桜島火山のマグマ溜り系の構成と機能(<特集>火山のモデル(II))

概要

論文の詳細を見る
In chemical composition historical lava flows in Sakurajima volcano have a streight-linear correlation, and progressively change with time from dacitic to andesitic. Plagioclase phenocrysts in them commonly show bimodal compositional distributions with two peaks at An_<58> and An_<85>. These two peaks stay at the same Positions, independently of progressive change in chemical composition of the host lavas. The An-rich peak grows and the other peak declines with time, suggesting the mixing between dacitic and basaltic magmas and the progressive increase in proportion of the basaltic component. The periodically refilled magma chamber model was improved. The new model consists of upper and lower chambers and a set of cylinder and plug of frustum shape. The upper chamber lies in the middle of the crust and was originally occupied by the dacitic magma. The lower chamber lies near the boundary between the mantle and the crust, which is occupied by the volatile-rich basaltic magma. The cumulate plug subsides into the lower chamber, drives the basaltic magma upward and mixes it with the magma in the upper chamber with intermitten gigantic explosions.
特定非営利活動法人日本火山学会の論文
1991-07-15