Equilibrium Fractionation of Non-traditional Isotopes: a Molecular Modeling Perspective

Blanchard, Marc; Balan, Etienne; Schauble, E. A.

doi:10.2138/rmg.2017.82.2

Cited by 77 publications

(42 citation statements)

References 196 publications

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“…This is consistent with the work of Colla et al (2013) who observed a correlation between calcium isotope fractionation and coordination number between solvated calcium ions and their solid hydrates, concluding that low-coordination environments result in heavier isotopic compositions, in agreement with the general rule of thumb (Schauble, 2004;Blanchard et al, 2017). In the carbonate-bearing models, the presence of the carbonate group affects both the Ca(I) and Ca(II) sites (Fig.…”

Section: Equilibrium Isotopic Fractionation Of Calciumsupporting

confidence: 91%

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Site-specific equilibrium isotopic fractionation of oxygen, carbon and calcium in apatite

Aufort

Ségalen

Gervais

et al. 2017

Geochimica et Cosmochimica Acta

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The stable isotope composition of biogenic apatite is an important geochemical marker that can record environmental parameters and is widely used to infer past climates, biomineralization processes, dietary preferences and habitat of vertebrates. In this study, theoretical equilibrium isotopic fractionation of oxygen, carbon and calcium in hydroxyapatite and carbonate-bearing hydroxyapatite is investigated using first-principles methods based on density-functional theory and compared to the theoretical isotopic fractionation properties of calcite, CO 2 and H 2 O. Considering the variability of apatite crystal-chemistry, special attention is given to specific contributions of crystal sites to isotopic fractionation. Significant internal fractionation is calculated for oxygen and carbon isotopes in CO 3 between the different structural sites occupied by carbonate groups in apatite (typically 7‰ for both 18 O/ 16 O and 13 C/ 12 C fractionation at 37°C). Compared with calcite-water oxygen isotope fractionation, occurrence of A-type substitution in apatite structure, in addition to the main B-type substitution, could explain the larger temperature dependence of oxygen isotope fractionation measured at low temperature between carbonate in apatite and water. Theoretical internal fractionation of oxygen isotopes between carbonate and phosphate in B-type carbonated apatite ($8‰ at 37°C) is consistent with experimental values obtained from modern and well-preserved fossil bio-apatites. Concerning calcium, theoretical results suggest a small fractionation between apatite and calcite (À0.17‰ at 37°C). Internal fractionation reaching 0.8‰ at 37°C occurs between the two Ca sites in hydroxyapatite. Furthermore, the Ca isotopic fractionation properties of apatite are affected by the occurrence of carbonate groups, which could contribute to the variability observed on natural samples. Owing to the complexity of apatite crystal-chemistry and in light of the theoretical results, measurements of site-specific isotopic fractionation properties could improve our understanding and the interpretation of isotopic records in apatites.

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Section: Equilibrium Isotopic Fractionation Of Calciumsupporting

confidence: 91%

“…Additional difficulties may also arise when non-conventional stable isotopes are investigated due to the small magnitude of isotopic fractionation factors (e.g. Blanchard et al, 2017). Experimental equilibrium fractionation laws may therefore be affected by large uncertainties at low temperatures.…”

Section: Introductionmentioning

confidence: 99%

Site-specific equilibrium isotopic fractionation of oxygen, carbon and calcium in apatite

Aufort

Ségalen

Gervais

et al. 2017

Geochimica et Cosmochimica Acta

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“…This can only be achieved through use of the double-spike technique. Equilibrium or kinetic fractionation effects (e.g., Blanchard et al, 2017;Watkins et al, 2017) in the data presented here can be related to two different realms of processes. First, the fractionation that occurred during the development of the components that were assembled to produce the meteorites (regardless of their degree of differentiation).…”

Section: Resultsmentioning

confidence: 88%

Stable strontium isotopic heterogeneity in the solar system from double-spike data

Charlier¹,

Parkinson²,

Burton³

et al. 2017

Geochem. Persp. Let.

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Strontium isotopic anomalies in meteorites are important in assessing nucleosynthetic sources to, and measuring the timing of, early solar system processes. However, conventional use of a constant 88 Sr/ 86 Sr value in correcting for instrumental mass fractionation during analysis renders measurements ambiguous and removes information on mass-dependent fractionation variations. From doublespike techniques we obtain data for the four stable strontium isotopes free of this ambiguity, and report measurements from a range of meteoritic, lunar and terrestrial materials. The Earth, Moon, basaltic eucrites and feldspars from angrites (differentiated samples) follow a single mass-dependent fractionation line and have a common nucleosynthetic origin in terms of their strontium isotopes. In contrast, bulk rock CI, CV3, CM and CO chondrite samples serve to define another mass-dependent fractionation line, displaced by 94 ± 28 ppm to heavier 84 Sr/ 86 Sr and/or 88 Sr/ 86 Sr ratios than that for the differentiated samples. Our Sr-isotopic data are consistent with a primary contrast in early solar system composition between an outer zone of primitive, mostly undifferentiated, materials and an inner zone of (almost entirely) differentiated materials that accumulated to form the terrestrial planets.

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“…i and ν i of the lightest and heaviest isotopologues respectively (Bigeleisen & Mayer, 1947;Blanchard et al, 2017):…”

Section: Equilibrium Isotopic Fractionation Factorsmentioning

confidence: 99%

Equilibrium isotopic fractionation between aqueous Zn and minerals from first-principles calculations

2018

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Theoretical mineral-solution equilibrium isotopic fractionation can contribute to the interpretation of Zn isotopic compositions. In this study, we investigate equilibrium isotopic fractionation properties of hexaaquo zinc complex, a major Zn aqueous species, using first-principles molecular dynamics (FPMD) based on density functional theory (DFT). Pentaaquo and tetraaquo zinc complexes, which can be relevant for specific mechanisms such as adsorption on mineral surfaces, are also considered. This approach takes into account both configurational and solvation effects that are less easily accounted for in molecular cluster models. The logarithmic value of the reduced partition function ratio of aqueous Zn (ln β 66 Zn/ 64 Zn) is 2.86 ± 0.04 at 295 K, while the same computational approach gave ln β 66 Zn/ 64 Zn in the range 2.2 − 4.1 for various Znbearing minerals. For example, calculations predict at 295 K, equilibrium fractionations between mineral and aqueous Zn of-0.46 for primary zinc sulfide sphalerite and of-0.20 and +0.34 for secondary phases gunningite and hydrozincite, respectively. Molecular clusters are also modelled, predicting isotopically heavier Zn with respect to related FPMD models (ln β increases by 0.09 to 0.23). These values are small but significant in the Zn isotopic system and supports the idea that a proper description of the dynamics of the system and the solvation effect are required for a reliable prediction of the isotopic properties of solvated ions.

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Equilibrium Fractionation of Non-traditional Isotopes: a Molecular Modeling Perspective

Cited by 77 publications

References 196 publications

Site-specific equilibrium isotopic fractionation of oxygen, carbon and calcium in apatite

Site-specific equilibrium isotopic fractionation of oxygen, carbon and calcium in apatite

Stable strontium isotopic heterogeneity in the solar system from double-spike data

Equilibrium isotopic fractionation between aqueous Zn and minerals from first-principles calculations

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