DOI: 10.1016/j.epsl.2018.08.047
Scopus记录号: 2-s2.0-85052955965
论文题名: Message in a bottle: Spontaneous phase separation of hydrous Vesuvius melt even at low decompression rates
作者: Allabar A. ; Nowak M.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2018
卷: 501 起始页码: 192
结束页码: 201
语种: 英语
英文关键词: hydrous melt
; magma ascent rate
; magma degassing
; phase separation
; spinodal decomposition
; vesicle number density
Scopus关键词: Activation energy
; Bottles
; Degassing
; Diffusion in liquids
; Explosives
; Free energy
; Silicates
; Spinodal decomposition
; Volcanoes
; Decompression experiments
; Experimental simulations
; Hydrous melts
; Hydrous silicate melt
; Magma ascents
; Magma degassing
; Number density
; Thermodynamic instability
; Phase separation
; degassing
; explosive volcanism
; magma chamber
; melting
; saturation
; silicate melt
; volcanic eruption
英文摘要: 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 H2O fluid from a supersaturated hydrous silicate melt. The number of formed H2O 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 logVND 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 H2O 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 H2O–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 H2O 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. © 2018 The Author(s) Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/109661
Appears in Collections: 影响、适应和脆弱性 气候变化事实与影响
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作者单位: Department of Geosciences, University of Tübingen, Germany
Recommended Citation:
Allabar A.,Nowak M.. Message in a bottle: Spontaneous phase separation of hydrous Vesuvius melt even at low decompression rates[J]. Earth and Planetary Science Letters,2018-01-01,501