Cooling and crystallization of rhyolite–obsidian lava: Insights from micron-scale projections on plagioclase microlites

Kyohei Sano, Atsushi Toramaru

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

To reveal the cooling process of a rhyolite–obsidian flow, we studied the morphology of plagioclase microlites in the Tokachi–Ishizawa lava of Shirataki, northern Hokkaido, Japan, where the structure of the lava can be observed from obsidian at the base of the flow to the innermost rhyolite. Needle-like micron-scale textures, known as “projections” occur on the short side surfaces of the plagioclase microlites. Using FE–SEM we discovered a positive correlation between the lengths and spacings of these projections. On the basis of the instability theory of an interface between melt and crystal, and to understand the length and spacing data, we developed a model that explains the positive correlation and allows us to simultaneously estimate growth rates and growth times. Applying the model to our morphological data and the estimated growth rates and growth times, we suggest that the characteristics of the projections reflect the degree of undercooling, which in turn correlates with lava structure (the obsidian at the margin of the flow experienced a higher degree of undercooling than the interior rhyolite). The newly developed method provides insights into the degree of undercooling during the final stages of crystallization of a rhyolitic lava flow.

Original languageEnglish
Pages (from-to)158-171
Number of pages14
JournalJournal of Volcanology and Geothermal Research
Volume341
DOIs
Publication statusPublished - Jul 15 2017
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

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