Recent posts

#51

The MELTS family of algorithms, and scientific discussion / setting oxygen fugacity for mo...

Last post by Melina - May 21, 2024, 05:49:04 AM

Hello everyone,

I have been trying to model the LLD for the volcanic system that I'm studying. I've been using the "MELTS v1.0.2 fractionation" Jupyter notebook on the ENKI portal sever for this and ran into a problem. I can't figure out how to change/set the oxygen fugacity? Can anyone give me a hint?

Also, I have excluded the phase sanidine from my calculations, but it is still included in my outputs? It doesn't happen with any other phase that I have excluded. Is there another way to exclude phases except with melts.set_phase_inclusion_status()?

#52

The MELTS family of algorithms, and scientific discussion / Re: How to explain the contino...

Last post by Paula - May 01, 2024, 05:49:59 PM

The main problem is that there aren't many solid phases in the MELTS models that take MnO or P2O5.

The only Mn-bearing solid phases are olivine and rhombohedral oxide (ilmenite). If ilmenite is not joining the assemblage early enough, you could try playing around with the fO2.

The only P-bearing solid phases are (hydroxy)apatite and whitlockite. MELTS underestimates the stability of apatite, mainly because of the lack of fluorine and chlorine in the system. There is a F, Cl-bearing version of MELTS under development. At the moment the most recent citation is this:

[CITATION] MELTS+ DEW: Modeling major element+ Cl+ F+ S phase equilibria, redox reactions and elemental partitioning in magmatic-hydrothermal systems
MS Ghiorso, S Matthews... - Goldschmidt 2023 ..., 2023 - conf.goldschmidt.info

Look out for more developments in the next few months.

Paula

#53

The MELTS family of algorithms, and scientific discussion / How to explain the continous i...

Last post by Wei-cheng Jiang - April 21, 2024, 04:53:14 PM

Hi everyone,

I tried to use Rhyolite-MELTS 1.2.0 to simulate the LLD evolution in my study area. It works quite well in most of the major oxides like MgO, FeO, Al2O3, CaO, Alkalis, and SiO2. Our phase-equilibria experiments also show a similar LLD pathway under similar conditions.

However, the main issue is that the concentration of MnO and P2O5 keep increasing throughout the magma evolution from my parental composition to rhyolite composition. This problem was also pointed out by some reviewers for my submitted paper. The phase assemblage does not contain any manganese- or phosphorus-rich minerals (the starting composition is a high-Mg andesite with plag + cpx + opx + ol + spinel + ilmenite). I am not sure if this is the reason.

Thank you!

#54

easyMelts / Re: Restarting from an earlier...

Last post by Paula - April 16, 2024, 02:31:33 PM

Hi Kevin,

I haven't managed to reproduce convergence failure, as opposed to just hanging, but there are two ways I would try to tackle it:

1. Write out a .melts file of the current state. Edit the file, then restart easyMelts and read in the file. This may be your only option for fractional melting.

2. Start from the top with "Set initial T & P", Save, "Set initial composition", Save. I think the Equilibrate button will reappear.

Note that, unlike the rhyolite-MELTS GUI, in easyMelts T, P, and composition are not updated in the input boxes as the calculation proceeds. So you may need to copy them from the last good step (if it's fractional crystallization) and/or the initial conditions (if it's a batch calculation). Drag the slider to the right to get the last good step.

Paul @asimow uses eayMelts more than me so may have a better workaround.

Paula

#55

easyMelts / Restarting from an earlier ste...

Last post by KevinFarries - April 13, 2024, 09:41:51 PM

Hi Paula,

I was previously using the rhyolite-Melts GUI and have switched across to easyMelts.  In rhyolite-Melts if the algorithm fails to converge, it is possible to tweak some of the parameters then continue with the analysis.  Is there a way to do this with easyMelts?  If the there is a convergence failure, the "equilibrate" button disappears and I can't see a way to continue the calculation.

Thanks!

Kevin

#56

alphaMELTS for MATLAB/Python / Re: How to set elements to be ...

Last post by Paula - April 02, 2024, 08:58:54 AM

Hi Isiah,

No, sorry, as we have decided to take a different route and have the (passive) trace elements handled in Python, so we can integrate with existing packages for trace element partitioning models etc. The water as a trace species (i.e. pHMELTS) is close to implemented. That will be integrated into the main alphaMELTS program more thoroughly, rather than as a tack on trace species engine. So it will feel similar to the interface to the fO2 buffering options.

Best wishes,
Paula

#57

The MELTS family of algorithms, and scientific discussion / Re: How to simulate isentropic...

