Hafnium Isotope Characteristics of Palaeoarchaean Zircon OG1/OGC from the Owens Gully Diorite,Pilbara Craton,Western Australia |
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| Authors: | Anthony I S Kemp Jeffrey D Vervoort Katarina E Bjorkman Linda M Iaccheri |
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| Institution: | 1. School of Earth Sciences, The University of Western Australia, Crawley, WA, Australia;2. School of the Environment, Washington State University, Pullman, WA, USA |
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| Abstract: | We report Hf isotope data for 3467 Ma igneous zircons from the Owens Gully Diorite of the Pilbara Craton. These zircons, designated OG1 or OGC, have simple, well‐defined U‐Pb age systematics. Measurements obtained by single crystal dissolution yield a moderate range in 176Hf/177Hf (mean 0.280633 ± 34) and 176Lu/177Hf (mean 0.00119) that translate into initial (3467 Ma) 176Hf/177Hf values that are equivalent within measurement uncertainty (mean 0.280554 ± 7, εHf = +0.6 ± 0.2, 2s). Laser ablation analysis yielded clustered initial 176Hf/177Hf ratios (mean 0.280560 ± 20, 2s) indistinguishable from those obtained by solution analysis. The antiquity and moderately high 176Lu/177Hf of these zircons result in significant corrections for radiogenic ingrowth of 176Hf (to 6 εHf units). Depth profiling by concurrent Pb‐Hf isotope determination reveals trends to lower 207Pb/206Pb in several crystals, although these are not accompanied by shifts in 176Hf/177Hf. We conclude that zircons from the Owens Gully Diorite are homogeneous for Hf isotopes at the scale of sampling and within the uncertainty limits of the measurement techniques employed. Zircon OG1/OGC would appear to be an ideal quality monitor for laser ablation Hf isotope determination in ancient zircons, and for laser ablation techniques where Hf isotope and age information are determined concurrently or simultaneously. |
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| Keywords: | zircon hafnium isotope ratios laser ablation isotope dilution mass spectrometry microanalysis OG1
OGC
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