An overview of the Canadian Cordilleran lithospheric mantleThis article is one of a series of papers published in this Special Issue on the theme <i>Lithoprobe — parameters, processes, and the evolution of a continent</i>.
Bibliographic record
Abstract
Recent alkaline basalts have brought xenoliths of the underlying lithospheric mantle to the surface at more than 20 localities along the strike length of the Canadian Cordillera. The populations of 13 of these xenolith suites display a common mode at 39–40 wt.% MgO and 3.0–3.5.0 wt.% Al2O3, corresponding to a relatively fertile lherzolite whose composition could reflect 8%–10% melting of primitive mantle. The present oxidation state of the Cordillera lithospheric mantle obtained from olivine–spinel equilibria is ∼1 log unit below the fayalite–magnetite–quartz (FMQ) buffer, which is essentially the same as the oxidation state at the time of the melting event that stabilized the Cordilleran lithospheric mantle in the mid-Proterozoic, as constrained by the relative variation of Sc and V. Two xenolith suites near the Yukon – British Columbia border exhibit a second stronger mode, corresponding to relatively refractory spinel harzburgite with significantly higher Mg contents (45–46 wt.% MgO) and lower Al contents (0.5–1.0 wt.% Al2O3). These bi-modal mantle xenolith suites overlie a teleseismic S-wave slowness anomaly in the underlying asthenospheric mantle, and the harzburgites appear to have been produced by a more recent, localized partial melting (∼15%) of the lherzolite lithosphere. The temperatures estimated from clinopyroxene–orthopyroxene equilibria indicate that the lithospheric mantle beneath the Canadian Cordillera is significantly hotter than that beneath the adjacent Archean of the North American craton, with temperatures at the Moho on the order of 800 °C, a minimum geothermal gradient of ∼10 °C/km, and a thickness of <∼65 km.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.006 | 0.009 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.010 | 0.001 |
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".