Papers

Peer-reviewed
Oct 25, 2019

Solubility behavior of δ-AlOOH and ϵ-FeOOH at high pressures

American Mineralogist
  • Chaowen Xu
  • ,
  • Masayuki Nishi
  • ,
  • Toru Inoue

Volume
104
Number
First page
1416
Last page
1420
DOI
10.2138/am-2019-7064

© 2019 Walter de Gruyter GmbH, Berlin/Boston. Low-pressure polymorphs of AlOOH and FeOOH are common natural oxyhydroxides at the Earth's surface, which may transport hydrogen to the deep mantle via subduction. At elevated pressures, the low-pressure polymorphs transform into δ-AlOOH and ϵ-FeOOH with CaCl2-type structure, which form a solid solution above 18 GPa. Nevertheless, few studies have examined the solid solution behavior of this binary system in detail. In this study, we ascertain the phase relations in the AlOOH-FeOOH binary system at 15-25 GPa and 700-1200 °C. X-ray diffraction (XRD) measurements of quenched samples show that δ-AlOOH and ϵ-FeOOH partly form solid solutions over wide pressure and temperature ranges. Our results demonstrate that a binary eutectic diagram is formed without dehydration or melting below 1200 °C at 20 GPa. We also observe that the maximum solubilities of Al and Fe in the solid solutions are more strongly influenced by temperature than pressure. Our results suggest that the CaCl2-type hydroxides subducted into the deep mantle form a solid solution over a wide composition range. As AlOOH and FeOOH are present in hydrous crust, these phases may be subducted into the deep interior, transporting a significant amount of hydrogen to deeper regions. Therefore, a better understanding of this binary system may help elucidate the model geodynamic processes associated with the deep water cycling in the Earth.

Link information
DOI
https://doi.org/10.2138/am-2019-7064
URL
https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85073217629&origin=inward
ID information
  • DOI : 10.2138/am-2019-7064
  • ISSN : 0003-004X
  • SCOPUS ID : 85073217629

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