著者
Yuzuki SHINJI Tatsuki TSUJIMORI
出版者
Japan Association of Mineralogical Sciences
雑誌
Journal of Mineralogical and Petrological Sciences (ISSN:13456296)
巻号頁・発行日
vol.114, no.1, pp.26-32, 2019 (Released:2019-03-08)
参考文献数
40

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.

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ざくろ石–藍閃石片岩, Garnet-blueschist 産地: 新潟県糸魚川市大字上路 Locality: Agero district, Itoigawa City, Japan まさしく"エモ断"。昨夏に採取、自宅に眠っ… https://t.co/h5RGZZM0zL
https://t.co/Vejsc0Jiid https://t.co/lCcZCCKzH8 https://t.co/H7TK0v8cPn https://t.co/w8zoGBNuLP… https://t.co/KUQsnN4F8q
https://t.co/SF1vqKM3N4 全岩組成はShinji and Tsujimori(2019)を参考にして、温度圧力範囲を広げてみた図

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