The Structure and Dynamics of the Uppermost Mantle of Southwestern Canada From a Joint Analysis of Geophysical Observations
Bibliographic record
Abstract
Abstract Geophysical imaging reveals significant changes in mantle properties from the Southern Canadian Cordillera to the Laurentian Craton in southwestern Canada. We examine mantle structure using shear wave velocity (VS) from seismic tomography and electrical resistivity from magnetotellurics. Independent analyses of VS and resistivity are poorly constrained because of the number of free parameters. To overcome these limitations, we conduct a joint analysis of VS and resistivity to quantify temperature and olivine water content at 75–150 km depth, corresponding to the cordillera asthenosphere and craton mantle lithosphere. For the cordillera, there is a trade‐off between temperature and water content; the observations are consistent with either warm, hydrated, and melt‐free mantle (∼1,240°C; ∼1,600 ppm H/Si in olivine) or hotter, less hydrated mantle (∼1,370°C; ∼600 ppm H/Si) with some melt at 75 km depth. In contrast, the craton mantle lithosphere is ∼350°C cooler and drier (<300 ppm H/Si). Temperatures depend strongly on the seismic attenuation model. If this is known, the temperature uncertainty is <100°C. There is significant uncertainty in olivine water content (>500 ppm H/Si), owing to observation uncertainties, the resistivity model, and mantle composition. Our results indicate that the cordillera asthenosphere has a low viscosity (1019–1021 Pa s) and is susceptible to small‐scale convection. Approximately below the Rocky Mountain Trench, there is a subvertical eastward increase in lithosphere thickness. The cratonic mantle lithosphere viscosity is 1022–1024 Pa s and the western edge of the craton may be unstable, suggesting that the present‐day geometry is a transient feature.
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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 | 0.003 |
| Science and technology studies | 0.001 | 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) | 0.001 | 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".