Precise determination of Phanerozoic zircon Pb/Pb age by multicollector SIMS without external standardization

Zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences. Modern microbeam techniques such as SIMS and LA‐ICPMS have been successfully applied to in situ U‐Pb zircon age determinations, at spatial resolutions of 20–30 μ m or less. Matrix‐matched calibration by external standardization of well‐characterized natural zircon references is a principal requirement for precise microbeam U‐Pb zircon age determination due to fractionation effects between Pb and U, which usually result in an external age error exceeding 1%. Alternatively, zircons with a closed U‐Pb system can be directly dated by measurement of 207 Pb/ 206 Pb isotopic ratio without external…