Two groups of fluid inclusions in the Yunotani eclogite from the Hida-Gaien Belt: Implications for changes of fluid salinity during exhumation

Yuzuki Shinji, Tatsuki Tsujimori, Tatsuhiko Kawamoto

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1 Citation (Scopus)

Abstract

Late Paleozoic Yunotani eclogites in the Itoigawa-Omi area of the Hida-Gaien Belt were subjected to a blueschist-facies recrystallization and deformation after the peak eclogite-facies metamorphism. We studied fluid inclusions in quartz domains of different metamorphic stages in the retrograde eclogite. Coarse-grained quartz filling pressure shadow of porphyroblastic garnets contains transgranular fluid inclusions (Group-I) with high salinity [6.0-8.0 eq mass% NaCl, with a mean value 7.2 ± 0.6 eq mass% NaCl (n = 12)]. In contrast, transgranular fluid inclusions in later stage quartz-rich band (Group-II) in parallel to a penetrative foliation developed in matrix are characterized by lower salinity [1.1-5.8 eq mass% NaCl, with a mean value 3.4 ± 1.2 eq mass% NaCl (n = 12)]. The occurrences of fluid inclusion trails suggest that each group corresponds to the fluids entrapped prior to the blueschist-facies recrystallization and the fluids entrapped during the blueschist-facies stage, respectively. The Group-II fluid inclusions formed at blueschist-facies conditions support the idea that aqueous fluids in the subduction channel have a salinity similar to seawater (~ 3.5 eq mass% NaCl). Moreover, the Group-I fluid inclusions indicate a possibility that aqueous fluids at the eclogite-facies depth in subduction channels possess a salinity higher than seawater.

Original languageEnglish
Pages (from-to)302-307
Number of pages6
JournalJournal of Mineralogical and Petrological Sciences
Volume114
Issue number6
DOIs
Publication statusPublished - 2019

Keywords

  • Aqueous fluid inclusion
  • Blueschist-facies recrystallization
  • Hida-Gaien Belt
  • Itoigawa-Omi area
  • Retrograde eclogite

ASJC Scopus subject areas

  • Geophysics
  • Geology

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