Paleomagnetic correlation of dykes in canada and greenland, and its bearing on the nares strait problem
Bibliographic record
Abstract
In 1915 Alfred Wegener proposed a major fault along the Nares Strait between Greenland and Ellesmere Island in Canada to account for the separation of Greenland from Labrador. The existence of this transform fault has been controversial; plate tectonic reconstructions using marine magnetic anomalies indicate sinistral displacement of about 200 km, but observations of Paleozoic sedimentary rocks across the Nares Strait allow movement of no more than 25 km. A major E-W trending dyke swarm (˜700 Ma) extends for more than 200 km in the Thule area of Greenland. The swarm does not appear to extend westwards along strike into central Ellesmere Island. Instead a possible offset continuation of the swarm appears in southern Ellesmere and Devon Islands. A positive correlation would indicate a sinistral offset of about 200 km as required by plate tectonic reconstructions. We plan to use paleomagnetic, geochemical and U-Pb geochronological analyses to test the correlation. Initial paleomagnetic results from five dykes on Ellesmere and Devon Islands and four dykes and two sills from Greenland indicate stable remanences, using either AF or thermal demagnetization. In both regions polarity reversals are observed. The results from Canada (D=276^o, I=6^o, α95=20^o, k=15, N=5) and Greenland (D=291^o, I= 9^o, α95 =11^o, k= 27, N=6) show similar directions within error and are therefore consistent with the two swarms having once been continuous. A preliminary baked-contact test of an Ellesmere Island dyke is positive, indicating primary magnetization. Petrographic observations of the dykes from both Canada and Greenland are virtually identical, with variations only in the degree of alteration. Preparation of samples for geochemical and U-Pb geochronological analyses is underway. A similar correlation between Greenland and Canada is also being attempted for N-NW trending dykes that may be part of the ca 1620 Ma Melville Bugt dyke swarm.
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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 | 0.003 | 0.004 |
| Science and technology studies | 0.002 | 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) | 0.001 | 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".