Augmented and reassessed U–Pb geochronological data from the Labradorian–Grenvillian front in the Smokey archipelago, eastern Labrador
Bibliographic record
Abstract
Four UPb dating sites straddling the Grenville front on the Labrador coast were investigated. Sites 1 and 2 exhibit complex intrusive, deformational, and metamorphic histories and were studied in detail, whereas two simpler outcrops (sites 3 and 4) were examined only at a reconnaissance level. At site 1, south of the Grenville front, a 1799+32 Ma granodioritic gneiss is intruded by two phases of mafic dykes, then by a 1647+75 Ma aplite and a ca. 16471500 Ma pegmatite, and lastly by the Michael gabbro. The pegmatite was metamorphosed at 1030 ± 10 Ma. Site 2 is on the Cut Throat Island thrust, which defines the Grenville front in the area. Early mylonitization occurred at 1790 ± 2 Ma, followed by 1730 ± 2 Ma pegmatite emplacement and then cooling at 1703 ± 15 Ma. A post-deformational melt pod gave a titanite age of 1662 ± 10 Ma. In the mylonitic host, based on positive correlation between Pb loss and degree of granularization in monazite, Grenvillian deformation was very short-lived. Sites 3 and 4 (north of the Cut Throat Island thrust), yielded 1709 ± 10 and 1726 ± 34 Ma ages, respectively. Lack of marked younger Pb loss demonstrates that these sites escaped both Labradorian and Grenvillian metamorphism. Emplacement, deformation, and (or) metamorphism occurred at 18001790 Ma, 17301700 Ma, 16601650 Ma, possibly at 1500 Ma, and at 10401030 Ma. The Cut Throat Island thrust was active during all events, but none was confined to it. The thrust marks the northern limit of Labradorian and Grenvillian orogenesis, but because similar pre-Labradorian history is preserved on both sides of the thrust, it is not a fundamental tectonic boundary after 1800 Ma. Nevertheless, because reactivation occurred during every geological orogenic event known in the region, it clearly represents a zone of persistent crustal weakness.
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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 | 0.004 | 0.003 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".