Postprint version. Published in Chemical Geology, Volume 259, Issue 3-4, February 1, 2009, pages 218-229.
NOTE: At the time of publication, the author Scott Johnston was not yet affiliated with Cal Poly.
The definitive version is available at https://doi.org/10.1016/j.chemgeo.2008.11.004.
U–Pb zircon geochronology is hampered by problems acquiring meaningful geologic ages on zoned grains that retain isotope signatures from multiple growth or thermal events. We present a new method using laser ablation-multicollector-inductively coupled plasma-mass spectrometry to overcome complications associated with intricately zoned zircon crystals through in situ sampling of zircon volumes as small as 12–14 µm in diameter by 4–5 µm in depth (< 3 ng of zircon). Using Channeltron multipliers to monitor Pb intensities in conjunction with a total ion counting method and errors calculated as function of the number of counts, the small-volume technique reproduced published ages on eight Mesoproterozoic–Cretaceous secondary zircon standards precise and accurate within 2%, and an age not, vert, similar 1 Ma too young on a Oligocene-aged grain. Two initial applications of the small-volume technique — the detrital zircon provenance of fine-grained mudstones and shales and the creation of zircon U–Pb age maps to investigate the detrital and metamorphic history of a granulite-facies paragneiss — demonstrate the utility of this technique to a variety of geologic problems and confirm the viability of laser ablation-multicollector-inductively coupled plasma-mass spectrometry as a tool for high spatial resolution U–Pb geochronology.