Syneruptive deep magma transfer and shallow magma remobilization during the 2011 eruption of Shinmoe-dake, Japan-Constraints from melt inclusions and phase equilibria experiments

Yuki Suzuki, Atsushi Yasuda, Natsumi Hokanishi, Takayuki Kaneko, Setsuya Nakada, Toshitsugu Fujii

研究成果: Article

30 引用 (Scopus)

抄録

The 2011 Shinmoe-dake eruption started with a phreatomagmatic eruption (Jan 19), followed by climax sub-Plinian events and subsequent explosions (Jan 26-28), lava accumulation in the crater (end of January), and vulcanian eruptions (February-April). We have studied a suite of ejecta to investigate the magmatic system beneath the volcano and remobilization processes in the silicic magma mush. Most of the ejecta, including brown and gray colored pumice clasts (Jan 26-28), ballistically ejected dense lava (Feb 1), and juvenile particles in ash from the phreatomagmatic and vulcanian events are magma mixing products (SiO2=57-58wt.%; 960-980°C). Mixing occurred between silicic andesite (SA) and basaltic andesite (BA) magmas at a fixed ratio (40%-30% SA and 60%-70% BA). The SA magma had SiO2=62-63wt.% and a temperature of 870°C, and contains 43vol.% phenocrysts of pyroxene, plagioclase, and Fe-Ti oxide. The BA magma had SiO2=55wt.% and a temperature of 1030°C, and contains 9vol.% phenocrysts of olivine and plagioclase. The SA magma partly erupted without mixing as white parts of pumices and juvenile particles.The two magmatic end-members crystallized at different depths, requiring the presence of two separate magma reservoirs; shallower SA reservoir and deeper BA reservoir. An experimental study reveals that the SA magma had been stored at a pressure of 125MPa, corresponding to a depth of 5km. The textures and forms of phenocrysts from the BA magma indicate rapid crystallization directly related to the 2011 eruptive activity. The wide range of H2O contents of olivine melt inclusions (5.5-1.6wt.%) indicates that rapid crystallization was induced by decompression, with olivine crystallization first (≤250MPa), followed by plagioclase addition. The limited occurrence of olivine melt inclusions trapped at depths of <5km is consistent with the proposed magma system model, because olivine crystallization ceased after magma mixing. Our petrological model is consistent with a geophysical model that explains whole crustal deformation as being due to a single source located 7-8km northwest of the Shinmoe-dake summit. However, even the shallowest estimated source of this deformation (7.5-6.2km) is deeper than the SA reservoir, which thus requires a contribution of deeper BA magmas to the observed deformation.Remobilization of mush-like SA magma occurred in two stages before the early sub-Plinian event. Firstly, precursor mixing with BA magma and associated heating occurred (925-871. °C; stage-1 of ≥. 350. h), followed by final mixing with BA magma (stage-2). MgO profiles of magnetite phenocrysts define timescales of 0.7-15.2. h from this final mixing to eruption. The mixed and heated magmas, and stagnant mush that existed in the SA reservoir in the precursor stage, were finally erupted together. Magnetite phenocrysts in the Feb 18 ash reveal the occurrence of continuous erosion of the stagnant mush during the course of the 2011 eruptive activity.

元の言語English
ページ(範囲)184-204
ページ数21
ジャーナルJournal of Volcanology and Geothermal Research
257
DOI
出版物ステータスPublished - 2013 5 1
外部発表Yes

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andesite
melt inclusion
remobilization
phase equilibrium
Phase equilibria
volcanic eruptions
magma
Japan
volcanic eruption
inclusions
Crystallization
Ashes
Ferrosoferric Oxide
experiment
Experiments
olivine
crystallization
plagioclase
Volcanoes
Oxides

