Articles | Volume 5, issue 1
https://doi.org/10.5194/gchron-5-1-2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gchron-5-1-2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Examination of the accuracy of SHRIMP U–Pb geochronology based on samples dated by both SHRIMP and CA-TIMS
Charles W. Magee Jr.
CORRESPONDING AUTHOR
Geoscience Australia, Cnr Jerrabomberra Ave and Hindmarsh Drive,
Symonston ACT 2609, Australia
Simon Bodorkos
Geoscience Australia, Cnr Jerrabomberra Ave and Hindmarsh Drive,
Symonston ACT 2609, Australia
Christopher J. Lewis
Geoscience Australia, Cnr Jerrabomberra Ave and Hindmarsh Drive,
Symonston ACT 2609, Australia
James L. Crowley
Department of Geosciences, Boise State University, Boise, Idaho 83725,
USA
Corey J. Wall
Pacific Centre for Isotopic and Geochemical Research, Department of
Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road,
Vancouver, British Columbia V6T 1Z4, Canada
Richard M. Friedman
Pacific Centre for Isotopic and Geochemical Research, Department of
Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road,
Vancouver, British Columbia V6T 1Z4, Canada
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Chemical abrasion (CA) is a two step method for reducing Pb loss where zircon is annealed then partially dissolved. We use SIMS to find closed and open system zircon domains in zircon that has been CA, annealed only, or untreated. Raman mapping shows to identify lattice damage in SIMS spots. Atom Probe (APT) results from both the discordant spots and concordant ones are all homogenous and identical. Thus APT cannot distinguish discordant and concordant zircon.
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Zircon is a mineral where uranium decays to lead. Some radiation damage lets lead escape. A method called chemical abrasion (CA) dissolves out the damaged portions of zircon so that remaining zircon retains lead. We compare ion beam analyses of untreated and chemically abraded zircons. The ion beam ages for untreated zircons match the reference values for untreated zircon. The ion beam ages for CA zircon match CA reference ages. Other elements are unaffected by the chemical abrasion process.
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Chemical abrasion (CA) is a two step method for reducing Pb loss where zircon is annealed then partially dissolved. We use SIMS to find closed and open system zircon domains in zircon that has been CA, annealed only, or untreated. Raman mapping shows to identify lattice damage in SIMS spots. Atom Probe (APT) results from both the discordant spots and concordant ones are all homogenous and identical. Thus APT cannot distinguish discordant and concordant zircon.
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Zircon is a mineral where uranium decays to lead. Some radiation damage lets lead escape. A method called chemical abrasion (CA) dissolves out the damaged portions of zircon so that remaining zircon retains lead. We compare ion beam analyses of untreated and chemically abraded zircons. The ion beam ages for untreated zircons match the reference values for untreated zircon. The ion beam ages for CA zircon match CA reference ages. Other elements are unaffected by the chemical abrasion process.
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Short summary
SHRIMP (Sensitive High Resolution Ion MicroProbe) is an instrument that for decades has used the radioactive decay of uranium into lead to measure geologic time. The accuracy and precision of this instrument has not been seriously reviewed in almost 20 years. This paper compares several dozen SHRIMP ages in our database with more accurate and precise methods to assess SHRIMP accuracy and precision. Analytical and geological complications are addressed to try to improve the method.
SHRIMP (Sensitive High Resolution Ion MicroProbe) is an instrument that for decades has used the...