Peridotites melting and volatile influence

[HaranHennig]

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.

[Paula]

The pMELTS model doesn't include CO2 so the results are undetermined. We've been trying to develop a pMELTS+CO2 model. There were a couple of AGU abstracts a few years back (before Covid) but it's been difficult to do much on it recently.

The only models that have CO2 are Rhyolite-MELTS 1.1.0 and 1.2.0. Neither of those is in alphaMELTS 1.9. The trace elements are not in the newer alphaMELTS (https://github.com/magmasource/alphaMELTS) so you'd need to post-process them.

Sorry not to be of more help.
Paula