Composition dependence of spin transition in (Mg,Fe)SiO 3 bridgmanite

Susannah Dorfman (1) , James Badro (2, 1) , Jean-Pascal Rueff (3, 4) , Paul Chow (5) , Yuming Xiao (5) , Philippe Gillet (1)

1 EPFL - Ecole Polytechnique Fédérale de Lausanne
2 IPGP (UMR_7154) - Institut de Physique du Globe de Paris
3 SSOLEIL - Synchrotron SOLEIL
4 LCPMR - Laboratoire de Chimie Physique - Matière et Rayonnement
5 Carnegie Institution of Washington

Spin transitions in (Mg,Fe)SiO3 bridgmanite have important implications for the chemistry and dynamics of Earth's lower mantle, but have been complex to characterize in experiments. We examine the spin state of Fe in highly Fe-enriched bridgmanite synthesized from enstatites with measured compositions (Mg0.61Fe0.38Ca0.01)SiO3 and (Mg0.25Fe0.74Ca0.01)SiO3. Bridgmanite was synthesized at 78-88 GPa and 1800-2400 K and X-ray emission spectra were measured on decompression to 1 bar (both compositions) and compression to 126 GPa [(Mg0.61Fe0.38Ca0.01)SiO3 only] without additional laser heating. Observed spectra confirm that Fe in these bridgmanites is dominantly high spin in the lower mantle. However, the total spin moment begins to decrease at similar to 50 GPa in the 74% FeSiO3 composition. These results support density functional theory predictions of a lower spin transition pressure in highly Fe-enriched bridgmanite and potentially explain the high solubility of FeSiO3 in bridgmanite at pressures corresponding to Earth's deep lower mantle.

Mots clés: Bridgmanite; spin transition; iron-bearing silicates; lower mantle

Domaines: Minéralogie; Matériaux

Susannah Dorfman, James Badro, Jean-Pascal Rueff, Paul Chow, Yuming Xiao, et al.. Composition dependence of spin transition in (Mg,Fe)SiO 3 bridgmanite. The American Mineralogist, 2015, 100 (10), pp.2246-2253. ⟨10.2138/am-2015-5190⟩. ⟨insu-02913653⟩