Ferrous Iron Under Oxygen-Rich Conditions in the Deep Mantle
Résumé
Recent experiments have demonstrated the existence of previously unknown iron oxides at high pressure and temperature including newly discovered pyrite‐type FeO2 and FeO2Hx phases stable at deep terrestrial lower mantle pressures and temperatures. In the present study, we probed the iron oxidation state in high‐pressure transformation products of Fe3+OOH goethite by in situ X‐ray absorption spectroscopy in laser‐heated diamond‐anvil cell. At pressures and temperatures of ~91 GPa and 1,500–2,350 K, respectively, that is, in the previously reported stability field of FeO2Hx, a measured shift of −3.3 ± 0.1 eV of the Fe K‐edge demonstrates that iron has turned from Fe3+ to Fe2+. We interpret this reductive valence change of iron by a concomitant oxidation of oxygen atoms from O2− to O−, in agreement with previous suggestions based on the structures of pyrite‐type FeO2 and FeO2Hx phases. Such peculiar chemistry could drastically change our view of crystal chemistry in deep planetary interiors.
Domaines
Géochimie
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Boulard_et_al-2019-Geophysical_Research_Letters.pdf (2.91 Mo)
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