The Okanagan subterrane: a 'Subduction Initiation Rule' ophiolite in the Canadian Cordillera
Bibliographic record
Abstract
The Okanagan subterrane in south-central British Columbia is commonly referred to as the basement to Quesnellia, a composite arc terrane in the Canadian Cordillera. Distinct geochemical, lithologic, and structural characteristics allow for interpretation of the Okanagan subterrane as a forearc ophiolite formed over a long-lived west-dipping subduction zone initiating in western Panthalassa. The forearc ophiolite model has significant impacts on existing Cordilleran models which focus on a North American origin for this terrane. The Okanagan subterrane is comprised of harzburgites, gabbros, basaltic lavas, and ocean basin sediments. The age of the subterrane spans the Middle Devonian through the Early Permian. New stratigraphic, structural, and whole rock geochemical data are presented together with a synthesis of pre-existing data from regional studies to better constrain the origins and evolution of the Okanagan subterrane. The results indicate a transition from quiet shallow ocean basin deposition to the initiation of subduction and construction of a new forearc crustal sequence and mantle wedge. The earliest crustal sequences were formed from the eruption of basalts geochemically similar to those produced at oceanic spreading centres in the Late Devonian to earliest Mississippian. A chemostratigraphic magmatic progression through the Early and Middle Mississippian resulted in lavas becoming increasingly island arc-like in composition. Uplift and erosion dominated through the Pennsylvanian and Permian, punctuated by periods of carbonate deposition and capped by a regional Permo-Triassic unconformity and a Mesozoic volcanic arc. The Okanagan subterrane was affected by two main compressional deformation events, both interpreted as products of ophiolite obduction. The first, in the Permo-Triassic, resulted in tight to isoclinal folding, uplift, and erosion yielding the Permo-Triassic unconformity and the obduction of the Okanagan subterrane onto an extinct island arc within the lower plate. The second, in the Middle Jurassic, resulted in a southwest-verging fold and thrust belt which likely records the subsequent accretion to pericratonic terranes of western Laurentia. Comparing this ophiolite to other supra-subduction zone ophiolites worldwide allows for an interpretation of the Okanagan subterrane as a forearc ophiolite constructed during Late Devonian intra-oceanic subduction initiation.
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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 | 0.003 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.007 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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".