Effect of chemical abrasion of zircon on SIMS U–Pb, <i>δ</i> <sup>18</sup> O, trace element, and LA-ICPMS trace element and Lu–Hf isotopic analyses
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Notice bibliographique
Résumé
Abstract. This study assesses the effect of chemical abrasion on in situ mass spectrometric isotopic and elemental analyses in zircon. Chemical abrasion improves the U–Pb systematics of SIMS (secondary ion mass spectrometry) analyses of reference zircons, while leaving other isotopic systems largely unchanged. SIMS 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 (thermal ionization mass spectrometry) reference ages, while SIMS 206Pb/238U ages of untreated zircons are within uncertainty of TIMS reference ages where chemical abrasion was not used. Chemically abraded and untreated zircons appear to cross-calibrate within uncertainty using all but one possible permutation 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 SIMS U–Pb ages of chemically abraded and untreated material differ beyond their respective 95 % confidence intervals. SIMS U–Pb analysis of chemically abraded zircon with multiple growth stages is more difficult to interpret. Treated igneous rims on zircon crystals from the S-type Mount Painter Volcanics are much lower in common Pb than the rims on untreated zircon grains. 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 zircon grains 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 zircon 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 zircon samples are known to be compositionally inhomogeneous in trace element composition, spot-to-spot differences dominated the trace element results. Even the 91500 megacrystic zircon pieces exhibited substantial chip-to-chip variation. The light rare earth elements (LREEs) in chemically abraded OG1 and TEMORA-2 were lower than in the untreated samples. Ti concentration and phosphorus saturation ((Y + REE) / P) were generally unchanged in all samples.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,001 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,004 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découle