Estimation of apatite saturation temperature AST

A strong temperature dependence on apatite/melt exchange equilibria has been recognized for some time, necessitating the determination of the temperature at which apatite crystallizes when making estimates of magmatic halogen concentrations or 

For metaluminous to slightly peraluminous systems, the Nemst partition coefficients presented by Harrison and Watson (1984) can be recast as an empirical solubility expression, and solved for temperature. Their results can be represented as 

In most cases, workers who calculate apatite saturation temperatures fail to make these corrections (in part due to their difficulty) although in some systems the corrections are small (for example, volcanic systems with low degrees of crystallization), however, they may be significant for mafic systems where initiation of crystallization of apatite occurs significantly below the liquidus. For the calculations that follow, either the AST can be used, or calculations can be performed using model temperatures (e.g., see 

A summary of over 1000 analyses included in the database can be found in Table 3. This compilation includes arithmetic means for each category of analyses in the database, the corresponding standard deviation (la) and number of analyses. No rigorous attempt has been made to evaluate the quality of data included in the compilation. Clearly when using an electron microprobe to determine chemistry (by far the most common analytical technique used for apatite analyses presented in this overview), there can be problems with the accurate and precise analyses of apatite due to anisotropy effects possibly due to diffusion (e.g., F, Cl, P and Ca Stormer et al. 1993), peak overlaps (e.g., F and P Potts 

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