Water and halogens in volcanic clasts: tracers of degassing processes during Plinian and dome-building eruptions
Water and halogens in volcanic clasts: tracers of degassing processes during Plinian and dome-building eruptions
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火山碎屑中的水和卤素：普林尼式喷发和圆顶喷发期间脱气过程的示踪剂
DOI：
10.1144/gsl.sp.2003.213.01.05
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
A. Michel
中科院分区：
文献类型：
--
作者：
B. Villemant;G. Boudon;S. Nougrigat;S. Poteaux;A. Michel
岩浆脱气可能发生在岩浆柱中没有明显气体逸出的情况下，这与典型的普林尼式喷发相对应，也可能发生在气体损失的情况下，这与典型的喷涌式（造穹）喷发相对应。岩浆脱气还可能导致熔体结晶，这改变了残余熔体的成分，进而可能显著影响脱气条件。我们提出了一种方法，通过测量喷发火山碎屑（浮石和圆顶碎屑）微晶基质和玻璃中的挥发物（H2O, Cl, Br）来模拟富氢流纹岩熔体的这些过程。这种方法应用于佩尔萨梅火山（马提尼克岛）和圣玛丽亚火山（危地马拉）的两次普林尼火山和圆顶建筑喷发。构造圆顶喷发过程中岩浆的极端脱气和结晶可以解释致密火山碎屑残余熔体中卤素和H2O含量的差异：它们显示出Cl含量的很大范围（几个ppm到几千ppm），而H2O含量的范围要窄得多，低于1%。这种方法可以预测火山气体化学的演变（如HCl含量或HCl/HF比）作为浅深度岩浆脱气方式的函数。
Abstract Magma degassing may occur either with no significant gas escape from the magma column, which corresponds with typical Plinian type eruptions, or with gas loss, which corresponds with typical effusive (dome-building) eruptions. Magma degassing may also lead to melt crystallization, which modifies the residual melt composition and, in turn, may significantly affect the degassing conditions. We propose a method for modelling these processes for H2O-rich rhyolitic melts through measurements of volatiles (H2O, Cl, Br) in the microcrystalline matrix and glass of erupted volcanic clasts (pumice and dome clasts). This method is applied to two Plinian and dome-building eruptions at Mount Pelée (Martinique) and Santa Maria (Guatemala) volcanoes. Extreme magma degassing and crystallization during dome-building eruptions may explain the contrasts in halogen and H2O contents of residual melts of dense volcanic clasts: they display very large ranges of Cl contents (few ppm to thousands of ppm), whereas the ranges of H2O contents are much narrower, and lower than 1%. This method allows prediction of the evolution of volcanic gas chemistry (as HCl content or HCl/HF ratio) as a function of the degassing style of magma at shallow depth.