Garnet Reference Materials for <i>In Situ</i> Lu‐Hf Geochronology
Bibliographic record
Abstract
In situ garnet Lu‐Hf geochronology has the potential to revolutionise the chronology of petrological and tectonic processes, yet there is a paucity of well‐characterised reference materials to account for laser‐induced matrix‐dependant elemental fractionation. Here, we characterise two reference garnets GWA‐1 (Lu ~ 7.0 μg g−1) and GWA‐2 (Lu ~ 8.5 μg g−1) for in situ garnet Lu‐Hf geochronology. Isochron ages from isotope dilution Lu‐Hf analyses yield crystallisation ages of 1267.0 ± 3.0 Ma with initial 176Hf/177Hfi of 0.281415 ± 0.000012 (GWA‐1), and 934.7 ± 1.4 Ma with 176Hf/177Hfi of 0.281386 ± 0.000013 (GWA‐2). In situ Lu‐Hf analyses yield inverse isochron ages up to 10% older than the known crystallisation age due to matrix effects between garnet and reference glass (NIST SRM 610) under different instrument tuning conditions. This apparent age offset is reproducible for both materials within the same session and can be readily corrected to obtain accurate ages. Our results demonstrate that GWA‐1 and GWA‐2 are robust reference materials that can be used to correct for matrix‐analytical effects and also to assess the accuracy of in situ Lu‐Hf garnet analyses across a range of commonly encountered garnet compositions.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.003 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.012 | 0.007 |
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".