Age of the Cabonga nepheline syenite, Grenville Province, western Quebec
Bibliographic record
Abstract
This study presents isotope dilution – thermal ionization mass spectrometry (ID–TIMS) U–Pb data for megacrystic zircon from the Cabonga Nepheline Syenite Complex of the Réservoir Cabonga terrane (Grenville Province). This terrane is an allochthonous slab metamorphosed under granulite-grade conditions ~1.18–1.14 Ga and transported onto migmatites of the Grenvillian Parautochthon at about 1.02 Ga. The very low uranium and lead concentrations of zircon from the Cabonga nepheline syenite (CNS) did not permit determination of a statistically significant crystallization age using laser ablation microbeam techniques. Consequently, extensive microsampling (15 zircon chips), guided by X-ray and electronic imaging, followed by ID–TIMS analyses were carried out on a single megacrystic zircon. A regression of 13 out of 15 U–Pb isotopic analyses results in a crystallization age of 1171 ± 3 Ma for the CNS. Criteria based on zircon morphologies, zoning patterns, varying Th/U ratios (0.3–0.9), and a highly fractionated Zr/Hf ratio (68) suggest an igneous derivation for the CNS. The Cabonga alkaline rocks, intruded under high-grade metamorphic conditions, preceded the onset of the widespread and ubiquitous (1.15 ± 0.01 Ga) anorthosite–mangerite–charnockite–granite magmatism in the southern part of the Grenville Province.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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".