Last post by Paula - April 02, 2024, 08:47:36 AM

Thanks for the video! I'm still not quite sure why it's working but I'm less surprised that it might work on Ubuntu 20.04 than 22.04, especially if that was upgraded from an earlier Ubuntu. Anyway I'm glad you have easyMelts working now - it's definitely the more convenient option these days.

Best wishes,
Paula

#58

The MELTS family of algorithms, and scientific discussion / Re: How to simulate isentropic...

Last post by Gary - April 01, 2024, 04:02:59 AM

Hi, Paula,

Thank you very much for your detailed answer! Followed your steps, my easyMELTS runs well. I will use easyMELTS next to simulate mantle partial melting because it is more convenient to operate. If I meet other difficulties, I will ask for your help.

I know you have some question about why the rhyolite-MELTS/pMELTS can run on my Ubuntu. I'm sorry I can't answer you well because I'm not familiar with these operations. I recorded my operating steps, maybe it will be helpful: https://youtu.be/_NW-fTJHNHA. If you have any questions about this, just tell me.

All the best
Gary

#59

alphaMELTS for MATLAB/Python / Re: How to set elements to be ...

Last post by IsaiahSpring - March 26, 2024, 11:34:01 AM

Hi Paula,

I was wondering if this Trace element capability was up and running, and if there were any materials or examples about its operation.

Thanks,
Isaiah

#60

The MELTS family of algorithms, and scientific discussion / Re: How to simulate isentropic...

Last post by Paula - March 18, 2024, 12:15:56 PM

I downloaded the rhyolite-MELTS/pMELTS via the link https://melts.ofm-research.org/unix.html and run it with my Ubuntu22. I have set a stopping pressure and a pressure increment as you said. It did work.

I checked and the version of rhyolite-MELTS/pMELTS at the link you posted doesn't work on Ubuntu 22.04. Are you actually on Windows (e.g. did you follow the guide for setting it up on the WSL and download the version from the alphaMELTS links page)? If so, that's a bit better, and explains why it worked. But it's still unsupported. I recently found a major bug in the subsolidus fO2 routines of all MELTS software. I'll be posting fixes for the newer alphaMELTS software and easyMelts when I get a chance. But it has become too difficult to build the old graphical user interface (GUI) on Linux, and it doesn't even run on the newest Macs. So I won't be updating the GUI (or alphaMELTS 1.X).

I found there was some difference between choosing or not choosing the "fractionate liquids". Could you tell me which mode is more appropriate for partial melting of mantle?

You mentioned that you want to do continuous melting, so "fractionate liquids" will be closest to that. In fact a tiny bit of liquid is retained during fractionation. This is mainly to stabilize the calculation, but you can think of it as the residual porosity. You don't get as much control over the amount retained in the GUI or easyMelts, as you do in alphaMELTS, but the default value should be alright.

The melts.out file gives you the accumulated fractional melts, though not in an easily usable way. The increments are simply summed, so whether it is appropriate depends on the melting regime you are trying to model. If it's a 1-D column, like a plume, then it's fine. But if you are modeling a 2-D triangular melting regime at a mid-ocean ridge then you will need to weight the increments from different depths (from the melts-liquid.tbl file) and sum them appropriately. Paul Asimow's paper "Calculation of Peridotite Partial Melting from Thermodynamic Models of Minerals and Melts, IV. Adiabatic Decompression and the Composition and Mean Properties of Mid-ocean Ridge Basalts", and references therein, discuss this in more detail.

Before I asked for your help, I have tried to use easyMelts to simulate the partial melting, but it is hard to work and always malfunctions: https://www.youtube.com/watch?v=2lF_0zU7jsw. If you are convenient, please help me to check out where is going wrong.

Does it crash and close the window, or is it hanging during the calculation? If it is crashing then make sure you have the latest version - there was a bug that meant that it crashed if there was no liquid. If it's hanging then try what I suggested in the previous post i.e. start at a higher temperature or lower pressure first (without "fractionate liquids", and isentropic mode). Then once you have the starting conditions you want, turn on "fractionate liquids" and isentropic mode, reset the pressure increment and number of steps to take.

It would be a good idea to turn off the fO2 buffer before you hit the solidus. Even without the bug in subsolidus fO2 that I mentioned above, it is difficult to cross the solidus with the fO2 buffer on, and it makes the isentropic calculations more difficult (and slower) to have the buffer on at the same time. In practice, for mantle melting once the iron is distributed between Fe2+ and Fe3+ in the starting composition it doesn't deviate from the buffered value during decompression too much.

Paula