<国立科博専報>隠岐島後産 accretionary lapilli について

概要

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Accretionary lapilli were sampled from Dogo, Oki Islands. The lapilli occur within the fine-ash deposits that rest on the middle Miocene diatomite. The lapilli are centimeter-size spheroids consisting of fine-grained fragments of glass, crystals of quartz, plagioclase and biotite, and lithic clasts. Glauconite and fragmental microfossils such as diatoms and siliceous sponge spicules are frequently included. Most of the microfossils are secondarily derived ones from the underlying strate during the eruption, because small blocky clasts of the diatomite are also present in the lapilli and matrix. The lapilli have two distinct textural zones : a massive core in which ash-particles are randomely distributed and a concentric rim consisting of fine- grained particles. The texture of the lapilli indicates that the core was formed as ill-sorted aggregates in the eruption plume and fine-grained as layers accreted on it. The formation of the lapilli were caused probably by rains of mud and lightning bolts in clouds of volcanic dust generated in relation to hydroexplosions.
国立科学博物館の論文
1986-12-01