Insights into a synorogenic origin for REE-bearing carbonatites in the Central Metasedimentary Belt Boundary Zone of the Grenville Province
Bibliographic record
Abstract
Several carbonate-rich intrusions (i.e., carbonatites) have been documented along the northwestern limit of the Central Metasedimentary Belt (CMB) in the Grenville Province of Canada, i.e., the Central Metasedimentary Belt Boundary Zone (CMBBZ), but their origin and timing of emplacement remains contentious. Our study focuses on the tectono-magmatic setting of one rare earth elements (REE)-bearing carbonatite, the Baie-Mercier REE occurrence, and its associated carbonate and silicate rocks, located on islets within the Baskatong Reservoir in western Quebec, Canada. We present new laser ablation inductively coupled plasma mass spectrometry U–Pb zircon ages from four igneous rock samples within the exposed CMBBZ in the Baskatong Reservoir area in the Grenville Province in southwestern Quebec: (1) 1162 ± (5) [analytical error only: nonpropagated error] 16 [error including systematic uncertainties: propagated error] Ma for a syntectonic orthopyroxene leucosome located in the extensional quadrant of a sheared mafic boudin; (2) 1157 ± (4) 16 Ma for a syntectonic syenitic pegmatite composed of euhedral titanite phenocrysts preferentially aligned parallel to the host rock lineation, and characterized by syndeformation carbonatitic melt micro-textures; (3) 1149 ± (12) 18 Ma for a deformed late-tectonic pegmatite; and (4) 1022 ± (6) 15 Ma for a post-deformation dyke unit. These new age constraints, along with field observations, show that the REE-bearing carbonatite of Baie-Mercier was emplaced at ca. 1160 Ma during the Shawinigan Orogeny (1190–1140 Ma). Geochemical data point to a mantle-derived origin for the Baie-Mercier REE occurrence. Our findings further imply that this carbonatite could constitute one of the rare examples of synorogenic carbonatites worldwide.
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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 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".