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Instantaneous fractional melt compositions

Started by nickdygert, December 21, 2015, 04:52:05 PM

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nickdygert

Hi,

I'm trying to calculate the major and trace element composition of an instantaneous near-fractional melt. I have successfully calculated partial melting of a Workman-Hart DMM along an adiabat (using alphamelts v1.2, at a potential temp of 1300deg).

Looking at the melt composition in Trace_main_tbl and Liquid_comp_tbl, I see the incompatible element concentrations of the liquid never reach the very low values they ought to, leading me to believe these outputs are the aggregated melt composition. Where can I see the instantaneous melt composition? Is there a switch I need to turn on, or am I just looking in the wrong place?

Thanks,

Nick

Paula

Hi Nick,

The values in Trace_main_tbl.txt and Liquid_comp.txt should be the instantaneous ones, if ALPHAMELTS_CONTINUOUS_MELTING is set. You can tell by looking at the mass column in either file.

There was a typo in the alphamelts_default_env.txt included with alphaMELTS 1.2 - it had ALPHAMELTS_CONTINUOUS instead of ALPHAMELTS_CONTINUOUS_MELTING. The variable had originally been ADIABAT_CONTINUOUS but was renamed as part of the Adiabat_1ph 3.0 rewrite and a warning added to run_adiabat.command. The same warning was not included in run_alphamelts.command but the typo was fixed a few days after alphaMELTS 1.2 was released.

So, have a look at your settings file. It would be a good idea to update to a later version of alphaMELTS too as there have been a few bug fixes over the years. Also, if you are still not quite getting the compositions you expect then check the partition coefficients - the default values are from compilations by McKenzie & O'Nions. You might have better success with something more recent (e.g. another user who had a similar problem a while back solved it by using values from Gibson & Geist, 2010 instead).

Cheers,
Paula

nickdygert

Hi Paula,

Thanks for your message and sorry for the slow-motion response. I downloaded v1.5 and successfully did a near-fractional run! The issue appears to have been turning on both:

ALPHAMELTS_MINF                 0.005
and
ALPHAMELTS_CONTINUOUS_RATIO     0.01

I turned off ALPHAMELTS_CONTINUOUS_RATIO. Now the liquid phase mass hovers near 0.5 and the incompatible trace elements go to 0 in both the liquid and residual solid.

I also had to rename "alphamelts_win64" to "alphamelts" to get run_alphamelts.command to work .

Nick

Paula

Hi Nick,

Glad you found the problem. Yes, ALPHAMELTS_CONTINUOUS_RATIO will override ALPHAMELTS_MINF.

Quote from: nickdygert on January 06, 2016, 02:44:45 PM
I also had to rename "alphamelts_win64" to "alphamelts" to get run_alphamelts.command to work .

Did you run the install script? It should have done the renaming for you.

Paula