Plastic strength of the crust evaluated from naturally deformed rocks

2022 Fiscal Year Final Research Report

• 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
• Keywords: 地殻 / 石英 / 長石 / 塑性変形 / 水 / 天然 / 実験

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.

Free Research Field

構造地質学、岩石力学

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。