Petrochemical evidence for coupled magma chambers beneath the Sakurajima volcano, Kyushu, Japan.

Yanagi, Tetsuo; Ichimaru, Yuji; Hirahara, Shogo

doi:10.2343/geochemj.25.17

Cited by 25 publications

(19 citation statements)

References 26 publications

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“…The 1914 -15 magma is andesitic (SiO 2 = 62 wt%; Table 1) and contains phenocrysts of plagioclase (Pl), orthopyroxene (Opx), clinopyroxene (Cpx), and magnetite (Mt). Olivine phenocrysts with a reaction -rim of Opx are included rarely in the pumice and commonly in the lava flows (SiO 2 = 60 -62 wt%; Yanagi et al, 1991) that erupted following the Plinian activity. The 1914 -15 magma is formed by mixing between dacitic and basaltic end -member magmas (Yanagi et al, 1991).…”

Section: Volcanological Backgrounds and Sample Descriptionmentioning

confidence: 99%

“…Olivine phenocrysts with a reaction -rim of Opx are included rarely in the pumice and commonly in the lava flows (SiO 2 = 60 -62 wt%; Yanagi et al, 1991) that erupted following the Plinian activity. The 1914 -15 magma is formed by mixing between dacitic and basaltic end -member magmas (Yanagi et al, 1991). The magma temperature after mixing is estimated at 950 -1050 °C by using pairs of rims of two pyroxene phenocrysts (T. Sato and M. Nakamura, unpublished data, 2012).…”

Section: Volcanological Backgrounds and Sample Descriptionmentioning

confidence: 99%

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Syn-eruptive desulfidation of pyrrhotite in the pumice of the Sakurajima 1914-15 eruption: Implication for potential magma ascent rate meter

Matsumoto¹,

Nakamura²

2012

Journal of Mineralogical and Petrological Sciences

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Pyrrhotite (Po) occurs as inclusions and as isolated crystals in pumice from the 1914 -15 eruption of the Sakurajima volcano, Kyushu, Japan. The Po crystals have partly reacted to form spongy Fe oxides. A similar texture has been reported in some previous studies (Hattori, 1993), but the mineral phases and formation processes of the spongy Fe oxides have not been clarified. Our quantitative and compositional map analyses with electron probe microanalysis (EPMA) reveal that the spongy Fe oxides are mostly magnetite (Mt), with a thin rim (<3 µm) of hematite on rare occasions. The spongy texture includes unreacted regions of Po, mesh -like pores, and S -rich spots, showing that it was formed by desulfidation of Po. No Ti was detected, even in the outermost rim; this indicates that the reaction occurred syn -eruptively. According to diffusion calculations, the spongy Mt was formed during the 4 h preceding quenching. Thermodynamic calculations showed that Po is stable at log f O 2 < NNO + 2 at a pressure of 1 bar and magmatic temperature, which is 1 -2 log units higher than the usual magmatic f O 2 . These constraints on the timing and oxidation condition of desulfidation lead to the conclusion that the reaction was caused by oxidation of the magma in a shallow volcanic conduit, not in magma chamber processes. The pumice groundmass consists mostly of glass, indicating that the rate of the desulfidation reaction is faster than the decompression -induced crystallization of microlites in the andesitic magma. Therefore, the desulfidation reaction of Po has the potential to be used as a geospeedometer for very fast magma ascent in vigorous explosive eruptions.

