Small-volume U-Pb zircon geochronology by laser ablation-multicollector-ICP-MS

Scott Johnston, George Gehrels, Victor Valencia, Joaquin Ruiz

Research output: Contribution to journalArticle

77 Scopus citations

Abstract

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 ∼ 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.

Original languageEnglish (US)
Pages (from-to)218-229
Number of pages12
JournalChemical Geology
Volume259
Issue number3-4
DOIs
StatePublished - Feb 25 2009

Keywords

  • LA-ICP-MS
  • U-Pb geochronology
  • Zircon

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology

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