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2021 Fiscal Year Final Research Report

Influence of upper mantle hydration on the initiation of oceanic plate subduction

Research Project

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Project/Area Number 19K04015
Research Category

Grant-in-Aid for Scientific Research (C)

Allocation TypeMulti-year Fund
Section一般
Review Section Basic Section 17040:Solid earth sciences-related
Research InstitutionShizuoka University

Principal Investigator

Ken-ichi Hirauchi  静岡大学, 理学部, 准教授 (10633290)

Co-Investigator(Kenkyū-buntansha) 大内 智博  愛媛大学, 地球深部ダイナミクス研究センター, 准教授 (60570504)
Project Period (FY) 2019-04-01 – 2022-03-31
Keywords沈み込み開始 / 蛇紋石 / 上部マントル / プレートテクトニクス / 変形実験
Outline of Final Research Achievements

To understand how the hydrothermal alteration of the upper mantle affects the strength of oceanic fracture zones, we conducted simple-shear experiments on water-saturated peridotite gouges using two deformation-DIA apparatuses at a confining pressure of 2.5 GPa, temperatures of 500-580 °C, and water contents of 4-30 wt.%. The gouges have a shear strength of 0.5-1 GPa. Olivine aggregates exhibit a B-type crystal preferred orientation indicative of the operation of the [001](010) slip system. Shear displacement is also accommodated by the development of serpentine-rich multiple shear zones including B, R1, and Y shears, where intense cataclasis-related grain size reduction occurs. These findings suggest that at the oceanic fault zones undergoing hydrothermal alteration, deformation is controlled by competition between dislocation creep in olivine and frictional sliding of serpentine.

Free Research Field

構造地質学

Academic Significance and Societal Importance of the Research Achievements

海洋プレートの沈み込みは、惑星表層とマントルの間の物質循環をもたらすことから、地球史における大気やマントルの進化を考える上で重要なプロセスである。本研究成果は、惑星表層に海洋が存在することで、プレートが沈み込みを開始するために必要なプレート間にかかる抵抗力(差応力)に打ち勝つことができることを明らかにした。つまり、太陽系の岩石惑星の中で地球にだけプレートテクトニクスがある理由として、惑星表層に唯一水が存在することが挙げられる。

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Published: 2023-01-30  

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