Zircons were separated from their host rock through standard methods of crushing as well as gravimetric and magnetic separation techniques using a Bico Braun “Chipmunk” jaw crusher, disc mill, hand pan, hand magnet, Frantz isodynamic separator, and methylene iodide. Zircons from the least magnetic and most dense mineral separate were transferred in bulk to quartz crucibles and annealed in a muffle furnace at 900°C for 48 hours after Mattinson (51). After annealing, 20 to 40 zircon grains from each sample were photographed (fig. S2) and picked in reagent-grade ethanol for analysis. Given the low radiogenic Pb content of the samples, cathodoluminescence images were not obtained. Euhedral grains with a range of morphologies were selected, while those with visible cracks, inclusions, and cores were avoided. Individual grains were transferred using stainless steel picking tools to separate 3-ml Savillex Hex beakers containing distilled acetone and taken to the clean laboratory for analysis.