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Configurational entropy of basaltic melts in Earth’s mantle

Lee, Sung Keun and Mosenfelder, Jed L. and Park, Sun Young and Lee, A. Chim and Asimow, Paul D. (2020) Configurational entropy of basaltic melts in Earth’s mantle. Proceedings of the National Academy of Sciences of the United States of America, 117 (36). pp. 21938-21944. ISSN 0027-8424. PMCID PMC7486762. doi:10.1073/pnas.2014519117.

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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.

Item Type:Article
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URLURL TypeDescription CentralArticle Information
Lee, Sung Keun0000-0002-3149-3421
Park, Sun Young0000-0002-4672-3074
Lee, A. Chim0000-0002-8279-2085
Asimow, Paul D.0000-0001-6025-8925
Additional Information:© 2020 National Academy of Sciences. Published under the PNAS license. Edited by W. G. Ernst, Stanford University, Stanford, CA, and approved August 5, 2020 (received for review July 10, 2020). PNAS first published August 24, 2020. 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. Data Availability: All study data are included in the article and SI Appendix. Author contributions: S.K.L. designed research; S.K.L., J.L.M., and S.Y.P. performed research; S.K.L., J.L.M., S.Y.P., and P.D.A. contributed new reagents/analytic tools; S.K.L., S.Y.P., and A.C.L. analyzed data; and S.K.L., J.L.M., and P.D.A. wrote the paper. The authors declare no competing interest. This article is a PNAS Direct Submission. This article contains supporting information online at
Funding AgencyGrant Number
National Research Foundation of Korea2017R1A2A1A17069511
National Research Foundation of Korea2020R1A3B2079815
Subject Keywords:configurational entropy; embryonic basaltic melts in Earth’s mantle; anomalous compression of melts
Issue or Number:36
PubMed Central ID:PMC7486762
Record Number:CaltechAUTHORS:20200825-084943976
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Official Citation:Configurational entropy of basaltic melts in Earth’s mantle. Sung Keun Lee, Jed L. Mosenfelder, Sun Young Park, A. Chim Lee, Paul D. Asimow. Proceedings of the National Academy of Sciences Sep 2020, 117 (36) 21938-21944; DOI: 10.1073/pnas.2014519117
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105096
Deposited By: Tony Diaz
Deposited On:25 Aug 2020 16:46
Last Modified:09 Feb 2022 23:19

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