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Long-term changes in explosive and effusive behaviour at andesitic arc volcanoes: Chronostratigraphy of the Centre Hills Volcano, Montserrat

Long-term changes in explosive and effusive behaviour at andesitic arc volcanoes: Chronostratigraphy of the Centre Hills Volcano, Montserrat
Long-term changes in explosive and effusive behaviour at andesitic arc volcanoes: Chronostratigraphy of the Centre Hills Volcano, Montserrat
Volcanism on Montserrat (Lesser Antilles arc) has migrated southwards since the formation of the Silver Hills ~ 2.5 Ma, and has formed three successively active volcanic centres. The Centre Hills volcano was the focus of volcanism from ~ 1–0.4 Ma, before activity commenced at the currently active Soufrière Hills volcano. The history of activity at these two volcanoes provides an opportunity to investigate the pattern of volcano behaviour on an andesitic arc island over the lifetime of individual volcanoes. Here, we describe the pyroclastic stratigraphy of subaerial exposures around central Montserrat; identifying 11 thick (> 1 m) pumiceous units derived from sustained explosive eruptions of Centre Hills from ~ 0.8–0.4 Ma. Over 10 other, less well- exposed pumiceous units have also been identified. The pumice-rich units are interbedded with andesite lava breccias derived from effusive, dome-forming eruptions of Centre Hills. The stratigraphy indicates that large (up to magnitude 5) explosive eruptions occurred throughout the history of Centre Hills, alongside effusive activity. This behaviour at Centre Hills contrasts with Soufrière Hills, where deposits from sustained explosive eruptions are much less common and restricted to early stages of activity at the volcano, from ~ 175–130 ka. Subsequent eruptions at Soufriere Hills have been dominated by andesitic effusive eruptions. The bulk composition, petrography and mineral chemistry of volcanic rocks from Centre Hills and Soufrière Hills are similar throughout the history of both volcanoes, except for occasional, transient departures to different magma compositions, which mark shifts in vent location or dominant eruption style. For example, the final recorded eruption of Centre Hills, before the initiation of activity at Soufrière Hills, was more silicic than any other identified eruption on Montserrat; and the basaltic South Soufrière Hills episode marked the transition to the current stage of predominantly effusive Soufrière Hills activity. The compositional stability observed throughout the history of Centre Hills and Soufrière Hills suggests that a predominance towards effusive or explosive eruption styles is not driven by major compositional shifts of magma, but may reflect local changes in long-term magma storage conditions that characterise individual episodes (on 105 year timescales) of volcanism on Montserrat.
0377-0273
15-35
Coussens, Maya
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Cassidy, Michael
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Watt, Sebastian F.L.
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Jutzeler, Martin
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Talling, Peter J.
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Barford, Dan
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Gernon, Thomas
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Taylor, Rex
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Hatter, Stuart J.
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Palmer, Martin R.
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Coussens, Maya
761d9bfc-bb42-4362-b5cd-91cbc85b53a5
Cassidy, Michael
fc0e9729-9c71-477d-a4e3-39698155e6fc
Watt, Sebastian F.L.
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Jutzeler, Martin
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Talling, Peter J.
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Barford, Dan
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Gernon, Thomas
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Taylor, Rex
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Hatter, Stuart J.
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Palmer, Martin R.
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Coussens, Maya, Cassidy, Michael, Watt, Sebastian F.L., Jutzeler, Martin, Talling, Peter J., Barford, Dan, Gernon, Thomas, Taylor, Rex, Hatter, Stuart J. and Palmer, Martin R. (2017) Long-term changes in explosive and effusive behaviour at andesitic arc volcanoes: Chronostratigraphy of the Centre Hills Volcano, Montserrat. Journal of Volcanology and Geothermal Research, 333-334, 15-35. (doi:10.1016/j.jvolgeores.2017.01.003).

Record type: Article

Abstract

Volcanism on Montserrat (Lesser Antilles arc) has migrated southwards since the formation of the Silver Hills ~ 2.5 Ma, and has formed three successively active volcanic centres. The Centre Hills volcano was the focus of volcanism from ~ 1–0.4 Ma, before activity commenced at the currently active Soufrière Hills volcano. The history of activity at these two volcanoes provides an opportunity to investigate the pattern of volcano behaviour on an andesitic arc island over the lifetime of individual volcanoes. Here, we describe the pyroclastic stratigraphy of subaerial exposures around central Montserrat; identifying 11 thick (> 1 m) pumiceous units derived from sustained explosive eruptions of Centre Hills from ~ 0.8–0.4 Ma. Over 10 other, less well- exposed pumiceous units have also been identified. The pumice-rich units are interbedded with andesite lava breccias derived from effusive, dome-forming eruptions of Centre Hills. The stratigraphy indicates that large (up to magnitude 5) explosive eruptions occurred throughout the history of Centre Hills, alongside effusive activity. This behaviour at Centre Hills contrasts with Soufrière Hills, where deposits from sustained explosive eruptions are much less common and restricted to early stages of activity at the volcano, from ~ 175–130 ka. Subsequent eruptions at Soufriere Hills have been dominated by andesitic effusive eruptions. The bulk composition, petrography and mineral chemistry of volcanic rocks from Centre Hills and Soufrière Hills are similar throughout the history of both volcanoes, except for occasional, transient departures to different magma compositions, which mark shifts in vent location or dominant eruption style. For example, the final recorded eruption of Centre Hills, before the initiation of activity at Soufrière Hills, was more silicic than any other identified eruption on Montserrat; and the basaltic South Soufrière Hills episode marked the transition to the current stage of predominantly effusive Soufrière Hills activity. The compositional stability observed throughout the history of Centre Hills and Soufrière Hills suggests that a predominance towards effusive or explosive eruption styles is not driven by major compositional shifts of magma, but may reflect local changes in long-term magma storage conditions that characterise individual episodes (on 105 year timescales) of volcanism on Montserrat.

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Accepted/In Press date: 2 January 2017
e-pub ahead of print date: 5 January 2017
Published date: 15 March 2017
Organisations: Geochemistry, Geology & Geophysics, Ocean and Earth Science, Marine Geoscience, National Oceanography Centre

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Local EPrints ID: 406602
URI: http://eprints.soton.ac.uk/id/eprint/406602
ISSN: 0377-0273
PURE UUID: 8776bc13-27c2-4d3f-9105-8ae92b973db2
ORCID for Thomas Gernon: ORCID iD orcid.org/0000-0002-7717-2092
ORCID for Rex Taylor: ORCID iD orcid.org/0000-0002-9367-0294
ORCID for Stuart J. Hatter: ORCID iD orcid.org/0000-0003-0760-5275

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Date deposited: 18 Mar 2017 02:23
Last modified: 28 Apr 2022 04:06

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Contributors

Author: Maya Coussens
Author: Michael Cassidy
Author: Sebastian F.L. Watt
Author: Martin Jutzeler
Author: Peter J. Talling
Author: Dan Barford
Author: Thomas Gernon ORCID iD
Author: Rex Taylor ORCID iD
Author: Stuart J. Hatter ORCID iD

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