Can we use Adiabat_1ph to calculate the parental magma?

[zhudan]

It's easy to calulate the liquid line of decent with a specific composition using Adiabat_1ph. So the first question is: can we calculate the reverse process to obtain the parental magma(assuming that the parental magma had fractionated at a fixed pressure)? If the answer is yes,  the second question is : is any convenient way to process this?

[Paula]

Short answer is 'sort of':

I have been working recently, with a couple of other people, towards incorporating and expanding the method described in the Appendix in Cooper et al. (2004; EPSL v220, p297-316) into the public version of Adiabat_1ph.  So far, I have added the 'back-fractionation' it mentions for use with multiply-saturated glasses.  This is used to get a starting guess composition for the forward fractional-crystallisation calculation.  The back-fractionation scheme calculates the liquidus phase(s) and adds them back in incrementally.  However, if more than one phase is stable then they will all continue to be stable as material is assimilated: in other words, the composition is buffered to stay on the cotectic.  You can try suppressing one or more of the mineral phases (e.g. 'Suppress: spinel' in the melts_file) to build up a family of potential parental magma compositions.

You are welcome to have a go with the test version of Adiabat_1ph with the back-fractionation included. If you let me know your operating system (from memory Windows?) I'll e-mail you a link and instructions. I have not yet implemented the 'amoeba' routine that it describes for adjusting the primary liquid composition so that forward-fractionation matches the more evolved samples in the suite.  In the meantime, you may be able to use a bit of trial-and-error forwards calculations and / or a priori knowledge to further constrain the primary or parental liquid composition.  I'll keep you posted when I get round to putting in the amoeba routine.

Cheers,
Paula

[Paula]

Hi Dan,
I'm having a bit of trouble getting through by e-mail (got 'host is busy' a few times followed by delay or failure). If you have an alternative e-mail address please could you send me a message from it and I'll try again.
Thanks,
Paula

[pmmx]

Paula,

I'm interested in the calculation of parental magma. Has the 'back-fractionation' routine been included in the Adiabat2 version ?

Thanks

Massimo

[Paula]

Hi Massimo,

The back-fractionation routine is hidden in the public version of Adiabat_1ph 2.  It's currently undocumented as it's not quite finalised.  The 'amoeba' routine is in the private version and we're testing at the moment.  You are welcome to have a try at the back-fractionation and / or amoeba, with the understanding that they are betas.  Just let me know what operating system you are on and I'll e-mail you instructions for downloading and using these options.  Both will be included in version 2.1, which should be happening fairly soon. 

Cheers,
Paula