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Experimental determination of fluorine and hydrogen partitioning between apatite and basaltic melt

  • Author(s): Huh, Michael Chahn
  • Advisor(s): Manning, Craig E;
  • Boyce, Jeremy W
  • et al.

The mineral apatite incorporates OH, F, and Cl into its structure, so volatile concentrations in apatite could be used as a proxy for their abundances in magmas. I investigated this by conducting experiments on F-OH exchange between apatite and a simplified arc basalt at 10 kb and 1100 to 1250 °C for 48 hours. The experiments succeeded in growing, for the first time, apatites that were large enough (25-50 µm) for analysis by secondary ion mass spectrometry (SIMS), measurements were also conducted with the electron probe microanalyzer (EPMA). Results indicated that F is preferentially partitioned into apatite, whereas OH slightly favors the liquid. The exchange of F and OH between apatite and melt can be represented as Fliquid + OHapatite = OHliquid + Fapatite, for which the equilibrium constant is Keq=[Fap][OHliq]/[OHap][Fliq], assuming unit activity coefficients. Weighted least squares fitting to data yielded Keq = 59.

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