<scp>U‐Th‐Pb</scp> and Trace Element Evaluation of Existing Titanite and Apatite <scp>LA‐ICP‐MS</scp> Reference Materials and Determination of <scp><sup>208</sup>Pb</scp>/<scp><sup>232</sup>Th‐<sup>206</sup>Pb</scp>/<scp><sup>238</sup>U</scp> Date Discordance in Archaean Accessory Phases
Bibliographic record
Abstract
The last decade has seen a marked increase in U‐Th‐Pb petrochronological studies focused on titanite and apatite. This has motivated the need for detailed, phase‐specific method development and well‐characterised reference materials with a wide variety of ages and chemical compositions. This study presents new U‐Th‐Pb isotope and major‐, minor‐ and trace‐element mass fraction data for ten titanite and five apatite reference materials based on integrated EPMA, LA‐ICP‐MS and isotope‐dilution (ID) multi‐collector (MC)‐ICP‐MS characterisation. Cross‐comparison of EPMA and LA‐ICP‐MS data for the same titanite reference material suite demonstrates that careful selection of EPMA primary reference materials is necessary to minimise inaccuracies. We further identify a significant X‐ray interference when measuring low Ce abundances in Ti‐bearing phases and outline a method for its correction. New ID‐MC‐ICP‐MS and LA‐ICP‐MS data suggest tri‐concordance (defined as concordant ages for the 238U‐206Pb, 235U‐207Pb and 232Th‐208Pb decay systems) of the MKED‐1 titanite reference material and demonstrate the reproducibility of 208Pb/232Th measurements in some secondary titanite reference materials. Integration of 208Pb/232Th results with U‐Pb geochronology provides a meaningful tool to help interpret complex U‐Th‐Pb isotopic age spectra. We provide example applications of 208Pb/232Th LA‐ICP‐MS measurements toward interpreting Archaean titanite ages from the Acasta Gneiss Complex, Northwest Territories, Canada.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".