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Determination of 17 O‐excess of terrestrial silicate/oxide minerals with respect to Vienna Standard Mean Ocean Water (VSMOW)
Author(s) -
Tanaka Ryoji,
Nakamura Eizo
Publication year - 2012
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.6453
Subject(s) - silicate , chemistry , fractionation , silicate minerals , oxide minerals , isotopes of oxygen , analytical chemistry (journal) , stable isotope ratio , oxygen isotope ratio cycle , oxygen , atmosphere (unit) , isotope analysis , mineralogy , environmental chemistry , geology , nuclear chemistry , chromatography , chemical reaction , physics , oceanography , organic chemistry , quantum mechanics , thermodynamics , biochemistry
RATIONALE 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. Copyright © 2012 John Wiley & Sons, Ltd.