Degassing of Laacher See phonolite – an experimental study

Laacher 的脱气参见响石 â 一项实验研究

• 批准号: 456692830
• 负责人: Professor Dr. Marcus Nowak
• 金额: --
• 依托单位: Forschungsbereich Mineralogie und Geodynamik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/456692830?language=en
• 关键词: Degassing; Laacher; See; phonolite; experimental

The H2O degassing of highly viscous SiO2-rich rhyolitic magma drives explosive volcanic eruptions. Less viscous phonolitic magma also tends to erupt explosively, although the fluid dynamics may be significantly different. The explosive eruption of the phonolitic Laacher See magma chamber 12900 years BP in the Eifel, which ejected ~ 6.3 km3 magma, devastated more than 1000 km2 of landscape by ash flows. A reactivation of the explosive Eifel volcanism could threaten thousands of people and valuable infrastructure in the heart of Europe. Therefore, it is necessary to experimentally investigate the degassing of hydrous Laacher See phonolite. The phase separation of a fluid from a hydrous melt by vesicle formation is a fundamental mechanism that drives explosive volcanic eruptions.Decompression experiments show that a supersaturation pressure of ~ 100 MPa is required to initiate phase separation of hydrous silicate melt by formation and growth of fluid vesicles. Supersaturation of H2O causes phase separation in rhyolitic melt by decompression rate dependent homogeneous nucleation of H2O clusters in the metastable state. Alternatively, as recently proposed for a potassium-rich and metaluminous phonolitic Vesuvius melt, supersaturation may trigger decompression rate independent spinodal decomposition in the unstable state. However, recent studies have left open important questions: (1) Which parameters cause the difference in degassing behavior of different melt compositions (rhyolite vs. Vesuvius phonolite)? (2) Is the decompression rate independent degassing behavior of the Vesuvius melt unique or does it represent a general phase separation mechanism of hydrous phonolitic melts that can differ significantly in their composition? (3) What role does temperature play in the decomposition of hydrous melts? Besides the possibility to gain insight into the degassing mechanisms of the Laacher See volcanic system, experimental investigation of the degassing behavior of the sodium-rich and peraluminous Laacher See phonolite is ideal to answer these fundamental questions. The experimental data in combination with the comparison of the vesicle textures of the natural pumice are important basics for the risk assessment of the Laacher See volcano and other sodium-rich phonolitic volcanic systems.

高粘度富SiO2流纹质岩浆的H2O脱气作用驱动了火山爆发。粘性较低的响岩岩浆也倾向于爆发，尽管流体动力学可能有很大的不同。12900年前，艾菲尔山的响岩Laacher See岩浆房爆发，喷出约6.3 km 3的岩浆，火山灰流摧毁了1000多km 2的景观。爆炸性的艾菲尔火山活动的重新激活可能会威胁到欧洲中心成千上万的人和宝贵的基础设施。因此，有必要对含水Laacher See响岩的脱气过程进行实验研究。火山爆发的一个基本机制是流体与含水熔体通过泡囊的形成而发生相分离，减压实验表明，通过泡囊的形成和生长而引发含水硅酸盐熔体的相分离需要~ 100 MPa的过饱和压力。水的过饱和导致流纹质熔体中的相分离是通过减压速率依赖的亚稳态水团簇的均匀成核来实现的。另外，最近提出的富钾和metaluminous phonolitic维苏威火山熔体，过饱和可能会引发减压速率独立的失稳分解的不稳定状态。然而，最近的研究留下了一些重要的问题：（1）哪些参数导致不同熔体成分（流纹岩与维苏威响岩）的脱气行为差异？(2)是减压速率独立的维苏威火山熔体的脱气行为独特的，或者它代表了一个一般的相分离机制的含水phonolitic熔体，可以显着不同的组成？(3)温度在含水熔体的分解中起什么作用？除了有可能深入了解Laacher See火山系统的脱气机制外，对富钠和过铝质Laacher See响岩的脱气行为进行实验研究是回答这些基本问题的理想方法。实验数据与天然浮石的泡状结构的比较相结合，是Laacher See火山和其他富钠响岩火山系统风险评估的重要基础。