Journal
GEOCHIMICA ET COSMOCHIMICA ACTA
Volume 157, Issue -, Pages 28-38Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.gca.2015.02.017
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Funding
- NSF Earth Sciences [0511049, 0711599, 1215714, EAR-1128799]
- Durrell Funds (Department of Earth and Planetary Sciences, UC Davis)
- Chrysalis Scholarship from the Association of Women Geoscientists
- Danish National Research Foundation
- U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory
- U.S. DOE [DE-AC02-06CH11357]
- Department of Energy, Geosciences [DE-FG02-94ER14466]
- [UCLab09-LR-03-227404]
- Direct For Mathematical & Physical Scien
- Division Of Materials Research [1104869] Funding Source: National Science Foundation
- Directorate For Geosciences [0511049, 1215714, 0711599] Funding Source: National Science Foundation
- Division Of Earth Sciences [0511049, 0711599, 1215714] Funding Source: National Science Foundation
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The pressure-induced densification of NaAlSi3O8 liquid is determined following annealing immediately above the glass transition and upon quenching from superliquidus temperatures. High-field Al-27 magic-angle-spinning NMR spectroscopy is used to investigate the corresponding changes in Al coordination environment that accompany the densification. We show that samples synthesized by quenching from superliquidus temperatures record lower fictive pressures (P-f) than annealed samples at the same nominal load and have lower recovered densities and average Al coordination number. Accounting for differences in Pf brings melt-quench and annealed samples into excellent agreement. The proportion of Al-[5] increases from similar to 3% to 29% and Al-[6] from 0% to 8% between 1.8 and 7.2 GPa. The production of high-coordinated Al (Al-[5] + Al-[6]) with pressure is most dramatic above 3 GPa. Changes in network topology and structural disorder as revealed by the high-field Al-27 NMR spectra provide new insights into the structural mechanisms of densification of the albite liquid. We posit that it is an overall weakening of the network structure on compression that is largely responsible for the anomalous pressure dependence of the transport properties observed for this liquid below similar to 5 GPa. (C) 2015 Elsevier Ltd. All rights reserved.
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