Hydrothermal minerals in phreatic eruption products at Zao volcano, NE-Japan

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Other Title
  • 東北日本、蔵王火山の水蒸気噴火噴出物に含まれる変質鉱物

Abstract

Hydrothermal minerals in ejecta of phreatic eruptions are derived from subvolcanic hydrothermal system. Mineral assemblage of such minerals reveal chemical composition and temperature of hydrothermal water. Zao volcano is located at the central part of the volcanic front, NE Japan. Some phreatic eruptions occurred frequently at this volcano and those products cover large area. The latest eruptions occur at 1895 and its ejecta distribute around Okama crater. These ejecta were used for X-ray diffraction (XRD) and electron probe microanalysis (EPMA) to determine mineral assemblages and mineral compositions. Abundant minerals are SiO2 minerals, CaSO4 minerals and alunite minerals. While gypsum was detected from layer around Okama crater, it was undetected from distant layers from Okama. This indicates that gypsum occurred in situ after the eruption and deposit of ejecta. Alunite group minerals are characteristic in acid sulfate alteration environments. EPMA analyses show that alunite group minerals in these ejecta are Ca-dominant alunite, named minamiite or huangite. It was precipitated from fluids of high acid, high temperature and low sulfate ion concentration.

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Details 詳細情報について

  • CRID
    1390282680521668224
  • NII Article ID
    130004601652
  • DOI
    10.14824/jakoka.2010.0.243.0
  • Text Lang
    ja
  • Data Source
    • JaLC
    • CiNii Articles
  • Abstract License Flag
    Disallowed

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