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The composition and redox state of hydrous partial melts generated at the top of the lower mantle

Huang, R; Boffa Ballaran, T; McCammon, CA; Frost, DJ; (2023) The composition and redox state of hydrous partial melts generated at the top of the lower mantle. Earth and Planetary Science Letters , 624 , Article 118447. 10.1016/j.epsl.2023.118447. Green open access

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Abstract

Seismic low-velocity zones, that are proposed to form through hydrous partial melting, have been observed at the top of the lower mantle. The buoyancy of such melts will depend significantly on their iron content, but little is known about how iron partitions into melts under these conditions. In this study, ferrous and ferric iron partitioning between bridgmanite and melt has been studied at 25 GPa and 1973 K. A model, based on these data, indicates that increasing oxygen fugacity and the Al content of bridgmanite can change the mineral–melt partitioning of iron from incompatible to compatible. Hydrous partial melts at the top of a pyrolitic lower mantle are calculated to have an Fe3+/∑Fe ratio of 0.26–0.5 and a total iron content of 5.9–7.8 wt. % in the fO2 range between IW+2 and IW+4. Such melts would be less dense than the surrounding lower mantle and would migrate upwards into the transition zone. This could facilitate the formation of superdeep diamonds and crystallize an assemblage that also contains ferropericlase as the melts lose water to the surrounding ringwoodite.

Type: Article
Title: The composition and redox state of hydrous partial melts generated at the top of the lower mantle
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.epsl.2023.118447
Publisher version: https://doi.org/10.1016/j.epsl.2023.118447
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher's terms and conditions.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery-pp.ucl.ac.uk/id/eprint/10182861
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