Development of rock texture and fluid generation processes within convergent plate boundary

2021 Fiscal Year Final Research Report

• Project/Area Number: 17H02981
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Petrology/Mineralogy/Economic geology
• Research Institution: Tohoku University
• Principal Investigator: Atsushi Okamoto 東北大学, 環境科学研究科, 教授 (40422092)
• Co-Investigator(Kenkyū-buntansha): 宇野 正起 東北大学, 環境科学研究科, 助教 (50748150) ; 清水 浩之 東北大学, 流体科学研究所, 助教 (60610178)
• Project Period (FY): 2017-04-01 – 2021-03-31
• Keywords: 沈み込み帯 / 岩石ー流体相互作用 / 脱水反応 / エクロジャイト / 蛇紋岩 / 炭酸塩化作用 / ざくろ石 / 組織発達

Outline of Final Research Achievements

Fluid generation and reaction processes in subduction zones are left as mirostructures of minerals in metamorphic rocks and serpentinites. In this study, we examined the crystal size distribution and compositional zoning of garnet in eclogite of high-pressure metamorphic belt and found that crystal growth is size-dependent and that the distribution, or fluid generation rate, varies from layer to layer in the same rock. We also found that carbonation of mantle wedge-derived serpentinites is caused by the inflow of CO2 fluids originating from carboniferous materials, and that it proceeded in self-promoting ways induced by the decrease in solid volume, high pore pressure, and magnesium mobility. Furthermore, through hydrothermal experiments and geochemical modeling, it was shown that solution pH varies along the subduction zone and has a significant effect on the reaction and volume change.

Free Research Field

岩石学

Academic Significance and Societal Importance of the Research Achievements

エクロジャイト中のざくろ石、蛇紋岩の炭酸塩化、玄武岩の熱水変質など様々な組織についての解析を行い、モデリン、溶液化学の解析、水熱実験を合わせて新たな方法論を構築した。特に、蛇紋岩体の炭酸塩化作用の研究を通じて、溶液化学をベースとして、物質移動、体積変化による破壊を含めた動的なモデルを示したことは固体地球を解析するの新たなアプローチとなるとともに、沈み込み帯の地震と反応プロセスの理解にも貢献できる。