Ages of several xenotime megacrysts by ID-TIMS: potential reference materials for ion microprobe U-Pb geochronology
Bibliographic record
Abstract
Four museum specimens of xenotime were tested for homogeneity in their U-Pb ages using isotope dilution - thermal-ionization mass spectrometry (ID-TIMS). The U-Pb ages of the samples ranged from about 500 Ma to 1020 Ma. Sample z6413, from a granitic pegmatite in the Grenville Province, yielded homogeneous 206Pb/238U and 207Pb/206Pb ages of 994 Ma and 997 Ma, respectively. This sample was selected as a primary candidate reference material for ion microprobe U-Pb geochronology. A second sample, z6410, yielded 206Pb/238U and 207Pb/206Pb ages of 897 Ma and 901 Ma, respectively, and is a potential secondary standard. The other samples displayed significant age heterogeneities, including the effects of Pb loss, making them unsuitable as standards.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".