Skip to content

Textures, formation and implications of palisade bubbles within felsic pyroclastic products

Shannen Mills1 , Anke Zernack1, Colin Wilson2, Jonathan Procter1, Joseph Fleming1, Andrew Stevenson3,4, Benedicta Arhatari3.

  • Affiliations:  1Volcanic Risk Solutions, School of Agriculture and Environment, Massey University, Palmerston North, New Zealand; 2School of Geography, Environment and Earth Sciences, Victoria University of Wellington, Wellington, New Zealand; 3Australian Synchrotron, Australian Nuclear Science and Technology Organisation (ANSTO), Clayton, Vic, 3168, Australia; 4Commonwealth Scientific and Industrial Research Organisation (CSIRO), Clayton, VIC 3168, Australia 

  • Presentation type: Poster

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

  • Poster Board Number: 208

  • Programme No: 3.6.12

  • Theme 3 > Session 6

Abstract

Bubble textural studies provide a snapshot into pre- and syn-eruptive processes occurring within magmas. A distinctive feature, where bubbles form a coarsely vesicular sheath around crystals within felsic pyroclasts, is known as palisade texture. It indicates early bubble growth that implies volatile saturation with bubble nucleation occurred on phenocrysts, either stably within the magma chamber or during the earliest slow stages of magma rise prior to general nucleation of bubbles in the melt. Subsequent decompression of the supersaturated magma causes expansion of these pre-existing bubbles to form the characteristic palisades before the runaway nucleation of bubbles occurs in the groundmass glass. While these textural features have little documentation, they hold the key to understanding pre-eruptive magmatic conditions within large felsic systems. Previously documented for (small) Fe-Ti oxide crystals, we present images of palisade textures from larger (mm-scale) quartz, feldspar and pyroxene phenocrysts. Using 3D Micro-Computed Tomography and 2D SEM imagery, we investigated 150 rhyolitic, dacitic and phonolitic pyroclasts from New Zealand, Germany, the USA and the Kermadec Arc for the presence of palisade bubbles, documenting the natural variability of internal bubble structures to develop a classification guide. Palisade bubbles often pull apart the crystals they surround, forming thin glass connections within the gaps and form augen structures within the distorting and flowing groundmass bubble textures, the latter suggesting that they were more viscous. Results from this study will contribute to better understanding the timescales of volatile supersaturation and magma ascent rates within felsic systems that produce explosive eruptions.