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equilibrium melting

Started by malidejo, February 08, 2013, 07:54:16 AM

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malidejo

Hello Paula,
I have been trying to make  equilibrium melting calculations from cumulate dunites to see whether I can produce meaningful estimates of their parental magmas. To simplify things, I am assuming that the melting is occurring isobarically. The calculation seems to work when I run it in MELTS, but when run in alphaMELTS I don't get the result that I am after. Following the initial step that is essentially all solid (olivine +cpx), a increase in T of +1 C leads to 99.9 % of the system's mass to be lost (i.e. new mass is 0.90), and F ~ 0.96 indicating that the melting is fractional. In the _env.txt file the line
"!ALPHAMELTS_CONTINUOUS true" is commented out. Can you suggest what I am doing wrong?
Thanks
Dejan

Paula

#1
Hi Dejan,

There was a mistake in the published default settings_file. The ALPHAMELTS_CONTINUOUS variable was renamed a while back to ALPHAMELTS_CONTINUOUS_MELTING to avoid confusion. Unfortunately, I forgot to update the name in alphamelts_default_env.txt. It's odd though as that should cause the opposite problem i.e. melting is always equilibrium rather than always fractional. Is is possible that ALPHAMELTS_CONTINUOUS_MELTING or ALPHAMELTS_FRACTIONATE_SOLIDS is on? If not, please post the full _env.txt file and I'll see if I can spot anything.

Cheers,
Paula

malidejo

Hi Paula,
I believe that neither ALPHAMELTS_CONTINUOUS_MELTING or ALPHAMELTS_FRACTIONATE_SOLIDS are on (both are commented out by !) Here is my _env.txt file:


!Default values of environment variables
!Variables preceded by '!' are 'unset' (i.e. 'false')

ALPHAMELTS_VERSION MELTS
!ALPHAMELTS_OLD_GARNET true
!ALPHAMELTS_OLD_SPINEL true
!ALPHAMELTS_OLD_BIOTITE true
!ALPHAMELTS_2_AMPH true
ALPHAMELTS_MODE isobaric
!ALPHAMELTS_PTPATH_FILE filename
!ALPHAMELTS_DELTAP +1000
ALPHAMELTS_DELTAT +1
!ALPHAMELTS_MAXP +5000
!ALPHAMELTS_MINP +5000
ALPHAMELTS_MAXT +2000
ALPHAMELTS_MINT +1200
!ALPHAMELTS_ALTERNATIVE_FO2 true
!ALPHAMELTS_LIQUID_FO2 true
!ALPHAMELTS_IMPOSE_FO2 true
!ALPHAMELTS_FO2_PRESSURE_TERM true
!ALPHAMELTS_METASTABLE_ISOGRAD true
!ALPHAMELTS_CONTINUOUS true
!ALPHAMELTS_MINF 0.005
!ALPHAMELTS_MINPHI 0.002
!ALPHAMELTS_CONTINUOUS_RATIO float
!ALPHAMELTS_CONTINUOUS_VOLUME true
!ALPHAMELTS_FRACTIONATE_SOLIDS true
!ALPHAMELTS_MASSIN  0.1
!ALPHAMELTS_FRACTIONATE_WATER true
!ALPHAMELTS_MINW float
!ALPHAMELTS_FRACTIONATE_TARGET true
!ALPHAMELTS_MGO_TARGET 8.0
!ALPHAMELTS_MGNUMBER_TARGET float
!ALPHAMELTS_ASSIMILATE true
!ALPHAMELTS_FLUX_MELTING true
!ALPHAMELTS_DRY_ITER_PATIENCE 100
!ALPHAMELTS_DO_TRACE true
!ALPHAMELTS_DO_TRACE_H2O true
!ALPHAMELTS_HK_OL_TRACE_H2O true
!ALPHAMELTS_HK_PXGT_TRACE_H2O true
!ALPHAMELTS_2X_OPX_TRACE_H2O true
!ALPHAMELTS_TRACE_DEFAULT_DPTX true
!ALPHAMELTS_TRACE_NORMALIZATION integer
!ALPHAMELTS_TRACE_INPUT_FILE filename
!ALPHAMELTS_TRACE_USELIQFEMG true
!ALPHAMELTS_MULTIPLE_LIQUIDS true
!ALPHAMELTS_FRACTIONATE_SECOND_LIQUID true
!ALPHAMELTS_FOCUS true
!ALPHAMELTS_FOCUS_FACTOR float
!ALPHAMELTS_V20_BIN_FILE true
ALPHAMELTS_CELSIUS_OUTPUT true
!ALPHAMELTS_SAVE_ALL true
ALPHAMELTS_SKIP_FAILURE true
ALPHAMELTS_INTEGRATE_FILE outmelts.txt

Thanks,
dejan

Paula

Nothing stands out. Is there anything in outmelts.txt afterwards (might indicate whether the problem is that alphaMELTS thinks melting is continuous or something else)? Otherwise, please post or send the melts file and output and I'll see if I can reproduce what you are getting.

Cheers,
Paula

malidejo

Hi Paula,
I figured out the problem. I had a fractionate olivine line in my .melts file that I forgot to comment out.
Sorry about that

Paula

No worries. Glad you found the problem and thanks for letting me know.

Paula