Accessibility navigation

Rheology of magmas with bimodal crystal size and shape distributions: insights from analog experiments

Cimarelli, C., Costa, A., Mueller, S. and Mader, H. M. (2011) Rheology of magmas with bimodal crystal size and shape distributions: insights from analog experiments. Geochemistry, Geophysics, Geosystems, 12 (7). Q07024. ISSN 1525-2027

Text - Published Version
· Please see our End User Agreement before downloading.


It is advisable to refer to the publisher's version if you intend to cite from this work. See Guidance on citing.

To link to this item DOI: 10.1029/2011GC003606


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 inves- tigate 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 pheno- crysts 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 tex- tural observations are compared with observations on natural samples.

Item Type:Article
Divisions:Science > School of Mathematical, Physical and Computational Sciences > Environmental Systems Science Centre
ID Code:23405
Publisher:AGU and Geochemical Society


Downloads per month over past year

University Staff: Request a correction | Centaur Editors: Update this record

Page navigation