GHR1 Zircon – A New Eocene Natural Reference Material for Microbeam U‐Pb Geochronology and Hf Isotopic Analysis of Zircon

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 206 Pb/ 238 U 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 (2 s analytical including tracer uncertainties, MSWD = 1.53) and is our recommended date for GHR 1 zircon. Microbeam 206 Pb/ 238 U 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 GHR 1 yield a mean 176 Hf/ 177 Hf of 0.283050 ± 17 (2 s , n = 10), corresponding to a εHf 0 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 206 Pb/ 238 U and 176 Hf/ 177 Hf ratios from GHR 1 zircon across a variety of measurement techniques demonstrates their homogeneity in most grains. Additionally, the effectively limitless reserves of GHR 1 material from an accessible exposure suggest that GHR 1 can provide a useful reference material for U‐Pb geochronology of Cenozoic zircon and Hf isotopic measurements of zircon with radiogenic 176 Hf/ 177 Hf.