Isentropic Melting Initial Temp Problem

[Mauro]

Hi, it appears that adiabat picks a different temperature than the one I input into the program.  I use the following to run it on my terminal

run_adiabat.pl -p RunFolder -f adiabat_DRY_env.dat -b batch_DRY_sequence.dat

with

(1) input

Title: DMM of Workmann & Hart 2005
Initial Composition: SiO2 44.71
Initial Composition: TiO2 0.13
Initial Composition: Al2O3 3.98
Initial Composition: Fe2O3 0.191
Initial Composition: FeO 8.008
Initial Composition: MgO 38.73
Initial Composition: CaO 3.17
Initial Composition: Na2O 0.28

(2) env

ADIABAT_VERSION       pMELTS

ADIABAT_MODE          isentropic

ADIABAT_DELTAP -100
ADIABAT_MAXP +40000         !!! pMELTS is valid from < 4 GPa
ADIABAT_MINP +6000

ADIABAT_CONTINUOUS  true
ADIABAT_MINPHI 0.01

ADIABAT_CELSIUS_OUTPUT true

Initial Temperature: 1380
Initial Pressure: 40000
Log fO2 Path: NONE
Initial entropy: 258.0

Melts Filename: input_DRY_file.melts
Output Filename: Output_DRY.out

(3) batch commands

1
input_DRY_file.melts
4
0
olivine
orthopyroxene
clinopyroxene
spinel
garnet
x
11
Output_DRY.out
0

and even though the program reads my temperature correctly "Norm calculated initial guess at: P 40000.000000, T 1653.150000"...which is 1380°C, the output temperature is

1485.85 °C

in the Liq_tbl file.

I tried dozens of different settings and I always find the same problem.  It appears that adiabat "chooses for me" an initial temperature that is "close" to the one I give.  Does anyone know why?

Thanks again!

Mauro.

[Paula]

Hi Mauro,

I think the problem is the 'Initial entropy: 258.0' line in your commands_file, which is then being added by the Perl script to your melts_file.  You can double check whether this is the case by seeing what the entropy reported in Liq_tbl.txt is (258.0?).  If you delete or comment out the Initial 'entropy:' line then make sure to do so in the melts_file also as it will have been modified.  In more detail:

If a user chooses to do a single option 3 calculation initially, rather than going straight to option 4, then the isentropic mode is temporarily turned off and the input temperature is used.  Once option 4 is called and the program has obtained a starting solution (in your case that is the norm calculation but it could, for example, be the result of a previous call to option 3) then the isentropic mode is turned back on.  If you have not previously set a reference entropy then the current entropy is used, which corresponds to the input temperature.  However, if the reference entropy was set previously, either by an 'Initial entropy:' line in the melts file or by using option 7 at the menu then that entropy will be used once isentropic mdoe is switched back on.  In this case temperature becomes the dependent variable and will be adjusted so that the reference entropy is matched.

The same is true for isenthalpic and isochoric modes except that reference values for these can only be set at the menu and in the latter case it is pressure rather than temperature that becomes the dependent variable on execution (i.e. option 4).  As an aside, I just noticed that I forgot to include the ADIABAT_CELSIUS_OUTPUT environment variable in the norm calculation routine so I'll fix that in the next update.

Hope that works,
Paula

[Mauro]

Dear Paula,

Thank you for the tip.  Yes that worked perfectly!

Best,

Mauro.