Characteristic microstructures of the volcanic ashes from the Sakurajima volcano: Insights into conduit environments

Abstract

Fine lithic fragments erupted recently from the Sakurajima volcano show microstructures characterized by (1) High degree of decompression-induced rapid crystallization at very low pressure and high temperature, (2) high porosity and irregular pores due to crystallization and dehydration, (3) exsolution, oxidation and reaction textures of phenocrysts (4) vapor phase minerals condensed from the hot volcanic gas flew through the pores (5) Minerals growth from low-temperature volcanic gas or in hydrothermal environments, accompanied by accretionary lapilli-like products. These microstructures may provide insights into the conduit conditions including high permeability.