Seismic Imaging of the Middle American Subduction Zone and Alaska-Northwestern Canada: News Insights into Subduction Dynamics and Tectonic Evolution
Bibliographic record
Abstract
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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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 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".