Small-Volume U-Pb Zircon Geochronology by Laser Ablation-Multicollector-ICP-MS

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 complicatio...

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Bibliographic Details
Main Authors: Johnston, Scott, Gehrels, George, Valencia, Victor, Ruiz, Joaquin
Other Authors: ARIZONA UNIV TUCSON DEPT OF GEOSCIENCES
Format: Text
Language:English
Published: 2008
Subjects:
Geology
Geochemistry and Mineralogy
*LASERS
*ABLATION
MONITORING
CRYSTALS
MASS SPECTROMETRY
VIABILITY
STANDARDS
STRUCTURAL GEOLOGY
GREENLAND
SHALE
NONDESTRUCTIVE TESTING
REPRINTS
HIGH RESOLUTION
*U-PB GEOCHRONOLOGY ZIRCON
LA-ICP-MSO
MESOPROTEROZOIC-CRETACEOUS
OLIGOCENE-AGED GRAIN
MUDSTONES
Greenland
Online Access:http://www.dtic.mil/docs/citations/ADA515753
http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA515753
Description
Summary: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 um in diameter by 4-5 um in depth (b3 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. Published in the Journal of Chemical Geology 2008.

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