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

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title = "Syneruptive deep magma transfer and shallow magma remobilization during the 2011 eruption of Shinmoe-dake, Japan-Constraints from melt inclusions and phase equilibria experiments",
abstract = "The 2011 Shinmoe-dake eruption started with a phreatomagmatic eruption (Jan 19), followed by climax sub-Plinian events and subsequent explosions (Jan 26-28), lava accumulation in the crater (end of January), and vulcanian eruptions (February-April). We have studied a suite of ejecta to investigate the magmatic system beneath the volcano and remobilization processes in the silicic magma mush. Most of the ejecta, including brown and gray colored pumice clasts (Jan 26-28), ballistically ejected dense lava (Feb 1), and juvenile particles in ash from the phreatomagmatic and vulcanian events are magma mixing products (SiO2=57-58wt.{\%}; 960-980°C). Mixing occurred between silicic andesite (SA) and basaltic andesite (BA) magmas at a fixed ratio (40{\%}-30{\%} SA and 60{\%}-70{\%} BA). The SA magma had SiO2=62-63wt.{\%} and a temperature of 870°C, and contains 43vol.{\%} phenocrysts of pyroxene, plagioclase, and Fe-Ti oxide. The BA magma had SiO2=55wt.{\%} and a temperature of 1030°C, and contains 9vol.{\%} phenocrysts of olivine and plagioclase. The SA magma partly erupted without mixing as white parts of pumices and juvenile particles.The two magmatic end-members crystallized at different depths, requiring the presence of two separate magma reservoirs; shallower SA reservoir and deeper BA reservoir. An experimental study reveals that the SA magma had been stored at a pressure of 125MPa, corresponding to a depth of 5km. The textures and forms of phenocrysts from the BA magma indicate rapid crystallization directly related to the 2011 eruptive activity. The wide range of H2O contents of olivine melt inclusions (5.5-1.6wt.{\%}) indicates that rapid crystallization was induced by decompression, with olivine crystallization first (≤250MPa), followed by plagioclase addition. The limited occurrence of olivine melt inclusions trapped at depths of <5km is consistent with the proposed magma system model, because olivine crystallization ceased after magma mixing. Our petrological model is consistent with a geophysical model that explains whole crustal deformation as being due to a single source located 7-8km northwest of the Shinmoe-dake summit. However, even the shallowest estimated source of this deformation (7.5-6.2km) is deeper than the SA reservoir, which thus requires a contribution of deeper BA magmas to the observed deformation.Remobilization of mush-like SA magma occurred in two stages before the early sub-Plinian event. Firstly, precursor mixing with BA magma and associated heating occurred (925-871. °C; stage-1 of ≥. 350. h), followed by final mixing with BA magma (stage-2). MgO profiles of magnetite phenocrysts define timescales of 0.7-15.2. h from this final mixing to eruption. The mixed and heated magmas, and stagnant mush that existed in the SA reservoir in the precursor stage, were finally erupted together. Magnetite phenocrysts in the Feb 18 ash reveal the occurrence of continuous erosion of the stagnant mush during the course of the 2011 eruptive activity.",
keywords = "Basaltic andesite magma, Diffusion profile, Eruption trigger, Magma mixing, Magma system, Silicic andesite magma",
author = "Yuki Suzuki and Atsushi Yasuda and Natsumi Hokanishi and Takayuki Kaneko and Setsuya Nakada and Toshitsugu Fujii",
year = "2013",
month = "5",
day = "1",
doi = "10.1016/j.jvolgeores.2013.03.017",
language = "English",
volume = "257",
pages = "184--204",
journal = "Journal of Volcanology and Geothermal Research",
issn = "0377-0273",
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TY - JOUR

T1 - Syneruptive deep magma transfer and shallow magma remobilization during the 2011 eruption of Shinmoe-dake, Japan-Constraints from melt inclusions and phase equilibria experiments

