Mantle variation within the Canadian Shield: Travel times from the portable broadband Archean‐Proterozoic Transect 1989
Bibliographic record
Abstract
We report travel times from the Archean‐Proterozoic Transect 1989. This type of data set recorded by a transect of portable broadband instruments allows us to make inferences about mantle structure in the region between the Wyoming Craton and the Superior Province of the Canadian Shield. With station separations of 50 to 100 km and frequencies up to 5 Hz the resolution of lateral changes is increased by nearly an order of magnitude over previous studies to a scale that allows us to study the relation between velocity variation in the continental upper mantle, surface geology, tectonic features and age provinces. Travel times of direct and later phases are obtained from waveform matching. The values are corrected for crustal contribution and inverted for the vertical path upper mantle delay δtUM under each station as well as the azimuthal dependence of this quantity. The prominent feature in the upper mantle delays δtUM is the variation by at least 1.5 s for S, much of which occurs over a narrow zone of just a few hundred kilometers width. This suggests a major lateral upper mantle transition which does not coincide with the surface geological edge of the Canadian Shield but is located within the shield. This same transition is also observed in shear wave splitting delay times. Surprisingly, however, the P delays do not exhibit a corresponding variation. We address this apparent contradiction and show how it may be explained in conjunction with anisotropy in the subcontinental lithosphere. A simplified thermal model of the lithospheric transition zone, in which temperature controls the degree of crystallographic alignment and thus seismic anisotropy, predicts this phenomenon.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.003 |
| Science and technology studies | 0.001 | 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".