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Section: Volcanological Backgrounds and Sample Descriptionmentioning

confidence: 99%

Section: Volcanological Backgrounds and Sample Descriptionmentioning

confidence: 99%

Syn-eruptive desulfidation of pyrrhotite in the pumice of the Sakurajima 1914-15 eruption: Implication for potential magma ascent rate meter

Matsumoto¹,

Nakamura²

2012

Journal of Mineralogical and Petrological Sciences

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“…The bulk rock chemistry of these lava flows changed systematically from silicic to basic over time, while the core composition of plagioclase phenocrysts changed from unimodal to bimodal over time. These trends are indicative of ongoing magma mixing within the magma chamber (Yanagi et al, 1991). The 1914 1915 eruption began with seismic activity that started on January 10, 1914 and continued for several days.…”

Section: Geological Setting and The 1914-1915 Eruption Of Sakurajima mentioning

confidence: 99%

“…gioclase, plagioclase with sieved texture, and plagioclase with dusty zoned rims (Yanagi et al, 1991). The groundmass glass of both Plinian fall pumices and lavas is of rhyolitic composition (Table 2 and Fig.…”

Section: Chemistry Of Glass and Microlitementioning

confidence: 99%

“…Preeruptive melt compositions of Taisho 2 and Taisho 2 Lava are 64 69 wt% and are slightly more basic than those of Plinian fall pumice and Taisho 1 Lavas. A change in preeruptive melt composition from silicic to basic is considered to reflect progressive magma mixing (Yanagi et al, 1991), which is also evident in the variable An content of plagioclase microlite within lavas. Hence, these results suggest that textural differences among type 1 and type 2 white pumice, type 3 darker colored pumice, and Taisho 1 Lava are not due to chemical heterogeneity of the preeruptive melt induced by magma mixing, but reflect variability in the decompression rate during the Plinian phase to early effusive phase of the eruption.…”

Section: Preeruptive Melt Composition Within the Magma Chambermentioning

confidence: 99%

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Textures of plagioclase microlite and vesicles within volcanic products of the 1914-1915 eruption of Sakurajima Volcano, Kyushu, Japan

Nakamura

2006

Journal of Mineralogical and Petrological Sciences

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We classify volcanic products of the 1914 1915 eruption of Sakurajima Volcano into four types according to vesicularity and the texture of plagioclase microlite. Type 1 is white Plinian fall pumice with high vesicularity (> 60 vol%) and low modal content (< 1.0 vol%) and number density (< 10 14 m ) of plagioclase microlite. Type 1 and type 2 pumices were mainly deposited within the lower and middle parts of the Plinian fall deposit, whereas type 3 pumices were mainly deposited in the upper part. Homogeneous chemical features of preeruptive melts of all types of pumices indicate that the observed variations in number density and modal content of plagioclase microlite, as well as the decreasing vesicularity from type 1 to type 3 pumices, are related to a decrease in the decompression rate of magma from early to late stages of the Plinian phase. Residual water contents and degree of vesicularity of Plinian fall pumices suggest a change in the degassing process during the Plinian phase of eruption from minor degassing during the eruption of type 1 pumices to effective degassing during the eruption of type 3 pumices. Differences in microlite texture between type 1 and type 2 pumices of the early to middle stages of the Plinian phase and late stage type 1, 2 and 3 pumices reflect changes in the decompression rate, perhaps related to differences between the central and marginal parts of conduits. A systematic increase in the An content of plagioclase microlites from Plinian fall pumice to Taisho Lava reflects a chemical change in the preeruptive melt from silicic to basic composition related to progressive magma mixing.

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Control of Magma Plumbing Systems on Long‐Term Eruptive Behavior of Sakurajima Volcano, Japan

Yamashita

Toramaru

2020

Geophysical Monograph Series

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Petrochemical evidence for coupled magma chambers beneath the Sakurajima volcano, Kyushu, Japan.

Cited by 25 publications

References 26 publications

Syn-eruptive desulfidation of pyrrhotite in the pumice of the Sakurajima 1914-15 eruption: Implication for potential magma ascent rate meter

Syn-eruptive desulfidation of pyrrhotite in the pumice of the Sakurajima 1914-15 eruption: Implication for potential magma ascent rate meter

Textures of plagioclase microlite and vesicles within volcanic products of the 1914-1915 eruption of Sakurajima Volcano, Kyushu, Japan

Control of Magma Plumbing Systems on Long‐Term Eruptive Behavior of Sakurajima Volcano, Japan

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