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Limiting the proportion of crystallization of a mineral

Started by Bhuvan, December 25, 2019, 11:48:57 PM

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Bhuvan

Hi,
I am trying to crystallize a gabbro from a primitive basaltic melt and I would like to put a constraint on the amount of Olivine that can crystallize out of the melt. The amount of Olivine crystallized from the melt exceeds 15% but I have made a thin section of the gabbro that I want to model and Olivine doesn't exceed 5%. Is there a way to do put a check on the amount of olivine crystallizing from the melt?

Paula

No, there isn't a way to do that. Olivine is either a potential phase, in which case if/how much it crystallizes is determined by the thermodynamics, or it is suppressed.

Assuming olivine is the liquidus phase, what you can do is control whether the olivine is retained in the gabbro. In the graphical user interface you can only turn on fractional crystallization for all phases (except fluid) or for none. In alphaMELTS you can choose to fractionate some phases but not others, so you may want to look into that.

For a start, I would turn on fractional crystallization on for all phases and see if you can get from the primitive basaltic melt composition to the gabbro composition. If you have olivine compositions, you could test whether the olivine in the gabbro is actually in equilibrium, or if it is cumulate.

Paula

Bhuvan

Thank you for your reply, Paula. I would try to get the composition of the olivine to recheck if the equilibrium exists and let you know if that helps.
Thanks again!