2023 Fiscal Year Final Research Report
Estimation of Antigorite Serpentinite Structure of Wedge Mantle in Subduction Zones
| Project/Area Number |
20K14575
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| Research Category |
Grant-in-Aid for Early-Career Scientists
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| Allocation Type | Multi-year Fund |
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| Review Section |
Basic Section 17040:Solid earth sciences-related
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| Research Institution | Tokyo Gakugei University (2023)
The University of Tokyo (2020-2022) |
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Principal Investigator |
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| Project Period (FY) |
2020-04-01 – 2024-03-31
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| Keywords | アンチゴライト蛇紋岩 / 前弧マントルレオロジー / 結晶軸選択配向(CPO)形成機構 / 変形機構 / 脱水分解反応 / ブルーサイト / トポタキシー / 深部Slow地震 |
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| Outline of Final Research Achievements |
This study aimed to estimate the antigorite (Atg) serpentinite structure in the wedge mantle. Field surveys were conducted in several areas in Japan, and natural rock samples were collected and used to measure and analyze the crystallographic orientations of Atg. Comparison and compilation with previously reported information on the alignment patterns of Atg crystal axes from several regions and samples revealed the mechanism by which specific alignment patterns are formed.
In addition, the changes in rock structure were experimentally reproduced during the dehydration reaction process that occurs at relatively low temperatures when serpentinite contains brucite. In particular, we succeeded for the first time in measuring the arrangement pattern of crystal axes of brucite by EBSD, and discovered and reported for the first time the existence of a relationship called topotaxy between olivine and brucite.
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| Free Research Field |
固体地球科学, 地質学, 地球内部物質科学, 構造地質－構造岩石－構造地震学, 岩石－鉱物学
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| Academic Significance and Societal Importance of the Research Achievements |
沈み込み帯プレート境界の含水化した大陸側上部マントル(ウェッジマントル, WM)は、アンチゴライト(Atg)主体の蛇紋岩で構成される。AtgはWMで結晶軸が強く配列する一方、複数の配列パターンの報告がある。本研究は一部の配列パターンと形成メカニズムの関係を解明した。
また蛇紋岩内の一部の脱水反応で生じる岩石構造変化を実験的に再現するとともに、反応後に形成するかんらん石が変形を伴わずとも結晶軸が配列するメカニズムを発見した。本研究で見出した含水WMでの岩石構造とその形成過程や変化は、一部深部Slow地震発生領域でも生じると考えられることもあり、WMの力学的・水理学的特性を理解する上で重要である。
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