Stratigraphic context, geochemical, and isotopic properties of magmatism in the Siluro-Devonian inliers of northern Maine: Implications for the Acadian Orogeny
Bibliographic record
Abstract
This paper reports detailed stratigraphic analysis, whole rock geochemistry and Nd isotopic ratios of basalts from the northern Maine inliers. These data place constraints on first-order controversies about the tectonic conditions leading up to and during the early stages of the Acadian Orogeny in northern Maine. Late Silurian and early Devonian stratigraphic sequences indicate a progressive change from shallow water and subaerial exposure (Ripogenus and The Forks formations, East Branch Group) to a rapidly subsiding basin prior to the onset of Acadian deformation. Subsidence was accompanied by mafic to intermediate volcanism of the West Branch, Spider Lake, and Fish Pond volcanics, and that continued with intrusion of the syn-deformational Greenville Plutonic Belt, including the Flagstaff Lake Igneous Complex, whose properties we report in this paper. Trace element geochemistry indicates that magmatism is transdiscriminant, showing aspects of within-plate, volcanic arc, and back-arc affinities and Nd isotopic ratios are moderately positive (+2.3 to +3.8) indicating either an uncontaminated and moderately enriched mantle source, or a depleted mantle source contaminated by continental crust. Four possible tectonic models of the Acadian Orogeny and the Siluro-Devonian sedimentary-volcanic sequences of northern Maine are evaluated in the context of a subsiding basin associated with this magmatism developed on the amalgamated Laurentian plate. These include 1) slab detachment during southeast-directed subduction of the Laurentian continental margin; 2) "Laramide-style" thrust basins above a shallow, northwest-dipping subduction zone; 3) back-arc extension followed by thin-skinned shortening above a northwest-dipping subduction zone; and 4) "Moluccan-style" dual-dipping subduction zones.
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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 | 0.000 | 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 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".