Eocene Basalt of Summit Creek: Slab breakoff magmatism in the central Washington Cascades, USA
Bibliographic record
Abstract
The early Eocene (52-44 Ma) was a time of tectonic reorganization and widespread magmatism in Washington, Oregon, and British Columbia (west coast of the United States and Canada) that culminated with establishment of the Cascade arc. Details of this tectonic transition remain enigmatic, and diverse scenarios involving ridge-trench interaction, slab breakoff, and/or plume magmatism have been proposed. This study focuses on the ca. 48 Ma Basalt of Summit Creek, a ~1500-m-thick sequence of subaerial lavas that erupted during the interval of time between accretion of the Siletzia terrane to the west and inception of the Cascade arc. The sequence dominantly consists of moderately evolved tholeiitic basalts (9.3-3.1 wt% MgO; Mg# = 0.66-0.29) and scarce rhyolites that erupted in the forearc but are chemically and isotopically similar to oceanic basalts of the Crescent Formation, found ~100 km to the west as part of the Siletzia terrane. Basalt of Summit Creek lavas lack subduction signatures (e.g., high field strength element depletions) and require a mechanism whereby asthenospheric melts were able to reach the surface having undergone little or no chemical interaction with fluids derived from the subducting slab or metasomatized mantle. We suggest that the accretion of Siletzia led to breakoff of the Farallon slab, and that Basalt of Summit Creek lavas formed by decompression melting of mantle that upwelled through the rupture. Slab breakoff typically produces a short-lived linear magmatic belt; the Basalt of Summit Creek appears to be part of such a belt, previously unrecognized, that parallels the Siletzia boundary and formed between 50 and 48 Ma.
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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 | 0.001 |
| Science and technology studies | 0.001 | 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) | 0.003 | 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".