GHR1 Zircon – A New Eocene Natural Reference Material for Microbeam U‐Pb Geochronology and Hf Isotopic Analysis of Zircon |
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Authors: | Michael P Eddy Mauricio Ibaez‐Mejia Seth D Burgess Matthew A Coble Umberto G Cordani Joel DesOrmeau George E Gehrels Xianhua Li Scott MacLennan Mark Pecha Kei Sato Blair Schoene Victor A Valencia Jeffrey D Vervoort Tiantian Wang |
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Institution: | Michael P. Eddy,Mauricio Ibañez‐Mejia,Seth D. Burgess,Matthew A. Coble,Umberto G. Cordani,Joel DesOrmeau,George E. Gehrels,Xianhua Li,Scott MacLennan,Mark Pecha,Kei Sato,Blair Schoene,Victor A. Valencia,Jeffrey D. Vervoort,Tiantian Wang |
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Abstract: | We present multitechnique U‐Pb geochronology and Hf isotopic data from zircon separated from rapakivi biotite granite within the Eocene Golden Horn batholith in Washington, USA. A weighted mean of twenty‐five Th‐corrected 206Pb/238U zircon dates produced at two independent laboratories using chemical abrasion‐isotope dilution‐thermal ionisation mass spectrometry (CA‐ID‐TIMS) is 48.106 ± 0.023 Ma (2s analytical including tracer uncertainties, MSWD = 1.53) and is our recommended date for GHR1 zircon. Microbeam 206Pb/238U dates from laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) and secondary ion mass spectrometry (SIMS) laboratories are reproducible and in agreement with the CA‐ID‐TIMS date to within < 1.5%. Solution multi‐collector ICP‐MS (MC‐ICP‐MS) measurements of Hf isotopes from chemically purified aliquots of GHR1 yield a mean 176Hf/177Hf of 0.283050 ± 17 (2s, n = 10), corresponding to a εHf0 of +9.3. Hafnium isotopic measurements from two LA‐ICP‐MS laboratories are in agreement with the solution MC‐ICP‐MS value. The reproducibility of 206Pb/238U and 176Hf/177Hf ratios from GHR1 zircon across a variety of measurement techniques demonstrates their homogeneity in most grains. Additionally, the effectively limitless reserves of GHR1 material from an accessible exposure suggest that GHR1 can provide a useful reference material for U‐Pb geochronology of Cenozoic zircon and Hf isotopic measurements of zircon with radiogenic 176Hf/177Hf. |
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Keywords: | U‐Pb geochronology zircon reference material Hf isotope ratios ID‐TIMS LA‐ICP‐MS secondary ion mass spectrometry MC‐ICP‐MS |
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