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The influence of low-spin ferrous iron on the oxidation state of the Earth's mantle
The Earth’s mantle has elevated Fe3+ contents relative to those of other telluric bodies, a property thought to reflect the disproportionation of ferrous iron into its metallic and ferric counterparts during core formation. However, how the oxidation and electronic state of iron change as a function of pressure in compositions relevant to that of Earth’s mantle are not fully understood. In this study, we present in-situ energy domain synchrotron Mössbauer spectra of 57Fe-enriched peridotitic- and basaltic glasses at 298 K compressed from 1 bar to 174 GPa in a diamond anvil cell. Glasses were synthesised with different Fe3+/[Fe3+ + Fe2+] ratios, 0.02 ± 0.02 and 1.00 ± 0.02, respectively, as determined by colorimetry. At 1 bar, the spectrum of the Fe3+-basaltic glass is well fit by a single doublet. In contrast, the spectra of both Fe2+-rich peridotitic and basaltic glass are fit by two doublets, D1 (~92 %) and D2 (~8 %) at 1 bar. As pressure increases, the integral area of the D2 doublet increases at the expense of D1 to reach a D2/(D1 + D2) ratio of 0.65 by 172 GPa. Because this transition is reversible with pressure and no metallic iron is detected, the D2 feature is ascribed to Fe2+ in its low spin (LS) state, whereas D1 is consistent with Fe2+ high spin (HS). This assignment resolves a long-standing controversy on the interpretation of the Mössbauer spectra of basaltic glasses. As a consequence of the stabilisation of Fe2+ with pressure, terrestrial planets more massive than Earth likely do not host increasingly oxidising mantles.
Date:
6 February 2026, 12:00
Venue:
Department of Earth Sciences, South Parks Road OX1 3AN
Venue Details:
Seminar rooms
Speaker:
Prof. Dr. Paolo Angelo Sossi (ETH Zürich)
Organising department:
Department of Earth Sciences
Part of:
Earth Sciences departmental seminars
Booking required?:
Not required
Booking url:
https://www.earth.ox.ac.uk/event/the-influence-of-low-spin-ferrous-iron-on-the-oxidation-state-of-the-earths-mantle
Audience:
Public
Editor:
Maria Petrunova
