Abstract
Our current understanding of the electronic state of iron in lowermantle minerals leads to a considerable disagreement in bulk sound speed with seismic measurements if the lower mantle has the same composition as the upper mantle (pyrolite). In the modeling studies, the content and oxidation state of Fe in the minerals have been assumed to be constant throughout the lower mantle. Here, we report high-pressure experimental results in which Fe becomes dominantly Fe2+ in bridgmanite synthesized at 40-70 GPa and 2,000 K, while it is in mixed oxidation state (Fe3+/∑Fe = 60%) in the samples synthesized below and above the pressure range. Little Fe3+ in bridgmanite combined with the strong partitioning of Fe2+ into ferropericlase will alter the Fe content for these minerals at 1,100- to 1,700-km depths. Our calculations show that the change in iron content harmonizes the bulk sound speed of pyrolite with the seismic values in this region. Our experiments support no significant changes in bulk composition for most of the mantle, but possible changes in physical properties and processes (such as viscosity and mantle flow patterns) in the midmantle.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 6468-6473 |
| Number of pages | 6 |
| Journal | Proceedings of the National Academy of Sciences of the United States of America |
| Volume | 114 |
| Issue number | 25 |
| DOIs | |
| State | Published - Jun 20 2017 |
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Keywords
- Bridgmanite
- Bulk sound speed
- Lower mantle
- Oxidation state
- Spin transition
ASJC Scopus subject areas
- General
Cite this
Stability of ferrous-iron-rich bridgmanite under reducing midmantle conditions. / Shim, Sang-Heon; Grocholski, Brent; Ye, Yu; Alp, E. Ercan; Xu, Shenzhen; Morgan, Dane; Meng, Yue; Prakapenka, Vitali B.
In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 114, No. 25, 20.06.2017, p. 6468-6473.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Stability of ferrous-iron-rich bridgmanite under reducing midmantle conditions
AU - Shim, Sang-Heon
AU - Grocholski, Brent
AU - Ye, Yu
AU - Alp, E. Ercan
AU - Xu, Shenzhen
AU - Morgan, Dane
AU - Meng, Yue
AU - Prakapenka, Vitali B.
PY - 2017/6/20
Y1 - 2017/6/20
N2 - Our current understanding of the electronic state of iron in lowermantle minerals leads to a considerable disagreement in bulk sound speed with seismic measurements if the lower mantle has the same composition as the upper mantle (pyrolite). In the modeling studies, the content and oxidation state of Fe in the minerals have been assumed to be constant throughout the lower mantle. Here, we report high-pressure experimental results in which Fe becomes dominantly Fe2+ in bridgmanite synthesized at 40-70 GPa and 2,000 K, while it is in mixed oxidation state (Fe3+/∑Fe = 60%) in the samples synthesized below and above the pressure range. Little Fe3+ in bridgmanite combined with the strong partitioning of Fe2+ into ferropericlase will alter the Fe content for these minerals at 1,100- to 1,700-km depths. Our calculations show that the change in iron content harmonizes the bulk sound speed of pyrolite with the seismic values in this region. Our experiments support no significant changes in bulk composition for most of the mantle, but possible changes in physical properties and processes (such as viscosity and mantle flow patterns) in the midmantle.
AB - Our current understanding of the electronic state of iron in lowermantle minerals leads to a considerable disagreement in bulk sound speed with seismic measurements if the lower mantle has the same composition as the upper mantle (pyrolite). In the modeling studies, the content and oxidation state of Fe in the minerals have been assumed to be constant throughout the lower mantle. Here, we report high-pressure experimental results in which Fe becomes dominantly Fe2+ in bridgmanite synthesized at 40-70 GPa and 2,000 K, while it is in mixed oxidation state (Fe3+/∑Fe = 60%) in the samples synthesized below and above the pressure range. Little Fe3+ in bridgmanite combined with the strong partitioning of Fe2+ into ferropericlase will alter the Fe content for these minerals at 1,100- to 1,700-km depths. Our calculations show that the change in iron content harmonizes the bulk sound speed of pyrolite with the seismic values in this region. Our experiments support no significant changes in bulk composition for most of the mantle, but possible changes in physical properties and processes (such as viscosity and mantle flow patterns) in the midmantle.
KW - Bridgmanite
KW - Bulk sound speed
KW - Lower mantle
KW - Oxidation state
KW - Spin transition
UR - http://www.scopus.com/inward/record.url?scp=85021148542&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85021148542&partnerID=8YFLogxK
U2 - 10.1073/pnas.1614036114
DO - 10.1073/pnas.1614036114
M3 - Article
VL - 114
SP - 6468
EP - 6473
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
SN - 0027-8424
IS - 25
ER -