We introduce a potential new working reference material – natural zircon megacrysts from an Early Pliocene alkaline basalt (from Penglai, northern Hainan Island, southern China) – for the microbeam determination of O and Hf isotopes, and U–Pb age dating. The Penglai zircon megacrysts were found to be fairly homogeneous in Hf and O isotopes based on large numbers of measurements by LA‐multiple collector (MC)‐ICP‐MS and SIMS, respectively. Precise determinations of O isotopes by isotope ratio mass spectrometry (IRMS) and Hf isotopes by solution MC‐ICP‐MS were in good agreement with the statistical mean of microbeam measurements. The mean δ18O value of 5.31 ± 0.10‰ (2s) by IRMS and the mean 176Hf/177Hf value of 0.282906 ± 0.0000010 (2s) by solution MC‐ICP‐MS are the best reference values for the Penglai zircons. SIMS and isotope dilution‐TIMS measurements yielded consistent 206Pb/238U ages within analytical uncertainties, and the preferred 206Pb/238U age was found to be 4.4 ± 0.1 Ma (95% confidence interval). The young age and variably high common Pb content make the Penglai zircons unsuitable as a primary U–Pb age reference material for calibration of unknown samples by microbeam analysis; however, they can be used as a secondary working reference material for quality control of U–Pb age determination for young (particularly < 10 Ma) zircon samples.

Samples were sawn into slabs and the central parts (4200 g) were used for bulk-rock analysis. The rocks were crushed into small fragments (50•5 cm in diameter) before being further cleaned and powdered in a corundum mill. Bulk-rock geochemical analyses were carried out at the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences. Bulk-rock major element oxides were analyzed by X-ray fluorescence (XRF) with analytical uncertainties better than 3% for SiO 2 , Al 2 O 3 , Fe 2 O 3 , MgO, CaO, Na 2 O and K 2 O, and better than 5% for TiO 2 , MnO and P 2 O 5. Trace elements were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS). Repeated runs give 53% RSD (relative standard deviation) for most trace elements analyzed. Fe/Mn ratios