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Experimental simulation of diktytaxitic groundmass formation

Ryosuke Sakurai1, Michihiko Nakamura 2, Satoshi Okumura2, Mayumi Mujin2, Takayuki Nakatani3

  • Affiliations: 1Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan; 2Department of Earth Science, Tohoku University, Sendai, Japan; 3Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan  

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 195

  • Programme No: 3.2.18

  • Theme 3 > Session 2

Abstract

Diktytaxitic texture, a groundmass containing abundant angular interstitial cavities between plagioclase laths, is commonly observed in lava dome interior, volcanic necks, and volcanic ash particles of a wide range of compositions, from basaltic to dacitic. Diktytaxitic texture has particular volcanological significance in eruption explosivity because lava consisting of such cavities is permeable and, therefore, expected to inhibit explosion attributable to late-stage volatile exsolution. However, the exact pressure and temperature conditions, besides the formation rate, remain poorly understood. With these parameters, the source and timing of volcanic ash production would also be clarified. In this context, Sakurai et al. (2024, Contrib. Mineral. Petrol.) experimentally simulated diktytaxitic texture using bulk andesitic magma with rhyolitic glass. They reported that diktytaxitic texture can be produced under water-saturated, near-solidus conditions (10--20 MPa and 850°C, which is within ± ~10 MPa and ± ~20°C of the solidus) in 4--8 days, along with condensation of vapor-phase minerals such as cristobalite and alkali feldspar. These reactions occurred via partial evaporation of the supercooled melt as a result of the system selecting the fastest crystallization pathway. The pressure and temperature conditions obtained are consistent with the common natural occurrence of diktytaxitic texture. The previously proposed mechanisms of halogen-induced corrosion or melt segregation by gas-driven filter pressing are not particularly necessary. These findings constrain the outgassing of lava domes and shallow magma intrusions and provide new insights into the final stages of hydrous magma crystallization on Earth.