How to fragment peralkaline rhyolites: Observations on pumice using combined multi-scale 2D and 3D imaging

Hughes, Ery C.; Neave, David N.; Dobson, Katherine J.; Withers, Philip J.; Edmonds, Marie

doi:10.1016/j.jvolgeores.2017.02.020

How to fragment peralkaline rhyolites: Observations on pumice using combined multi-scale 2D and 3D imaging

Hughes, Ery C.; Neave, David N.; Dobson, Katherine J.; Withers, Philip J.; Edmonds, Marie

Authors

Ery C. Hughes

David N. Neave

Katherine J. Dobson

Philip J. Withers

Marie Edmonds

Abstract

Peralkaline rhyolites are volatile-rich magmas that typically erupt in continental rift settings. The high alkali and halogen content of these magmas results in viscosities two to three orders of magnitude lower than in calc-alkaline rhyolites. Unless extensive microlite crystallisation occurs, the calculated strain rates required for fragmentation are unrealistically high, yet peralkaline pumices from explosive eruptions of varying scales are commonly microlite-free. Here we present a combined 2D scanning electron microscopy and 3D X-ray microtomography study of peralkaline rhyolite vesicle textures designed to investigate fragmentation processes. Microlite-free peralkaline pumice textures from Pantelleria, Italy, strongly resemble those from calc-alkaline rhyolites on both macro and micro scales. These textures imply that the pumices fragmented in a brittle fashion and that their peralkaline chemistry had little direct effect on textural evolution during bubble nucleation and growth. We suggest that the observed pumice textures evolved in response to high decompression rates and that peralkaline rhyolite magmas can fragment when strain localisation and high bubble overpressures develop during rapid ascent.

Citation

Hughes, E. C., Neave, D. N., Dobson, K. J., Withers, P. J., & Edmonds, M. (2017). How to fragment peralkaline rhyolites: Observations on pumice using combined multi-scale 2D and 3D imaging. Journal of Volcanology and Geothermal Research, 336, 179-191. https://doi.org/10.1016/j.jvolgeores.2017.02.020

Journal Article Type	Article
Acceptance Date	Feb 27, 2017
Online Publication Date	Mar 1, 2017
Publication Date	Apr 15, 2017
Deposit Date	Feb 27, 2017
Publicly Available Date	Feb 27, 2017
Journal	Journal of Volcanology and Geothermal Research
Print ISSN	0377-0273
Publisher	Elsevier
Peer Reviewed	Peer Reviewed
Volume	336
Pages	179-191
DOI	https://doi.org/10.1016/j.jvolgeores.2017.02.020

Files

Accepted Journal Article (49.7 Mb)
PDF

Publisher Licence URL
http://creativecommons.org/licenses/by/4.0/

Copyright Statement
This article is available under the terms of the Creative Commons Attribution License (CC BY).
You may copy and distribute the article, create extracts, abstracts and new works from the article, alter and revise the article, text or data mine the article and otherwise reuse the article commercially (including reuse and/or resale of the article) without permission from Elsevier. You must give appropriate credit to the original work, together with a link to the formal publication through the relevant DOI and a link to the Creative Commons user license above. You must indicate if any changes are made but not in any way that suggests the licensor endorses you or your use of the work.