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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Magma degassing process during Plinian eruptions
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Magma degassing process during Plinian eruptions

机译：普利尼亚火山爆发期间的岩浆脱气过程

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To assess magma degassing processes during Plinian eruption, noble gas abundances and isotopic ratios have been determined in pumices by crushing under vacuum. Samples come from Plinian eruptions, which occur along different subduction zones. In addition, two pumice samples come from the Azores hotspot. All samples are characterized by a systematic enrichment in neon over argon, a depletion of krypton relative to argon and an isotopically fractioned ~(38)Ar/~(36)Ar ratio. These features do not depend on geological setting, or on pumice age, or eruption intensity. However, they are similar for pumices from the same eruption. A correlation is observed between ~(84)Kr/~(35)Ar and the ~(38)Ar/~(36)Ar ratio. This illustrates that only one physical process is at the origin of the fractionation. We propose here a model of kinetic magma degassing before fragmentation to explain the elemental and isotopic fractionation. Noble gases diffuse in a magma shell surrounding a preexisting bubble. The model put forward an alternative to the model of Pinti et al. (1999), in which diffusion occurs after pumice quenching in Plinian plume. The model explains measurements and shows the rapidity of the magma degassing process in the conduit (few hundreds of seconds).
机译：为了评估普利尼山喷发过程中的岩浆脱气过程，已通过真空破碎确定了浮渣中稀有气体的丰度和同位素比。样品来自普林尼火山喷发，喷发沿不同的俯冲带。此外，两个浮石样品来自亚速尔群岛热点。所有样品的特征是系统地富集了氖气中的氖气，relative气相对于氩气的贫乏率以及同位素分馏的〜（38）Ar /〜（36）Ar比。这些特征不取决于地质背景，浮石年龄或喷发强度。但是，对于相同喷发的脓疱，它们相似。观察到〜（84）Kr /〜（35）Ar与〜（38）Ar /〜（36）Ar比之间的相关性。这说明分馏的起点只有一个物理过程。我们在这里提出一个动能岩浆在破碎之前脱气的模型，以解释元素和同位素的分离。稀有气体在围绕先前存在的气泡的岩浆壳中扩散。该模型提出了Pinti等人模型的替代方案。 （1999年），其中浮石在Plinian羽中淬灭后发生扩散。该模型解释了测量结果，并显示了导管中岩浆脱气过程的速度（几百秒）。

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