DOI: 10.1016/j.earscirev.2020.103402
论文题名: Dynamics of degassing in evolved alkaline magmas: Petrological, experimental and theoretical insights
作者: Buono G. ; Fanara S. ; Macedonio G. ; Palladino D.M. ; Petrosino P. ; Sottili G. ; Pappalardo L.
刊名: Earth Science Reviews
ISSN: 00128252
出版年: 2020
卷: 211 语种: 英语
中文关键词: Alkaline melts
; Magma ascent
; Magma degassing
; Volcanic hazard
英文关键词: alkaline rock
; degassing
; experimental study
; formation mechanism
; geological hazard
; magma
; magma chamber
; petrology
; theoretical study
; volcanic earthquake
; volcanic eruption
; volcanology
; Alban Hills
; Apennines
; Azores
; Campania [Italy]
; Campi Flegrei
; Canary Islands
; Indonesia
; Italy
; Lazio
; Lesser Sunda Islands
; Napoli [Campania]
; Portugal
; Spain
; Sumbawa
; Tambora
; Vesuvius
; West Nusa Tenggara
; Serinus canaria
英文摘要: In the last few decades, advanced monitoring networks have been extended to the main active volcanoes, providing warnings for variations in volcano dynamics. However, one of the main tasks of modern volcanology is the correct interpretation of surface-monitored signals in terms of magma transfer through the Earth's crust. In this frame, it is crucial to investigate decompression-induced magma degassing as it controls magma ascent towards the surface and, in case of eruption, the eruptive style and the atmospheric dispersal of tephra and gases. Understanding the degassing behaviour is particularly intriguing in the case of poorly explored evolved alkaline magmas. In fact, these melts frequently feed hazardous, highly explosive volcanoes (e.g., Campi Flegrei, Somma-Vesuvius, Colli Albani, Tambora, Azores and Canary Islands), despite their low viscosity that usually promotes effusive and/or weakly explosive eruptions. Decompression experiments, together with numerical models, are powerful tools to examine magma degassing behaviour and constrain field observations from natural eruptive products and monitoring signals. These approaches have been recently applied to evolved alkaline melts, yet numerous open questions remain. To cast new light on the degassing dynamics of evolved alkaline magmas, in this study we present new results from decompression experiments, as well as a critical review of previous experimental works. We achieved a comprehensive dataset of key petrological parameters (i.e., 3D textural data for bubbles and microlites using X-ray computed microtomography, glass volatile contents and nanolite occurrence) from experimental samples obtained through high temperature-high pressure isothermal decompression experiments on trachytic alkaline melts at super-liquidus temperature. We explored systematically a range of final pressures (from 200 to 25 MPa), decompression rates (from 0.01 to 1 MPa s−1), and volatile (H2O and CO2) contents. On these grounds, we integrated coherently literature data from decompression experiments on evolved alkaline (trachytic and phonolitic) melts under various conditions, with the aim to fully constrain the degassing mechanisms and timescales in these magmas. Finally, we simulated numerically the experimental conditions to evaluate strengths and weaknesses in decrypting degassing behaviour from field observations. Our results highlight that bubble formation in evolved alkaline melts is primarily controlled by the initial volatile (H2O and CO2) content during magma storage. In these melts, bubble nucleation needs low supersaturation pressures (≤ 50–112 MPa for homogeneous nucleation, ≤ 13–25 MPa for heterogeneous nucleation), resulting in high bubble number density (~ 1012–1016 m−3), efficient volatile exsolution and thus in severe rheological changes. Moreover, the bubble number density is amplified in CO2-rich melts (mole fraction XCO2 ≥ 0.5), in which continuous bubble nucleation predominates on growth. These conditions typically lead to highly explosive eruptions. However, moving towards slower decompression rates (≤ 10−1 MPa s−1) and H2O-rich melts, permeable outgassing and inertial fragmentation occur, promoting weakly explosive eruptions. Finally, our findings suggest that the exhaustion of CO2 at deep levels, and the consequent transition to a H2O-dominated degassing, can crucially enhance magma vesiculation and ascent. In a hazard perspective, these constraints allow to postulate that time-depth variations of unrest signals could be significantly weaker/shorter (e.g., minor gas emissions and short-term seismicity) during major eruptions than in small-scale events. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/166019
Appears in Collections: 气候变化与战略
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作者单位: Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Napoli - Osservatorio Vesuviano, Naples, Italy; University of Naples Federico II, Department of Earth, Environmental and Resources Science, Naples, Italy; Georg-August University of Göttingen, Department of Experimental and Applied Mineralogy, Göttingen, Germany; Sapienza-University of Rome, Department of Earth Sciences, Rome, Italy
Recommended Citation:
Buono G.,Fanara S.,Macedonio G.,et al. Dynamics of degassing in evolved alkaline magmas: Petrological, experimental and theoretical insights[J]. Earth Science Reviews,2020-01-01,211