噴火時のマグマプロセスを噴出物組織から探る手法

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書誌事項

タイトル別名
  • Methods to Investigate Syneruptive Magma Processes Using Textures in Ejecta
  • 噴火時のマグマプロセスを噴出物組織から探る手法 : 過去10年間の研究進展のレビュー
  • フンカジ ノ マグマプロセス オ フンシュツブツ ソシキ カラ サグル シュホウ : カコ 10ネンカン ノ ケンキュウ シンテン ノ レビュー
  • —過去10年間の研究進展のレビュー—
  • —A Review of Progress in Last 10 Years—

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抄録

<p>This paper reviews recent (last 10 years) progress in petrological and textural studies on eruptive products relevant to syneruptive magma ascent in the conduit. Compared with the period when petrological and textural studies focused only on magma behavior in the reservoir, they came to have more potential to link various volcanological research fields including geophysics and geology.</p><p>The target of the present review is narrowed down to 1) analysis of groundmass crystals (microlites) for revealing eruption mechanism of specific eruption, and 2) decompression experiment for general understanding of crystallization kinetics and 3) accompanying techniques in collecting eruptive products in the field, in selecting representative samples for detailed textural analyses, in conducting textural analyses of ejecta and experimental products, and in running decompression experiments.</p><p>The basis in revealing magma ascent rates using microlites is that higher magma ascent rate results in larger magnitude of undercooling, resulting in nucleation-dominated crystallization. Its validity has been repeatedly confirmed in decompression experiments, as in the period before 2006. New trend in the last decade is that increasing number of experiments came to deal with basaltic and rhyolitic magmas, which is in contrast with the predominance of experiments for andesitic and dacitic magmas over the period before 2006. Similar trend is found for studies for specific eruption with or without experimental replication of microlite textures. The appearance of microlite number density water exsolution rate meter (Toramaru et al., 2008) made it easier to estimate absolute magma ascent rate, even when experimental facilities are not available.</p><p>The author proposes the method by which further development of this research field is possible. The method includes a) utilization of different types of eruption products (e.g. ash) and b) utilization of different sizes of groundmass crystal (e.g. nanolites) and c) acquisition of knowledge on crystallization kinetics at low pressure. The last two points are necessary when we try to infer final emplacement process of the ejecta at the surface (e.g. to solve the genetic problems of clastogenic lava flow and rootless cone), in conjunction with geological studies.</p>

収録刊行物

  • 火山

    火山 61 (2), 367-384, 2016

    特定非営利活動法人 日本火山学会

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