Lithospheric thickness and the backarc–craton lithosphere step in southwestern Canada imaged by a 3D magnetotelluric study
Bibliographic record
Abstract
A 3D electrical resistivity model extending to a depth of 400 km in southwestern Canada and the northwestern United States was created by inverting long-period magnetotelluric (MT) data collected at 331 locations. Detailed analyses of this resistivity model, sensitivity tests including synthetic 3D MT inversions, and comparisons with seismic velocity models were used to investigate the depth and geometry of the lithosphere–asthenosphere boundary (LAB) and the transition in mantle structure from the Canadian Cordillera to the North American craton. Mantle resistivity increases from west to east, indicating an eastward increase in LAB depth. The model also shows that the LAB dips northward in southern-to-central Alberta, with lithospheric thickness increasing from ∼150 km (at 49–50°N) to 250 km or more (at 53–54°N). A conceptual model was created, including a backarc–craton lithosphere step located beneath the southern Omineca belt, somewhere between the western boundary of the Kootenay Arc and the 87Sr/86Sr = 0.706 isopleth. This is 90–200 km west of the southern Rocky Mountain Trench, where earlier studies had placed the western edge of the thick craton based on surface heat flow, seismic velocities, and mantle xenoliths. This difference in location could reflect limitations in the resolution of the various geophysical methods or complex present-day mantle dynamics at the subvertical lithosphere step.
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".