Melt thermodynamics and divalent element partitioning between anorthite and CMAS liquids

Quantifying the effect of melt composition on trace element partitioning in natural systems has been hampered by correlated variations in mineral chemistry, temperature, and pressure. We have isolated the influence of melt composition on divalent element (Mg, Ca, Sr, Ba) partitioning between stoichiometric anorthite and a range of synthetic melts. Data were obtained from electron microprobe analysis of anorthite rims from dynamic crystallization experiments. Melt compositions contain near constant SiO_2, CaO/Al_2O_3 ranging from 0.8-1.6, and MgO from 1-15 wt. %. Holding X_(mineral), T, and P constant, we observe partitioning behavior that varies systematically with melt chemistry.