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The nature and formation of cristobalite at the Soufrière Hills volcano, Montserrat: implications for the petrology and stability of silicic lava domes

Horwell, C.J.; Williamson, B.J.; Llewellin, E.W.; Damby, D.E.; Le Blond, J.S.

The nature and formation of cristobalite at the Soufrière Hills volcano, Montserrat: implications for the petrology and stability of silicic lava domes Thumbnail


Authors

B.J. Williamson

D.E. Damby

J.S. Le Blond



Abstract

Cristobalite is commonly found in the dome lava of silicic volcanoes but is not a primary magmatic phase; its presence indicates that the composition and micro-structure of dome lavas evolve during, and after, emplacement. Nine temporally and mineralogically diverse dome samples from the Soufrière Hills volcano (SHV), Montserrat, are analysed to provide the first detailed assessment of the nature and mode of cristobalite formation in a volcanic dome. The dome rocks contain up to 11 wt.% cristobalite, as defined by X-ray diffraction. Prismatic and platy forms of cristobalite, identified by scanning electron microscopy (SEM), are commonly found in pores and fractures, suggesting that they have precipitated from a vapour phase. Feathery crystallites and micro-crystals of cristobalite and quartz associated with volcanic glass, identified using SEM-Raman, are interpreted to have formed by varying amounts of devitrification. We discuss mechanisms of silica transport and cristobalite formation, and their implications for petrological interpretations and dome stability. We conclude: (1) that silica may be transported in the vapour phase locally, or from one part of the magmatic system to another; (2) that the potential for transport of silica into the dome should not be neglected in petrological and geochemical studies because the addition of non-magmatic phases may affect whole rock composition; and (3) that the extent of cristobalite mineralisation in the dome at SHV is sufficient to reduce porosity—hence, permeability—and may impact on the mechanical strength of the dome rock, thereby potentially affecting dome stability.

Citation

Horwell, C., Williamson, B., Llewellin, E., Damby, D., & Le Blond, J. (2013). The nature and formation of cristobalite at the Soufrière Hills volcano, Montserrat: implications for the petrology and stability of silicic lava domes. Bulletin of Volcanology, 75, Article 696. https://doi.org/10.1007/s00445-013-0696-3

Journal Article Type Article
Acceptance Date Jan 31, 2013
Online Publication Date Feb 21, 2013
Publication Date 2013
Deposit Date Apr 23, 2012
Publicly Available Date Jul 11, 2013
Journal Bulletin of Volcanology
Print ISSN 0258-8900
Electronic ISSN 1432-0819
Publisher Springer
Peer Reviewed Peer Reviewed
Volume 75
Article Number 696
DOI https://doi.org/10.1007/s00445-013-0696-3
Keywords Cristobalite, Quartz, Soufrière Hills, Montserrat, Lava dome, Vapour-phase silica.

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

Copyright Statement
© The Author(s) 2013. This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.







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