Precise analyses of micro inclusions within anorthite megacrysts in island arc volcanoes and estimation of parental magmas

2015 Fiscal Year Final Research Report

• Project/Area Number: 25400508
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Petrology/Mineralogy/Economic geology
• Research Institution: University of Tsukuba
• Principal Investigator: ARAKAWA Yoji 筑波大学, 生命環境系, 教授 (00192469)
• Co-Investigator(Kenkyū-buntansha): MATSUI Tomoaki 鹿児島大学, 教育学部, 准教授 (40295233)
• Co-Investigator(Renkei-kenkyūsha): IKEHATA Kei 筑波大学, 生命環境系, 助教 (70622017)
• Project Period (FY): 2013-04-01 – 2016-03-31
• Keywords: 灰長石巨晶 / 島弧火山 / 微小包有物

Outline of Final Research Achievements

Ca-rich plagioclase (anorthite) megacrysts occurs as disequilibrium crystals n island arc volcanic rocks. The purpose of this study is to clarify chemical and mineralogical characteristics of the anorthite megacryst and micro inclusions. Our study was focused on the anorthite megacryst in volcanic rocks in Take-shima (S. Kyushu), Hokiyadake volcano (central Japan), and Miyakejima volcano in Izu volcanic arc. In the Take-shima volcano, anorthite megacrysts often contain micro inclusions that were identified to be native iron (Fe). Yellow colored anorthite megacrysts in Hokiyadake volcano are thought to be a result of substitution of Fe for Alin crystal structure. In Miyakejima volcano, disordered distribution of Si/Al in anorthite crystal structure was identified. This finding is interpreted as metastable phase of the anorthite megacryst.
The growth of the anorthite megacrysts were interpreted to be due to rapid changing of phyisical condition nearly at melting temperature of anorthite.

Free Research Field

岩石学、岩石化学、年代学