Study of Melt Inclusions in Feldspars from Three Holocene Eruptions of Changbaishan Tianchi Volcano  

作　　者：Li Ni Nicole Metrich Fan Qicheng 

机构地区：[1]Institute of Geology, China Earthquake Administration, Beijing 100029, China [2]Laboratoire Pierre Sue, CEA-CNRS, Saclay, 91191 Gif sur Yvette, France

出　　处：《Earthquake Research in China》2008年第2期153-163,共11页中国地震研究（英文版）

基　　金：This research was jointly supported by basic scientific research project of Institute of Geology, CEA (DF-IGCEA-060719);National Natural Science Foundation of China(40672043);Science and Technology Tackling Project of CEA (2006BAC01B040104);China Scholarship Council,Ministry of Education

摘　　要：There occurred several eruptions from Changbaishan Tianchi volcano in Holocene, and at least three of them were believed to be true according to the formal studies. The products of three eruptions were yellow comenditic pumice of - 5000a B.P. （Eruption Ⅰ ）, gray comenditic pumice and pyroclastic flow of - 1000a B.P. （ Eruption II, i.e. the millennium explosive eruption）, black trachy pumice and welded tuff of - 300a B.P. （ Eruption Ⅲ ） respectively. There were a large number of melt inclusions found in phenocrysts, which differ in size and color. The Leitz 1350 heating stage experiments for melt inclusions in host feldspars from three Holocene eruptions of Changbaishan Tianchi volcano imply that there were little differences between the homogenization temperatures of melt inclusions from Eruptions Ⅰ and Ⅲ, whereas it was rather complicated for Eruption H, i.e. there might be two kinds of melt with different homogenization temperature periods, which gave the evidence for the assumption that the explosive millennium eruption of Tianchi volcano was triggered by injection and mixing of two different magmas. The experimental results also indicate that （ 1 ） small melt inclusion is easy to be homogenized, while the large one, especially the one with lots of daughter crystals, is rather difficult to be homogenized; （2） homogenization temperature closely correlates with the size of melt inclusion within host crystal, with the temperature point switching from high heating rate to low heating rate, and correlates with whether it is the first time to obtain homogenization as well; and （3） a melt inclusion can get different homogenization temperatures when it is repeatedly heated. Even more, the next homogenization temperature is usually higher than the former one, which testifies the phenomenon that hydrogen migration occurs during repeated heating.There occurred several eruptions from Changbaishan Tianchi volcano in Holocene,and at least three of them were believed to be true according to the formal studies.The products of three eruptions were yellow comenditic pumice of～5000a B.P.(Eruption I),gray comenditic pumice and pyroclastic flow of～1000a B.P.(Eruption II,i.e.the millennium explosive eruption),black trachy pumice and welded tuff of～300a B.P.(Eruption Ⅲ)respectively.There were a large number of melt inclusions found in phenocrysts,which differ in size and color.The Leitz 1350 heating stage experiments for melt inclusions in host feldspars from three Holocene eruptions of Changbaishan Tianchi volcano imply that there were little differences between the homogenization temperatures of melt inclusions from Eruptions Ⅰ and Ⅲ,whereas it was rather complicated for Eruption II,i.e.there might be two kinds of melt with different homogenization temperature periods,which gave the evidence for the assumption that the explosive millennium eruption of Tianchi volcano was triggered by injection and mixing of two different magmas.The experimental results also indicate that(1)small melt inclusion is easy to be homogenized,while the large one,especially the one with lots of daughter crystals,is rather difficult to be homogenized;(2)homogenization temperature closely correlates with the size of melt inclusion within host crystal,with the temperature point switching from high heating rate to low heating rate,and correlates with whether it is the first time to obtain homogenization as well;and(3)a melt inclusion can get different homogenization temperatures when it is repeatedly heated.Even more,the next homogenization temperature is usually higher than the former one,which testifies the phenomenon that hydrogen migration occurs during repeated heating.

关 键 词：Changbaishan Tianchi volcano Alkaline feldspar Melt inclusion Heating stage Homogenization temperature 

分 类 号：P317[天文地球—固体地球物理学]