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Experimental investigation of F, Cl, and OH partitioning between apatite and Fe-rich basaltic melt at 1.0–1.2 GPa and 950–1000 °C

McCubbin, Francis M.; Vander Kaaden, Kathleen E.; Tartèse, Romain; Boyce, Jeremy W.; Mikhail, Sami; Whitson, Eric S.; Bell, Aaron S.; Anand, Mahesh; Franchi, Ian A.; Wang, Jianhua and Hauri, Erik H. (2015). Experimental investigation of F, Cl, and OH partitioning between apatite and Fe-rich basaltic melt at 1.0–1.2 GPa and 950–1000 °C. American Mineralogist, 100(8-9) pp. 1790–1802.

DOI (Digital Object Identifier) Link: https://doi.org/10.2138/am-2015-5233
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Abstract

Apatite-melt partitioning experiments were conducted in a piston-cylinder press at 1.0–1.2 GPa and 950–1000 °C using an Fe-rich basaltic starting composition and an oxygen fugacity within the range of ΔIW-1 to ΔIW+2. Each experiment had a unique F:Cl:OH ratio to assess the partitioning as a function of the volatile content of apatite and melt. The quenched melt and apatite were analyzed by electron probe microanalysis and secondary ion mass spectrometry techniques. The mineral-melt partition coefficients (D values) determined in this study are as follows: DFAp-Melt = 4.4–19, DClAp-Melt = 1.1–5, DOHAp-Melt = 0.07–0.24. This large range in values indicates that a linear relationship does not exist between the concentrations of F, Cl, or OH in apatite and F, Cl, or OH in melt, respectively. This non-Nernstian behavior is a direct consequence of F, Cl, and OH being essential structural constituents in apatite and minor to trace components in the melt. Therefore mineral-melt D values for F, Cl, and OH in apatite should not be used to directly determine the volatile abundances of coexisting silicate melts. However, the apatite-melt D values for F, Cl, and OH are necessarily interdependent given that F, Cl, and OH all mix on the same crystallographic site in apatite. Consequently, we examined the ratio of D values (exchange coefficients) for each volatile pair (OH-F, Cl-F, and OH-Cl) and observed that they display much less variability: KdCl-FAp-Melt=0.21±0.03, KdOH-FAp-Melt=0.014±0.002, and KdOH-ClAp-Melt=0.06±0.02. However, variations with apatite composition, specifically when mole fractions of F in the apatite X-site were low (XF < 0.18), were observed and warrant additional study. To implement the exchange coefficient to determine the H2O content of a silicate melt at the time of apatite crystallization (apatite-based melt hygrometry), the H2O abundance of the apatite, an apatite-melt exchange Kd that includes OH (either OH-F or OH-Cl), and the abundance of F or Cl in the apatite and F or Cl in the melt at the time of apatite crystallization are needed (F if using the OH-F Kd and Cl if using the OH-Cl Kd). To determine the H2O content of the parental melt, the F or Cl abundance of the parental melt is needed in place of the F or Cl abundance of the melt at the time of apatite crystallization. Importantly, however, exchange coefficients may vary as a function of temperature, pressure, melt composition, apatite composition, and/or oxygen fugacity, so the combined effects of these parameters must be investigated further before exchange coefficients are applied broadly to determine volatile abundances of coexisting melt from apatite volatile abundances.

Item Type: Journal Item
Copyright Holders: 2015 Mineralogical Society of America
ISSN: 0003-004X
Project Funding Details:
Funded Project NameProject IDFunding Body
Secular evolution of water in the lunar mantle (SE-10-037-MA)ST/I001298/1STFC (Science & Technology Facilities Council)
Extra Information: Special Collection: Apatite: A Common Mineral, Uncommonly Versatile
Keywords: lunar water; water on Mars; QUE 94201; phosphates; piston cylinder
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Research Group: Space
Item ID: 45141
Depositing User: Mahesh Anand
Date Deposited: 14 Jan 2016 10:48
Last Modified: 08 May 2019 13:39
URI: http://oro.open.ac.uk/id/eprint/45141
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