Retrograde pumpellyite in the Yunotani garnet blueschist of the Omi area, Japan: An update on the cooling path

• SHINJI Yuzuki

  Department of Earth Science, Tohoku University

• TSUJIMORI Tatsuki

  Department of Earth Science, Tohoku University Center for Northeast Asian Studies, Tohoku University

抄録

Retrograde pumpellyite was newly found in garnet blueschist that is Mg–rich equivalent of late Paleozoic retrograde eclogite of the Yunotani Valley in the Omi area, Hida–Gaien Belt. The pumpellyite with high Al/(Al + Mg + Fe) occurs in pressure shadows around garnets; it is associated with secondary glaucophane, epidote, chlorite, titanite, phengite, albite, and quartz, which all characterize a retrograde blueschist–facies mineral assemblage after peak eclogite–facies mineral assemblage. This feature is comparable with retrograde pumpellyite in late Paleozoic garnet blueschist (with relict eclogite–facies mineral assemblage) in the Osayama area of the Chugoku Mountains. Equilibrium phase calculation confirmed that the pumpellyite is stable at a low temperature and pressure portion of the lawsonite–blueschist–facies. T–bulk–composition (Mg) pseudosection suggests that pumpellyite appears preferentially in high Mg/(Mg + Fe) bulk composition. The limited occurrence of retrograde pumpellyite in the Yunotani garnet blueschist and retrograde eclogite would be explained by Mg–rich bulk compositions. Also, the limited occurrence in pressure shadows around garnets suggests that the fluid trapped in the pressure shadows might have enhanced growth (or precipitation) of pumpellyite. This finding provides a strong evidence that the deeply subducted (eclogite–facies) metabasaltic rocks both in the Hida–Gaien Belt and the Chugoku Mountains were subjected to a very similar blueschist–facies overprinting locally reached the pumpellyite stability field. The ‘Franciscan–type’ cooling path suggests a ‘steady–state’ underflow of the paleo–Pacific oceanic plate in late Paleozoic at a convergent margin of the South China Craton.

収録刊行物

• Journal of Mineralogical and Petrological Sciences

  Journal of Mineralogical and Petrological Sciences 114 (1), 26-32, 2019

  一般社団法人　日本鉱物科学会

キーワード

• Pumpellyite
• Retrograde <i>P–T</i> path
• Retrograde eclogite
• Omi
• Hida–Gaien Belt

詳細情報

• CRID: 1390001288126621184
• NII論文ID: 130007610378
• DOI: 10.2465/jmps.180716
• ISSN: 13493825
• ISSN: 13456296
• Web Site: https://www.jstage.jst.go.jp/article/jmps/114/1/114_180716/_pdf
• 本文言語コード: en
• データソース種別:
  • JaLC
  • Crossref
  • CiNii Articles
  • KAKEN
• 抄録ライセンスフラグ: 使用不可