Characterization of the potential reference material SA02 for micro-beam U–Pb geochronology and Hf–O isotopic composition analysis of zircon

Abstract

In the present work, a natural zircon megacryst SA02 (the exact provenance unknown) is investigated as a new potential reference material for U–Pb geochronology and Hf–O isotopic composition analysis via micro-beam methods. The precise and accurate U–Pb age is determined by the chemical abrasion isotope dilution thermal ionization mass-spectrometry (CA-ID-TIMS) method. The resultant mean ²⁰⁶Pb/²³⁸U date is 535.10 ± 0.24 Ma (2s, n = 2), interpreted as the crystallization age of the zircon megacryst. The mean ID-TIMS ²⁰⁶Pb/²³⁸U date of 533.7 ± 3.7 Ma (2s, n = 8) is recommended as the working value for micro-beam analyses when using untreated SA02 zircon grains as the primary reference material. ²⁰⁶Pb/²³⁸U dates of 533.0 ± 6.2 Ma (2s, n = 57) and 534 ± 8 Ma (2s, n = 101) obtained by secondary ion mass spectrometry (SIMS) and laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) respectively are reproducible and in agreement with the results of ID-TIMS within < 0.3% relative analytical errors. Solution data of Hf isotope compositions measured by multi-collector ICP-MS (MC-ICP-MS) from SA02 zircon yield a mean ¹⁷⁶Hf/¹⁷⁷Hf of 0.282287 ± 0.000016 (2s, n = 31), which is recommended as a reference value for microbeam analysis. Hf isotope analyses by LA-MC-ICP-MS yield homogeneous Hf isotopic compositions with a mean ¹⁷⁶Hf/¹⁷⁷Hf of 0.282289 ± 0.000033 (2s, n = 142) identical to the solution value. The mean δ¹⁸O value measured by laser fluorination is 6.03 ± 0.28‰ (2s, n = 13), which is consistent with the result of SIMS analysis.