Melting History and Magmatic Evolution of Basalts and Picrites from the Accreted Wrangellia Oceanic Plateau, Vancouver Island, Canada
Bibliographic record
Abstract
The accreted Wrangellia oceanic plateau in the Pacific Northwest of North America provides important insights into the volcanic architecture of major oceanic plateaus, as well as the nature of their mantle source, conditions of melting and subsequent magmatic evolution. The ∼20 000 km2 Karmutsen Formation flood basalts (Vancouver Island) were emplaced at c. 225–230 Ma onto Middle Triassic marine sediments and Late Devonian to Early Permian island-arc volcanic and sedimentary sequences, and are overlain by Late Triassic platformal carbonates. The basalts form an emergent sequence consisting of a basal sediment–sill complex (600–900 m thick), pillowed and massive submarine flows (>2·5 km), pillow breccia and hyaloclastite (<1·5 km), and massive subaerial flows (<2·5 km). Although the Karmutsen Formation is predominantly composed of tholeiitic basalt, the submarine part of the stratigraphy on northern Vancouver Island also contains picritic basalts. These high-MgO (9–20 wt %) lavas are depleted in light rare earth elements (LREE; La/YbCN = 0·5 ± 0·2), whereas the tholeiitic lavas (6–8 wt % MgO) are LREE-enriched (La/YbCN = 2·2 ± 0·3). Both lava groups have overlapping initial εHf(+10·3 ± 2·1) and εNd(+7·7 ± 1·3), indicating a common, plume-type Pacific mantle source with geochemical characteristics similar to the source of basalts from the Ontong Java and Caribbean plateaus. Major-element modeling results indicate that the picrites formed by extensive melting (23–27%) of anomalously hot mantle (∼1500°C), which is consistent with a mantle plume initiation model for formation of the Karmutsen flood basalts on Vancouver Island. Trace element constraints indicate that the picrites require melting of a depleted spinel lherzolite source, whereas the tholeiitic basalts involved melting of garnet and spinel lherzolite. The tholeiitic basalts underwent significant fractional crystallization (>50%) and the fractionated residues may be represented by high-velocity rocks beneath Vancouver Island identified from seismic reflection studies.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 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 teacher head, 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".