Volatile content and degassing processes in the AD 79 magma chamber at Vesuvius (Italy)
Volatile content and degassing processes in the AD 79 magma chamber at Vesuvius (Italy)
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公元 79 年维苏威火山岩浆房（意大利）的挥发物含量和脱气过程
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
R. Cioni
中科院分区：
文献类型：
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作者：
R. Cioni
摘要通过对不同成因晶体中熔体包裹体的研究，探讨了维苏威火山（意大利）AD 79岩浆房中挥发分的演化。采用FTIR和EMPA对不同熔体中的H2O、CO2、S和Cl进行了测定。这使我们能够确定最进化的，phonolitic部分的岩浆房和镁铁质熔体喂养室的挥发性成分。MI透长石从phonolitic和tephri-phonolitic浮石显示系统的组成和挥发分含量的差异，这可以解释为在同喷发混合过程中的主机矿物的再吸收。喷前的响岩岩浆含量似乎已占主导地位的H2O和Cl（分别为6.0至6.5重量%和6700 ppm），而岩浆房的再填充发生通过反复注入的H2O，CO2和富S的火山岩浆（分别为3%，1500 ppm和1400 ppm）。强CO2脱气可能发生在减压路径的镁铁质批次向岩浆房，而硫可能是由岩浆结晶和混合过程中释放。水和氯在岩浆中大量积累，只有在喷发期间才达到溶解度极限。氯的溶解度似乎已经强烈的成分控制，和Cl释放被抑制的白榴石，这转移了剩余液体的组合物向更高的Cl溶解度的基质结晶。
Abstract The evolution of volatiles in the AD 79 magma chamber at Vesuvius (Italy) was investigated through the study of melt inclusions (MI) in crystals of different origins. FTIR spectroscopy and EMPA were used to measure H2O, CO2, S and Cl of the different melts. This allowed us to define the volatile content of the most evolved, phonolitic portion of the magma chamber and of the mafic melts feeding the chamber. MI in sanidine from phonolitic and tephri-phonolitic pumices show systematic differences in composition and volatile content, which can be explained by resorption of the host mineral during syn-eruptive mixing. The pre-eruption content of phonolitic magma appears to have been dominated by H2O and Cl (respectively 6.0 to 6.5 wt% and 6700 ppm), while magma chamber refilling occurred through the repeated injection of H2O, CO2 and S-rich tephritic magmas (respectively 3%, 1500 ppm and 1400 ppm). Strong CO2 degassing probably occurred during the decompressional path of mafic batches towards the magma chamber, while sulphur was probably released by the magma following crystallization and mixing processes. Water and chlorine strongly accumulated in the magma and reached their solubility limits only during the eruption. Chlorine solubility appears to have been strongly compositionally controlled, and Cl release was inhibited by groundmass crystallization of leucite, which shifted the composition of the residual liquid towards higher Cl solubilities.