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Isentropic melting

Started by cjmanning81, April 23, 2013, 06:17:36 AM

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cjmanning81

Hi

I am trying to run isentropic fractional melting models, using a DMM composition.  I can calculate the entropy for a specific mantle potential temperature using the method outlined in an old version of the manual by suppressing liquid and setting my T to be equal to my desired Tp and P =1bar.  I input the calculated entropy as the initial entropy using option 7, turn liquid back on and execute using 4.  It runs fine but when I open the output files the entropy changes through the run quite significantly (276-135; 30000kbr-1kbar).  Am I wrong in expecting the entropy to be more constant than this?  I am sure it must be something that I am missing.

Thanks
Christina

Paula

#1
Hi Christina,

The melting step is isentropic but when melt is extracted the entropy of that melt is subtracted from the system total. So the reference entropy decreases as melting proceeds, but so does the total mass. If you look in Phase_main_tbl.txt there will be a table for liquid that includes the entropy of each melt increment, as well as its composition. If you have ALPHAMELTS_IMPOSE_FO2 set there will also be a small variation in the entropy of the solids, which is the entropy associated with oxygen entering or leaving the system.

Cheers,
Paula

cjmanning81

Hi Paula

Many thanks for your help, much appreciated.

Christina