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First measurements of OH-C exchange and temperature-dependent partitioning of OH and halogens in the system apatite - silicate melt

Riker, J.; Humphreys, M.C.S.; Brooker, R.A.; de Hoog, J.C.M.; EIMF

First measurements of OH-C exchange and temperature-dependent partitioning of OH and halogens in the system apatite - silicate melt Thumbnail


Authors

J. Riker

R.A. Brooker

J.C.M. de Hoog

EIMF



Abstract

We present the first integrated study of carbonate, hydroxyl, fluoride, and chloride ion partitioning in the apatite-melt system. We determined volatile partitioning behavior between apatite and silicate melt for both haplobasaltic andesite and trachyte bulk compositions at 0.5–1 GPa and 1250°C using the piston-cylinder apparatus. All volatile species were analyzed directly in both apatite and glass using secondary ion mass spectrometry (SIMS) and electron probe microanalysis. Distribution coefficients for OH-halogen exchange are similar to those from previous studies, and together with literature data, reveal a significant log-linear relationship with temperature, while the effects of pressure and melt composition are minimal. Meanwhile, halogen-free experiments generate very high C contents (up to 5000 ppm) in apatite. Stoichiometry calculations and infrared spectra indicate that this C is mainly incorporated onto the channel volatile site together with hydroxyl. In halogen-bearing experiments, apatite crystals contain significantly lower C (≤500 ppm), which may be partly incorporated onto the phosphate site while the channel volatile site is filled by OH+F+Cl+C. Our experiments give the first constraints on H2O-CO2 exchange between apatite and silicate melt, with a KD of 0.355 ± 0.05 for the trachyte and 0.629 ± 0.08 for the haplobasaltic andesite. The new constraints on the temperature-dependence of partitioning will enable quantitative modeling of apatite-volatile exchange in igneous systems, while this new partitioning data and method for direct, in situ analysis of C in apatite mark a significant advance that will permit future studies of magmatic C and other volatiles. This has a broad range of potential applications including magmatic differentiation, fractionation, and degassing; quantification of volatile budgets in extraterrestrial and deep earth environments; and mineralization processes.

Citation

Riker, J., Humphreys, M., Brooker, R., de Hoog, J., & EIMF. (2018). First measurements of OH-C exchange and temperature-dependent partitioning of OH and halogens in the system apatite - silicate melt. American Mineralogist, 103(2), 260-270. https://doi.org/10.2138/am-2018-6187ccby

Journal Article Type Article
Acceptance Date Oct 7, 2017
Online Publication Date Feb 1, 2018
Publication Date Feb 1, 2018
Deposit Date Oct 10, 2017
Publicly Available Date Oct 11, 2017
Journal American Mineralogist
Print ISSN 0003-004X
Electronic ISSN 1945-3027
Publisher Mineralogical Society of America
Peer Reviewed Peer Reviewed
Volume 103
Issue 2
Pages 260-270
DOI https://doi.org/10.2138/am-2018-6187ccby

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