岩石の変形特性に対する水の効果と大陸・海洋プレートのレオロジー構造  [in Japanese] Effect of water on rock deformation and rheological structures of continental and oceanic plates  [in Japanese]

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Author(s)

    • 片山 郁夫 Katayama Ikuo
    • 広島大学大学院理学研究科地球惑星システム学 Department of Earth and Planetary Systems Science, Hiroshima University
    • 東 真太郎 Azuma Shintaro
    • 九州大学大学院理学研究院地球惑星科学部門 Department of Earth and Planetary Sciences, Kyushu University

Abstract

<p>岩石の変形特性は水の存在に強い影響を受けるため,地球内部のレオロジー構造は水の有無によって大きく異なる.本総説では,最新の岩石変形実験の結果に基づき,大陸プレートと海洋プレートのレオロジー構造を作成し,両地域でみられるテクトニクスと水の関連性を議論した.その結果,1)大陸地殻の下部には強度の弱面が存在するため変形が集中すること,2)大陸下のリソスフェアが対流に巻きこまれず安定的に存在するには水に乏しい必要があること,3)大陸縁辺部では,前弧側は沈み込むプレートからの供給により水に富んでいるのに対し,背弧側では島弧マグマの形成により水に乏しいこと,4)海洋リソスフェアは,中央海嶺での水の分別作用により,全体的に水に乏しいこと,5)海溝付近の海洋プレートの一部は,アウターライズ断層沿いの水の侵入により弱化していること,などがレオロジー構造から推察された.</p>

<p>Rheological structures for continental and oceanic plates were calculated using the laboratory-based frictional and flow laws. Our results show that Peierls creep becomes the dominant mechanism for plastic deformation at low temperatures and high stresses under both dry and wet conditions. When Peierls creep, rather than dislocation-accommodated power-law creep, is the dominant mechanism, there is a lower maximum mechanical strength, and a shallower depth to the brittle-plastic transition in our model. The rheology of continental lithosphere is complex, but may feature a weak lower crust sandwiched between a strong upper crust and mantle. Extensive deformation of this weak zone may explain crustal duplication in continental collision zone. The thick continental lithosphere beneath craton is stable for billions of years. This is partly because partial melting has depleted these regions of water, causing an increase in the mechanical strength of the continental lithosphere. The depth of brittle-plastic transition at island arcs, which we inferred from the maximum depth of seismicity, suggests that the fore-arc regions are enriched in water, but that the back-arc regions are depleted. The rheological structure of oceanic plate is dependent on the age of the plate, and the thickness of oceanic lithosphere is largely consistent with a dry rheology. A relatively thin elastic thickness found for the oceanic lithosphere in the Mariana and Bonin arcs may be explained by local weakening as a result of hydration along outer-rise faults.</p>

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 123(6), 365-377, 2017

    The Geological Society of Japan

Codes

  • NII Article ID (NAID)
    130005858622
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • ISSN
    0016-7630
  • NDL Article ID
    028363861
  • NDL Call No.
    Z15-174
  • Data Source
    NDL  J-STAGE 
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