Abstract: Controlling mechanisms for dyke emplacement and fluid flow around strike-slip faults in the Campbellton region, northern New Brunswick
Bibliographic record
Abstract
In a strike-slip regime, the bulk compressive stresses are near horizontal, and as such there has been much debate about the space generating mechanism required for magma emplacement. In the Campbellton region of New Brunswick numerous intermediate, fineto medium-grained sheets intrude Late Ordovician to Late Silurian, sedimentary rocks and Early Devonian, subvolcanic to subaerial igneous rocks. Intrusions are most prevalent proximal to regional-scale, strike-slip faults where cross-cutting relationships indicate coeval magma emplacement and fault displacement. In sedimentary rocks, intrusions are typically oriented along a pre-existing fabric (bedding) along which abundant bedding-parallel slip has occurred. Analysis of fault orientation and movement history allows for an approximation of the far-field stress directions, with σ1 oriented WNW-ESE. Traditional theories on magma emplacement in strike-slip regimes suggest that magma should orient itself perpendicular to the maximum tensile stress. However, in the study area, this is uniformly not apparent with all intrusions oriented oblique to, or parallel with, far-field σ3. It is very difficult for a dyke to intrude a pre-existing fracture that is misaligned with σ3 unless the resolved shear stress on the plane is small relative to excess magma pressure, or the effective dyke-normal stress is small relative to the rock tensile strength. Without these conditions the magma will propagate into a selfgenerated crack perpendicular to σ3. During mode I-II fracture propagation, maximum tensile stress occurs at the dyke tip and parallel to the dyke; thus, if the tensile stress exceeds the tensile strength of the rock, the dyke cannot propagate into the pre-existing plane. However, for mode I-III fractures effective tension at a dyke tip is significantly lower and may allow propagation along the pre-existing front. The Campbellton region experienced a transpressive stress regime during dyke emplacement and thus fracture propagation was dominantly mode IIII. In addition, during major fault development, subsidiary fracture propagation can significantly alter stress trajectories around the parent fault and introduce local dilatant zones that are misaligned with far-field σ3. As such, the combination of a far-field transpressive stress regime and local stress perturbations are considered feasible mechanisms for controlling dyke orientation around major displacement surfaces.
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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 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".