Late Neoarchean to middle Paleoproterozoic geology of Devon and Ellesmere islands, Canadian Arctic
Bibliographic record
Abstract
The northernmost exposure of the Laurentian shield in Canada outcrops on Devon and Ellesmere islands within the Canadian Arctic Archipelago. Due to the remote location, the basement rocks of these islands have received little attention. From this study, zircon crystallization ages demonstrate that Devon Island is underlain by a late Neoarchean terrane comprising orthogneisses emplaced at ca. 2.55–2.51 Ga and an interleaved metasedimentary sequence deposited at ca. ≥2.47 Ga. On northern Devon Island, younger metasedimentary sequence(s) were deposited at ca. 2.2–1.9 Ga and intruded by ca. 2.01–1.95 Ga granitoids. Devon and Ellesmere islands experienced widespread metamorphic activity associated with the Thelon orogeny between ca. 1.95–1.87 Ga, peaking at ca. 1.91 Ga. Minimum peak temperatures of metamorphism are estimated at ca. >800 ℃ throughout Devon and Ellesmere islands and the first documented sapphirine + quartz assemblage in the Devon and Ellesmere islands area is diagnostic evidence of ultrahigh temperature conditions (>900 ℃). The abundance of spinel + quartz (ca. ≥940 ℃) metasedimentary rocks on Ellesmere Island likely provides further evidence of widespread ultrahigh temperature conditions. Peak pressures of ca. 1.9 Ga metamorphism are estimated at ca. 9 kbar on southern Devon Island and ca. 6–7.5 kbar for northern Devon and Ellesmere islands. Earlier, poorly constrained metamorphic events are recorded at ca. 2.54, 2.47 and 2.30 Ga, possibly associated with pulses of the Arrowsmith orogeny. The late Neoarchean Devon terrane potentially extends to the southwest on Boothia Peninsula and to the northeast in the Prudhoe Land area of northwestern Greenland. The juvenile middle Paleoproterozoic rocks of northern Devon and Ellesmere islands represent a northern extension of the Thelon tectonic zone, which we term the Ellesmere tectonic zone.
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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 | 0.004 | 0.004 |
| Science and technology studies | 0.003 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".