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Title: Stability of ferrous-iron-rich bridgmanite under reducing midmantle conditions

Abstract

Our current understanding of the electronic state of iron in lower-mantle minerals leads to a 8 considerable disagreement in bulk sound speed with seismic measurements if the lower mantle 9 has the same composition as the upper mantle (pyrolite). In the modelling studies, the content 10 and oxidation state of Fe in the minerals have been assumed to be constant throughout the lower 11 mantle. Here, we report high pressure experimental results in which Fe becomes dominantly 1 Fe2+ 12 in bridgmanite synthesized at 40–70GPa and 2,000K, while it is in mixed oxidation state (Fe3+/ P Fe = 60%) in the samples synthesized below and above the pressure range. Little Fe3+ 13 14 in bridgmanite combined with the strong partitioning of Fe2+ into ferropericlase will alter the Fe 15 content for these minerals at 1,100–1,700 km depths. Our calculations show that the change in 16 iron content harmonizes the bulk sound speed of pyrolite with the seismic values in this region. 17 Our experiments support no significant changes in bulk composition for most of the mantle, 18 while possible changes in physical properties and processes (such as viscosity and mantle flow 19 patterns) in the mid mantle.

Authors:
ORCiD logo; ; ; ; ; ; ;
Publication Date:
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)
OSTI Identifier:
1376706
DOE Contract Number:  
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Proceedings of the National Academy of Sciences of the United States of America; Journal Volume: 114; Journal Issue: 25
Country of Publication:
United States
Language:
English
Subject:
Ferrous-Iron-Rich

Citation Formats

Shim, Sang-Heon, Grocholski, Brent, Ye, Yu, Alp, E. Ercan, Xu, Shenzhen, Morgan, Dane, Meng, Yue, and Prakapenka, Vitali B.. Stability of ferrous-iron-rich bridgmanite under reducing midmantle conditions. United States: N. p., 2017. Web. doi:10.1073/pnas.1614036114.
Shim, Sang-Heon, Grocholski, Brent, Ye, Yu, Alp, E. Ercan, Xu, Shenzhen, Morgan, Dane, Meng, Yue, & Prakapenka, Vitali B.. Stability of ferrous-iron-rich bridgmanite under reducing midmantle conditions. United States. doi:10.1073/pnas.1614036114.
Shim, Sang-Heon, Grocholski, Brent, Ye, Yu, Alp, E. Ercan, Xu, Shenzhen, Morgan, Dane, Meng, Yue, and Prakapenka, Vitali B.. Mon . "Stability of ferrous-iron-rich bridgmanite under reducing midmantle conditions". United States. doi:10.1073/pnas.1614036114.
@article{osti_1376706,
title = {Stability of ferrous-iron-rich bridgmanite under reducing midmantle conditions},
author = {Shim, Sang-Heon and Grocholski, Brent and Ye, Yu and Alp, E. Ercan and Xu, Shenzhen and Morgan, Dane and Meng, Yue and Prakapenka, Vitali B.},
abstractNote = {Our current understanding of the electronic state of iron in lower-mantle minerals leads to a 8 considerable disagreement in bulk sound speed with seismic measurements if the lower mantle 9 has the same composition as the upper mantle (pyrolite). In the modelling studies, the content 10 and oxidation state of Fe in the minerals have been assumed to be constant throughout the lower 11 mantle. Here, we report high pressure experimental results in which Fe becomes dominantly 1 Fe2+ 12 in bridgmanite synthesized at 40–70GPa and 2,000K, while it is in mixed oxidation state (Fe3+/ P Fe = 60%) in the samples synthesized below and above the pressure range. Little Fe3+ 13 14 in bridgmanite combined with the strong partitioning of Fe2+ into ferropericlase will alter the Fe 15 content for these minerals at 1,100–1,700 km depths. Our calculations show that the change in 16 iron content harmonizes the bulk sound speed of pyrolite with the seismic values in this region. 17 Our experiments support no significant changes in bulk composition for most of the mantle, 18 while possible changes in physical properties and processes (such as viscosity and mantle flow 19 patterns) in the mid mantle.},
doi = {10.1073/pnas.1614036114},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 25,
volume = 114,
place = {United States},
year = {Mon Jun 05 00:00:00 EDT 2017},
month = {Mon Jun 05 00:00:00 EDT 2017}
}