Ultramafic xenoliths from the 1.15 Ga Certac kimberlite, eastern Superior Craton
Bibliographic record
Abstract
ABSTRACT Xenoliths and xenocrysts of mantle material from kimberlite dikes located underground at the Certac Au mine, Québec, in the eastern Superior Craton, were studied in terms of the major element composition of their constituent minerals. The kimberlite was dated at 1151 ± 46 Ma by the U-Pb perovskite method. This suite thus provides a rare glimpse into the Mesoproterozoic mantle of the Superior Craton. Two parageneses of mantle material unrelated to the kimberlite magmatism occur: (1) an olivine + ilmenite ± magnetite association characterized by relatively Fe-rich olivine (Mg# = 0.68–0.84) and ilmenite enriched in Mg and Cr (4–13 wt.% MgO, Cr2O3 up to 3 wt.%), and (2) spinel peridotite characterized by Mg-rich olivine (Mg# = 0.91–0.94). The Fe-rich association is interpreted as a magmatic cumulate likely unrelated to the kimberlite. No mantle-derived garnet occurs in the xenoliths or as xenocrysts. The presence of Cr-rich spinel (Cr# = 0.84–0.98) in high temperature (860–953 °C) chromite peridotite indicates bulk compositions too depleted in Al for garnet to be stable, although geothermometry suggests they equilibrated at depths corresponding to garnet stability (90–131 km, depending on the geothermal gradient). Alternatively, the presence of phlogopite in two of the three high temperature (i.e., deepest) chromite peridotites suggests the absence of garnet and presence of low-Al chromite may have been caused by metasomatism from a K-rich fluid that replaced garnet with phlogopite + clinopyroxene ± chromite. Less depletion at shallower depths is indicated by a chromite (Cr# = 0.60) dunite that equilibrated at 831 °C and a low temperature (752 °C) Mg-Al-spinel lherzolite.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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 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".