Résumé
Experimental studies have been performed to constrain sulphur behaviour during apatite crystallization and to determine the sulphur partition coefficient between apatite and melt at oxidizing conditions. Crystallization experiments have been conducted with a hydrous rhyolitic melt and different bulk sulphur contents at 900 and l,000 degrees C, 200 MPa and Delta log fO (sub 2) , = NNO + 3.6. The sulphur content in the glass increases with increasing amount of added S. Anhydrite crystallizes for S added = 0.75 wt.% (0.10 and 0.13 wt.% SO (sub 3) in glass at 900 and l,000 degrees C, respectively). The amount of anhydrite increases and the amount of apatite decreases with increasing amount of added sulphur. The sulphur exchange reaction in apatite is influenced by the bulk composition of the melt (e.g., P content). However, changing melt composition has only little effect on Kd (sub S) (super apatite/melt) for the investigated rhyolitic composition. The combination of experimental data obtained for rhyolitic and andesitic melts reveals that the sulphur partition coefficient tends toward a value of 2 for high-sulphur content in the glass (> 0.2 wt% SO (sub 3) ). Using S in apatite as proxy for determining S content in melt is promising but additional experimental data are needed to clarify the individual effects of T, f S (sub 2) , and P and Ca content in the melt on S partitioning.