Experiments were conducted to investigate the effects of temperature and fluorine content of water-saturated peraluminous granitic melt on the diffusion of phosphorus and calcium away from dissolving apatite (Ap) crystals. Runs were done at 200 MPa(H2O) and either 750°C or 850°C, for 1- or 2-week durations, and most initially contained ~3 wt.% F. These experiments follow up on the F-absent, 750°C Ap dissolution experiments of Wolf and London (1994; GCA 58:4127-4145).

Diffusivity calculations were done using inverse error function methods. The diffusivity of P (DP) in the 1-week run at 750°C ranges from 1.4E-10 to 3.7E-10 cm 2/s, based on measurements along different profiles away from Ap. In the 2-week run at 750°C DP ranges from 2.1E-10 to 5.0E-9 cm2/s. In the 1-week run at 850°C DP ranges from 1.3E-10 to 1.6E-9 cm2/s. In one 2-week, 850°C run DP ranges from 8.5E-11 to 1.5E-10. In another 2-week run at 850°C with 2.4 wt.% F in the initial melt, DP ranges from 4.7E-10 to 1.5E-9 cm2/s. The ranges of P diffusivity values overlap for these 750°C and 850°C runs. The Ca diffusivity data are much less coherent than the P data, however, a few good data sets give DCa between 4.0E-10 and 2.0E-9 cm2/s, with the DCa of 750°C and 850°C runs overlapping.

The F-absent, 750°C runs done by Wolf and London (1994) had DP values that averaged ~1E-11 cm2/s and DCa values that averaged ~1E-10 cm2/s. Thus it appears that the addition of fluorine increases the diffusivity of P by ~1-2 orders of magnitude and Ca by ~1 order of magnitude in wet granitic melts.