Geological analysis for grain boundary sliding creep of olivine and its possible contribution to non-steady state behaviours of subduction boundaries

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K04128
• 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: Kanazawa University
• Principal Investigator: Mizukami Tomouyuki 金沢大学, 地球社会基盤学系, 助教 (80396811)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: かんらん岩の構造解析 / 動的再結晶 / 電子線チャネリングコントラスト

Outline of Final Research Achievements

Grain boundary sliding (GBS) creep of mantle olivine can potentially induce non-steady-state behaviours of subduction boundaries at mantle depth. In order to understand the potential importance of the GBS creep, this study made structural analyses of natural peridotite, such as the Higashi-akaishi peridotite body and the Horoman peridotite body. Challenges for non-destructive dislocation observation using electron channeling contrast imaging, that is expected as a new methodology in earth science, are successful. The structural analyses of the fine-grained and ultra-fine grained peridotites in the Horoman body depict that various processes of dynamic recrystallization have worked to cause transitions of deformational mechanism from grain-size insensitive dislocation creep to grain-size sensitive creeps. The most striking result is the microstructural evidence that reactions between olivine and pyroxenes under strain play a major role in grain-size reduction in natural mantle rocks.

Free Research Field

構造地質学

Academic Significance and Societal Importance of the Research Achievements

プレート境界型地震の震源域の上盤を持ち上げる応力の蓄積は、より深部の歪み解消過程と関連している。テクトニック微動やスロースリップが観測されるゆっくりすべり域が直接的な影響を及ぼすが、さらに深部のかんらん岩の流動現象も連動する一つのシステムとして捉えるべきであろう。その深部で優勢と予想される、かんらん石の粒径依存型クリープの実態を示した地質学的研究の例が少ない。今回、幌満岩体において輝石を含む典型的なマントルかんらん岩に見出された構造は普遍性を持つ。そして、この岩石の動的再結晶組織の定量的解析、そして岩石の非定常的な強度変化の解析へと道を開いた。