Plastic strength of the crust evaluated from naturally deformed rocks

• Project/Area Number: 19K04041
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Osaka Metropolitan University (2022); Kobe University (2019-2021)
• Principal Investigator: Fukuda Junichi 大阪公立大学, 大学院理学研究科, 准教授 (10726764)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Project Status: Completed (Fiscal Year 2022)
• Budget Amount: ¥4,290,000 (Direct Cost: ¥3,300,000、Indirect Cost: ¥990,000); Fiscal Year 2021: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000); Fiscal Year 2020: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000); Fiscal Year 2019: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000)
• Keywords: 地殻 / 石英 / 長石 / 塑性変形 / 水 / 天然 / 実験 / 強度 / 脆性塑性遷移 / 細粒化 / すべり系 / 応力 / 歪速度 / 破砕 / 粒径 / 石英粒成長実験 / 微細組織 / 天然石英 / 含水量 / 赤外分光法 / 流動則 / 水の効果

Outline of Research at the Start

石英や長石は大陸地殻の主要構成鉱物であり，両物質の塑性変形は内陸型地震発生の前駆運動となる．従って，塑性変形強度を試料組織，塑性変形機構と共に理解することは重要である．岩石鉱物の塑性変形は，応力，歪速度，粒子サイズ，水の効果，温度などをパラメータとして表され，これは流動則と呼ばれる．本研究では過去に断層運動により塑性変形を被った天然試料の組織観察，分析を通して流動則を適用し，塑性変形強度を評価することを目的とする．また，天然試料に関する結果も踏まえて，流動則中の各パラメータの関係性を新たに評価する．

Outline of Final Research Achievements

Within the depth at shallower than 8-12 kilometers in fault zones, rocks and minerals are deformed by fracturing; this type of deformation is called brittle deformation. On the other hand, at the greater depth, rocks and minerals are deformed by stretching; this type of deformation is called plastic deformation which accommodates permanent strain. Plastic deformation of rocks and minerals is enhanced by the presence of water as impurities.
In this study, we measured water contents and distributions in plastically deformed quartz in granite mylonite samples. In the samples, fine-grained quartz is formed by development of plastic deformation (dynamic recrystallization). We found that the water contents in the fine-grained quartz regions are lower than those in the adjacent original quartz grains. This suggests that water is released from grain interiors of quartz due to the grain size reduction process and released water distributes within the fault zone.

Academic Significance and Societal Importance of the Research Achievements

断層深部で起こる塑性変形は、上部地殻に歪を蓄積させ、歪の解放が地震となる。このように塑性変形は地震発生の前駆運動として振る舞う。
塑性変形は岩石鉱物に不純物として含まれる水により促進されるため、塑性変形を被った水の量や分布を測定することは重要である。本研究では地殻の主要構成鉱物である石英の塑性変形の進展と含水量分布の変化を明らかにした。また、岩石変形実験により、長石試料中に水を加えることによって、塑性変形が促進されることを見出した。このことは、実際の地殻内部において、水のバリエーションによって、塑性変形挙動が異なることを示唆する。

Research Products

• [Journal Article] Water release and homogenization by dynamic recrystallization of quartz (2023)
  • Author(s): Fukuda Junichi、Okudaira Takamoto、Ohtomo Yukiko
  • Journal Title: Solid Earth Volume: 印刷中
  • DOI: 10.5194/egusphere-2022-1487
  • Peer Reviewed / Open Access
• [Journal Article] Enhancement of ductile deformation in polycrystalline anorthite due to the addition of water (2022)
  • Author(s): Fukuda Junichi、Muto Jun、Koizumi Sanae、Sawa Sando、Nagahama Hiroyuki
  • Journal Title: Journal of Structural Geology Volume: 156 Pages: 104547-104547
  • DOI: 10.1016/j.jsg.2022.104547
  • Peer Reviewed
• [Journal Article] A centennial-resolution terrestrial climatostratigraphy and Matuyama-Brunhes transition record from a loess sequence in China (2020)
  • Author(s): Hyodo, M., Banjo, K., Yang, T.S., Katoh, S., Shi, M., Yasuda, Y., Fukuda, J., Miki, M., Bradak, B.
  • Journal Title: Progress in Earth and Planetary Science Volume: 7 Issue: 1 Pages: 1-18
  • DOI: 10.1186/s40645-020-00337-z
  • NAID: 120006940225
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Nano-sized authigenic magnetite and hematite particles in mature-paleosol phyllosilicates: New evidence for a magnetic enhancement mechanism in loess sequences of China. (2020)
  • Author(s): Hyodo, M., Sano, T., Matsumoto, M., Seto, Y., Bradak, B., Suzuki, K., Yang, T.
  • Journal Title: Journal of Geopysical Research Volume: 125 Issue: 3 Pages: 1-21
  • DOI: 10.1029/2019jb018705
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Experimental grain growth of quartz aggregates under wet conditions and its application to deformation in nature (2019)
  • Author(s): Fukuda, J., Raimbourg,_H., Shimizu, I., Neufeld, K., Stunitz, H.
  • Journal Title: Solid Earth Volume: 10 Issue: 3 Pages: 621-636
  • DOI: 10.5194/se-10-621-2019
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Water distribution in quartz schists of the Sanbagawa Metamorphic Belt, Japan: infrared spectroscopic mapping and comparison of the calibrations proposed for determining water contents (2019)
  • Author(s): Jun-ichi Fukuda, Ichiko Shimizu
  • Journal Title: Earth, Planets and Space Volume: 71 Issue: 1 Pages: 1-14
  • DOI: 10.1186/s40623-019-1117-4
  • NAID: 120006811096
  • Peer Reviewed / Open Access
• [Presentation] 石英の動的再結晶の発展と含水量の変化 (2022)
  • Author(s): 福田惇一、奥平敬元、大友幸子
  • Organizer: 日本地質学会第129年学術大会
• [Presentation] Centennial-resolution terrestrial climatostratigraphy and Matuyama-Brunhes transition from a loess sequence in China (2020)
  • Author(s): 兵頭 政幸、番匠 健太、楊 天水、加藤 茂弘、時 美楠、安田 裕紀、福田 惇一、三木 雅子、ブラダック バラージュ
  • Organizer: JpGU-AGU Joint Meeting 2020
  • Int'l Joint Research
• [Presentation] Normal grain growth of quartz by experiment and discussion on the effect of grain size reduction by deformation in natural conditions (2019)
  • Author(s): Jun-ichi Fukuda, Hugues Raimbourg, Ichiko Shimizu, Kai Neufeld, Holger Stunitz
  • Organizer: American Geophysical Union Fall Meeting
  • Int'l Joint Research
• [Remarks] 神戸大学大学院 理学研究科 惑星学専攻 福田惇一 ホームページ
  • URL: http://www2.kobe-u.ac.jp/~jfukuda/
• [Remarks] ResearchGate
  • URL: https://www.researchgate.net/profile/Jun-ichi_Fukuda2