Partial Deoxygenation and Dehydration of Ferric Oxyhydroxide in Earth's Subducting Slabs. Issue 17 (28th August 2021)

• Record Type: Journal Article
• Authors: Gan, Bo; Zhang, Youjun; Huang, Yuqian; Li, Xiaohong; Wang, Qiming; Li, Jun; Zhuang, Yukuai; Liu, Yun; Jiang, Gang
• Is Part Of: Geophysical research letters. Volume 48:Issue 17(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-08-28
• Subjects: FeOOH -- deoxygenation -- dehydration -- high pressure and temperature -- Great Oxidation Event; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL094446
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The thermal stability of hydrous minerals in Earth's deep interior is key to understanding the evolution and physicochemical states of the planet. The recently discovered pyrite‐type (Py) FeO2 H x ( x ≤ 1) phase, which can be transformed from α/ε‐FeOOH at ∼80 GPa, is believed to be a crucial candidate in transporting water and hydrogen to the lowermost mantle through subducting slabs. Here, we examined the stability and decomposition behavior of FeOOH through a set of shock‐recovery experiments up to ∼70 GPa and ∼2, 750 K. Our results show that FeOOH partially decomposes to iron oxides Fe2 O3 and Fe3 O4 at 35–70 GPa and 1, 150–2, 750 K, which indicates that H2 O and O2 are released during the decomposition of FeOOH in subducting slabs. The released H2 O and O2 may have altered the physical and chemical properties of the surrounding mantle and contributed to the oxidation of surface Earth. Plain Language Summary: The mineral goethite (α‐FeOOH), a primary component of rusts and bog iron ores, is widespread on our planet. Early studies show that FeOOH polymorphs could transport water and hydrogen to the lowermost mantle when the minerals are transformed into hydrogen‐bearing iron peroxides at ∼1, 800 km depths. However, the thermal stability of FeOOH at the mid‐lower mantle equivalent pressure‐temperature conditions is poorly known. Here, we used a shock‐recovery approach to examine the stability of FeOOH at pressures up to ∼70 GPa and temperatures to ∼2, 750 K. Our results show that FeOOH partially decomposes to form hematite and magnetite, releasing water and oxygen at the equivalent pressure‐temperature conditions of a subducting slab in the mid‐lower mantle, thus indicating a narrower FeOOH‐stable region in the lower mantle than previously proposed. The released oxygen via FeOOH decomposition may have provided extra oxidation power for the long‐term oxidation of Earth's surface. Key Points: The thermal stability of FeOOH has been investigated by shock recovery experiments up to ∼70 GPa and ∼2, 750 K FeOOH partially decomposes and releases water and oxygen in the mid‐lower mantle The deoxygenation of FeOOH is a potential sporadic oxygen source for the Great Oxidation Event of Earth