Initial Hf/Hf in meteoritic zircons

Zircons from the Simmern H5 chondrite and Pomozdino eucrite have been analyzed for their Hf-W isotope systematics. Zircons have high intrinsic Hf contents and coupled with low W, make them ideal Hf-W chronometers. However, measurements of (¹⁸²Hf/¹⁸⁰Hf)₀ are far from straightforward with low signals of radiogenic ¹⁸²W and difficulties in calibrating Hf/W ratios. Zircons were analyzed from the Simmern chondrite, and the Pomozdino eucrite. The Simmern zircon has an ultrarefractory-enriched trace element pattern, a feature commonly associated with refractory inclusions. Analyses of Simmern zircon show variable Hf/W that is likely due to surface contamination. Simmern chondrite zircon yields a (¹⁸²Hf/¹⁸⁰Hf)₀ of 7.2 (± 4.5) × 10⁻⁵. Pomozdino eucrite zircon analyses show very high Hf/W values indicating (¹⁸²Hf/¹⁸⁰Hf)₀ of 1.7 (± 1.1) × 10⁻⁵. The Simmern value is in good agreement with the initial value of the solar system indicated from Hf-W systematics of chondrites. The Pomozdino value is lower than expected if eucrites formed within several million years of refractory inclusions as suggested from Al-Mg systematics of eucrites.