An experimental study of partitioning of fluorine between K-richterite,apatite, phlogopite,and melt at 20 kbar |
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| Authors: | A D Edgar L A Pizzolato |
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| Institution: | (1) Department of Earth Sciences, University of Western Ontario, N6A 5B7 London, Canada |
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| Abstract: | Phase relations have been determined at 20 kbar and primarily under suprasolidus conditions in the Fe−Ti-free F-bearing K-richterite—phlogopite
and K-richterite—apatite systems in order to assess the partitioning of F among phlogopite, K-richterite, apatite, and melt
under upper-mantle conditions. Both systems are pseudoternary because they contain forsterite, enstatite and a diopside-rich
clinopyroxene from the breakdown of the mica and K-richterite. The F-bearing K-richterite systems have lower minimum melting
temperatures than the F-bearing phlogopite —apatite system at the same pressure. However in the systems studied, F in phlogopite
appears the most effective component in altering minimum liquid compositions whereas comparison between the present study
and previous systems suggests that the presence of P2O5 during melting may result in more K-enriched melts. Variations in the compositions of the F-bearing phases are primarily
controlled by the bulk compositions of the end-member minerals and by temperature, although buffering by non-F bearing minerals
(e.g. clinopyroxene) may be effective. Distribution coefficients (as wt% ratios) between F-bearing minerals and coexisting
liquids have been determined as functions of bulk composition and temperature for products of experiments. Distribution coefficients
between K-richterite—liquid, apatite—liquid, and phlogopite—liquid are ≥1 to slightly <1 for most bulk compositions, indicating
thatF is generally a compatible element. This conclusion is in agreement with the sequence ofF distribution for similar phases in ultrapotassic rocks. These results preclude F-bearing mineral reservoirs in the mantle,
at depths corresponding to 20 kbar, being capable of producing F-enrichment in ultrapotassic magmas, or being effective in
redox melting processes.
Editorial responsibility: K. Hodges |
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