Cape St. Marys shear zone and the Halifax Group – Rockville Notch Group disconformity, southwestern Nova Scotia: structural development and tectonic significance
Bibliographic record
Abstract
The Cape St. Marys shear zone, situated in a corridor of Alleghanian reworking in the southwestern Meguma terrane, contains the deformed, discordant contact of Lower Ordovician slate of the Halifax Group with the Silurian White Rock Formation. Close to the contact, the Alleghanian cleavage (S2) is parallel to the contact in both units, with S0 in the White Rock Formation metavolcanic rocks and Halifax slate parallel to and discordant to the contact. The geometry of deformed Neoacadian minor folds, quartz fringes on sulphide grains, and micro-porphyroclasts demonstrate thrust-sense shear (White Rock Formation over Halifax slate). Pure shear and volume loss are inferred as components of the strain path from S2 microstructure and estimates of strain in the Halifax slate. Estimates of shear strain imply moderate displacements within the Cape St. Marys shear zone during deformation of the northwestern limb of the Cape St. Marys syncline. The discordant contact of the Halifax slate with the White Rock formation cannot be a thrust plane because younger rocks overlie older rocks. Thus the contact is what it appears to be: an angular unconformity embedded within a ductile shear zone. Brittle-ductile faults, quartz vein arrays, and centimetre-scale kink bands disturb S2 in the Halifax slate a few metres northwest of the contact. The geometry of the brittle-ductile structures and the orientation of stretching lineation in the ductile structures link the episodes kinematically. Quartz veins accompanying brittle-ductile deformation suggest that fluids derived during pressure solution development of S2 drove the change from ductile to brittle-ductile deformation in the Cape St. Marys shear zone during the latter stages of convergence. In a regional context, the moderate shear values of the Cape St. Marys shear zone are reasonable for the diminishing displacement expected near the termination of a northwest-propagating regional shear system. Whereas the transition from ductile to brittle-ductile deformation occurred late in the development of the Cape St. Marys shear zone, brittle-ductile structures were dominant closer to the northwest border of the zone of Alleghanian deformation. The fluids required for the transition may have been driven along a pressure gradient from more internal parts of the corridor, where pressure solution was more active.
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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 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".