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Hey All, Paula & Paul!
I'm trying to model some melting of peridotites and pyroxenites using pMELTS under the influence of a CO₂ controlled environment (and much less H₂O one, as inferred from melt inclusions volatile analysis).

The system seems to be running quite stable with results that meet the collected data (!), but only when I sum up CO₂ & H₂O to be at least 1000 ppm (input as 0.1 wt.% major oxide to influence melting conditions, for example CO₂= 0.08 ; H₂O= 0.02 or any other combination), which is more than my current estimations for the mantle volatile values (CO₂~400 ppm, H₂O~20 ppm).
Also, although I am more interested in the trace elements results, the liquid composition of the major oxides seems to be going really crazy. This is especially true if CO₂ is modeled to be the only volatile species present, which makes me doubt the validity of the results.

I would really appreciate if you could share some of your knowledge on how to approach these kind of calculations, and to maybe provide some key notes for validation of the outputs.

--At the moment I'm running the UBUNTU alphaMELTS 1.9 version.
Melting at 30-40 kb, continuous melting with 0.02 minF, isobaric for the moment. No exsolution of water or multiple liquids.--

Cheers,
Haran.

[file used:]

Hi Paula/Paul,
I have a chemical analysis of Spinel-Hertzburgite Xenolite which i would like to partial-melt at ~9 Kbar and approx. 1200 c  , to see which % melting could be my parental melt for the field assemblage.
the P/T was determined previously using melt inclusions.
The problem:
at those conditions, if i just enter the *.melts file and using the manu "option 3" the program gives a ~3.5% melt which is ultra-low on silica(22%).
I would expect to form at least 40% silica in a 3.5% partial melt liquid or even higher than that, without getting to 20+% partial melting which is unreasonable for me.

file used:
Title:Xenolite smp. BH-16-G Hertzburgite
Initial Composition: SiO2 44.06
Initial Composition: TiO2 0.055
Initial Composition: Al2O3 1.15
Initial Composition: Fe2O3 1.49
Initial Composition: FeO 9.18
Initial Composition: MnO 0.165
Initial Composition: MgO 42.72
Initial Composition: CaO 1.48
Initial Composition: Na2O 0.19
Initial Composition: K2O 0.04
Initial Composition: P2O5 0.03
Initial Temperature: 1200.00
Initial Pressure: 9000.00
Log fO2 Path: none

and the results:
Initial alphaMELTS calculation at: P 9000.000000, T 1200.000000
liquid: 3.410 g 22.07 0.28 0.40 33.31 35.82 0.01 4.19 0.22 3.63 0.01 0.06
Activity of H2O = 0  Melt fraction = 0.0339143
olivine: 70.503555 g, composition (Ca0.00Mg0.90Fe''0.10Mn0.00Co0.00Ni0.00)2SiO4
orthopyroxene: 21.148919 g, composition opx Na0.01Ca0.05Fe''0.17Mg1.68Fe'''0.03Ti0.00Al0.15Si1.91O6
clinopyroxene: 5.241394 g, composition cpx Na0.06Ca0.72Fe''0.10Mg0.93Fe'''0.06Ti0.01Al0.26Si1.86O6
leucite: 0.194745 g, composition K0.94Na0.06AlSi2O6.00(OH)0.00
whitlockite: 0.061 g, composition Ca3(PO4)2


AM i doing it right? or is it another way of approaching this kind of calculation?
thank you,
Haran.

Hi Fede,
I think i had the same problem running multiple liquids.
the solution was in the files format.
try to name your files 1.tar.melts  2.tar.melts etc.
and then use the wildcard in the input line : ?.tar.melts

it worked for me with 4 liquid compositions.