Formation of curvature of the Median Tectonic Line: Implications from high density sampling paleomagnetic investigations

2020 Fiscal Year Final Research Report

• Project/Area Number: 17K05680
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Geology
• Research Institution: Aichi University of Education
• Principal Investigator: Hoshi Hiroyuki 愛知教育大学, 教育学部, 教授 (90293737)
• Project Period (FY): 2017-04-01 – 2021-03-31
• Keywords: 地質学 / テクトニクス / 島弧衝突 / 回転運動 / 古地磁気 / 年代測定 / 中央構造線

Outline of Final Research Achievements

The geology and paleomagnetism of Miocene volcanic rocks in central Nagano Prefecture were investigated to clarify the formation of curvature of the Median Tectonic Line. A radiometric age of about 15.8 Ma (15.8 million years ago) was obtained from andesitic lava in the Moriya-san area. Based on the radiometric data and geological relationships, the volcanic rocks in the Moriya-san and Takato areas were formed in a short geological time (within a few hundred thousand years) around 16 Ma. The paleomagnetic directions of the two areas are similar and indicate a counterclockwise rotation of 30-40 degrees relative to the Asian continent. Prior to the rotation, the surface trace of the Median Tectonic Line from eastern Aichi Prefecture to central Nagano Prefecture is thought to have been straight.

Free Research Field

地質学，古地磁気学

Academic Significance and Societal Importance of the Research Achievements

我が国で最大規模の断層である中央構造線は本州中部で大きく八の字型に屈曲している。この地質構造は我が国の地質で最も目立つ変形構造であり，その形成プロセスの解明は日本列島の形成の理解に不可欠である。本研究で得られた放射年代と古地磁気のデータは，およそ1600万年前には愛知県東部から長野県中部にかけての中央構造線はほぼ直線状で，屈曲はその後に起こったことを強く示唆する。また，長野県中部の守屋山地域と高遠地域の中新世火山岩類が地質学的には短期間（数10万年以内）に形成されたことも判明し，地域地質の理解が深まった。