K-Ar dating constraints on the tectonothermal evolution of the external Humber zone, southern Quebec Appalachians
Bibliographic record
Abstract
In the external Humber zone, the emplacement episodes of allochthonous nappes and related low-grade metamorphism are mainly based on paleontological ages from the St. Lawrence Lowlands. In fact, Late Ordovician flysches are affected by thrusting, and it is not clear if the nappe imbrication is the result of the Taconian or the Acadian deformation. Along the Chaudière River transect, fourteen shales and phyllites of Cambrian to Ordovician age were sampled for determination of the KAr values of their < 2 µm-size fractions. To interpret the KAr data, mineral composition and clay mineral crystallinity of the < 2 µm-size fractions and maturation of the organic matter were determined. In addition, the intensity of deformation was characterized by describing the rock texture at macroscopic and microscopic scale. The combined approach used in this study emphasized that nearly all KAr dates are mixed or partly reset values. However, it can be stated that in the Quebec Promontory nappe and part of the Chaudière nappe, a Cretaceous thermal overprint might have occurred on the basis of a low KAr value at 256 Ma. Furthermore, the KAr dates of 491467 Ma obtained in the Chaudière nappe to the southeast, most probably represent mixed values of detrital material affected by diagenetic or tectonic processes. It might also be stated that the base of the Sainte-Hénédine nappe appears to be characterized by southeast-dipping thrust sheets with KAr dates of 439418 Ma, which may represent either a late-stage emplacement of the nappe or a yet unrecognized structural effect of hinterland-directed deformation that characterizes the internal Humber zone. In the southeastern part of the Sainte-Hénédine nappe, the thermal grade increases to epizonal conditions and the KAr dates that, in this case, could be of meaningful geological significance increase to 455445 Ma. Such ages are consistent with Ordovician 40Ar/39Ar metamorphic ages attributed to the Taconian orogeny in the internal Humber zone.
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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 | 0.002 | 0.002 |
| 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".