长白山天池火山全新世3期浮岩长石斑晶中熔体包裹体高温热台实验研究  

HEATING STAGE EXPERIMENTS OF MELT INCLUSIONS IN FELDSPARS OF PUMICE FROM THREE ERUPTIONS OF CHANGBAISHAN TIANCHI VOLCANO IN HOLOCENE

作　　者：李霓[1] Nicole Métrich 樊祺诚[1] 

机构地区：[1]中国地震局地质研究所 [2]Laboratoire Pierre Süe,CEA-CNRS,Saclay,91190,France

出　　处：《地震地质》2007年第3期459-469,共11页Seismology and Geology

基　　金：中国地震局地质研究所基本科研业务专项(DF-IGCEA-060719);国家自然科学基金(40672043);地震科学联合基金(106052);教育部国家公派留学基金共同资助

摘　　要：长白山天池火山在全新世曾多次喷发,以往研究结果基本上认定至少有3期喷发物:距今约5,000a前淡黄色碱流质浮岩、距今约1,000a前灰白色碱流质浮岩和碎屑流以及距今约300a的黑色粗面质浮岩和熔结凝灰岩。喷发物斑晶矿物中含有众多熔体包裹体,形貌特征各有不同。经Leitz1350高温热台对天池火山全新世3期喷发物长石中熔体包裹体的均一法测温实验,结果表明第1,3喷发期的岩浆温度相差不大,而千年大喷发期较为复杂,揭示当时有2个不同温度段的熔体存在,为大喷发可能由2种岩浆注入和混合而触发的论点提供了线索。实验还证实,个体小的熔体包裹体易于均一,而个体较大的、尤其是含有大量子晶的熔体包裹体则很难均一;均一温度与熔体包裹体大小、何时从较快升温速率变为较慢升温速率、是否为初次升温时测量得出有关。同一颗熔体包裹体多次数升温至均一,每次得到的均一温度不同,而且每升温一次得到的均一温度均比前一次高,证实了均一过程中的确有H扩散的现象。Melt inclusions are the tiny silicate drops（usually 〈 300μm）of magma trapped during crystals growing in the magma chamber. As phenocrysts completely enclose the melt, forming pressure vessels that prevent the included melt drop from outgassing during decompression and eruption, the melt inclusions have the potential to preserve the pre-eruptive composition of the melt. If unaltered, melt inclusions represent the major, trace and volatile element chemistries of pre-eruptive magma during the complicated effusive and explosive eruptions. Silicate-melt inclusions provide a unique possibility of reconstructing the chemical composition of a magma at a specific stage of its evolution. They are usu- ally solid in the room temperature. It＇s the counterreaction of the actual procedure that heats melt in- clusions and makes them homogenized. Theoretically, the homogenized melt inclusions are thought to keep magma characteristics when they were trapped. The temperature at which the daughter crystal disappears can be deemed as the temperature when magma was trapped. At present, the heating stage experiments provide the only access to the knowledge of magma before eruption. Based on previous works, it is believed there are at least three eruption periods in Holocene, for Tianchi volcano, i. e. the yellow comenditic pumice of- 5000a BP（ Eruption Ⅰ ）, the gray comendit- ic pumice and pyroclastic flow of-1000a BP（Eruption I1 , i.e. ＂the millennium great eruption＂）, and the black trachy pumice and tuff of-300a BP（Eruption m ）. There are a large number of melt inclusions found in the alkali feldspars of the pumice and pyroclastic flow, which are different in size and color. We have made experimental studies on the homogenization temperatures of the melt inclu- sions in feldspars from these eruptions of Tianchi volcano in Holocene using Leitz 1350 heating stage. For Eruption I , the homogenization temperatures are from 938℃ to 1014~C. There are two tempera- ture intervals for Eruption I] ： 850 -926~C

关 键 词：长白山天池火山 碱性长石 熔体包裹体 高温热台 均一温度 

分 类 号：P317.3[天文地球—固体地球物理学]