Preprints
https://doi.org/10.5194/egusphere-2023-2928
https://doi.org/10.5194/egusphere-2023-2928
12 Dec 2023
 | 12 Dec 2023

Effect of chemical abrasion of zircon on SHRIMP U/Pb, δ18O, Trace element, and LA-ICPMS trace element and Lu-Hf isotopic analyses

Cate Kooymans, Charles W. Magee Jr., Kathryn Waltenberg, Noreen Evans, Simon Bodorkos, Yuri Amelin, Sandra Kamo, and Trevor Ireland

Abstract. Chemical abrasion improves the U/Pb systematics of SHRIMP analyses of reference zircons, while leaving other isotopic systems largely unchanged. SHRIMP 206Pb/238U ages of chemically abraded reference materials TEMORA 2, 91500, QGNG, and OG1 are precise to within 0.25 to 0.4 %, and are within uncertainty of chemically abraded TIMS reference ages, while SHRIMP 206Pb/238U ages of untreated zircons are within uncertainty of TIMS ages of zircons which are untreated by chemical abrasion. Chemically abraded and untreated zircons appear to cross-calibrate within uncertainty using all but one possible permutations of reference materials, provided that the corresponding chemically abraded or untreated reference age is used for the appropriate material. In the case of reference zircons QGNG and OG1, which are slightly discordant, the SHRIMP U-Pb ages of chemically abraded and untreated material differ beyond their respective 95 % confidence intervals.

SHRIMP U/Pb analysis of chemically abraded zircons with multiple growth stages are more difficult to interpret. Treated igneous rims on zircons from the S-type Mount Painter Volcanics are much lower in common Pb than the rims on untreated zircons. However, the analyses of chemically abraded material show excess scatter. Chemical abrasion also changes the relative abundance of the ages of zircon cores inherited from the sedimentary protolith, presumably due to some populations being more likely to survive the chemical abrasion process than others. We consider these results from inherited S-type zircon cores to be indicative of results for detrital zircons from unmelted sediments.

Trace element, δ18O, and εHf analyses were also performed on these zircons. None of these systems showed substantial changes as a result of chemical abrasion. The most discordant reference material, OG1, showed a loss of OH as a result of chemical abrasion, presumably due to dissolution of hydrous metamict domains, or thermal dehydration during the annealing step of chemical abrasion. In no case did zircons gain fluorine due to exchange of lattice-bound substituted OH or other anions with fluorine during the HF partial dissolution phase of the chemical abrasion process. As the OG1, QGNG, and TEMORA 2 zircons are known to be compositionally inhomogenous in trace element composition, spot-to-spot differences dominated the trace element results. Even the 91500 megacrystic zircon exhibited substantial chip-to-chip variation. The LREE in chemically abraded OG1 and TEMORA 2 were lower than in the untreated samples. Ti and phosphorus saturation ((Y+REE)/P) were generally unchanged in all samples.

Cate Kooymans, Charles W. Magee Jr., Kathryn Waltenberg, Noreen Evans, Simon Bodorkos, Yuri Amelin, Sandra Kamo, and Trevor Ireland

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2928', Anonymous Referee #1, 24 Jan 2024
    • RC2: 'Comment on egusphere-2023-2928', Anonymous Referee #2, 29 Jan 2024
      • AC2: 'Reply on RC2', Charles Magee, 19 Feb 2024
    • AC1: 'Reply on RC1', Charles Magee, 19 Feb 2024
Cate Kooymans, Charles W. Magee Jr., Kathryn Waltenberg, Noreen Evans, Simon Bodorkos, Yuri Amelin, Sandra Kamo, and Trevor Ireland
Cate Kooymans, Charles W. Magee Jr., Kathryn Waltenberg, Noreen Evans, Simon Bodorkos, Yuri Amelin, Sandra Kamo, and Trevor Ireland

Viewed

Total article views: 354 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
247 84 23 354 25 14 11
  • HTML: 247
  • PDF: 84
  • XML: 23
  • Total: 354
  • Supplement: 25
  • BibTeX: 14
  • EndNote: 11
Views and downloads (calculated since 12 Dec 2023)
Cumulative views and downloads (calculated since 12 Dec 2023)

Viewed (geographical distribution)

Total article views: 386 (including HTML, PDF, and XML) Thereof 386 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 13 Apr 2024
Download
Short summary
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.