UPb ages constraining structural development of an Archean terrane boundary in the Lake of the Woods area, western Superior Province, Canada
Bibliographic record
Abstract
Layered gneisses in the Winnipeg River subprovince contain magmatic zircon with UPb ages of 3317 ± 9 and 3055 ± 4 Ma at Tannis Lake, and ~3170 and 3255 ± 5 Ma at Cedar Lake, indicating widespread occurrence of Mesoarchean crust. This is in contrast to the well-documented Neoarchean age of the western Wabigoon subprovince. Further geochronology using both SHRIMP (sensitive high resolution ion microprobe) and ID-TIMS (isotope dilution thermal ionization mass spectrometry), combined with structural observations, in the Kenora area and Lake of the Woods greenstone belt show the effects of juxtaposition of these two terranes. Isoclinally folded gneiss north of the subprovince boundary zone near Kenora gives a magmatic age of 2882 ± 2 Ma with 3051 ± 6 Ma inheritance. Ages of syntectonic dykes show that asymmetric refolding of these gneisses occurred between 2717 ± 2 and about 2713 ± 1 Ma. Subsequent regional vertical flattening and horizontal extension are dated at 2708 ± 2 Ma by syntectonic tonalite sheets. These events are broadly coeval with deposition of orogenic sediments in the Warclub Group and a first stage of regional folding (age brackets of 27162709 Ma) in the Lake of the Woods greenstone belt to the south. A second stage of folding and regional faulting in the greenstone belt occurred about 2695 ± 4 Ma and is approximately coeval with open upright folding in the Winnipeg River subprovince. These observations are consistent with overthrusting and collapse of a Mesoarchean continental terrane by a juvenile Neoarchean arc terrane over the time span 27172695 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 | 0.002 | 0.002 |
| Science and technology studies | 0.002 | 0.000 |
| 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".