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Title: Valence and spin states of iron are invisible in Earth’s lower mantle

Heterogeneity in Earth’s mantle is a record of chemical and dynamic processes over Earth’s history. The geophysical signatures of heterogeneity can only be interpreted with quantitative constraints on effects of major elements such as iron on physical properties including density, compressibility, and electrical conductivity. However, deconvolution of the effects of multiple valence and spin states of iron in bridgmanite (Bdg), the most abundant mineral in the lower mantle, has been challenging. Here we show through a study of a ferric-iron-only (Mg 0.46Fe 3+0.53)(Si 0.49Fe 3+ 0.51)O 3 Bdg that Fe 3+ in the octahedral site undergoes a spin transition between 43 and 53 GPa at 300 K. The resolved effects of the spin transition on density, bulk sound velocity, and electrical conductivity are smaller than previous estimations, consistent with the smooth depth profiles from geophysical observations. For likely mantle compositions, the valence state of iron has minor effects on density and sound velocities relative to major cation composition.
Authors:
ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [2] ; ORCiD logo [3] ; ORCiD logo [4] ;  [5] ;  [6] ;  [7]
  1. Michigan State Univ., East Lansing, MI (United States). Dept. of Earth and Environmental Sciences
  2. Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Earth and Environmental Sciences
  3. Center for High Pressure Science and Technology Advanced Research (HPSTAR), Beijing (China)
  4. Univ. of Hawaii at Manoa, Honolulu, HI (United States). Hawaii Inst. of Geophysics and Planetology
  5. Carnegie Inst. of Washington, Argonne, IL (United States). Geophysical Lab., High Pressure Collaborative Access Team (HPCAT)
  6. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS); Univ. of Illinois, Urbana-Champaign, IL (United States). Dept. of Geology
  7. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Publication Date:
Grant/Contract Number:
AC02-06CH11357; FG02-94ER14466; NA0001974; EAR-1634415; FG02-99ER45775
Type:
Accepted Manuscript
Journal Name:
Nature Communications
Additional Journal Information:
Journal Volume: 9; Journal Issue: 1; Journal ID: ISSN 2041-1723
Publisher:
Nature Publishing Group
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Aeronautic and Space Administration (NASA); USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Geophysics; Mineralogy
OSTI Identifier:
1433056