The actual temperature and the liquidus of the mixed magma

[zhudan]

Hi Paula,
I've been attempting to model the magma mixing process. For example, I assume that the system is totally adiabatic, and the mixed magma is the mixing of the parental magma (e.g. Morb ) and its fractionated melt (e.g. the Morb after 30 % fractionated crystallization) with different proportions. It is easy to calculate the liquidus of the mixed magma using adiabat_1ph, and the actual temperature of the mixed magma is calculated based on heat balance using the respective Cp (heat capacity). The results show that sometime the actual temperature> the liquidus of the mixed magma, and sometimes not, why? Is that right for my method to calculate the actual temperature of the mixed magma? Is there any convenient way to calculate them using adiabat_1ph?

Best regards

Dan

[Paula]

Hi Dan,

I think the easiest way to do this calculation would be to set ADIABAT_MODE to 'isenthalpic' mode.  Now, source mixer won't actually work out what the reference Enthalpy for the mixed system should be but there are a couple of ways around that:

One would be to turn on ADIABAT_ASSIMILATE, use the parental melt as the starting composition for a single calculation to find the liquidus and then 'execute' to do a single assimilation step of the fractionated melt composition. If you set ADIABAT_DELTAT and ADIABAT_DELTAP to zero the program should ask you how many iterations to do. You can read in the fractionated composition and its temperature from an enrichment_file or from a binary restart file. You will be asked how many grams of assimilant to add so, assuming you have 100 grams of the parental melt, you'll have to adjust this value to get the proportions you want (e.g. 25 grams for 20%).

The other approach is to get the temperature, mass and corresponding total system enthalpy of the parental melt at the liquidus and of the fractionated melt at 30% fractionation from the 'liquid' table in the Phase_main_tbl.txt file generated when you did the fractionation calculation. The 'liquid' table repeats the compositions from Liquid_comp_tbl.txt but also includes thermodynamic data and viscosity. Then you can calculate what the reference enthalpy should be for mixing, say, 80 grams of parental melt at liquidus temperatures and 20 grams melt after 30% fractionation. Start adiabat_1ph and read in the parental melt. Use source mixer to add the desired proportion of fractionated melt and then menu option 7 to set the reference Enthalpy to the correct value. Then menu option 3 should give you the actual temperature of the combined system.

Hope that works. Let me know if you are still getting odd results.

Best wishes,
Paula

[zhudan]

many thanks!