Late Devonian shear zone reactivation in the Canadian Appalachian orogen
Bibliographic record
Abstract
Accretionary orogens are characterized by sequential collisions of buoyant crustal material with a continental margin or an oceanic arc. Because the timing, kinematics, and intensity of deformation are controlled by the obliquity of the collisions, pre-accretionary shape, and rheology of the accreted crustal material, it is often difficult to determine what processes controlled the generation or reactivation of shear zones not located in the immediate vicinity of a suture marking a collision. In the Canadian Appalachians, this problem is compounded by the lack of tectonic interpretation for the regional deformation occurring during the Late Devonian oblique collision of Meguma to composite Laurentia during the Neoacadian Orogeny. To address these issues, this thesis targets the Eastern Highlands and Pocologan-Kennebecasis shear zones (Nova Scotia and New Brunswick, respectively) which were part of the composite margin of Laurentia at the time of the Neoacadian orogeny. Several characteristics of these shear zones are quantified including 1) the timing of deformation, through U-Pb and ⁴⁰Ar/³⁹Ar geochronology; 2) the kinematics based on field and thin section observations and quartz crystallographic preferred orientations; and 3) the potential impact of fluid-rock interaction on shear zone rheology. The new information from this work is combined with regional interpretation of aeromagnetic and gravimetric depth slices, and compilation of shear zone deformation ages and ⁴⁰Ar/³⁹Ar cooling ages to provide insight into the tectonic setting of the Neoacadian Orogeny. In the northern Appalachians, between the Late Devonian and Mississippian, regionally extensive NE-SW and ENE-WSW oriented shear zones were formed, or reactivated, with a dextral strike-slip shear sense consistent with a large-scale C-C’ system. Aeromagnetic and gravity geophysical data indicate that several of these structures are listric, and thus formed a lateral succession of transpressive and transtensive segments crosscut by antithetic sinistral shear zones. These structures appear to define a syntaxis in New England. ⁴⁰Ar/³⁹Ar age transects across the region outline Neoacadian cooling and exhumation that correlates spatially to an area of high paleo-elevation that was contemporaneous to the opening of the Maritimes and Catskills basins. Such a setting is similar to the present-day oblique collision of Yakutat terrane to Western North America.
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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 | 0.003 |
| Science and technology studies | 0.003 | 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) | 0.002 | 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".