clinopyroxene

[kilgoretrout]

When fractionating certain phases is it possible to differentiate between Ca-rich clinopyroxene (e.g. augite) and Ca-poor clinopyroxene (e.g. pigeonite)?

[Paula]

Sort of...  Currently, it is not possible to specify anything about the composition of fractionated phases directly (e.g. Ca content of clinopyroxene) but it is possible to choose between the clinopyroxenes by the order in which they join the assemblage.  This means you should run the calculation twice.  (In practice augite will probably be first but it is worth checking as the energy difference between opx and cpx is very small.)  For example, if you wanted to fractionate pigeonite but not augite then try the following:

The first time run Adiabat_1ph with 'Fractionate:' lines for all the phases you would like to fractionate, except clinopyroxene, in the melts_file (and make sure that ADIABAT_FRACTIONATE_SOLIDS is not set, of course).   On the screen output observe whether the first clinopyroxene is augite-like or pigeonite-like.  If the first cpx is augite-like and the second one is pigeonite-like then add a 'Fractionate: clinopyroxene 2' line to your melts_file.  Then restart Adiabat_1ph and repeat the calculation.  If the first cpx is pigeonite-like then add a 'Fractionate: clinopyroxene 1' line to your melts_file and repeat the calculation.  If pigeonite is dropped from the assemblage and that reappears later then things would get a bit more complicated but it would still be possible to do the calculation.  Try it first and let me know what happens.  If it doesn't work at all the please post or e-mail me your files and I'll see what I can do.

Hope that helps,
Paula