Stokes et al. Mn in apatite (2019) final full version accepted.pdf (2.24 MB)
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The effect of melt composition and oxygen fugacity on manganese partitioning between apatite and silicate melt

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journal contribution
posted on 28.04.2020, 09:03 by Thomas N. Stokes, Geoff D. Bromiley, Nicky J. Potts, Kate E. Saunders, Andrew J. Miles, EIMF
Oxygen fugacity and melt composition are both known to have a strong influence on the partitioning of trace elements between coexisting minerals and melt. Previous work has suggested that Mn partitioning between apatite and silicate melt may be strongly affected by oxygen fugacity and could, therefore, act as an oxybarometer. Here, we present a new study on the partitioning of Mn between apatite and melt at high temperature (1400–1250 °C) and 1 GPa pressure, for various melt compositions and oxygen fugacities (NNO +4.7 to NNO -10). We find that there is no demonstrable variation in the partition coefficient for Mn between apatite and silicate melt (D MnAp-m ) across the range of fO 2 conditions studied here. Instead, we find that D MnAp-m varies significantly with melt composition and that in particular, the proportion of non-bridging oxygens strongly influences partitioning of Mn between apatite and melt. We propose that variations in the Mn content of natural apatite, previously thought to reflect variations in fO 2 , are instead related to the degree of melt polymerisation. These findings are consistent with the results of Mn K-edge XANES spectroscopy, which demonstrate that Mn in coexisting apatite and silicate glass is present predominantly as Mn 2+ regardless of fO 2. Furthermore, XANES spectra from a series of silicate glasses synthesised at various oxygen fugacities demonstrate that Mn 2+ is the predominant species, and that the average Mn oxidation state does not vary over a wide range of fO 2 -T conditions.

Funding

NERC E3DTP studentship (NERC grant NE/L002558/1)

History

Citation

Chemical Geology, Volume 506, 2019, Pages 162-174

Author affiliation

School of Geography, Geology and the Environment

Version

AM (Accepted Manuscript)

Published in

Chemical Geology

Volume

506

Pagination

162 - 174

Publisher

Elsevier

issn

0009-2541

eissn

1872-6836

Acceptance date

19/12/2018

Copyright date

2019

Available date

21/12/2018

Publisher version

https://www.sciencedirect.com/science/article/pii/S0009254118306004

Language

en