Petrological study of Takayubaru lava which effused immediately before Aso-4 large-scale eruption

2015 Fiscal Year Final Research Report

• Project/Area Number: 25400491
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Geology
• Research Institution: Kumamoto University
• Principal Investigator: Hasenaka Toshiaki 熊本大学, 自然科学研究科, 教授 (50202429)
• Co-Investigator(Renkei-kenkyūsha): MIYOSHI Masaya 福井大学, 教育地域科学部, 講師 (50557353)
• Research Collaborator: SEKIGUCHI Yuko 気象庁, 地震火山部, 技術職員 ; TAMURA Tomohisa 西日本技術開発株式会社, 技術職員 ; KUROKAWA Kiyoshi 熊本大, 大学院自然科学研究科, 院生 ; YAMASAKI Hideto 熊本大, 大学院自然科学研究科, 院生 ; SHIIHARA Kosuke 熊本大, 大学院自然科学研究科, 院生
• Project Period (FY): 2013-04-01 – 2016-03-31
• Keywords: 大峰火山 / 阿蘇火山 / 阿蘇-4噴火 / 高遊原溶岩 / マグマ供給系 / 前駆噴火

Outline of Final Research Achievements

Omine scoria and associated Takayubaru lava flow effused immediately before Aso-4 pyroclastic eruption, which formed one of the largest caldera in Japan, We compared the compositions of Aso-4 products with those of the precursor, in terms of bulk rock, plagioclase, and melt inclusions found in phenocrysts. Result of analyses showed overlapping but distinct compositional trends between the two. Compositional differences among the earliest, climax, and late stage of Aso-4 products indicate evolution of magma from a single composition to a mixed composition indicating multiple origin.
A possible model to interpret the observation consists of 1) a supply of heat and basaltic magma from the deep source, 2) growth of a shallow crustal silicic stratified magma reservoir, and 3) branched small but relatively hot and dry reservoir outside the caldera which caused a precursory eruption.

Free Research Field

火山岩岩石学