RKV01 Rutile – A New Potential Archaean Reference Material for Microbeam U-Pb Dating

Abstract

Rutile stands as a classical mineral within U-Pb geochronology, offering insights into both magmatic and metamorphic events, and contributing to the understanding of provenance of detrital sedimentary rocks. Addressing the paucity of high-quality Archaean rutile reference materials suitable for microbeam U-Pb dating, we present a natural rutile (RKV01) sourced from the Kaap Valley pluton, South Africa, positing it as a potential Archaean reference material. Major element determination was executed via electron probe microanalysis, while trace element determination was conducted using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The determination of U-Pb ages involved the application of isotope dilution-thermal ionisation mass spectrometry (ID-TIMS), secondary ion mass spectrometry (SIMS) and LA-ICP-MS. The ID-TIMS mean ²⁰⁷Pb/²⁰⁶Pb age is 3225.61 ± 0.64 Ma (2s, MSWD = 0.83), interpreted as the best estimate for the crystallisation age. The relatively high U mass fraction (~ 83 μg g^-1), extremely low Th mass fraction (~ 0.003 μg g^-1), negligible common Pb and isotopically homogeneous compositions collectively facilitated precise ²⁰⁷Pb/²⁰⁶Pb age determination via microbeam methods. Both LA-ICP-MS and SIMS ²⁰⁷Pb/²⁰⁶Pb ages are characterised by reproducibility and were consistent with the ID-TIMS age within 2s analytical uncertainty. The results underscore the potential of RKV01 rutile as an Archaean reference material for microbeam U-Pb dating.