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Iron spin transition in Earth's mantle
S Speziale1, A Milner, V E Lee
1Department of Earth and Planetary Science, University of California, Berkeley, 94720, USA.
Summary
Ferrous iron (Fe(2+)) in Earth's mantle undergoes a high-spin to low-spin transition, causing a significant volume change. This spin transition impacts mineral properties and may explain seismic anomalies in the deep Earth.
Area of Science:
- Mineral Physics
- Geochemistry
- Solid Earth Geophysics
Background:
- Magnesiowüstite ((Mg,Fe)O) is a major component of Earth's lower mantle.
- Understanding iron spin states under high pressure is crucial for interpreting seismic data.
Purpose of the Study:
- To investigate the high-spin to low-spin transition of ferrous iron (Fe(2+)) in magnesiowüstite.
- To quantify the associated volume change and its implications for Earth's deep interior.
Main Methods:
- High-pressure Mössbauer spectroscopy was used to study iron spin states.
- High-resolution X-ray diffraction measured volume changes during the spin transition.
Main Results:
- Ferrous iron (Fe(2+)) in magnesiowüstite undergoes a pressure-induced spin transition relevant to Earth's mantle.
- A significant volume change of 4-5% was observed across the spin transition.
- The spin transition can lead to the dissociation of magnesiowüstite.
Conclusions:
- The spin transition of Fe(2+) in magnesiowüstite is a key factor influencing lower mantle properties.
- This phenomenon can cause seismological anomalies and alter phase equilibria in Earth's deep interior.
- Mineral properties and phase behaviors in the deep Earth are more complex than previously thought.