Publication Date:
2020-12-14
Description:
Magmas in volcanic conduits commonly contain microlites in association with preexisting phenocrysts,
as often indicated by volcanic rock textures. In this study, we present two different experiments that investigate
the flow behavior of these bidisperse systems. In the first experiments, rotational rheometric methods
are used to determine the rheology of monodisperse and polydisperse suspensions consisting of smaller,
prolate particles (microlites) and larger, equant particles (phenocrysts) in a bubble‐free Newtonian liquid
(silicate melt). Our data show that increasing the relative proportion of prolate microlites to equant phenocrysts
in a magma at constant total particle content can increase the relative viscosity by up to three orders
of magnitude. Consequently, the rheological effect of particles in magmas cannot be modeled by assuming
a monodisperse population of particles. We propose a new model that uses interpolated parameters based
on the relative proportions of small and large particles and produces a considerably improved fit to the data
than earlier models. In a second series of experiments we investigate the textures produced by shearing
bimodal suspensions in gradually solidifying epoxy resin in a concentric cylinder setup. The resulting
textures show the prolate particles are aligned with the flow lines and spherical particles are found in
well‐organized strings, with sphere‐depleted shear bands in high‐shear regions. These observations may
explain the measured variation in the shear thinning and yield stress behavior with increasing solid fraction
and particle aspect ratio. The implications for magma flow are discussed, and rheological results and textural
observations are compared with observations on natural samples.
Description:
Published
Description:
Q07024
Description:
3.6. Fisica del vulcanismo
Description:
JCR Journal
Description:
restricted
Keywords:
analog experiments
;
crystal bearing
;
polydisperse suspensions
;
rheology
;
04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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