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Many thanks Paula!

Hi,

I am trying to understand/confirm how rhyolite-Melts calculates liquid, mineral and system density but have not been able to build up a complete picture from the details given in the literature and have not be able to obtain a copy of Lange and Carmichael (1990).

If I follow correctly the density each oxide component of the liquid is calculated based on the EOS: V = a + b(T-Tr) + c(P-Pr) + D(T-Tr)(P-Pr) + e(P-Pr)^2.  This gives the molar volume which can be divided by the molar weight to get the density of each component, which can then be combined based on the mass percentage to get the liquid density.

Are the mineral densities calculated in the same way? Or are they determined based on a reference density and the co-efficient of thermal expansion?

Thanks in advance for any help!

Thanks Paula, much appreciated!

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

Hi Paula,

I was previously using the rhyolite-Melts GUI and have switched across to easyMelts.  In rhyolite-Melts if the algorithm fails to converge, it is possible to tweak some of the parameters then continue with the analysis.  Is there a way to do this with easyMelts?  If the there is a convergence failure, the "equilibrate" button disappears and I can't see a way to continue the calculation.

Thanks!

Kevin

That is fantastic!  Thanks so much Paula.  I will check out easyMelts and implement your suggestions.

Cheers,

Kevin

Hi,
Apologies in advance, I am new to both the MELTS programs and to petrology/mineralogy. 

I am running the rhyolite-Melts GUI as part of an investigation into the viability of melting lunar regolith to make construction materials.  I am running experiments in the lab using lunar regolith simulants which I will use in conjunction with the rhyolite-METLS GUI to determine the thermo-physical properties of the regolith melt which I will feed into a computational fluid dynamics model of the casting process. 

Lunar material is generally either basaltic (for lowland areas) or anorthositic. It has a low silica content (40-50%). Typical composition is as below:

Sample  SiO2  Al2O3  FeO    CaO    MgO      TiO    Na2O    K20      SiO2
LMS_1  46.9%  12%    8.6%  7.0%  16.8%  3.6%  1.7%    0.7%  46.9%


Most of the casting experiments will be in air, though I will need to extend the results of the CFD model to casting in a vacuum. 

For each rhyolite-MELTS analysis, I first enter the chemical composition of the material and calculate the liquidous temperature for a given oxygen fugacity and run down to just below solidus before running back up to above liquidous. Typical variation of mineral content with temperature is as the graphs below (apologies if these do not show up I am struggling to see how to attach images).





I have a few questions about how to best model the processes using rhyolite melts:

1.    When running the analysis the quadratic minimization algorithm quite often fails to converge.  To overcome this issue I either: change the oxygen fugacity for a small increment before changing back; skip over the problem temperature (by changing the starting temperature); or if the issue occurs below solidus, then I adopt a minimum temperature higher than the problem temperature. Are these approaches valid?  On-line it suggests making a minor change to composition, but I am unsure of what element's composition I should change or by how much.

2.    I get a higher solidus for heating compared to cooling. On heating, quite often the solidus temperature is problematic for quadratic convergence, and the solidus temperature I obtain is quite sensitive to the approach I take to overcoming this issue. Can I clarify what aspect melts-rhyolite algorithm and its calibration give rise to this asymmetry in the solidus temperature for cooling and heating and the best approach to accurately predict the solidus temperature.
 
3.    The data I have on the regolith precursor will always give total Fe either as FeO or Fe2O3 equivalent, so I need to impose a buffer to determine the initial proportions of FeO and Fe2O3.  I am currently running analyses with a range of buffers, but comparing my experimental results to the rhyolite-Melts output I a tending towards QFM for the process in atmosphere, and Fe-FeO to model the process in vacuum. Are these values reasonable?  I notice that rhyolite-Melts will automatically remove the buffer if the algorithm encounters convergence problems. Should I maintain the buffer throughout the analysis (from liquidous through to solidus and back) or is it more appropriate to set a buffer to determine the composition at the liquidous temperature and the to remove the buffer thereafter?

4.    In the original formulation of MELTS and rhyolite-MELTS it appeared from the referenced papers that sub-solidus calibration data was limited. As a result, I am terminating the analyses at around 900 degrees C.  However, I think I read somewhere that additional sub-solidus datapoint were later added. Can you provide any advice on the temperature range for which the rhyolite-MELTS model as implemented by the GUI has been calibrated?

Thanks in advance for any advice you are able to give.