2019 Fiscal Year Final Research Report
Temporal change in crustal strength based on the analysis of deformation microstructures in the lower crustal rocks
| Project/Area Number |
16K05613
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Research Field |
Petrology/Mineralogy/Economic geology
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| Research Institution | Osaka City University |
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Principal Investigator |
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| Project Period (FY) |
2016-04-01 – 2020-03-31
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| Keywords | 延性剪断帯 / 下部地殻 / 破壊 / 地震発生領域 / 変形機構 / 斜長石 |
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| Outline of Final Research Achievements |
Since the deformation in the lower crust immediately below a seismogenic fault can accumulate the stress on the fault, understanding the dominant deformation mechanism and the formation of ductile shear zones in the lower crust is crucial to reveal the occurrence of intraplate earthquakes. Based on the petrological and microstructural analyses for deformed rocks developed in Lofoten and Vesteralen, northern Norway, we revealed that dynamic fracturing is a dominant grain-size reduction mechanism and subsequent grain-size-sensitive creep (e.g., grain-boundary sliding) is a dominant deformation mechanism at high temperatures. Fracturing facilitates fluid flow due to the increased dilatancy and connectivity of pore spaces. An influx of fluid enhances hydration reactions, which form small, strain-free recrystallized grain. This process would promote grain-size-sensitive creep in the narrow zones, and result in the development of ductile shear zones in the lower crust.
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| Free Research Field |
構造岩石学
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| Academic Significance and Societal Importance of the Research Achievements |
地震発生帯直下の下部地殻が局所的に延性変形すれば，その直上の断層に応力が集中することが期待されるため，地震発生帯直下の下部地殻延性剪断帯の発生・発達過程は，内陸地震の発生において重要である．本研究では，下部地殻剪断帯を詳細に観察できるノルウェー北部ベステローデン諸島において地質調査を行い，採取された変形岩を解析し，動的破壊が下部地殻の延性剪断帯の発生・発達過程において重要であることを明らかにした．
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