title: Determination of 17O-excess of terrestrial silicate/oxide minerals with respect to Vienna Standard Mean Ocean Water (VSMOW).
abstract: BACKGROUND
  Oxygen triple isotope compositions give key information for understanding physical processes during isotopic fractionation between the geo-, hydro-, bio-, and atmosphere. For detailed discussion of these topics, it is necessary to determine precise (17)O-excess values of terrestrial silicate/oxide minerals with respect to Vienna Standard Mean Ocean Water (VSMOW).
  
  
  METHODS
  Water was fluorinated in an electrically heated Ni-metal tube into which water and BrF(5) were loaded for the quantitative extraction of oxygen. Silicate/oxide minerals were fluorinated by heating with a CO(2) laser in an atmosphere of BrF(5). The extracted oxygen was purified and isotope ratios of the oxygen triple isotope compositions were determined using a Finnigan MAT253 isotope ratio mass spectrometer.
  
  
  RESULTS
  The oxygen triple isotope compositions of meteoric water and terrestrial silicate/oxide minerals fall on statistically distinguishable fractionation lines, defined as [ln(δ(17)O + 1) = λln(δ(18) O + 1) + Δ], where λ and Δ correspond to the slope and intercept, respectively. The fractionation line for meteoric water has λ = 0.5285 ± 0.0005 and Δ = 0.03 ± 0.02‰ and for terrestrial silicate/oxide minerals has λ = 0.5270 ± 0.0005 and Δ = -0.070 ± 0.005‰, at the 95% confidence limit.
  
  
  CONCLUSIONS
  All the analyzed terrestrial silicate/oxide minerals including internationally accepted reference materials (NBS-28, UWG-2, and San Carlos olivine) have a negative (17)O-excess with respect to VSMOW. We propose that it is necessary to specify if the determined δ(17)O values of terrestrial and extraterrestrial samples are expressed as the difference from VSMOW or the terrestrial silicate mineral-corrected value.
authors.affiliation: The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori 682-0193, Japan. ryoji@misasa.okayama-u.ac.jp
authors.forename: Ryoji
authors.initials: R
authors.lastname: Tanaka
authors.forename: Eizo
authors.initials: E
authors.lastname: Nakamura
mesh_terms: D005618:Fresh Water / Q000737:chemistry*; D054879:Halogenation; D058085:Iron Compounds / Q000737:chemistry; D016014:Linear Models; D017616:Magnesium Compounds / Q000737:chemistry; D013058:Mass Spectrometry; D010087:Oxides / Q000737:chemistry*; D010103:Oxygen Isotopes / Q000032:analysis*; D012015:Reference Standards; D017640:Silicates / Q000737:chemistry*
chemical_list: D058085:Iron Compounds; D017616:Magnesium Compounds; D010087:Oxides; D010103:Oxygen Isotopes; D017640:Silicates; C034475:olivine