AU - Suzuki, Yuki

AU - Yasuda, Atsushi

AU - Hokanishi, Natsumi

AU - Kaneko, Takayuki

AU - Nakada, Setsuya

AU - Fujii, Toshitsugu

PY - 2013/5/1

Y1 - 2013/5/1

N2 - The 2011 Shinmoe-dake eruption started with a phreatomagmatic eruption (Jan 19), followed by climax sub-Plinian events and subsequent explosions (Jan 26-28), lava accumulation in the crater (end of January), and vulcanian eruptions (February-April). We have studied a suite of ejecta to investigate the magmatic system beneath the volcano and remobilization processes in the silicic magma mush. Most of the ejecta, including brown and gray colored pumice clasts (Jan 26-28), ballistically ejected dense lava (Feb 1), and juvenile particles in ash from the phreatomagmatic and vulcanian events are magma mixing products (SiO2=57-58wt.%; 960-980°C). Mixing occurred between silicic andesite (SA) and basaltic andesite (BA) magmas at a fixed ratio (40%-30% SA and 60%-70% BA). The SA magma had SiO2=62-63wt.% and a temperature of 870°C, and contains 43vol.% phenocrysts of pyroxene, plagioclase, and Fe-Ti oxide. The BA magma had SiO2=55wt.% and a temperature of 1030°C, and contains 9vol.% phenocrysts of olivine and plagioclase. The SA magma partly erupted without mixing as white parts of pumices and juvenile particles.The two magmatic end-members crystallized at different depths, requiring the presence of two separate magma reservoirs; shallower SA reservoir and deeper BA reservoir. An experimental study reveals that the SA magma had been stored at a pressure of 125MPa, corresponding to a depth of 5km. The textures and forms of phenocrysts from the BA magma indicate rapid crystallization directly related to the 2011 eruptive activity. The wide range of H2O contents of olivine melt inclusions (5.5-1.6wt.%) indicates that rapid crystallization was induced by decompression, with olivine crystallization first (≤250MPa), followed by plagioclase addition. The limited occurrence of olivine melt inclusions trapped at depths of <5km is consistent with the proposed magma system model, because olivine crystallization ceased after magma mixing. Our petrological model is consistent with a geophysical model that explains whole crustal deformation as being due to a single source located 7-8km northwest of the Shinmoe-dake summit. However, even the shallowest estimated source of this deformation (7.5-6.2km) is deeper than the SA reservoir, which thus requires a contribution of deeper BA magmas to the observed deformation.Remobilization of mush-like SA magma occurred in two stages before the early sub-Plinian event. Firstly, precursor mixing with BA magma and associated heating occurred (925-871. °C; stage-1 of ≥. 350. h), followed by final mixing with BA magma (stage-2). MgO profiles of magnetite phenocrysts define timescales of 0.7-15.2. h from this final mixing to eruption. The mixed and heated magmas, and stagnant mush that existed in the SA reservoir in the precursor stage, were finally erupted together. Magnetite phenocrysts in the Feb 18 ash reveal the occurrence of continuous erosion of the stagnant mush during the course of the 2011 eruptive activity.

AB - The 2011 Shinmoe-dake eruption started with a phreatomagmatic eruption (Jan 19), followed by climax sub-Plinian events and subsequent explosions (Jan 26-28), lava accumulation in the crater (end of January), and vulcanian eruptions (February-April). We have studied a suite of ejecta to investigate the magmatic system beneath the volcano and remobilization processes in the silicic magma mush. Most of the ejecta, including brown and gray colored pumice clasts (Jan 26-28), ballistically ejected dense lava (Feb 1), and juvenile particles in ash from the phreatomagmatic and vulcanian events are magma mixing products (SiO2=57-58wt.%; 960-980°C). Mixing occurred between silicic andesite (SA) and basaltic andesite (BA) magmas at a fixed ratio (40%-30% SA and 60%-70% BA). The SA magma had SiO2=62-63wt.% and a temperature of 870°C, and contains 43vol.% phenocrysts of pyroxene, plagioclase, and Fe-Ti oxide. The BA magma had SiO2=55wt.% and a temperature of 1030°C, and contains 9vol.% phenocrysts of olivine and plagioclase. The SA magma partly erupted without mixing as white parts of pumices and juvenile particles.The two magmatic end-members crystallized at different depths, requiring the presence of two separate magma reservoirs; shallower SA reservoir and deeper BA reservoir. An experimental study reveals that the SA magma had been stored at a pressure of 125MPa, corresponding to a depth of 5km. The textures and forms of phenocrysts from the BA magma indicate rapid crystallization directly related to the 2011 eruptive activity. The wide range of H2O contents of olivine melt inclusions (5.5-1.6wt.%) indicates that rapid crystallization was induced by decompression, with olivine crystallization first (≤250MPa), followed by plagioclase addition. The limited occurrence of olivine melt inclusions trapped at depths of <5km is consistent with the proposed magma system model, because olivine crystallization ceased after magma mixing. Our petrological model is consistent with a geophysical model that explains whole crustal deformation as being due to a single source located 7-8km northwest of the Shinmoe-dake summit. However, even the shallowest estimated source of this deformation (7.5-6.2km) is deeper than the SA reservoir, which thus requires a contribution of deeper BA magmas to the observed deformation.Remobilization of mush-like SA magma occurred in two stages before the early sub-Plinian event. Firstly, precursor mixing with BA magma and associated heating occurred (925-871. °C; stage-1 of ≥. 350. h), followed by final mixing with BA magma (stage-2). MgO profiles of magnetite phenocrysts define timescales of 0.7-15.2. h from this final mixing to eruption. The mixed and heated magmas, and stagnant mush that existed in the SA reservoir in the precursor stage, were finally erupted together. Magnetite phenocrysts in the Feb 18 ash reveal the occurrence of continuous erosion of the stagnant mush during the course of the 2011 eruptive activity.

KW - Basaltic andesite magma

KW - Diffusion profile

KW - Eruption trigger

KW - Magma mixing

KW - Magma system

KW - Silicic andesite magma

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