Lithospheric models of the North American continent
Bibliographic record
Abstract
We constructed NACr14, a 3D model of the North American (NA) crust, based on the most recent seismic data\nfrom the USGS database. In comparison with the global crustal model CRUST 1.0, NACr14 is more heterogeneous,\nshowing a larger spatial variability of the thickness and average velocities of the crustal layers. Velocities of the\nlower crust vary in a larger range than those of the other layers, while the thickness of all the three layers is on\naverage between 11 and 13 km. The largest velocities of the crystalline crust (>6.6 km/s) reflect the presence\nof a 7.x layer (>7.0 km/s) in the lowermost part of the crust. Using NACr2014, a regional (NA07) and a global\n(SL201sv) tomography model, and gravity data, we apply an iterative technique, which jointly interprets seismic\ntomography and gravity data, to estimate temperature and compositional variations in the NA upper mantle. The\nresults obtained demonstrate that temperature of the cratonic mantle is up to 150C higher than when using a\nuniform compositional model. The differences between the two tomography models influence the results more\nstrongly than possible changes of the depth distribution of compositional variations. Strong negative compositional\ndensity anomalies, corresponding to Mg # >92, characterize the upper mantle of the northwestern part of the\nSuperior craton and the central part of the Slave and Churchill craton. The Proterozoic upper mantle of the western\nand more deformed part of the NA cratons, appears weakly depleted (Mg# 91) when NA07 is used, in agreement\nwith the results based on the interpretation of xenolith data. When we use SL2013sv, the same areas are locally\ncharacterized by high density bodies, which might be interpreted as the effect due to fragments of subducted\nslabs, as those close to the suture of the Appalachians and Grenville province. We used the two thermal models to\nestimate the integrated strength and the effective elastic thickness (Te) of the lithosphere. In the peripheral parts\nof the cratons, as the Proterozoic Canadian Platform and Grenville, the integrated strength for model NA07 is ten\ntimes larger than in model SL2013sv, due to a model-dependent temperature difference of >200°C in the uppermost\nmantle. In both models, Proterozoic regions reactivated by Meso-Cenozoic tectonics (e.g., Rocky Mountains and\nthe Mississippi Embayment) show a weak lithosphere due to the absence of the mechanically strong part of the\nmantle lithospheric layer. Intraplate earthquakes are distributed along the edges of the cratons, characterized by a\nweak lithosphere or pronounced variations in integrated lithospheric strength and Te. In addition, the sum of the\nseismic moments shows that most of the energy is released by the weak lithosphere. These results suggest that the\nedges of the cratons are more prone to accumulation of tectonic stress and subsequent release by earthquakes, in\ncomparison with the stable cratonic regions which resist deformation.
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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 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.006 | 0.001 |
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".