S1, S4: Earth materials science related to igneous processes and plate convergence region (Joint Special Session)

[S1,S4-09] Crystal habit change of groundmass pyroxenes depending on magma ascent paths revealed by single-step decompression experiments

[Presentation award entry]

*Shota Okumura¹, Satoshi Okumura², Akira Miyake¹ (1. Kyoto Uni. Sci., 2. Tohoku Uni. Sci.)

Keywords:pyroxene, crystal habit, decompression experiment, Sakurajima volcano

We experimentally found that crystal habits (i.e., combination of crystallographic planes) of groundmass pyroxene crystals reflect the degree of effective undercooling during the ascent. We conducted single-step decompression experiments with pumices from the Sakurajima volcano and welded glass as staring materials. Our results indicate that the habit changes in the order of octagonal, hexagonal, and quadrangular prism as the degree of effective undercooling increases, and that a magma batch with few crystals ascended quickly during the 1914 eruption of Sakurajima.