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

Hughes, Ery C. and Neave, David A. and Dobson, Katherine J. and Withers, Philip J. and Edmonds, Marie (2017) How to fragment peralkaline rhyolites: Observations on pumice using combined multi-scale 2D and 3D imaging. Journal of Volcanology and Geothermal Research. ISSN 03770273 DOI 10.1016/j.jvolgeores.2017.02.020 (In Press)

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Official URL: http://doi.org/10.1016/j.jvolgeores.2017.02.020

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.

Item Type: Article
Uncontrolled Keywords: 2016AREP; IA72;
Subjects: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
06 - Part-III Projects
Divisions: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
06 - Part-III Projects
08 - Green Open Access
Journal or Publication Title: Journal of Volcanology and Geothermal Research
Identification Number: 10.1016/j.jvolgeores.2017.02.020
Depositing User: Sarah Humbert
Date Deposited: 03 Mar 2017 11:53
Last Modified: 07 Mar 2017 11:43
URI: http://eprints.esc.cam.ac.uk/id/eprint/3836

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