Late-orogenic retrograde zircon growth
Bibliographic record
Abstract
Metamorphic zircon is commonly assumed to record growth during prograde or peak metamorphic conditions. However, numerical models of zircon predict growth during cooling. Linking the relative timing of zircon growth to a metamorphic evolution requires determining the potential zircon forming reactions during protracted metamorphic cycles. Meta-granitoids from the Grenville Province in Ontario contain a high proportion of igneous zircon with metamorphic rims that provide a rare opportunity to study zircon forming reactions in situ; acquiring U-Pb dates while maintaining their petrographic context and textural setting in thin section. Textures and trace element composition of major minerals indicate that metamorphic zircon grew as a result of melt crystallization and breakdown of titanomagnetite. Phase equilibrium modelling shows that these reactions occurred during retrograde metamorphism. Measured U-Pb dates of these retrograde metamorphic zircons are between ca. 1100 and 1070 Ma. This contradicts previous interpretations of regional geology that suggest prograde and peak metamorphism occurred between 1080 and 1050 Ma. These results highlight the need to carefully analyze the metamorphic textures of zircon to provide the necessary context to assess the zircon-forming reaction and its link to the pressure-temperature history of the rock. Without this context, pressure-temperature-time paths determined with zircon dates should be treated with caution and could be incorrectly linked to disparate stages of orogenic cycles. Supplementary Information: The online version contains supplementary material available at 10.1007/s00410-025-02219-3.
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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 | 0.001 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.025 | 0.010 |
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".