The effect of saturating haplogranitic melts with sillimanite at 2 kbar was examined by determining near-eutectic or near-minimum melt phase relations in the sillimanite-free and sillimanite-saturated haplogranite systems. Three series of compositions were studied with Ab/(Ab + Sa) ratios of 0, 0.545, and 1.0. The solubilities of sillimanite in these melts were nearly indistinguishable from each other (3.5 ± 0.5, 3.7 ± 0.3, and 3.7 ± 0.5 wt%, respectively). Under sillimanite-saturated conditions, the eutectic or minimum-melt temperatures were lowered by 15–29 °C, and the melt compositions were shifted to more quartz-rich compositions by 1.5–2.5 wt%.

At 2 kbar, the temperatures and compositions (on an anhydrous, sillimanite-free basis) of the four- and five-phase points are

Ab + Qz + Liq + V 748 ± 5 °C 36 ± 1.0 wt% Qz 
Ab + Qz + Sill + Liq + V 736 ± 5 °C 38 ± 1.0 wt% Qz 
Sa + Qz + Liq + V 767 ± 7 °C 42 ± 1.0 wt% Qz 
Sa + Qz + Sill + Liq + V 737 ± 5 °C 43.5 ± 1.0 wt% Qz 
Fsp + Qz + Liq + V 685 ± 7 °C 33.5 ± 2 wt% Qz 
Fsp + Qz + Sill + Liq + V 656 ± 10 °C 36.0 ± 2 wt% Qz. 
Ab + Qz + Liq + V 748 ± 5 °C 36 ± 1.0 wt% Qz 
Ab + Qz + Sill + Liq + V 736 ± 5 °C 38 ± 1.0 wt% Qz 
Sa + Qz + Liq + V 767 ± 7 °C 42 ± 1.0 wt% Qz 
Sa + Qz + Sill + Liq + V 737 ± 5 °C 43.5 ± 1.0 wt% Qz 
Fsp + Qz + Liq + V 685 ± 7 °C 33.5 ± 2 wt% Qz 
Fsp + Qz + Sill + Liq + V 656 ± 10 °C 36.0 ± 2 wt% Qz. 
The solubility of sillimanite in these melts was found to be insensitive to P and T over the range studied, 2.0 and 6.0 kbar, 680–900 °C, but preliminary experiments indicate that it is increased by the presence of mafic components. This lowering of the minimummelt temperature may explain the observation of apparently primary magmatic andalusite in some granitic rocks.

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