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Prediction of equilibrium isotopic fractionation of the gypsum/bassanite/water system using first-principles calculations
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dc.contributor.author | Liu, Tao | |
dc.contributor.author | Artacho, Emilio | |
dc.contributor.author | Gázquez, Fernando | |
dc.contributor.author | Walters, Gregory | |
dc.contributor.author | Hodell, David | |
dc.date.accessioned | 2019-09-04T23:39:49Z | |
dc.date.available | 2019-09-04T23:39:49Z | |
dc.date.issued | 2019-01-01 | |
dc.identifier | 255764922 | |
dc.identifier | df113c06-7d1e-4882-a1fb-e97d82e17cc7 | |
dc.identifier | 85054559270 | |
dc.identifier | 000451066300001 | |
dc.identifier.citation | Liu , T , Artacho , E , Gázquez , F , Walters , G & Hodell , D 2019 , ' Prediction of equilibrium isotopic fractionation of the gypsum/bassanite/water system using first-principles calculations ' , Geochimica et Cosmochimica Acta , vol. 244 , pp. 1-11 . https://doi.org/10.1016/j.gca.2018.08.045 | en |
dc.identifier.issn | 0016-7037 | |
dc.identifier.other | RIS: urn:EC8CA88AB2FCBA9D7CF683822C286204 | |
dc.identifier.uri | https://hdl.handle.net/10023/18422 | |
dc.description | This research was supported by the ERC WIHM Project [#339694] to DAH. | en |
dc.description.abstract | The stable isotopes (18O/16O, 17O/16O and 2H/1H) of structurally-bound water (also called hydration water) in gypsum (CaSO4•2H2O) and bassanite (CaSO4•0.5H2O) can be used to reconstruct the isotopic composition of paleo-waters. Understanding the variability of the isotope fractionation factors between the solution and the solid (α17Omineral-water, α18Omineral-water and αDmineral-water) is crucial for applying this proxy to paleoclimatic research. Here we predict the theoretical equilibrium fractionation factors for triple oxygen and hydrogen isotopes in the gypsum-water and bassanite-water systems between 0 °C and 60 °C. We apply first-principles using density functional theory within the harmonic approximation. Our theoretical results for α18Ogypsum-water (1.00347±0.00037) are in agreement with previous experimental studies, whereas αDgypsum-water agrees only at temperatures above 25 °C. At lower temperatures, the experimental values of αDgypsum-water are consistently higher than theoretical values (e.g. 0.9749 and 0.9782, respectively, at 3 °C), which can be explained by kinetic effects that affect gypsum precipitation under laboratory conditions at low temperature. We predict that α18Obassanite-water is similar to α18Ogypsum-water in the temperature range of 0 °C to 60 °C. Both α18Ogypsum-water and α18Obassanite-water show a small temperature dependence of ∼0.0000122 per °C, which is negligible for most paleoclimate studies. The theoretical relationship between α17Ogypsum-water and α18Ogypsum-water (θ =lnα17Olnα18O) from 0 °C to 60 °C is 0.5274±0.00063. The relationship is very insensitive to temperature (0.00002 per °C). The fact that δ18O values of gypsum hydration water are greater than free water (α18Ogypsum-water >1) whereas δD values of gypsum hydration water are less than free water (αDgypsum-water <1) is explained by phonon theory. We conclude that calculations from first-principles using density functional theory within the harmonic approximation can accurately predict fractionation factors between structurally-bound water of minerals and free water. | |
dc.format.extent | 1509119 | |
dc.format.extent | 1020942 | |
dc.language.iso | eng | |
dc.relation.ispartof | Geochimica et Cosmochimica Acta | en |
dc.subject | Gypsum | en |
dc.subject | Bassanite | en |
dc.subject | Fractionation factor | en |
dc.subject | First-principles | en |
dc.subject | GE Environmental Sciences | en |
dc.subject | NDAS | en |
dc.subject.lcc | GE | en |
dc.title | Prediction of equilibrium isotopic fractionation of the gypsum/bassanite/water system using first-principles calculations | en |
dc.type | Journal article | en |
dc.contributor.institution | University of St Andrews. School of Earth & Environmental Sciences | en |
dc.identifier.doi | 10.1016/j.gca.2018.08.045 | |
dc.description.status | Peer reviewed | en |
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