Influence of alteration on the mechanical behaviour and failure mode of andesite: implications for shallow seismicity and volcano monitoring

Volcanoes often host hydrothermal systems that alter the host rock. To understand the influence of alteration on mechanical behaviour of edifice-forming rock, we performed a series of triaxial deformation experiments on variably altered andesite from Mt. Ruapehu (New Zealand) under constant effectiv...

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Bibliographic Details
Published in:Bulletin of volcanology 2019-08, Vol.81 (8), p.1-12, Article 44
Main Authors: Mordensky, S. P., Heap, M. J., Kennedy, B. M., Gilg, H. A., Villeneuve, M. C., Farquharson, J. I., Gravley, D. M.
Format: Article
Language:English
Subjects:
Andesite
Clay
Deformation
Earth and Environmental Science
Earth Sciences
Fluid flow
Fractures
Geology
Geophysics
Geophysics/Geodesy
Mineralogy
Porosity
Research Article
Rocks
Sciences of the Universe
Sedimentology
Seismicity
Volcano monitoring
Volcanoes
Volcanology
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Summary:Volcanoes often host hydrothermal systems that alter the host rock. To understand the influence of alteration on mechanical behaviour of edifice-forming rock, we performed a series of triaxial deformation experiments on variably altered andesite from Mt. Ruapehu (New Zealand) under constant effective pressure. Under the imposed conditions, andesite with intermediate argillic alteration deforms in a brittle manner forming fractures. By contrast, andesite with advanced argillic alteration deforms in a ductile manner, with sample failure driven by distributed cataclastic pore collapse. We consider this the result of an increase in porosity and clay content with increasing alteration. Ancillary experiments highlight that the brittle-ductile transition occurs at lower effective pressure (i.e. at shallower depths) in andesites with advanced argillic alteration relative to unaltered andesites of comparable porosity. We conclude that advanced argillic alteration can create an anomalous shallow ductile zone, which has important implications for fluid flow and pre-eruptive seismicity.
ISSN:0258-8900
1432-0819
DOI:10.1007/s00445-019-1306-9