Multistage exhumation and juxtaposition of lower continental crust in the western Canadian Shield: Linking high‐resolution U‐Pb and <sup>40</sup>Ar/<sup>39</sup>Ar thermochronometry with pressure‐temperature‐deformation paths
Bibliographic record
Abstract
New U‐Pb (titanite, apatite, rutile) and 40Ar/39Ar (hornblende, muscovite, biotite) data are linked with existing pressure‐temperature‐deformation paths to impose detailed temporal constraints on the juxtaposition and unroofing of domains in an extensive (>20,000 km2) region of exhumed lower crust in the East Lake Athabasca region of the western Canadian Shield. In the ∼200 m.y. between circa 1.9 Ga high‐pressure granulite facies metamorphism and circa 1.7 Ga unconformable deposition of Athabasca basin sediments on the exhumed rocks, our analysis reveals at least three distinct phases of unroofing at different rates. Specifically, we distinguish (1) an early phase of extensional unroofing in the Chipman domain at rates of 1.5–2.0 km/m.y. from ∼1.0 GPa to ∼0.8 GPa associated with mafic magmatism and metamorphism, (2) an episode of regional contractional uplift and associated unroofing along the Legs Lake shear zone at circa 1850 Ma from 0.7–0.8 GPa to 0.4–0.5 GPa, and (3) a final period of extensional unroofing at rates of 0.2–0.3 km/m.y. from 0.4 to 0.5 GPa that culminated in transport of current exposures to near‐surface conditions. The cooling patterns and retrograde assemblages are consistent with pauses between exhumational phases. The apparent convergence of disparate higher temperature histories in several deep crustal domains at circa 1.89–1.88 Ga implies their juxtaposition at 0.7–0.8 GPa conditions. Regional east directed thrusting of the deep crustal domains as a coherent unit at 1.85 Ga juxtaposed the granulites with middle crustal Hearne domain rocks at 0.4–0.5 GPa conditions. The detailed exhumational history allows correlation with changing regional tectonic regimes associated with the amalgamation of Laurentia. The temporal and spatial heterogeneity of exhumation patterns in the East Lake Athabasca region may be a common feature of the unroofing histories of lower crustal rocks.
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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 | 0.002 | 0.002 |
| 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) | 0.001 | 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".