strain localization promoted by dynamic recrystallization of orthopyroxene studied by high-pressure deformation experiments

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K14816
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Kyushu University (2020-2022); Ehime University (2019)
• Principal Investigator: TSUBOKAWA YUMIKO 九州大学, 理学研究院, 助教 (40824280)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: 斜方輝石 / 海洋プレート / 高温高圧変形実験

Outline of Final Research Achievements

To explain weakening mechanism of subducting oceanic lithosphere in the Earth, high-pressure and high-temperature deformation experiments of orthopyroxene, which is the second dominant mineral in the oceanic lithosphere, were conducted. Recrystallization and localized deformation of orthopyroxene was occurred with recrystallized grain size of ~1 micron. Based on the relationship between recrystallized grain size and stress of orthopyroxene, grain size reduction by recrystallization would induce the transition of the dominant creep mechanism from dislocation creep to grain-size sensitive creep of orthopyroxene and would thus result in weakening.

Free Research Field

固体地球科学

Academic Significance and Societal Importance of the Research Achievements

海洋プレートの最主要鉱物であるカンラン石の転位クリープ強度は非常に大きく、プレートが変形し沈み込むための理論強度を大幅に超過している。地球におけるこのようなプレートテクトニクスの矛盾を説明するために、本研究ではプレートの第二成分である斜方輝石が変形に誘発される細粒化（動的再結晶）の結果、一般的な転位クリープではなく粒径依存性を持つ変形メカニズムが強度を支配するようになり強度弱化する可能性を実験的に示した。