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Earth, Planets and Space

, Volume 54, Issue 11, pp 1127–1132 | Cite as

Water-rock interaction observed in the brittle-plastic transition zone

  • Koichiro Fujimoto
  • Tomoyuki Ohtani
  • Norio Shigematsu
  • Yukari Miyashita
  • Tomoaki Tomita
  • Hidemi Tanaka
  • Kentaro Omura
  • Yoji Kobayashi
Open Access
Article

Abstract

Rock alteration and geochemistry of the fault rocks are examined to infer the characteristics of the fluid phase related to the ancient fault activity. The Hatagawa Fault Zone, northeast Japan, is an exhumed seismogenic zone which is characterized by close association of brittlely and plastically deformed fault rocks mostly derived from Cretaceous granitoids. Epidote and chlorite are dominant alteration minerals in both rocks. However, calcite is characteristically developed in the cataclastic part only. Decrease in oxygen isotope ratio and existence of epidote and chlorite, even in weakly deformed granodiorite, is evidence of water-rock interaction. The water/rock ratio is interpreted to be relatively small and fluid chemistry is buffered by host rock chemistry in the mylonite. The occurrence of calcite in brittle structures is explained by changes in water chemistry during shear zone evolution. CO2-rich fluid was probably introduced during cataclastic deformation and increased CO2 concentration resulted in precipitation of calcite.

Keywords

Calcite Shear Zone Oxygen Isotope Ratio Fault Rock Mylonitic Foliation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. 2002

Authors and Affiliations

  • Koichiro Fujimoto
    • 1
  • Tomoyuki Ohtani
    • 1
  • Norio Shigematsu
    • 1
  • Yukari Miyashita
    • 1
  • Tomoaki Tomita
    • 2
  • Hidemi Tanaka
    • 3
  • Kentaro Omura
    • 4
  • Yoji Kobayashi
    • 2
  1. 1.Geological Survey of JapanAISTTsukuba, IbarakiJapan
  2. 2.Institute of GeoscienceUniversity of TsukubaTsukuba, IbarakiJapan
  3. 3.Department of Earth and Planetary SciencesUniversity of TokyoHongo, TokyoJapan
  4. 4.National Research Institute for Earth Science and Disaster PreventionTsukuba, IbarakiJapan

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