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Mass-independent fractionation of oxygen isotopes during thermal decomposition of carbonates

Miller, Martin F.; Franchi, Ian A.; Thiemens, Mark H.; Jackson, Teresa L.; Brack, Andre; Kurat, Gero and Pillinger, Colin T. (2002). Mass-independent fractionation of oxygen isotopes during thermal decomposition of carbonates. Proceedings of the National Academy of Sciences of the USA, 99(17) pp. 10988–10993.

DOI (Digital Object Identifier) Link: http://dx.doi.org/10.1073/pnas.172378499
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Abstract

Nearly all chemical processes fractionate 17O and 18O in a mass-dependent way relative to 16O, a major exception being the formation of ozone from diatomic oxygen in the presence of UV radiation or electrical discharge. Investigation of oxygen three-isotope behavior during thermal decomposition of naturally occurring carbonates of calcium and magnesium in vacuo has revealed that, surprisingly, anomalous isotopic compositions are also generated during this process. High-precision measurements of the attendant three-isotope fractionation line, and consequently the magnitude of the isotopic anomaly (17O), demonstrate that the slope of the line is independent of the nature of the carbonate but is controlled by empirical factors relating to the decomposition procedure. For a slope identical to that describing terrestrial silicates and waters (0.5247 ± 0.0007 at the 95% confidence level), solid oxides formed during carbonate pyrolysis fit a parallel line offset by –0.241 ± 0.042. The corresponding CO2 is characterized by a positive offset of half this magnitude, confirming the mass-independent nature of the fractionation. Slow, protracted thermolysis produces a fractionation line of shallower slope (0.5198 ± 0.0007). These findings of a 17O anomaly being generated from a solid, and solely by thermal means, provide a further challenge to current understanding of the nature of mass-independent isotopic fractionation.

Item Type: Journal Article
ISSN: 1091-6490
Extra Information: Some of the symbols may not have transferred correctly into this bibliographic record and/or abstract
Academic Unit/Department: Science > Physical Sciences
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID: 4834
Depositing User: Users 6044 not found.
Date Deposited: 11 Jul 2006
Last Modified: 02 Dec 2010 19:52
URI: http://oro.open.ac.uk/id/eprint/4834
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