OG1: A natural reference material for quantifying SIMS instrumental mass fractionation of Pb isotopes during zircon dating  


Authors / CoAuthors

Bodorkos, S. | Stern, R.A. | Kamo, S.L. | Corfu, F. | Hickman, A.H.

Abstract

Over the last 20 years, it has become common practice to treat SIMS measurements of <sup>207</sup>Pb/<sup>206</sup>Pb in zircon as unfractionated. Consequently, uncertainties associated with composite <sup>207</sup>Pb/<sup>206</sup>Pb values are often limited only by population statistics of the weighted mean, and citation of 95% confidence limits of 1- (or less) on Meso- to Paleoarchean mean ages is increasingly commonplace. In such cases, the presence of undiagnosed SIMS instrumental mass fractionation of <sup>207</sup>Pb/<sup>206</sup>Pb of similar magnitude (1-2-) could have serious ramifications for the accuracy of the measured age: in extreme cases, the 'true' <sup>207</sup>Pb/<sup>206</sup>Pb may not even lie within the artificially narrow 95% confidence interval of the measured value. This possibility has important implications for high-precision zircon geochronology via SIMS, and the correlation of Precambrian events. Our previous work has characterized (via ID-TIMS) a Paleoarchean igneous zircon reference material ('OG1'). Its reference <sup>207</sup>Pb/<sup>206</sup>Pb is 0.29907 ± 0.00011 (3465.4 ± 0.6 Ma) for natural (air-abraded) zircon, and 0.29939 ± 0.00012 (3467.1 ± 0.6 Ma) for zircon annealed and chemically abraded using the Mattinson technique. The corresponding reference <sup>206</sup>Pb/<sup>238</sup>U ages are 3440.7 ± 3.2 Ma and 3463.3 ± 3.6 Ma respectively.

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nonGeographicDataset

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69443

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  • External PublicationAbstract
Australian and New Zealand Standard Research Classification (ANZSRC)
  • Earth Sciences
  • Published_Internal

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2009-01-01T00:00:00

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