U-Pb zircon geochronology of a post-kinematic, pegmatitic syenogranite dyke, northern Baffin Island, Nunavut
Bibliographic record
Abstract
The Geological Survey of Canada (GSC) GEM-2 North Baffin project (2017-2020) involved 1:100,000-scale bedrock mapping and associated geochronological studies of northern Baffin Island, with the aim of building on previous, less-detailed (1:250,000-scale) mapping to fill a knowledge gap in our understanding of the geology of the area. Along the northern coast of Baffin Island, southwest of the community of Pond Inlet, Neoarchean tonalitic gneiss has been thrust over Neoarchean metasedimentary rocks along the Qimivvik thrust. The thrust is cross-cut by a ~7 m wide, pegmatitic leucogranite (syenogranite) dyke, which also cross-cuts foliation in tonalitic gneiss in the hanging wall of the thrust. Uranium-Pb zircon geochronology was conducted on a sample collected from the syenogranite dyke, as the crystallization age of the dyke provides a younger age limit on the Qimivvik thrust and on foliation in the tonalitic gneiss. The dyke yielded three chemically and texturally distinct populations with various U contents, Th/U ratios, and Hf/Yb ratios. Regardless of textural/chemical population, the analyses produced equivalent dates (within errors at 95% confidence level), implying that they formed at approximately the same time during melt crystallization. The combined weighted average age of all three populations, 1809 ± 4 Ma, is considered to be the crystallization age of the dyke. Thus, movement along the Qimivvik thrust and foliation development in tonalitic gneiss in the hanging wall are interpreted to have ceased before ca. 1809 Ma.
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".