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Small-Volume U-Pb Zircon Geochronology by Laser Ablation-Multicollector-ICP-MS
Chemical Geology
  • Scott Johnston, University of Arizona
  • George Gehrels, University of Arizona
  • Victor Valencia, University of Arizona
  • Joaquin Ruiz, University of Arizona
Publication Date

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.

Citation Information
Scott Johnston, George Gehrels, Victor Valencia and Joaquin Ruiz. "Small-Volume U-Pb Zircon Geochronology by Laser Ablation-Multicollector-ICP-MS" Chemical Geology Vol. 259 Iss. 3-4 (2009) p. 218 - 229
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