The relatively low durability of detrital apatite during sedimentary transport means that U-Pb detrital apatite ages tend to represent first cycle provenance ages from the immediate source catchment, in contrast to the greater potential for polycyclic behavior of highly resistant detrital zircon. However, the low U concentration in apatite, its tendency to incorporate high amounts of common lead during crystallization, and the lack of good matrix-matched apatite reference material to monitor fractionation has previously limited the accuracy and hence widespread application of this method. Apatite is a common U-bearing accessory mineral in magmatic, sedimentary, and metamorphic rocks, with a U-Pb closure temperature of 450–550☌ making U-Pb dating of apatite a potential widely applicable medium-temperature thermochronometer and a complement to the similar closure temperature 40Ar/ 39Ar hornblende system, especially in rocks where hornblende is absent. The accuracy of our detrital results is supported by a good age match with similar closure temperature 40Ar/ 39Ar detrital hornblende ages from the same sediment. For single detrital apatite grains with ages of ∼500 Ma, precision of <4% (2 σ) was achieved by pooling 2 to 3 spots per grain. Such limitations can be overcome by using spot sizes 65 μm or greater, but at the expense of substantial grain damage. Data quality in apatite with low U concentrations, low 206Pb/ 204Pb values (<∼30) and young ages (<∼75 Ma) is compromised by the goal of avoiding significant grain damage.

We accurately reproduce ages of numerous independently characterized apatites, regularly achieving precision of <2% (2 σ) by pooling as few as five 30 μm spot analyses. Common Pb is corrected using measured 204Pb isobarically corrected for Hg interference and a five-step iterative process using Stacey and Kramers' common Pb model. We overcome previous limitations by using a Nu Plasma multicollector ICPMS with an attached short-pulse excimer laser, and by identifying two new matrix-matched reference apatites to correct for elemental fractionation: gem-quality 485 Myr old apatite from Madagascar which we independently characterized by ID-TIMS analysis, and 523.5 Ma apatite from the McClure Mountain syenite (source of the 40Ar/ 39Ar reference MMhb). However, its low U concentration and tendency to incorporate common lead has limited widespread application to destructive isotope dilution methods. Apatite is a common U-bearing accessory mineral with a U-Pb closure temperature of ∼500☌, making U-Pb dating of apatite a potentially valuable thermochronometer.

Nu laser fission uranium