New U–Pb geochronological constraints on the tectono-magmatic evolution of the Chibougamau–Chapais region, northeastern Abitibi greenstone belt, Québec
Bibliographic record
Abstract
The tectonomagmatic evolution of the Chibougamau–Chapais area, a peripheral part of the Abitibi belt, is revealed using compiled and new high-resolution geochronological data. Results indicate that volcanism, as old as 2803 Ma and best documented in the 2730–2714 Ma time interval, was dominantly tholeiitic and mafic at first, and progressively became more felsic and calc-alkaline. Melts extracted from mantle and mafic crustal sources formed coeval magmatic systems that hybridized locally to produce diorite. Most large volume tonalite and diorite intrusions assembled at ca. 2720–2714 Ma, as a sagging central volcano got established in the northern half of the Chibougamau–Chapais area and induced deformation (possibly uplift and erosion) in the basalt-dominated southern half of the area. Felsic magmatism then migrated to the south, producing the youngest volcanic unit (ca. 2715 Ma Phooey Member) and tonalite intrusion (ca. 2712 Ma Hazeur pluton) of the area prior to compressional deformation at ca. 2712–2710 Ma. The subsequent time interval is characterized by extension, basin-restricted sedimentation, and by medium to large volume K-enriched magmatism in the upper crust, with magma production peaking at 2697–2695 Ma prior to the main regional north–south shortening event. This is followed by localized extension (stress relaxation) in the central part of the study area and along a WNW-ESE corridor defined by ca. 2688–2685 Ma alkaline magmatism.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 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".