Dynamism of fluid pressure in subduction zones revealed by tracer-diffusion experiments on reaction zones

2019 Fiscal Year Final Research Report

• Project/Area Number: 18K13628
• 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: Tohoku University
• Principal Investigator: Uno Masaoki 東北大学, 環境科学研究科, 助教 (50748150)
• Project Period (FY): 2018-04-01 – 2020-03-31
• Keywords: 沈み込み帯 / 地殻流体 / 岩石ー流体反応 / 流体圧 / 浸透率 / 反応輸送モデル

Outline of Final Research Achievements

To understand the fluid activities in the deep crust, we have developed a novel method that reveals fluid pressure and permeability of the crustal material from metamorphic reaction zones. Application of reactive-transport model to crustal fluid-rock reaction zone was verified by hydrothermal experiments replacing marble by apatite. Analyses of natural metamorphic reaction zone revealed that the time-scales of fluid activities in the fractures ranged from hours to years. Permeability (in log10 [m2] unit) significantly change from -22~-20 in intact crust to -15~-10 in fractures. It is suggested that the widely accepted crustal permeability (-18) is a ~Myr-scale temporal average, and crustal permeability fluctuates for more than 5 orders in the time-scales of hours to years.

Free Research Field

岩石学，地球化学

Academic Significance and Societal Importance of the Research Achievements

地震波観測などで間接的に推測されていた，地殻流体圧と浸透率の変動を，岩石ー流体反応帯から定量的に示した．従来，示されていた地殻浸透率の値は，百万年スケールの時空間平均であり，年ー時間スケールでは，ダイナミックに変動していることを明らかにした．
本研究では，地震波から観測される地殻流体活動と，地質学的に観察される岩石ー流体反応帯を，具体的な時間スケールや流体圧，浸透率をとおして定量的な比較を可能とした．