Origin and Evolution of Silicic Magmatism atYellowstone Based on Ion Microprobe Analysis of Isotopically Zoned Zircons

The origin of large-volume Yellowstone ignimbrites and smaller-volume intra-caldera lavas requires shallow remelting of enormous volumes of variably 18O-depleted volcanic and sub-volcanic rocks altered by hydrothermal activity. Zircons provide probes of these processes as they preserve older ages and inherited d18O values.This study presents a high-resolution, oxygen isotope examination of volcanism at Yellowstone using ion microprobe analysis with an average precision of 02ø and a 10 mm spot size.We report 357 analyses of cores and rims of zircons, and isotope profiles of 142 single zircons in 11 units that represent majorYellowstone ignimbrites, and post-caldera lavas. Many zircons from these samples were previously dated in the same spots by sensitive high-resolution ion microprobe (SHRIMP), and all zircons were analyzed for oxygen isotope ratios in bulk as a function of grain size by laser fluorination. We additionally report oxygen isotope analyses of quartz crystals i