Timing and tectonic setting of Ordovician volcanic rocks of the Miramichi terrane in eastern Maine, USA, and southwestern New Brunswick, Canada
Bibliographic record
Abstract
New U-Pb LA-ICP-MS ages and geochemical data from volcanic rocks in the southwestern part of the Miramichi terrane in Maine, USA, and the Eel River area, New Brunswick, Canada, indicate that calc-alkaline continental arc volcanism began in the earliest Ordovician (ca. 480 Ma) and continued into the Middle Ordovician (at least as late as ca. 463 Ma). The overlap of volcanic rock ages from the Greenfield (ca. 478–463 Ma) and Danforth, Maine (ca. 467–475 Ma), and Eel River, New Brunswick (ca. 480–468 Ma), segments of the terrane confirm previously uncertain correlations of the Olamon Stream (Greenfield), Stetson Mountain (Danforth), and Porten Road and Eel River (Eel River) formations in these areas. The youngest Middle Ordovician ages overlap those of the oldest units of the Tetagouche Group in northern New Brunswick which are attributed to crustal extension leading to opening of the Tetagouche back-arc basin.Silicic and mafic Tetagouche Group rocks plot in within-plate fields on tectonic discrimination diagrams, distinctly different from the volcanic arc fields for the coeval silicic and mafic rocks in the two Maine segments and the Eel River segment in New Brunswick. Continental arc volcanism in the southwestern Miramichi terrane did not cease when arc extension/rifting leading to formation of the Tetagouche back-arc basin began at ca 470 Ma in New Brunswick, as proposed in a previous model that invoked a single migrating arc. Instead, southwestern Miramichi volcanism had extended from at least ca. 480 to 463 Ma—incompatible with short-lived Meductic-phase arc volcanism (ca. 476–472 Ma) proposed in that model.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".