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Title: Iron isotopic fractionation in mineral phases from Earth's lower mantle: Did terrestrial magma ocean crystallization fractionate iron isotopes?

Abstract

Iron is the most abundant transition metal in the Earth's interior, yet considerable uncertainties remain as to why mantle-derived rocks have diverse iron isotopic compositions. In particular, the isotopic fractionation behavior of iron in the lower-mantle minerals bridgmanite and ferropericlase are largely unexplored. The reason is that it is challenging to study isotopic fractionation at the high pressures relevant to the deep mantle. Here we report in situ measurements of the mean force constants of iron bonds in these minerals pressurized in diamond anvil cells using the technique of nuclear resonant inelastic X-ray scattering (NRIXS). We find that the transition from high- to low-spin iron in ferropericlase ((Mg 0.75Fe 0.25)O) at approximately 60 GPa drastically stiffens its iron bonds in the low-spin state. The mean force constant of iron bonds in both Fe-bearing and (Fe,Al)-bearing bridgmanite exhibits softening by 21% at approximately 40-60 GPa, which seems to be associated with changes in the iron local environment during the transition from low to high quadrupole splitting states. These results indicate that in the lower mantle, low-spin ferropericlase is enriched in heavy iron isotopes relative to bridgmanite and metallic iron by +0.15 parts per thousand and +0.12 parts per thousand, respectively. Basedmore » on these results, we investigate whether terrestrial magma ocean crystallization could have fractionated iron isotopes. We conclude that this process cannot be responsible for the heavy iron isotope enrichment measured in terrestrial basalts.« less

Authors:
 [1]; ORCiD logo [2];  [3];  [4];  [5];  [3];  [3]; ORCiD logo [6];  [6];  [7];  [8]; ORCiD logo [9]
  1. Center for High Pressure Science and Technology Advanced Research (HPSTAR), Pudong, Shanghai (China)
  2. Univ. of Texas, Austin, TX (United States). Dept. of Geological Sciences, Jackson School of Geosciences
  3. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
  4. Inst. de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), Paris (France); Sorbonne Univ., Paris (France); Muséum National d'Histoire Naturelle, Paris (France); National Centre for Scientific Research (CNRS), Paris (France)
  5. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS); Univ. of Illinois, Urbana-Champaign, IL (United States). Dept. of Geology
  6. Univ. of Texas, Austin, TX (United States).Dept. of Geological Sciences, Jackson School of Geosciences
  7. Columbia Univ., New York, NY (United States). Lamont-Doherty Earth Observatory, Dept. of Applied Physics and Applied Mathematics and Dept. of Earth and Environmental Sciences
  8. Okayama Univ., Misasa, Tottori (Japan). Inst. for Planetary Materials
  9. Univ. of Chicago, IL (United States). Enrico Fermi Inst., and Origins Lab., Dept. of the Geophysical Sciences
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
National Aeronautic and Space Administration (NASA); National Science Foundation (NSF); Agence Nationale de la recherche (ANR); Consortium for Materials Properties Research in Earth Sciences (COMPRES); USDOE Office of Science (SC)
OSTI Identifier:
1503568
Grant/Contract Number:  
AC02-06CH11357
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Earth and Planetary Science Letters
Additional Journal Information:
Journal Volume: 506; Journal Issue: C; Journal ID: ISSN 0012-821X
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Core-mantle interaction; Iron isotopic fractionation; Magma ocean crystallization; Nuclear Resonant Spectroscopy; spin transition

Citation Formats

Yang, Hong, Lin, Jung-Fu, Hu, Michael Y., Roskosz, Mathieu, Bi, Wenli, Zhao, Jiyong, Alp, Esen E., Liu, Jin, Liu, Jiachao, Wentzowitch, Renata M., Okuchi, Takuo, and Dauphas, Nicolas. Iron isotopic fractionation in mineral phases from Earth's lower mantle: Did terrestrial magma ocean crystallization fractionate iron isotopes?. United States: N. p., 2018. Web. doi:10.1016/j.epsl.2018.10.034.
Yang, Hong, Lin, Jung-Fu, Hu, Michael Y., Roskosz, Mathieu, Bi, Wenli, Zhao, Jiyong, Alp, Esen E., Liu, Jin, Liu, Jiachao, Wentzowitch, Renata M., Okuchi, Takuo, & Dauphas, Nicolas. Iron isotopic fractionation in mineral phases from Earth's lower mantle: Did terrestrial magma ocean crystallization fractionate iron isotopes?. United States. doi:10.1016/j.epsl.2018.10.034.
Yang, Hong, Lin, Jung-Fu, Hu, Michael Y., Roskosz, Mathieu, Bi, Wenli, Zhao, Jiyong, Alp, Esen E., Liu, Jin, Liu, Jiachao, Wentzowitch, Renata M., Okuchi, Takuo, and Dauphas, Nicolas. Fri . "Iron isotopic fractionation in mineral phases from Earth's lower mantle: Did terrestrial magma ocean crystallization fractionate iron isotopes?". United States. doi:10.1016/j.epsl.2018.10.034.
@article{osti_1503568,
title = {Iron isotopic fractionation in mineral phases from Earth's lower mantle: Did terrestrial magma ocean crystallization fractionate iron isotopes?},
author = {Yang, Hong and Lin, Jung-Fu and Hu, Michael Y. and Roskosz, Mathieu and Bi, Wenli and Zhao, Jiyong and Alp, Esen E. and Liu, Jin and Liu, Jiachao and Wentzowitch, Renata M. and Okuchi, Takuo and Dauphas, Nicolas},
abstractNote = {Iron is the most abundant transition metal in the Earth's interior, yet considerable uncertainties remain as to why mantle-derived rocks have diverse iron isotopic compositions. In particular, the isotopic fractionation behavior of iron in the lower-mantle minerals bridgmanite and ferropericlase are largely unexplored. The reason is that it is challenging to study isotopic fractionation at the high pressures relevant to the deep mantle. Here we report in situ measurements of the mean force constants of iron bonds in these minerals pressurized in diamond anvil cells using the technique of nuclear resonant inelastic X-ray scattering (NRIXS). We find that the transition from high- to low-spin iron in ferropericlase ((Mg0.75Fe0.25)O) at approximately 60 GPa drastically stiffens its iron bonds in the low-spin state. The mean force constant of iron bonds in both Fe-bearing and (Fe,Al)-bearing bridgmanite exhibits softening by 21% at approximately 40-60 GPa, which seems to be associated with changes in the iron local environment during the transition from low to high quadrupole splitting states. These results indicate that in the lower mantle, low-spin ferropericlase is enriched in heavy iron isotopes relative to bridgmanite and metallic iron by +0.15 parts per thousand and +0.12 parts per thousand, respectively. Based on these results, we investigate whether terrestrial magma ocean crystallization could have fractionated iron isotopes. We conclude that this process cannot be responsible for the heavy iron isotope enrichment measured in terrestrial basalts.},
doi = {10.1016/j.epsl.2018.10.034},
journal = {Earth and Planetary Science Letters},
issn = {0012-821X},
number = C,
volume = 506,
place = {United States},
year = {2018},
month = {11}
}

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