The influence of alkaline-earth oxides (BeO, MgO, CaO, SrO, BaO) on the viscosity of a haplogranitic melt; systematics of non-Arrhenian behavior

The effect of the addition of 5, 10 20 wt.% of the alkaline-earth oxides on the viscosity of a haplogranitic melt composition was investigated at 1 atm and 640-1675 degrees C. The effects are extremely variable; the viscosity decreases with added alkaline-earth oxide content in a non-linear fashion. The first few mole % decreases viscosity up to several orders of magnitude, whereas subsequent additions have a much smaller effect. The effects are quite distinct on a molar basis: the viscosity of the melts decreases with the size of the added alkaline-earth cation in the order Ba <<<$I> Sr <<<$I> Ca <<<$I> Mg <<<$I> Be. This trend of viscosity vs cation size is the reverse to that observed for the effects of alkali oxide additions on the melt viscosity. The alkaline-earth-bearing melts are significantly non-Arrhenian; this aspect is discussed in some detail.