The Proterozoic building of North America: insights from broadband seismic tomography
Bibliographic record
Abstract
Cratons, the Archean (≥ 2.5 Ga) cores of the continents are the longest-lived features of Earth’s surface. They are underlain by cold, iron-depleted, thick (>250 km), seismically fast lithospheric mantle roots or keels that have survived thermal and chemical erosion over multiple Wilson cycles. Recently however, numerous studies have shown that cratonic mantle lithosphere can undergo modification andmay be removed entirely. I use passive-source seismology to investigate this further for the Superior Craton of North America and its abutting Proterozoic platform. Initially, I use P- and S-wave relative arrival-time tomography to investigate the regional seismic structure of southeast Canada. Here, three broad zones of decreasing seismic wavespeed span the Archean Superior, Proterozoic Grenville and Phanerozoic Appalachian provinces, respectively. A vertical boundary in wavespeed beneath the Grenville Front is interpreted as evidence for subduction-driven metasomatic enrichment of the Laurentian margin. Due to the loss of the background mean velocity structure, relative arrival-time datasets are not easily combined and are also unsuitable for estimation of the physical properties of the mantle. To address this, I develop the Absolute Arrival-time Recovery Method (AARM) to retrieve absolute arrival-times from temporary seismograph networks, whose data are often noisy. Tests indicate that AARM picks are accurate to ≤0.25 s, akin to uncertainties in ISC bulletins. As a result, small aperture, temporary deployments now represent an exploitable resource with which to fill gaps in global seismic tomographic studies. Finally, I incorporate multiple regional networks from eastern Canada into a continental P-wave absolute arrival-time tomographic inversion to produce the most up-to-date compressional wavespeed image of the North American lithosphere. These results show along-strike variability in upper lithospheric velocity structure within the Proterozoic Grenville Orogen (1.3 − 1.0 Ga). When reconciled with the geological record, these results may provide the first seismological evidence for delamination of subcontinental lithospheric mantle in a Proterozoic large, hot, orogen.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.002 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".