Recent advances in U{\textendash}Pb geochronology allow unprecedented levels of precision in the determination of geological ages. However, increased precision has also illuminated the importance of understanding subtle sources of open-system behavior such as Pb-loss, inheritance, intermediate daughter product disequilibria, and the accuracy of the model assumptions for initial Pb. Deconvolution of these effects allows a much richer understanding of the power and limitations of U{\textendash}Pb geochronology and thermochronology. In this study, we report high-precision ID-TIMS U{\textendash}Pb data from zircon, baddelleyite, titanite and apatite from the McClure Mountain syenite, from which the~40Ar/39Ar hornblende standard MMhb is derived. We find that excess~206Pb in zircon due to inclusions of high-Th minerals and elevated Th/U in titanite and apatite jeopardize the utility of the~238U{\textendash}206Pb system in this rock. Strongly air-abraded zircons give dates that are younger than chemical-abraded zircons, which yield a statistically robust~207Pb/235U date of 523.98{\textpm}0.12~Ma that is interpreted as the crystallization age. We explore the best method of Pbc~correction in titanite and apatite by analyzing the U{\textendash}Pb isotopes of K-feldspar and using 2-D and 3-D regression methods{\textemdash}the latter of which yields the best results in each case. However, the calculated compositions of Pbcfor titanite, apatite and K-feldspar are different, implying that using a single Pbc~correction for multiple U{\textendash}Pb thermochronometers may be inaccurate. The U{\textendash}Pb thermochronological results are used to predict a closure time for Ar in hornblende of 522.98{\textpm}1.00~Ma. Widely cited K{\textendash}Ar and~40Ar/39Ar dates overlap with the U{\textendash}Pb date, and relatively large errors make it impossible to verify whether U{\textendash}Pb dates are systematically <=1\% older than K{\textendash}Ar and~40Ar/39Ar dates.
}, year = {2006}, journal = {Contributions to Mineralogy and Petrology}, volume = {151}, pages = {615 - 630}, month = {05/2006}, url = {https://doi.org/10.1007/s00410-006-0077-4}, doi = {10.1007/s00410-006-0077-4}, language = {eng}, }