Tectonic reconstruction of deformation structures in the western Newfoundland Appalachians
Bibliographic record
Abstract
The Northern Appalachians expose a foreland fold-and-thrust belt in the deformed Laurentian margin (Humber zone) of western Newfoundland, extending from the structural front to the more metamorphosed interior parts of the orogen. Existing accounts emphasize Taconian (Ordovician) deformation, but fail to explain complex map patterns throughout the region. The frontal thrust of the orogen emerges along the western part of Port au Port Peninsula, where it records a complex history of normal faulting, followed by "thin-skinned" emplacement of allochthonous thrust sheets during the Ordovician Taconian orogeny, followed by basement-cored "thick-skinned" fault reactivation during the Devonian Acadian orogeny. Interpretation of seismic reflection data produced a detailed three-dimensional (3D) subsurface model, which delineates fault geometries and identifies three prominent seismic reflectors corresponding to the base, mid-, and top of the carbonate-dominated platform that formed on the Laurentian margin. A seismic-to-well tie constrains the interpretation of formation contacts. These contacts are projected to the topographic surface, delineating expected outcrop traces in areas lacking field data or where exposure is limited. Combining 3D subsurface modelling, field observations, high-resolution digital elevation model, and recent satellite imagery allows the development of a new and improved geological map on Port au Port Peninsula. Palinspastic restoration of the 3D model for Port au Port Peninsula yields movement vectors of individual fault blocks. Basement structures, misoriented relative to the Acadian shortening direction, were reactivated in the Devonian, resulting in oblique displacement of fault-bounded blocks, particularly the hanging wall above basement-cored inversion structures. Newly formed shortcut thrusts, characterized by mostly dip-slip movement, developed within the prevailing Acadian stress field. Composite fault-surface geometries observed in the subsurface reflect the interplay between inherited structures and newly formed faults responding to changing Ordovician and Devonian displacement directions. This interaction accounts for variably oriented open folds in the hanging wall of the basement-cored inversion structure, at the topographic surface. The restored geometry shows that approximately 15° of clockwise rotation occurred during displacement, explaining previous paleomagnetic results. The more interior parts of the fold-and-thrust belt preserve tectonic fabrics associated with Taconian emplacement of allochthons above a carbonate platform and foreland basin, subduction polarity reversal during Salinian orogeny, and reactivation of older structures during Acadian shortening. Distinct stratigraphic successions — including deep-water and shelf units derived from the Laurentian passive margin — are contained within in-sequence west-vergent thin-skinned (D1a) and platform-cutting (D1b) thrusts, dated between ~477 Ma and ~459 Ma. D1a thrust contacts are characterized by disrupted units and mélange. The Sandbar Window, a newly discovered tectonic window, represents the lowest D1b thrust, whose hanging-wall strata can be traced to the nonconformably underlying Long Range Inlier. This structurally lowest D1b thrust is interpreted to represent a shear zone which involved crystalline basement of the Long Range Inlier. During Salinian D2 deformation, thrust stacks of D1b were further uplifted and deformed. F2 east-vergent map-scale folds with regional northwest-dipping axial planar S2 cleavage deform earlier thrust sheets and related structures. Subduction polarity reversal and therefore the onset of a proto-Salinian orogenic episode is constrained by syn-tectonic monazite along cleavage planes at ~451 Ma. The regional northwest-dipping cleavage S2 dated at ~443 Ma formed during D2 Salinian deformation. Thrusts associated with the west-vergent D3 episode are mainly unfolded, cut up-section to the west, and offset older thrust stacks leading to a complex compartmentalisation of three generations of faults. S3 cleavage planes are preserved locally, recording an age around 419 Ma. Isotopic age dates associated with oppositely dipping fabrics demonstrate that subduction polarity reversal happened over only a few million years. These results show that the Appalachian orogen in western Newfoundland was modified in a succession of deformation episodes that parallel those documented elsewhere in the orogen, and that Taconian structures were heavily modified during Salinian (Silurian) and Acadian (Devonian) deformation to produce the current complex map patterns.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 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".