Seismic Imaging of the Middle American Subduction Zone and Alaska-Northwestern Canada: News Insights into Subduction Dynamics and Tectonic Evolution
Notice bibliographique
Résumé
How the properties of the subducting slabs govern the mantle flow patterns, the spatial distribution of arc volcanism, and the growth of continents remains as an open subject of fundamental importance in geosciences. In this thesis, I employ advanced seismological techniques to uncover crustal and upper mantle structures beneath the Middle American subduction zone, as well as Alaska and northwestern Canada. I aim to provide new seismic insights into the influence of subduction on lithospheric rheology and the distribution patterns of volcanism, thereby advancing our understanding of tectonic evolution over geologic time. A typical subduction of an oceanic plate beneath a continent is expected to be accompanied by arc volcanoes. Subduction of the Cocos plate at the Middle American subduction system has resulted in an uneven distribution of magmatism and volcanism along strike. I develop a new three-dimensional shear-wave velocity model of the Middle American subduction system, using full-wave ambient noise tomography (Chapter 2). The model reveals significant variations of the oceanic plates along strike and down dip, in correspondence with either weakened or broken slabs after subduction. I suggest that the presence of slab tearing at both edges of the Mexican flat slab has been modifying the mantle flows, resulting in the unusual arc volcanism. The northwestern part of North America has recorded multiple tectonic events, such as terrane accretion, strike-slip motion, and subduction of the Pacific and Yakutat plates, providing an iconic setting to investigate the tectonic evolution of the continental crust. I first analyze the receiver functions to estimate the crustal thickness, as well as possible slab signature, across Alaska and northwestern Canada (Chapter 3). The Moho signal can be clearly detected within the continental region. Specifically, in northwestern Canada, the thickest crust is observed beneath the Cordilleran Deformation Front, which marks the structural boundary between the North American Craton and the North American Margin. There are several distinct offsets in the Moho depth located both within the tectonic units and approximately across the major faults between the tectonic units. I propose that the Moho offsets reflect the cumulative impact of the accretionary orogenies and post-orogenic tectonic events on crustal modification. The continental Moho signal is weak or obscure in Aleutian and southcentral Alaska, and the oceanic Moho within the subducting plates is likely detected. I also construct a shear-wave velocity model for south-central Alaska and northwesternmost Canada, using ambient noise wave propagation simulation and inversion (Chapter 4). The model reveals three key features, including the presence of the subducting Yakutat slab with apparent velocity reductions near the trench and within its flat segment, two slab segments beneath the Wrangell volcanic field, differing in steepness, depth, and seismic velocity, and aligning spatially with the northwestern and southeastern volcano clusters, and the existence of slab windows between the Yakutat and Wrangell slabs and between the northwestern and southeastern portions of the Wrangell slab. The findings reinforce that the Wrangell volcanoes are predominantly influenced by subduction-related magmatism. Furthermore, the two slab windows could have induced asthenospheric upwelling, contributing to the volcanism in the Wrangell clustered volcanoes. Overall, high resolution velocity models reveal a tight correlation between variations in slab geometry and the distribution of arc volcanoes in the Middle American subduction zone and south-central Alaska. Moreover, the Moho depth map for Alaska and northwestern Canada offers a comprehensive view of the crustal thickness variations, which are crucial for understanding the impacts of tectonic events, such as terrane accretion and subduction, on continental formation and evolution.
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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 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 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) | 0,001 | 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 ».