Please use this identifier to cite or link to this item: http://hdl.handle.net/2122/7599
AuthorsCimarelli, C.* 
Costa, A.* 
Mueller, S.* 
Mader, H. M.* 
TitleRheology of magmas with bimodal crystal size and shape distributions: Insights from analog experiments
Issue Date28-Jul-2011
Series/Report no.7/12(2011)
DOI10.1029/2011GC003606
URIhttp://hdl.handle.net/2122/7599
Keywordsanalog experiments
crystal bearing
polydisperse suspensions
rheology
Subject Classification04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous 
AbstractMagmas 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.
Appears in Collections:Papers Published / Papers in press

Files in This Item:
File Description SizeFormat 
cimcos2011.pdfMain article2.25 MBAdobe PDFView/Open    Request a copy
Show full item record

Page view(s)

107
checked on May 23, 2017

Download(s)

19
checked on May 23, 2017

Google ScholarTM

Check

Altmetric