Complex Late Triassic-Middle Jurassic Subduction-Related Magmatic History from Detritus of Nominal Middle Jurassic Brooks Range Ophiolite, Northern Alaska
Bibliographic record
Abstract
Abstract In northern Alaska, the Early Cretaceous sedimentary Yukon-Koyukuk basin documents the progressive unroofing of the adjacent Brooks Range orogen. Igneous clasts in the lower conglomerate are believed to originate from ophiolitic rocks of the two uppermost allochthons in the Brooks Range, the Brooks Range ophiolite and the Angayucham terrane. The emplacement of these oceanic terranes onto the continental margin of the Arctic Alaska terrane documents the initiation of Brookian orogenesis. While most agree that the Angayucham terrane represents a widespread distribution of Late Devonian oceanic crust and Triassic-Early Jurassic oceanic plateau(s)/island(s), the age and origin of the Brooks Range ophiolite remains controversial. We present new age, whole-rock chemistry, and isotopic data from igneous clasts as well as a few Angayucham terrane outcrop samples from the NE Yukon-Koyukuk basin. Our results show that the igneous clasts are mostly subduction-related and more likely to represent eroded material from the Brooks Range ophiolite rather than the Angayucham terrane. Our Late Triassic, and Early and Middle Jurassic zircon crystallization ages for the igneous clasts, combined with their immobile trace element compositions documenting various stages of oceanic subduction (mature arc and later rifting), suggest a long-lived subduction system that was active in the Late Triassic and throughout the Middle Jurassic. Radiogenic lead and neodymium isotopic results yield juvenile signatures for both the igneous clasts and the Angayucham terrane, pointing to their formation in an intraoceanic setting distal from the continental rocks and sediments of the Arctic Alaska terrane. These new data, combined with the published data of others, allow us to propose a revised tectonic model that integrates Late Triassic island arc formation with the tectonic development and emplacement of the Brooks Range ophiolite.
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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 | 0.000 |
| Science and technology studies | 0.001 | 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 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".