What is the viscosity model used in the rhyolite-MELTS 1.2.0

[zihanwei]

Hi,

I am currently using rhyolite-MELTS 1.2.0 and I noticed  that it can give the viscosity of the liquid phase in the result. However, I cannot find any information about what viscosity model it is based on in the papers about MELTS. Could you please tell me what the viscosity model is or where I can find it? Thanks a lot!

[Paula]

Hi,

It's Shaw 1972 (AJS November 1972 vol. 272 no. 9 870-893)
DOI: 10.2475/ajs.272.9.870

You're right it is not cited in Ghiorso and Sack 1995, though it has been included in the software for many years.

Paula

[ritabrata.dobe]

Hi,
I am new to MELTS and am trying to model viscosity variations in a 'wet' granitic magma. I am using the MS Excel based GUI for Rhyolite MELTS. I cannot find a tab in the results which shows the computed viscosity after equilibration. Could anyone tell me what I am doing wrong?
Regards,
Ritabrata

[Paula]

Hi Ritabrata,

You are right that viscosity is not in the output from MELTS for Excel. If you use one of the other GUI's (either the original rhyolite-MELTS or easyMelts) and then the "Combine tbl" function on the Tools tab in MELTS for Excel then viscosity will be the last column in the "liquid" tab of the output. You can get more information on these options at: https://magmasource.caltech.edu/alphamelts/links.php

As noted above, the viscosity model used in the GUI is rather old. The code for rhyolite-MELTS on the ENKI Portal has an option to use Giordano D, Russell JK, Dingwell DB (2008), Viscosity of magmatic liquids: A model. EPSL 271, 123-134. So far as I know the only way to access it, without compiling the code yourself, is via alphaMELTS for MATLAB/Python.

Paula

[ritabrata.dobe]

Thank you for the assistance!

[KevinFarries]

Hi,

In addition to Shaw's model, do you know what algorithm is used to allow for the effect of suspended crystals on the system viscosity?

Thanks,

Kevin

[Paula]

The equation used is Einstein-Roscoe form, with n=2 and φ_c=0.5 i.e:

η / η₀ = (1 - 2φ)^-2

[KevinFarries]

Thanks Paula, much appreciated!