Comment on “Complementarity of Hf isotopes from detrital and igneous zircon: an example from the Central Gneiss Belt, Grenville Province, Ontario”
Bibliographic record
Abstract
In a recent paper presenting 30 new Hf isotope analyses for orthogneisses from the Grenvillian Central Gneiss Belt in Ontario, Slagstad et al. (Slagstad, T., Easton, R.M., Huyskens, M., and Culshaw, N. 2024. Complementarity of Hf isotopes from detrital and igneous zircon: an example from the Central Gneiss Belt, Grenville Province, Ontario. Canadian Journal of Earth Sciences, 61: 19) suggested that these new data “may serve as a basis for some cautionary notes on the application of isotopic data alone to distinguish allochthonous from parautochthonous rocks”. These “cautionary notes” evidently arise from the poor fit of the new Hf isotope data to these authors’ expectations based on published work. However, we show that the new data are in complete agreement with our own published tectonic maps, based on Nd isotope mapping supported by other available geological evidence. Far from serving as the basis for “cautionary notes” about our use of Nd isotope mapping, the new data completely validate our approach. On the other hand, we show that the mantle model used by Slagstad et al. (2024) to calculate Hf crustal formation ages was based on erroneous old data, and does not yield realistic Hf model ages for Precambrian gneisses. Therefore, we propose a more robust model, based on applying the principles of DePaolo’s Nd isotope model to Hf mantle evolution. We term the resulting Hf ages TDP model ages and show that they yield realistic crustal formation ages for the Ontario Grenville Province.
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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 | 0.002 | 0.012 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.003 | 0.004 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.003 | 0.001 |
| Research integrity | 0.011 | 0.010 |
| Insufficient payload (model declined to judge) | 0.004 | 0.004 |
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".