Message in a bottle: Spontaneous phase separation of hydrous Vesuvius melt even at low decompression rates
Message in a bottle: Spontaneous phase separation of hydrous Vesuvius melt even at low decompression rates
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瓶中信：即使在低减压率下，含水维苏威火山也会自发相分离
DOI：
10.1016/j.epsl.2018.08.047
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发表时间：
2018
影响因子：
5.3
通讯作者：
Nowak M
中科院分区：
文献类型：
--
作者：
Allabar A;Nowak M
剧烈的火山喷发具有破坏性，威胁着数百万人和基础设施。喷出的灰烬、浮石和气体是源自岩浆室和管道深处的火山工厂的最终产品。不同的生产阶段无法直接观察到。然而，实验模拟揭示了动态火山过程的不同阶段。火山喷发的起始点是由过饱和水合硅酸盐熔体中 H 2 O 流体的相分离决定的。每单位体积硅酸盐熔体形成的H 2 O流体囊泡的数量（VND）是控制流体-熔体分离、上升速度和最终爆发火山作用的效率的基本性质。我们在超液相温度下进行了减压实验，以模拟单相水合硅酸盐熔体在上升过程中的相分离，使用 AD79 维苏威火山白色浮石组合物，减压率为 0.024–1.7 MPa·s− 1。白色浮石掩埋了赫库兰尼姆和庞贝古城，是其他灾难性的声石和粗面爆发性喷发的代表，例如猛烈的 39 ka Campi Flegrei 爆发。以及公元 1815 年坦博拉火山喷发。在这里，我们报告了 5.2（以 mm−3 为单位）的高 log VND，该值与研究范围内的减压率无关。即使在 0.024 MPa·s− 1 的减压速率下，由于 H 2 O 从熔体到流体囊泡的扩散距离较短，高 VND 的形成也不可避免地会导致快速脱气。基于成核理论的减压速率计通常用于使用火山喷出物的 VND 来估计火山喷发期间的岩浆上升速度，但无法用来解释我们通过实验确定的与减压速率无关的 VND。或者，减压引起的 H 2 O-硅酸盐熔体相分离可以通过达到最大过饱和度的扩散控制旋节线分解来描述。如果含水熔体被驱动进入热力学不稳定状态，其中混合自由能对 H 2 O 含量的二阶导数≤ 0，则该过程自发发生并且没有活化能。然而，与减压速率无关的 VND 对天然多相含水岩浆相分离的动力学具有深远的影响。即使在低上升速率下，自发的含水熔体相分离也会促进密度快速下降，同时伴随着岩浆浮力的突然增加，引发爆炸性喷发。
Violent explosive volcanic eruptions are destructive and threaten millions of people and infrastructure. Ejected ash, pumice and gases are end-products of volcanic factories sourced deep within magma chambers and conduits. The different production stages are not directly observable. However, experimental simulation reveals different stages of dynamic volcanic processes. The starting point of explosive volcanic eruptions is determined by the phase separation of an H 2 O fluid from a supersaturated hydrous silicate melt. The number of formed H 2 O fluid vesicles per unit volume of silicate melt (VND) is a basic property that controls the efficiency of fluid-melt separation, ascent velocity and finally explosive volcanism. We performed decompression experiments at superliquidus temperatures to simulate phase separation of a single phase hydrous silicate melt during ascent with AD79 Vesuvius white pumice composition using decompression rates of 0.024–1.7 MPa⋅ s− 1. The white pumice buried Herculaneum and Pompeii and is representative of other catastrophic phonolitic and trachytic explosive eruptions like the violent 39 ka Campi Flegrei and the 1815 AD Tambora eruption. Here we report a high log VND of 5.2 (in mm− 3) that is independent from decompression rate within the investigated range. Even at a decompression rate of 0.024 MPa⋅ s− 1 the formation of a high VND inevitably causes rapid degassing due to short H 2 O diffusion distances from the melt into fluid vesicles. A decompression rate meter based on nucleation theory, which is commonly used to estimate magma ascent velocity during volcanic eruptions using VND of volcanic ejecta, cannot be adapted to explain our experimentally determined decompression rate independent VND. Alternatively, decompression induced H 2 O–silicate melt phase separation may be described by diffusion controlled spinodal decomposition where maximum supersaturation is reached. This process occurs spontaneously and free of activation energy if hydrous melt is driven into thermodynamic instability where the second derivative of free energy of mixing to the H 2 O content is≤ 0. However, the decompression rate independent VND has profound consequences for the dynamics of natural polyphase hydrous magma phase separation. Even at low ascent rates spontaneous hydrous melt phase separation facilitates rapid density decrease accompanied by sudden increase of magma buoyancy triggering explosive eruptions.
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影响因子：
3.5
作者：
Cluzel, N.;Laporte, D.;Kannewischer, I.
通讯作者：
Kannewischer, I.
在多组分矿物溶液中通过旋节线分解进行溶出
影响因子：
9.4
作者：
E. Petrishcheva;R. Abart
通讯作者：
R. Abart
高压光散射装置研究聚合物溶液中压力诱导的相分离
DOI：
--
发表时间：
1998
期刊：
影响因子：
--
作者：
Y. Xiong;E. Kiran
通讯作者：
E. Kiran
响石熔体中的水溶性：熔体成分和温度的影响
影响因子：
3.9
作者：
B. Schmidt;H. Behrens
通讯作者：
H. Behrens
影响因子：
64.8
作者：
B. Scaillet;B. Scaillet;M. Pichavant;M. Pichavant;R. Cioni
通讯作者：
B. Scaillet;B. Scaillet;M. Pichavant;M. Pichavant;R. Cioni