Contractional uplift of deep crustal rocks along the Legs Lake shear zone, western Churchill Province, Canadian Shield
Bibliographic record
Abstract
The Legs Lake shear zone juxtaposes high-pressure (1.0+ GPa) granulite- and eclogite-facies rocks with low-pressure (~0.5 GPa) amphibolite- to granulite-facies rocks, and thus may represent an important crustal-scale, exhumation-related structure in the western Canadian Shield. Field mapping and structural and petrologic analysis document the deformation and metamorphic history of rocks within and adjacent to the shear zone. At least two important phases of deformation are recorded: (1) early oblique thrusting (D2) that placed high-grade rocks over lower grade rocks, and (2) more discrete and lower grade brittleductile normal faulting (D3) that may represent the later part of the exhumation history. The northwest-dipping shear zone consists of 58 km of mylonite in map view, which bounds the southeast margin of the East Athabasca mylonite triangle. High-pressure granulite-facies metamorphism (~750850 °C, 1.01.2 GPa) occurred in the East Athabasca mylonite triangle at ca. 1900 Ma, prior to D2 juxtaposition with the adjacent low-pressure Hearne domain. Thermobarometry from GrtCrdSilBtQtz metapelites in the Hearne domain suggests peak conditions reached 600700 °C and 0.450.5 GPa, which are interpreted to have occurred late during D2. Published and preliminary UPb isotope dilution - thermal ionization mass spectrometry (ID-TIMS) zircon geochronology and electron microprobe monazite geochronology suggest that deformation in the Legs Lake shear zone coincided with the ca. 18301810 Ma terminal collision in the Trans-Hudson orogeny. Extensional faulting during D3 most likely occurred after ca. 1780 Ma. A multi-stage process of exhumation involving both thrust and normal-sense shearing, may serve as a model for the exhumation of other regionally extensive deep-crustal exposures.
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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 | 0.004 | 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) | 0.004 | 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".