News:

alphaMELTS 1.9 is available at the download and information site.
alphaMELTS 2 standalone & for MATLAB/Python are available on request
(see the Version 2 tab on the download site for more details).
For news of all MELTS software see the MELTS Facebook page.

Main Menu

How to set parameters to run a mantle adiabat with fixed potential temperature?

Started by zackary2018, July 09, 2019, 03:14:18 PM

Previous topic - Next topic

zackary2018

Hi,

I am trying to draw a mantle adiabat with different potential temperatures (Tp). I have set my melting_file as below:

ALPHAMELTS_VERSION         pMELTS
ALPHAMELTS_MODE            isentropic
ALPHAMELTS_DELTAP        -100
ALPHAMELTS_DELTAT        0
ALPHAMELTS_MAXP          40000
ALPHAMELTS_MINP          100
ALPHAMELTS_MAXT          2400
ALPHAMELTS_MINT          500
ALPHAMELTS_CONTINUOUS_MELTING   true
ALPHAMELTS_MINF                 0.005

I also chose superliquidus instead of subsolidus, but I don't know how to set starting Temperature and starting Pressure.

What can I do or is there any wrong in my dealing process?

Thank you,
Zack

Paula

What does your .melts file look like? You can set the Temperature and Pressure there, or use menu option 2 (or, in alphaMELTS 1.9, you can use a PTpath file etc; this option is not available in alphaMELTS 2 yet). If you want to set a particular Potential Temperature then that is a little more involved. This is the relevant bit from the (old) MELTS camp exercises for a Tp of 1350 oC:

Quote
First thing we need is to obtain the initial entropy that corresponds to our desired potential temperature. Potential temperature is defined as the T of an equilibrated but metastable subsolidus assemblage at 1 bar with the same total entropy as the starting peridotite down in the mantle. So if we want to calculate for a potential temperature of 1350 Ã,°C, we need to get the entropy of our bulk composition, subsolidus, at 1350 Ã,°C and 1 bar. But this is metastable, so weââ,¬â,,¢ll have to turn off the liquid phase temporarily. So:
choose option 1 to read the input file, tell it the filename. Note that it adds H2O to the trace element list automatically.
choose option 2 and set T = 1350 Ã,°C and P = 1 bar.
choose option 9 and suppress the liquid (0).
choose option 3 to equilibrate, option 0 for subsolidus initial guess, and give it the list of phases (one per line): olivine, orthopyroxene, clinopyroxene, spinel, feldspar; and then ââ,¬Ëœxââ,¬â,,¢ to finish the list. This carries out a special norm calculation that assigns your bulk composition to these solid minerals.

It should run and give you an equilibrated assembage at the desired conditions; now it knows the entropy we want, so choose option 7. It tells you the current entropy; in the future to recover this potential temperature, you can just put this number as an initial entropy in the input or settings files, or type it here at option 7.

There are versions of this calculation in the more recent MELTS short course materials on the alphaMELTS archive page.

Paula