Isotopic and geochemical evidence for a recent transition in mantle chemistry beneath the western Canadian Cordillera
Bibliographic record
Abstract
New petrologic, geochemical, and isotopic data are reported from a suite of mafic dike and lava flow samples collected from sites within the western Canadian Cordillera. Samples range in age from Eocene to Quaternary and document a significant transition in mantle chemistry that occurred sometime after 10 Ma. Eocene to late Miocene basalts emplaced as dikes within the Coast Mountains Batholith contain abundant hornblende, are enriched in large ion lithophile elements (LILE) (Ba, Rb, K), have negative high field strength element (HFSE) (Nb, Ta) anomalies, and were likely derived from lithospheric mantle (87Sr/86Sr = 0.70353–0.70486; ɛNd = +2.5 to +5.7) that was stabilized after the cessation of arc magmatism in the area. By contrast, Quaternary lava flows have lower LILE concentrations, positive Nb‐Ta anomalies, and were likely generated by upwelling asthenosphere (87Sr/86Sr = 0.70266–0.70386; ɛNd = +7.4 to +8.8) or at least a mantle source with different chemical and isotopic characteristics. A regional comparison of mafic rocks from western Canada that are also Eocene to Quaternary in age indicates that the transition in mantle chemistry after 10 Ma was pervasive and widespread and was not limited to the present study area. This transition occurred ∼40 Ma after the cessation of Cordilleran arc magmatism in central British Columbia, suggesting that large‐scale transitions in mantle chemistry beneath magmatic arcs may occur on the order of tens of millions of years after the final subduction of oceanic lithosphere, in this case as a result of lithospheric thinning by continental extension.
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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 | 0.002 | 0.002 |
| Science and technology studies | 0.002 | 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) | 0.002 | 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".