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Viscosity measurements of crystallizing andesite from <scp>T</scp> ungurahua volcano ( <scp>E</scp> cuador)
- Source :
- Geochemistry, Geophysics, Geosystems : G(3)
- Publication Year :
- 2015
- Publisher :
- American Geophysical Union (AGU), 2015.
-
Abstract
- Viscosity has been determined during isothermal crystallization of an andesite from Tungurahua volcano (Ecuador). Viscosity was continuously recorded using the concentric cylinder method and employing a Pt‐sheathed alumina spindle at 1 bar and from 1400°C to subliquidus temperatures to track rheological changes during crystallization. The disposable spindle was not extracted from the sample but rather left in the sample during quenching thus preserving an undisturbed textural configuration of the crystals. The inspection of products quenched during the crystallization process reveals evidence for heterogeneous crystal nucleation at the spindle and near the crucible wall, as well as crystal alignment in the flow field. At the end of the crystallization, defined when viscosity is constant, plagioclase is homogeneously distributed throughout the crucible (with the single exception of experiment performed at the lowest temperature). In this experiments, the crystallization kinetics appear to be strongly affected by the stirring conditions of the viscosity determinations. A TTT (Time‐Temperature‐Transformation) diagram illustrating the crystallization “nose” for this andesite under stirring conditions and at ambient pressure has been constructed. We further note that at a given crystal content and distribution, the high aspect ratio of the acicular plagioclase yields a shear‐thinning rheology at crystal contents as low as 13 vol %, and that the relative viscosity is higher than predicted from existing viscosity models. These viscosity experiments hold the potential for delivering insights into the relative influences of the cooling path, undercooling, and deformation on crystallization kinetics and resultant crystal morphologies, as well as their impact on magmatic viscosity.<br />Key Points: Viscosity determination at subliquidus temperatures of an andesitic sampleUse of disposable Pt‐sheathed alumina spindlesDescription of viscosity and crystallization kinetics under constant stirring
- Subjects :
- Relative viscosity
Volcanology
Physics::Optics
Thermodynamics
Mineralogy
Lava Rheology and Morphology
law.invention
Physics::Fluid Dynamics
Crystal
Viscosity
Rheology
Geochemistry and Petrology
law
Condensed Matter::Superconductivity
Instruments and Techniques
crystallization kinetics
concentric cylinder
Crystallization
Supercooling
Experimental Volcanism
Research Articles
Mineralogy and Petrology
Acicular
Physics and Chemistry of Magma Bodies
andesite
magma
Geochemistry
Geophysics
Temperature dependence of liquid viscosity
viscosity
Cryosphere
Geology
Research Article
Subjects
Details
- ISSN :
- 15252027
- Volume :
- 16
- Database :
- OpenAIRE
- Journal :
- Geochemistry, Geophysics, Geosystems
- Accession number :
- edsair.doi.dedup.....8dafcd039d9fb0bcf22ac8131df0fbf2