Mesoproterozoic lamprophyres in the Labrieville Massif, Quebec: clues to the origin of alkalic anorthosites?
Bibliographic record
Abstract
Mesoproterozoic lamprophyre dikes occur at four localities within the ~1010 Ma Labrieville anorthosite in the Grenville Province of southern Quebec. All dikes are thin (<20 cm wide), oriented ~N57W, and steeply dipping. Three are biotite lamprophyres, but the fourth is dominated by amphibole. Laser total-fusion 40Ar/39Ar analyses on amphibole or biotite yield minimum ages for the dikes of 945.5 ± 8 Ma, 907.0 ± 5.9 Ma, 892.0 ± 6.2 Ma, and 889.2 ± 9.8 Ma. A crystallization age of ~1 Ga for all dikes is consistent with these data and RbSr isotopic systematics. All lamprophyres contain high levels of Cr (284393 ppm), Ni (101180 ppm), Ba (13805580 ppm), Sr (23593109 ppm), and rare-earth elements (REE; LaN = 191288), with average LaN/LuN = 26 and no Eu-anomalies. At 1 Ga, all lamprophyres have a similar initial Sr isotopic ratio of ~0.7034, similar to Bulk Earth. In contrast, εNd values vary considerably from 4 to 10.2, indicating sources with variable long-term light-REE enrichment. Negative correlations between 143Nd/144Nd and La/Nb and K suggest involvement of at least two source components, probably asthenosphere and metasomatized subcontinental lithosphere. The lamprophyres are only slightly younger than ~1010 Ma Labrieville massif, which is also alkalic and enriched in Sr and Ba relative to most other anorthosites. The lamprophyres provide unequivocal evidence for a Sr- and Ba-rich component in the lithospheric mantle that may have contributed to the parental magmas of Labrieville and other andesine anorthosites in this part of Quebec.
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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 | 0.002 | 0.001 |
| 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".