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

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
• Public URL: https://durham-repository.worktribe.com/output/1347164