Variety of the drift pumice clasts from the 2021 Fukutoku-Oka-no-Ba eruption, Japan

IF 1 4区 地球科学 Q4 GEOSCIENCES, MULTIDISCIPLINARY Island Arc Pub Date : 2022-02-09 DOI:10.1111/iar.12441
Kenta Yoshida, Yoshihiko Tamura, Tomoki Sato, Takeshi Hanyu, Yoichi Usui, Qing Chang, Shigeaki Ono
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引用次数: 21

Abstract

Pumice rafts that arrived at the Nansei Islands, Japan, provided a unique opportunity to investigate the Fukutoku-Oka-no-Ba (FOB) eruption of August 2021. Despite drifting for 2 months for ~1300 km, the drift pumice raft had a large volume and contained a variety of pumice clasts, some of which were deposited during a high tide in a typhoon, while others were washed up on a sandy beach. Most of the drift pumice clasts are gray in color, vesicular, and have a groundmass containing black enclaves. Rare black pumice and the main gray pumice components have similar trachytic compositions, with SiO2 = 61–62 mass% and total alkalis = 8.6–10 mass% (on an anhydrous basis). Both pumice types contain clinopyroxene, plagioclase, and rare olivine phenocrysts. Thin-section observations show that the gray pumice has more elongated vesicles as compared with the black pumice that has spherical vesicles, even where the two types of pumice are in the same clast. The glass in the black pumice is transparent and brown in color, while that in the gray pumice is colorless. No micro or nano-crystals were observed during electron and optical microscopy. Raman spectra of the brown-colored glass exhibit a clear magnetite peak, suggesting magnetite nanolites cause the brown color. High-Mg olivine in the black pumice has an equilibrium temperature of c. 1200 °C and a rim diffusion profile indicative of re-equilibration with the surrounding melt over a period of hours to days. The textural relationships between the gray and black pumice suggest that the black pumice had become black and viscous before the two types of pumice mixed. Therefore, crystallization of magnetite nanolites and a corresponding increase in melt viscosity were important in the eruption preparation process, which then resulted in a large-scale Plinian eruption.

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2021年日本福冈火山喷发的浮石碎屑种类
抵达日本南成群岛的浮冰筏为调查2021年8月的福冈火山喷发提供了一个独特的机会。尽管漂流了约1300公里的2个月,但漂流浮石筏的体积很大,含有各种浮石碎屑,其中一些是在台风高潮期间沉积的,而另一些则被冲上了沙滩。大多数漂移浮石碎屑颜色为灰色,呈泡状,并且具有包含黑色包体的基质。罕见的黑色浮石和主要的灰色浮石成分具有相似的粗管成分,SiO2=61–62质量%,总碱=8.6–10质量%(基于无水)。两种浮石类型都含有单斜辉石、斜长石和罕见的橄榄石斑晶。薄片观察表明,与具有球形囊泡的黑色浮石相比,灰色浮石具有更多细长的囊泡,即使这两种浮石位于同一碎屑中。黑色浮石中的玻璃是透明的棕色,而灰色浮石中是无色的。在电子和光学显微镜下未观察到微米或纳米晶体。棕色玻璃的拉曼光谱显示出清晰的磁铁矿峰,表明磁铁矿纳米石导致了棕色。黑色浮石中的高镁橄榄石的平衡温度约为1200°c,边缘扩散剖面表明在数小时至数天内与周围熔体重新平衡。灰色和黑色浮石之间的质地关系表明,在这两种浮石混合之前,黑色浮石已经变得黑色和粘稠。因此,磁铁矿纳米石的结晶和熔体粘度的相应增加在火山喷发准备过程中很重要,这导致了大规模的普林尼火山喷发。
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来源期刊
Island Arc
Island Arc 地学-地球科学综合
CiteScore
2.90
自引率
26.70%
发文量
32
审稿时长
>12 weeks
期刊介绍: Island Arc is the official journal of the Geological Society of Japan. This journal focuses on the structure, dynamics and evolution of convergent plate boundaries, including trenches, volcanic arcs, subducting plates, and both accretionary and collisional orogens in modern and ancient settings. The Journal also opens to other key geological processes and features of broad interest such as oceanic basins, mid-ocean ridges, hot spots, continental cratons, and their surfaces and roots. Papers that discuss the interaction between solid earth, atmosphere, and bodies of water are also welcome. Articles of immediate importance to other researchers, either by virtue of their new data, results or ideas are given priority publication. Island Arc publishes peer-reviewed articles and reviews. Original scientific articles, of a maximum length of 15 printed pages, are published promptly with a standard publication time from submission of 3 months. All articles are peer reviewed by at least two research experts in the field of the submitted paper.
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