Metamorphic evolution, mineral chemistry and thermobarometry of the Ujaraaluk unit in the Nuvvuagittuq greenstone belt, northern Canada
Bibliographic record
Abstract
The dominant lithologies of the Nuvvuagittuq Greenstone belt (Northeastern Superior Province, Canada) are composed of mafic amphibolite-facies rocks (referred as the Ujaraaluk unit). With a minimum age of 3.8 Ga and possibly as old as 4.3 Ga, these rocks are among the oldest in the world. The Nuvvuagittuq Greenstone belt occurs in the western Hudson Bay terrane, which was last pervasively metamorphosed at ca. 2.7 Ga. In the Ujaraaluk unit, petrography and mineral chemistry study reveal two different rock types: garnet + biotite + plagioclase + quartz schist without amphibole (garnet schist), occurring primarily in the central part of the area, and amphibole schist composed of biotite + amphibole + plagioclase + quartz ± garnet distributed through the entire unit. Amphibole may be cummingtonite or anthophyllite or Mg- or Fe-hornblende occurring alone or in combination. Although the mineral assemblages are different, no systematic geographical distribution is found in the field. Garnets, primarily in the central part of the Nuvvuagittuq Greenstone Belt, are mainly unzoned with respect to major cations; most have thin rims reflecting cation exchange on cooling. Garnet-bearing samples have higher whole-rock FeO* and Al2O3 than garnet-free samples. Conventional geothermobarometry was applied to both rock types, and gives temperatures and pressures clustering around 612°C and 4.2 kbar, respectively. Pseudosection calculations confirmed the results from conventional thermobarometry. Whole-rock chemistry, garnet mineral chemistry and thermometry across the region suggest that the presence of garnet is mainly the result of the whole-rock chemistry rather than metamorphic grade. I suggest that the event responsible for metamorphism of the western Hudson Bay terrane at 2.7 Ga was also the main metamorphic event that affected the Nuvvuagittuq Greenstone Belt and the Ujaraaluk unit. Neoarchean Sm-Nd ages obtained in the garnets also support this conclusion. Any earlier metamorphism, likely given the protracted history of these rocks, has apparently been obliterated.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.002 |
| Science and technology studies | 0.002 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.002 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
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 teacher head, 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".