Recent Posts

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1
alphaMELTS / Re: rhyolite-MELTS graphs
« Last post by Paula on September 19, 2017, 02:56:29 pm »
Hi,

Sorry, there are no plotting tools included in the graphical user interface to Rhyolite-MELTS. For more info see:

[FAQ] Melts Graphics Output Window is inactive

(Ignore the bit about Fink, that was required on early Mac versions of MELTS but hasn't been needed for many years now.)

Cheers,
Paula
2
alphaMELTS / rhyolite-MELTS graphs
« Last post by bpsimpson on September 18, 2017, 10:22:22 pm »
I'm struggling to output graphs in the rhyoliteMELTS included with alphaMELTS.

There doesn't appear to be any documentation for how to output graphs using the software. Could someone please point me in the direction of some resources that can help me output my results as a graph?

Thanks
3
Melting processes / Re: 2D Integrated Ouput - integration bounds
« Last post by Paula on June 23, 2017, 01:09:28 pm »
Hi Brandon,

The base (Po) is the initial pressure of melting and the top is the pressure at the base of the crust (Pc). The 1-D columns are for a column and the 2-D for a triangular melting regime, from which it is assumed that all the melt is extracted. The matrix streamlines are simplified (borrowing this image from an old post so ignore the coloured lines) and the melt ones aren't considered:


FB is the mean extent of melting, where melting stops at Pc. The routine solves for Pc so that the pressure due to the overlying crust (assumed to have a density of 2.62 g.cm-3) is Pc and the amount of extracted melt corresponds to FB. See Asimow et al. (2001) for more details, including equations.

Hope that helps. Sorry for delay.

Paula




4
Melting processes / 2D Integrated Ouput - integration bounds
« Last post by bshuck on June 23, 2017, 12:01:09 pm »
Hi Paula,

I have a question about the integrated output option of alphaMELTS...

Specifically -- how does the program determine the bounds of the 2D melting/extraction windows? Does it just use values of initial pressure of melting and pressure at the base of the crust, and a thermal profile to determine F laterally away from the ridge axis? If I understand correctly from the literature, Spiegelman and McKenzie defined streamlines for the melt extraction window, which Asimow and Stolper approximate the 2D window with a 1D column using focusing factors. Does the 2D integration simply assume all melt produced makes it to the base of the crust, or if some is trapped off-axis? Lastly, how does the program actually define the "base of crust?"

I apologize if this is a simple question that I may have overlooked in the literature and/or documentation of alphaMELTS.

Any help would be greatly appreciated,
Brandon
5
Melting processes / Re: Melting by ratio
« Last post by Paula on June 05, 2017, 02:11:03 pm »
Hi,

There isn't a way to set the melting ratios, and it wouldn't really make sense to do so in the context of MELTS. However, I guess you could construct a garnet peridotite bulk composition with typical mineral compositions and the initial ratios you would like. Then try running forward models for a range of potential temperatures and see which one most closely matches the target ratio in the residue (e.g. 0.52:0.24:0.07:0.05 approx).

Sorry not to be of more help. If I've misunderstood what you would like to do, let me know...

Paula



6
MELTS, pMELTS and pHMELTS algorithms / Re: liquidus temperature hi mg basalt
« Last post by Paula on June 05, 2017, 01:46:48 pm »
Hi Alberto,

Sorry for the delay in replying. A few thoughts:
  • There is a known systematic offset of ~100 oC in T versus F for (Rhyolite-)MELTS. Near the peridtotie solidus, pMELTS overestimates T(F) by about 60 oC so that give you a rough estimate of the offset for the calculated basalt liquidus. See Ghiorso et al. (2002) for more details.
  • See Hirschmann et al. (1999) for a discussion of how MELTS overstabilises opx at the expense of olivine. Note that the Rhyolite-MELTS and MELTS models behave identically when quartz and Ksp are absent, as here.
  • Although, you don't have Cr2O3 in this bulk composition, some of Paul's comments on your other Find Liquidus post do still apply here.
  • Also note that pMELTS is not calibrated for MnO or P2O5 so those should not be included in this comparison.
  • You might consider putting K and P as trace species too (this shouldn't affect the liquidus temperature, it may affect whether you can completely crystallize the liquid).

Cheers,
Paula
7
Melting processes / Melting by ratio
« Last post by Dengeo on May 24, 2017, 10:18:45 am »
Hi Paula,

I was wondering if there was a way to model fractional melting of a garnet-peridotite source using mineral ratios. For example, modeling the source Ol:Opx:Cpx:Grt with a ratio of 0.55:0.25:0.12:0.08 to a melted ratio of 0.05:0.05:0.45:0.45. The only way I can think to do this is by melting a typical garnet-peridotite and calculating multiple ratios as I melt it using the adiabat.

Thanks for the help!
8
MELTS, pMELTS and pHMELTS algorithms / liquidus temperature hi mg basalt
« Last post by roman@ipgp.fr on May 23, 2017, 08:37:15 am »
Dear all,
I am trying to simulate a simple equilibrium crystallization of the following hi mg basalts at 10kbar without any constrained buffer. The input file is attached below.
However, I get very different liquidus temperatures if I use pmelts, rhyolite melts, and petrolog.

Tl = 1357 C with pmelts
Tl = 1446 C with rhyolite melts
Tl=1260C with petrolog

Moreover, even if I reduce pressure up to 5kbar the liquidus temperature with rhyolite melts is always pretty high (>1330 C) and the phase in the liquid is always orthopyroxene, while I'd expect olivine. Does anybody know from where these differences come?
Thank you!
alberto
 

Title: dummy
Initial Composition: SiO2 51.57
Initial Composition: TiO2 0.78
Initial Composition: Al2O3 13.02
Initial Composition: Fe2O3 1.02
Initial Composition: FeO 7.62
Initial Composition: MnO 0.17
Initial Composition: MgO 11.96
Initial Composition: CaO 10.08
Initial Composition: Na2O 2.33
Initial Composition: K2O 0.55
Initial Composition: P2O5 0.13
Initial Temperature: 1200.00
Final Temperature: 800.00
Increment Temperature: 1.00
Initial Pressure: 10000
Final Pressure: 10000
Increment Pressure: 0.00
dp/dt: 0.00
log fo2 Path: None



9
General usage / Re: water again...
« Last post by roman@ipgp.fr on May 23, 2017, 07:44:30 am »
Hi Paula,
thank you very much for the detailed answer and sorry for the late reply. I will have a look into all this and let you know.
All the best,
Alberto
10
General usage / Re: water again...
« Last post by Paula on May 03, 2017, 08:51:18 am »
Hi Alberto,

Do you mean Rhyolite-MELTS or alphaMELTS? I'd need to check the Ghiorso & Gualda, 2015 paper but I'm pretty sure all the data that went into VolatileCalc was included in the Rhyolite-MELTS+H2O+CO2 calibration.

If you are using alphaMELTS (which doesn't have Rhyolite-MELTS, though it's imminent) then you have a couple of options for performing volatile saturation calculations using GG15. There's MagmaSat, which is a Mac app but there is a online web app too. There are also python wrappers included with the newly open source MELTS code. There are some Jupyter notebook examples, which don't do what you need but might point you in the right direction if you are familiar with python.

Paula
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