Tectonic reconstruction of deformation structures in the western Newfoundland Appalachians
Notice bibliographique
Résumé
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.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,002 |
| Études des sciences et des technologies | 0,001 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,003 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».