Revealing the petrogenesis of igneous activities above a stagnant slab

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K14419
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Petrology/Mineralogy/Economic geology
• Research Institution: Osaka City University
• Principal Investigator: Sakuyama Tetsuya 大阪市立大学, 大学院理学研究科, 准教授 (80553081)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 背弧域火成活動 / アルカリ玄武岩 / 停滞スラブ / 上部マントル / 流体

Outline of Final Research Achievements

Petrological and geochemical investigation has been conducted on the late Cenozoic basaltic samples taken from the southwestern Japan, the eastern and northeastern China, and the seamount in the Japan Sea. Estimated melting temperature and pressure for each volcano under hydrous condition suggests that the the potential mantle temperature of the upper mantle beneath the eastern margin of the Eurasian continent is as high as that beneath mid-ocean ridges. Enrichment of fluid-mobile trace elements as well as hydrous nature of the estimated primary magmas for the studied samples suggests that the magmatism is originated not in the high-temperature upwelling but in the upwelling of the hydrous mantle probably from the mantle transition zone above the stagnant Pacific slab.

Free Research Field

火成岩岩石学

Academic Significance and Societal Importance of the Research Achievements

ユーラシア大陸東縁部に噴出した背弧域火山の起源として，従来は高温かつ水に富むマントルの上昇流が考えられてきた．一方，この10年で，マントル上昇流は高温ではなく，水に富む組成不均質によるという考えが提案されるようになってきたが，研究対象が限られており，西南日本，日本海，中国にいたる広い範囲で同様のモデルが適用できるか不明であった．本研究では，広域的に試料を採取し，岩石学的にマントル融解条件を推定した．その結果，広域的に見ても当該地域下の上部マントルは高温ではないことが明らかになり，含水マントルモデルがより広く適用できる可能性を示した．