anomalous high liquidus temperature for More.melts

[qy2014]

Hi all,

I am new for Melts and have met a basic problem after installing the alphamelts_1-9 on Mac.

I first tried to reproduce the example for isobaric fractionation of Morb.melts given by Paula at https://magmasource.caltech.edu/forum/index.php/topic,840.msg1195.html#msg1195.
However, the liquidus temperature calculated by my software at the beginning was too high at 1473.15 K, which is about 250 higher than the one in that tutorial. I noticed previous posts about "liquidus temperature high mg magma", while my sample is just a reference case here and should be the same results as the tutorial.

Here are my terminal command lines: run_alphamelts.command -f frac_xtal_env.txt
Outputs:
ALPHAMELTS_MINP 1
ALPHAMELTS_MINT 500
ALPHAMELTS_MAXP 30000
ALPHAMELTS_VERSION MELTS
ALPHAMELTS_FRACTIONATE_SOLIDS true
ALPHAMELTS_DELTAP 0
ALPHAMELTS_MAXT 2400
ALPHAMELTS_DELTAT -1
ALPHAMELTS_MODE isobaric

The Morb.melts output is:
MELTS filename: Morb.melts
input file open
Successfully read 'title: allan et al. 1989 (see ghiorso 1997)'
Successfully read 'initial composition: sio2 48.68'
Successfully read 'initial composition: tio2 1.01'
Successfully read 'initial composition: al2o3 17.64'
Successfully read 'initial composition: fe2o3 0.89'
Successfully read 'initial composition: cr2o3 0.03'
Successfully read 'initial composition: feo 7.59'
Successfully read 'initial composition: mgo 9.10'
Successfully read 'initial composition: cao 12.45'
Successfully read 'initial composition: na2o 2.65'
Successfully read 'initial composition: k2o 0.03'
Successfully read 'initial composition: p2o5 0.08'
Successfully read 'initial composition: h2o 0.20'
Successfully read 'initial temperature: 1200.00'
Successfully read 'initial pressure: 500.00'
Successfully read 'log fo2 path: none'
Successfully read 'mode: fractionate solids'

I then selected the Single (batch) calculation, and the output for this is:
Your choice: 3
Superliquidus (1) or subsolidus (0) initial guess ? 1
...Adding the solid phase feldspar to the assemblage.
...Adding the solid phase olivine to the assemblage.
Initial alphaMELTS calculation at: P 500.000000, T 1473.150000
liquid: 82.239 g 49.00 1.23 15.85 1.08 0.04 8.49 8.71 12.39 2.83 0.04 0.10 0.24
Activity of H2O = 0.0266901  Melt fraction = 0.819522
olivine: 4.275507 g, composition (Ca0.01Mg0.85Fe''0.15Mn0.00Co0.00Ni0.00)2SiO4
feldspar: 13.835487 g, composition K0.00Na0.21Ca0.79Al1.79Si2.21O8

I tried to remove the software and reinstalled it, while does not help. Any helps will be greatly appreciated.

Qian

[asimow]

Hi Qian,

If you do not set the environment variable ALPHAMELTS_CELSIUS_OUTPUT, then the temperatures are displayed in Kelvin. So, your calculation is at 1200Ã,°C, which is 1473.15 K. In Paula's tutorial, the temperatures are being displayed in Ã,°C. So, your calculation is fine. Nothing wrong with the liquidus. For consistency with prior tutorial output, though, why don't you go ahead and add ALPHAMELTS_CELSIUS_OUTPUT True to your commands file.

-- Paul

[qy2014]

Hi Paul,

Thank you so much for your prompt reply. You solved my puzzle~ Cannot believe I did not think of it as I found the temperatures of all my calculations are all too high~ Will do that for sure~ Thanks again~


Qian

[Paula]

Hi Qian,

Also, that version of the tutorial that you linked is for alphaMELTS 2 only (which outputs temperature in ^oC by default). Finding the liquidus, which is about 1220^oC in this example, is a bit more involved in alphaMELTS 1.9. You should follow this version of the tutorial:

https://magmasource.caltech.edu/forum/index.php/topic,131.0.html

The settings_file that you need, with the ALPHAMELTS_CELSIUS_OUTPUT variable set, is linked there.

Paula

[qy2014]

Hi Paula, Thanks a lot for telling me that.
Also, I am also thinking if somewhere has the 1.9 version tutorial for this exercise: 
Melts camp exercises (https://magmasource.caltech.edu/alphamelts/1/exercises-for-melts.htm).
I tested using 1.9 and it does not completely match.

The last question is that I am trying to find the equilibrate solid residual for a melt composition I have (based on fine-grain diabase). According to other literature and my trace element plots, the source rocks should be in spinel-peridotite facies. Thus, if I have P, T and oxygen fugacity, plus the melt composition, how can I use them to infer the solid residual so that I can further add to the melt to get the source composition? After getting the source composition I can then test if it is stable under spinel-peridotite facies. Or is it much practical to do isentropic melting of mantle rocks until I found the melt composition similar to the melt I have?

Any suggestions will be greatly appreciated!

Qian

[Paula]

Also, I am also thinking if somewhere has the 1.9 version tutorial for this exercise: 
Melts camp exercises (https://magmasource.caltech.edu/alphamelts/1/exercises-for-melts.htm).
I tested using 1.9 and it does not completely match.

There isn't a more recent version. In fact, that MELTS camp originally used Adiabat_1ph, the precursor to alphaMELTS and was only updated to alphaMELTS 1.2 (=Adiabat_1ph 3.2). Much of the material was included in a slightly different format for the series of NSF-sponsored workshops that we did in 2014-2015. The most recent one was at Rice in 2015 - you can browse the files HERE.

It would have used alphaMELTS 1.4.1; NSF-sponsored workshops since then have used alphaMELTS 2. You can see how much the software has changed between 1.4 and 1.9 in the README. Otherwise, if you have a more specific question about one of the MELTS camp exercises, we might be able to help bring it up to date with 1.9.

The last question is that I am trying to find the equilibrate solid residual for a melt composition I have (based on fine-grain diabase). According to other literature and my trace element plots, the source rocks should be in spinel-peridotite facies. Thus, if I have P, T and oxygen fugacity, plus the melt composition, how can I use them to infer the solid residual so that I can further add to the melt to get the source composition? After getting the source composition I can then test if it is stable under spinel-peridotite facies. Or is it much practical to do isentropic melting of mantle rocks until I found the melt composition similar to the melt I have?

Having the melt composition doesn't allow you to uniquely determine the source composition. See the documentation about "reverse fractional crystallization" and the "amoeba" function in alphaMELTS 1.9 for comparison. So, yes, the normal way would be to run forward models of isentropic mantle melting. In principle it would be possible to apply the amoeba algorithm to fit the modeled aggregate melt composition to the (fractionation-corrected) observed compositions. It's something I've toyed with doing in alphaMELTS 2, but there are other more urgent things to get finished before that...

Paula

[qy2014]

Hi Paula, I am very appreciative of your systematic response. Cool, and I think I will just keep practicing with what is available for me now. Will ask for help if more to come. Thanks~