Isentropic fractional crystallization with fO2 buffer

[Ri Cao]

Dear Paula,
This is Ri. Sorry for my interruption again and hope you are doing well.

I have a question there regarding the isentropic calculation for fractional crystallization on Rhyolite-MELTS changes both temperature and pressure simultaneously.

Basically, I setup the initial composition, oxygen fugacity. I tried both decrease temperature and pressure (or increase temperature or pressure) during the calculation, but the calculation cannot stops (Rhyolite-MELTS just keep iteration....).

I tried to setup the temperature step size or pressure step size the same the exercise I did previously for isobaric fractional crystallisation. I was wondering did I miss some fundamental understanding of the isentropic calculation? or are there any particular requirements for temperature and pressure setup? Any thoughts on this will be very helpful! Thank you very much and I look forward to your response.

Sincerely,
Ri Cao   

[Paula]

Hi Ri,

I split your posts, as there are six different topics covered and it's difficult to find the original advice posted for the FAQ about quadratic minimization failure.

I'm not quite sure from the information you've given, but if you are using the OFM version of the graphical user interface then there is a bug that can mean that isenthalpic / isentropic calculations get into an infinite loop. See this similar issue:

https://magmasource.caltech.edu/forum/index.php/topic,900.msg1331.html#msg1331

There are Mac and Linux builds that fix this problem on the alphaMELTS links page:

https://magmasource.caltech.edu/alphamelts/links.php?software=gui

The Mac version was built on Mojave, so your mileage may vary now that it is four macOS releases behind the current one. It has become too cumbersome to keep building the old GUI, so if it doesn't work I recommend trying easyMelts instead:

https://magmasource.caltech.edu/alphamelts/links.php

eayMelts doesn't suffer from the bug mentioned above because you always input the number of steps you want it to take.

Paula