Thermal evolution of the Shames River mylonite zone, Coast Mountains, British Columbia
Bibliographic record
Abstract
The Shames River mylonite (SRM) zone is a major extensional shear zone that represents the tectonic boundary between the Coast Plutonic Complex and the Stikine accreted terrain in western British Columbia. Based on U-Pb and 40Ar/39Ar geochronology, the SRM zone was active between 54 and 48 Ma. This study applied the hornblende-plagioclase thermometer to orthogneiss and amphibolite samples collected from within the Shames River mylonite zone. Conventional thermobarometers were also applied to rocks from the hanging wall and footwall of the shear zone. Rocks of the Central Gneiss Complex in the footwall followed an isothermal decompression pressure-temperature (P-T) path from ∼8 kbar to ∼3 kbar at temperatures above ∼800°C. Rocks of the Stikine Terrane in the hanging wall followed isobaric heating and cooling P-T paths through the andalusite stability field with peak metamorphic P-T conditions restricted to the margins of plutons. The Shames River mylonite deformed plastically at temperatures of ∼750°C and then cooled during shearing, deforming by brittle failure at the end of deformation. Recrystallized pseudotachylite from plutons immediately above the mylonite records greenschist facies metamorphic conditions of ∼400°C and 2 kbar indicating the onset of brittle deformation between the two terranes at ∼5 to 6 km depth between 51 and 48 Ma. The combined metamorphic data set indicates approximately 16 km of uplift of the footwall during extension. These results show that contrasting metamorphic and tectonic histories between the Stikine Terrane and central gneiss complex are the result of large scale extensional deformation that juxtaposed upper crustal rocks with deep crustal rocks during arc magmatism.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.002 | 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) | 0.002 | 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".