Assessing the role of orogen-parallel faulting in post-orogenic exhumation: low-temperature thermochronology across the Norumbega Fault System, Maine
Bibliographic record
Abstract
As a part of a regional effort to determine the extent of low-temperature thermochronological discontinuities across major orogen-parallel faults in northern New England, 41 apatite fission track (AFT) ages and 11 (U–Th)/He ages are used to constrain the ∼65 to 100 °C cooling history of rocks flanking a 160 km long segment of the Norumbega fault system in southern and south-central Maine. These data are used to evaluate the role of this structure in the late Mesozoic and younger exhumation history of the northern Appalachians. AFT ages flanking the fault system range from 159 to 95 Ma and record cooling below ∼100 °C in the late Mesozoic. (U–Th)/He ages from the same region range from 126 to 100 Ma and record cooling below ∼65 °C. Previously published AFT ages from an ∼40 km long segment of the fault system just north of Casco Bay reveal a dramatic time–temperature discontinuity across the structure and suggest kilometre-scale late Mesozoic displacement in this region. However, new AFT and (U–Th)/He ages along the strike of the Norumbega fault system to the northeast and southwest of this discontinuity show no significant differences in late Mesozoic cooling and suggest no significant displacements occurred along these portions of the fault system during this time. Collectively the data suggest differential late Mesozoic reactivation of the Norumbega fault system with the reactivation localized in areas that had previously experienced episodes of vertical displacement in the late Paleozoic (i.e., the “Casco Bay restraining bend”).
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".