Configurational entropy of basaltic melts in Earth's mantle

Sung Keun Lee, Jed L. Mosenfelder, Sun Young Park, A. Chim Lee, Paul D. Asimow

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

Although geophysical observations of mantle regions that suggest the presence of partial melt have often been interpreted in light of the properties of basaltic liquids erupted at the surface, the seismic and rheological consequences of partial melting in the upper mantle depend instead on the properties of interstitial basaltic melt at elevated pressure. In particular, basaltic melts and glasses display anomalous mechanical softening upon compression up to several GPa, suggesting that the relevant properties of melt are strongly pressure-dependent. A full understanding of such a softening requires study, under compression, of the atomic structure of primitive small-degree basaltic melts at their formation depth, which has proven to be difficult. Here we report multiNMR spectra for a simplified basaltic glass quenched at pressures up to 5 GPa (corresponding to depths down to ~150 km). These data allow quantification of short-range structural parameters such as the populations of coordination numbers of Al and Si cations and the cation pairs bonded to oxygen atoms. In the model basaltic glass, the fraction of [5,6]Al is ~40% at 5 GPa and decreases to ~3% at 1 atm. The estimated fraction of nonbridging oxygens at 5 GPa is ~84% of that at ambient pressure. Together with data on variable glass compositions at 1 atm, these results allow us to quantify how such structural changes increase the configurational entropy of melts with increasing density. We explore how configurational entropy can be used to explain the anomalous mechanical softening of basaltic melts and glasses.

Original languageEnglish (US)
Pages (from-to)21938-21944
Number of pages7
JournalProceedings of the National Academy of Sciences of the United States of America
Volume117
Issue number36
DOIs
StatePublished - Sep 8 2020

Bibliographical note

Funding Information:
This study was supported by a grant from the National Research Foundation, Korea (2017R1A2A1A17069511 and 2020R1A3B2079815), to S.K.L. We appreciate reviewers' constructive comments, which greatly improved the quality and clarity of the manuscript.

Publisher Copyright:
© 2020 National Academy of Sciences. All rights reserved.

Keywords

  • Anomalous compression of melts
  • Configurational entropy
  • Embryonic basaltic melts in Earth's mantle

PubMed: MeSH publication types

  • Journal Article

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